{"id":229,"date":"2016-11-04T03:32:52","date_gmt":"2016-11-04T03:32:52","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/microbiology\/?post_type=chapter&#038;p=229"},"modified":"2018-07-11T18:38:46","modified_gmt":"2018-07-11T18:38:46","slug":"gram-positive-bacteria","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/chapter\/gram-positive-bacteria\/","title":{"raw":"Gram-Positive Bacteria","rendered":"Gram-Positive Bacteria"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\n<ul>\r\n \t<li>Describe the unique features of each category of high G+C and low G+C gram-positive bacteria<\/li>\r\n \t<li>Identify similarities and differences between high G+C and low G+C bacterial groups<\/li>\r\n \t<li>Give an example of a bacterium of high G+C and low G+C group commonly associated with each category<\/li>\r\n<\/ul>\r\n<\/div>\r\nProkaryotes are identified as gram-positive if they have a multiple layer matrix of peptidoglycan forming the cell wall. Crystal violet, the primary stain of the Gram stain procedure, is readily retained and stabilized within this matrix, causing gram-positive <strong>prokaryotes<\/strong> to appear purple under a brightfield microscope after Gram staining. For many years, the retention of Gram stain was one of the main criteria used to classify prokaryotes, even though some prokaryotes did not readily stain with either the primary or secondary stains used in the Gram stain procedure.\r\n\r\nAdvances in nucleic acid biochemistry have revealed additional characteristics that can be used to classify gram-positive prokaryotes, namely the guanine to cytosine ratios (G+C) in DNA and the composition of 16S rRNA subunits. Microbiologists currently recognize two distinct groups of gram-positive, or weakly staining gram-positive, prokaryotes. The class <strong>Actinobacteria<\/strong> comprises the <strong>high G+C gram-positive bacteria<\/strong>, which have more than 50% guanine and cytosine nucleotides in their DNA. The class <strong>Bacilli<\/strong> comprises <strong>low G+C gram-positive bacteria<\/strong>, which have less than 50% of guanine and cytosine nucleotides in their DNA.\r\n<h2>Actinobacteria: High G+C Gram-Positive Bacteria<\/h2>\r\nThe name Actinobacteria comes from the Greek words for <em>rays<\/em> and <em>small rod<\/em>, but Actinobacteria are very diverse. Their microscopic appearance can range from thin filamentous branching rods to coccobacilli. Some Actinobacteria are very large and complex, whereas others are among the smallest independently living organisms. Most Actinobacteria live in the soil, but some are aquatic. The vast majority are aerobic. One distinctive feature of this group is the presence of several different peptidoglycans in the cell wall.\r\n\r\nThe genus <strong><em>Actinomyces<\/em><\/strong> is a much studied representative of Actinobacteria. <em>Actinomyces<\/em> spp. play an important role in soil ecology, and some species are human pathogens. A number of <em>Actinomyces<\/em> spp. inhabit the human mouth and are opportunistic pathogens, causing infectious diseases like <strong>periodontitis<\/strong> (inflammation of the gums) and oral abscesses. The species <em>A. israelii<\/em> is an anaerobe notorious for causing <strong>endocarditis<\/strong> (inflammation of the inner lining of the heart) (Figure\u00a01).\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1300\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154148\/OSC_Microbio_04_04_Actinobac.jpg\" alt=\"a) A micrograph of branched cells. B) A micrograph of cells arranged in a V-shape \u2013 these are labeled palisades. C) A micrograph of corn-flake shaped cells with a nucleus. Smaller cells outside of these are identified with an arrow.\" width=\"1300\" height=\"372\" \/> Figure\u00a01. (a) <em>Actinomyces israelii<\/em> (false-color scanning electron micrograph [SEM]) has a branched structure. (b) <em>Corynebacterium diphtheria<\/em> causes the deadly disease diphtheria. Note the distinctive palisades. (c) The gram-variable bacterium <em>Gardnerella vaginalis<\/em> causes bacterial vaginosis in women. This micrograph shows a Pap smear from a woman with vaginosis. (credit a: modification of work by \"GrahamColm\"\/Wikimedia Commons; credit b: modification of work by Centers for Disease Control and Prevention; credit c: modification of work by Mwakigonja AR, Torres LM, Mwakyoma HA, Kaaya EE)[\/caption]The genus <strong><em>Mycobacterium<\/em><\/strong> is represented by bacilli covered with a mycolic acid coat. This waxy coat protects the bacteria from some antibiotics, prevents them from drying out, and blocks penetration by Gram stain reagents (see <a href=\".\/chapter\/staining-microscopic-specimens\/\" target=\"_blank\" rel=\"noopener\">Staining Microscopic Specimens<\/a>). Because of this, a special acid-fast staining procedure is used to visualize these bacteria. The genus <em>Mycobacterium<\/em> is an important cause of a diverse group of infectious diseases. <em>M. tuberculosis<\/em> is the causative agent of <strong>tuberculosis<\/strong>, a disease that primarily impacts the lungs but can infect other parts of the body as well. It has been estimated that one-third of the world\u2019s population has been infected with <em>M. tuberculosis<\/em> and millions of new infections occur each year. Treatment of <em>M. tuberculosis<\/em> is challenging and requires patients to take a combination of drugs for an extended time. Complicating treatment even further is the development and spread of multidrug-resistant strains of this pathogen.\r\n\r\nAnother pathogenic species, <em>M. leprae<\/em>, is the cause of <strong>Hansen\u2019s disease (leprosy)<\/strong>, a chronic disease that impacts peripheral nerves and the integrity of the skin and mucosal surface of the respiratory tract. Loss of pain sensation and the presence of skin lesions increase susceptibility to secondary injuries and infections with other pathogens.\r\n\r\nBacteria in the genus <strong><em>Corynebacterium<\/em><\/strong> contain diaminopimelic acid in their cell walls, and microscopically often form <strong><em>palisades<\/em><\/strong>, or pairs of rod-shaped cells resembling the letter V. Cells may contain metachromatic <strong>granules<\/strong>, intracellular storage of inorganic phosphates that are useful for identification of <em>Corynebacterium<\/em>. The vast majority of <em>Corynebacterium<\/em> spp. are nonpathogenic; however, <em>C. diphtheria<\/em> is the causative agent of <strong>diphtheria<\/strong>, a disease that can be fatal, especially in children (Figure\u00a01b). <em>C. diphtheria<\/em> produces a toxin that forms a pseudomembrane in the patient\u2019s throat, causing swelling, difficulty breathing, and other symptoms that can become serious if untreated.\r\n\r\nThe genus <strong><em>Bifidobacterium<\/em><\/strong> consists of filamentous anaerobes, many of which are commonly found in the gastrointestinal tract, vagina, and mouth. In fact, <em>Bifidobacterium<\/em> spp. constitute a substantial part of the human gut microbiota and are frequently used as probiotics and in yogurt production.\r\n\r\nThe genus <strong><em>Gardnerella<\/em><\/strong>, contains only one species, <em>G. vaginalis<\/em>. This species is defined as \"gram-variable\" because its small coccobacilli do not show consistent results when Gram stained (Figure\u00a01c). Based on its genome, it is placed into the high G+C gram-positive group. <em>G. vaginalis<\/em> can cause bacterial vaginosis in women; symptoms are typically mild or even undetectable, but can lead to complications during pregnancy.\r\n\r\nTable 1 summarizes the characteristics of some important genera of Actinobacteria. Additional information on Actinobacteria appears in\u00a0<a href=\"https:\/\/courses.lumenlearning.com\/microbiology\/chapter\/proteobacteria\/chapter\/taxonomy-of-clinically-relevant-microorganisms\/\" target=\"_blank\" rel=\"noopener\">Taxonomy of Clinically Relevant Microorganisms<\/a>.\r\n<table id=\"fs-id1172100595032\" class=\"span-all\" summary=\"Table titled Class Actinobacteria: High G+C Gram-Positive. Three columns: Genus, Microscopic Morphology and Unique Characteristics. Genus Actinomyces: Gram-positive bacillus; in colonies, shows fungus-like threads (hyphae). Characteristics: Facultative anaerobes; in soil, decompose organic matter; in the human mouth, may cause gum disease. Genus Arthrobacter: Gram-positive bacillus (at the exponential stage of growth) or coccus (in stationary phase). Characteristics: Obligate aerobes; divide by \">\r\n<thead>\r\n<tr>\r\n<th colspan=\"3\">Table 1. Actinobacteria: High G+C Gram-Positive<\/th>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<th>Example Genus<\/th>\r\n<th>Microscopic Morphology<\/th>\r\n<th>Unique Characteristics<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td><em>Actinomyces<\/em><\/td>\r\n<td>Gram-positive bacillus; in colonies, shows fungus-like threads (hyphae)<\/td>\r\n<td>Facultative anaerobes; in soil, decompose organic matter; in the human mouth, may cause gum disease<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Arthrobacter<\/em><\/td>\r\n<td>Gram-positive bacillus (at the exponential stage of growth) or coccus (in stationary phase)<\/td>\r\n<td>Obligate aerobes; divide by \"snapping,\" forming V-like pairs of daughter cells; degrade phenol, can be used in bioremediation<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Bifidobacterium<\/em><\/td>\r\n<td>Gram-positive, filamentous actinobacterium<\/td>\r\n<td>Anaerobes commonly found in human gut microbiota<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Corynebacterium<\/em><\/td>\r\n<td>Gram-positive bacillus<\/td>\r\n<td>Aerobes or facultative anaerobes; form palisades; grow slowly; require enriched media in culture; <em>C. diphtheriae<\/em> causes diphtheria<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Frankia<\/em><\/td>\r\n<td>Gram-positive, fungus-like (filamentous) bacillus<\/td>\r\n<td>Nitrogen-fixing bacteria; live in symbiosis with legumes<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Gardnerella<\/em><\/td>\r\n<td>Gram-variable coccobacillus<\/td>\r\n<td>Colonize the human vagina, may alter the microbial ecology, thus leading to vaginosis<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Micrococcus<\/em><\/td>\r\n<td>Gram-positive coccus, form microscopic clusters<\/td>\r\n<td>Ubiquitous in the environment and on the human skin; oxidase-positive (as opposed to morphologically similar <em>S. aureus<\/em>); some are opportunistic pathogens<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Mycobacterium<\/em><\/td>\r\n<td>Gram-positive, acid-fast bacillus<\/td>\r\n<td>Slow growing, aerobic, resistant to drying and phagocytosis; covered with a waxy coat made of mycolic acid; <em>M. tuberculosis<\/em> causes tuberculosis; <em>M. leprae<\/em> causes leprosy<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Nocardia<\/em><\/td>\r\n<td>Weakly gram-positive bacillus; forms acid-fast branches<\/td>\r\n<td>May colonize the human gingiva; may cause severe pneumonia and inflammation of the skin<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Propionibacterium<\/em><\/td>\r\n<td>Gram-positive bacillus<\/td>\r\n<td>Aerotolerant anaerobe; slow-growing; <em>P. acnes<\/em> reproduces in the human sebaceous glands and may cause or contribute to acne<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Rhodococcus<\/em><\/td>\r\n<td>Gram-positive bacillus<\/td>\r\n<td>Strict aerobe; used in industry for biodegradation of pollutants; <em>R. fascians<\/em> is a plant pathogen, and <em>R. equi<\/em> causes pneumonia in foals<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Streptomyces<\/em><\/td>\r\n<td>Gram-positive, fungus-like (filamentous) bacillus<\/td>\r\n<td>Very diverse genus (&gt;500 species); aerobic, spore-forming bacteria; scavengers, decomposers found in soil (give the soil its \"earthy\" odor); used in pharmaceutical industry as antibiotic producers (more than two-thirds of clinically useful antibiotics)<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<h2>\r\nLow G+C Gram-positive Bacteria<\/h2>\r\nThe <strong>low G+C gram-positive bacteria<\/strong> have less than 50% guanine and cytosine in their DNA, and this group of bacteria includes a number of genera of bacteria that are pathogenic.\r\n<h3>Clostridia<\/h3>\r\nOne large and diverse class of <strong>low G+C gram-positive bacteria<\/strong> is Clostridia. The best studied genus of this class is <strong><em>Clostridium<\/em><\/strong>. These rod-shaped bacteria are generally obligate anaerobes that produce endospores and can be found in anaerobic habitats like soil and aquatic sediments rich in organic nutrients. The endospores may survive for many years.\r\n\r\n[caption id=\"\" align=\"alignright\" width=\"399\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154151\/OSC_Microbio_04_04_Clostridia.jpg\" alt=\"A micrograph of many rod shaped cells.\" width=\"399\" height=\"236\" \/> Figure\u00a02. <strong><em>Clostridium difficile<\/em><\/strong>, a gram-positive, rod-shaped bacterium, causes severe colitis and diarrhea, often after the normal gut microbiota is eradicated by antibiotics. (credit: modification of work by Centers for Disease Control and Prevention)[\/caption]\r\n\r\n<em>Clostridium<\/em> spp. produce more kinds of protein toxins than any other bacterial genus, and several species are human pathogens. <em>C. perfringens<\/em> is the third most common cause of food poisoning in the United States and is the causative agent of an even more serious disease called <strong>gas gangrene<\/strong>. Gas gangrene occurs when <em>C. perfringens<\/em> endospores enter a wound and germinate, becoming viable bacterial cells and producing a toxin that can cause the necrosis (death) of tissue. <em>C. tetani<\/em>, which causes <strong>tetanus<\/strong>, produces a neurotoxin that is able to enter neurons, travel to regions of the central nervous system where it blocks the inhibition of nerve impulses involved in muscle contractions, and cause a life-threatening spastic paralysis. <em>C. botulinum<\/em> produces <strong>botulinum neurotoxin<\/strong>, the most lethal biological toxin known. Botulinum toxin is responsible for rare but frequently fatal cases of <strong>botulism<\/strong>. The toxin blocks the release of acetylcholine in neuromuscular junctions, causing flaccid paralysis. In very small concentrations, botulinum toxin has been used to treat muscle pathologies in humans and in a cosmetic procedure to eliminate wrinkles. <em>C. difficile<\/em> is a common source of hospital-acquired infections (Figure\u00a02) that can result in serious and even fatal cases of colitis (inflammation of the large intestine). Infections often occur in patients who are immunosuppressed or undergoing antibiotic therapy that alters the normal microbiota of the gastrointestinal tract.\u00a0<a href=\"https:\/\/courses.lumenlearning.com\/microbiology\/chapter\/proteobacteria\/chapter\/taxonomy-of-clinically-relevant-microorganisms\/\" target=\"_blank\" rel=\"noopener\">Taxonomy of Clinically Relevant Microorganisms<\/a>\u00a0lists the genera, species, and related diseases for Clostridia.\r\n<h3>Lactobacillales<\/h3>\r\nThe order <strong>Lactobacillales<\/strong> comprises low G+C gram-positive bacteria that include both <strong>bacilli<\/strong> and <strong>cocci<\/strong> in the genera <strong><em>Lactobacillus<\/em><\/strong>, <strong><em>Leuconostoc<\/em><\/strong>, <strong><em>Enterococcus<\/em><\/strong>, and <strong><em>Streptococcus<\/em><\/strong>. Bacteria of the latter three genera typically are spherical or ovoid and often form chains.\r\n\r\n<em>Streptococcus<\/em>, the name of which comes from the Greek word for <em>twisted chain<\/em>, is responsible for many types of infectious diseases in humans. Species from this genus, often referred to as <strong>streptococci<\/strong>, are usually classified by serotypes called Lancefield groups, and by their ability to lyse red blood cells when grown on blood agar.\r\n\r\n<em>S. pyogenes<\/em> belongs to the <strong>Lancefield group<\/strong> A, \u03b2-hemolytic <em>Streptococcus<\/em>. This species is considered a pyogenic pathogen because of the associated pus production observed with infections it causes (Figure\u00a03). <em>S. pyogenes<\/em> is the most common cause of bacterial pharyngitis (<strong>strep throat<\/strong>); it is also an important cause of various skin infections that can be relatively mild (e.g., <strong>impetigo<\/strong>) or life threatening (e.g., <strong>necrotizing fasciitis<\/strong>, also known as flesh eating disease), life threatening.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"814\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154154\/OSC_Microbio_04_04_Strep.jpg\" alt=\"a) A micrograph of spherical cells in a chain. B) A photograph of colonies on agar. The agar is red, and there is a clearing around each colony.\" width=\"814\" height=\"408\" \/> Figure\u00a03. (a) A gram-stained specimen of <em>Streptococcus pyogenes<\/em> shows the chains of cocci characteristic of this organism\u2019s morphology. (b) <em>S. pyogenes<\/em> on blood agar shows characteristic lysis of red blood cells, indicated by the halo of clearing around colonies. (credit a, b: modification of work by American Society for Microbiology)[\/caption]\r\n\r\nThe nonpyogenic (i.e., not associated with pus production) streptococci are a group of streptococcal species that are not a taxon but are grouped together because they inhabit the human mouth. The <strong>nonpyogenic streptococci<\/strong> do not belong to any of the Lancefield groups. Most are commensals, but a few, such as <em>S. mutans<\/em>, are implicated in the development of dental caries.\r\n\r\n<em>S. pneumoniae<\/em> (commonly referred to as pneumococcus), is a <strong><em>Streptococcus<\/em><\/strong> species that also does not belong to any <strong>Lancefield group<\/strong>. <em>S. pneumoniae<\/em> cells appear microscopically as diplococci, pairs of cells, rather than the long chains typical of most streptococci. Scientists have known since the 19th century that <em>S. pneumoniae<\/em> causes <strong>pneumonia<\/strong> and other respiratory infections. However, this bacterium can also cause a wide range of other diseases, including meningitis, septicemia, osteomyelitis, and endocarditis, especially in newborns, the elderly, and patients with immunodeficiency.\r\n<h3>Bacilli<\/h3>\r\nThe name of the class <strong>Bacilli<\/strong> suggests that it is made up of bacteria that are bacillus in shape, but it is a morphologically diverse class that includes bacillus-shaped and cocccus-shaped genera. Among the many genera in this class are two that are very important clinically: <strong><em>Bacillus<\/em><\/strong> and <strong><em>Staphylococcus<\/em><\/strong>.\r\n\r\nBacteria in the genus <em>Bacillus<\/em> are bacillus in shape and can produce <strong>endospores<\/strong>. They include aerobes or facultative anaerobes. A number of <em>Bacillus<\/em> spp. are used in various industries, including the production of antibiotics (e.g., barnase), enzymes (e.g., alpha-amylase, BamH1 restriction endonuclease), and detergents (e.g., subtilisin).\r\n\r\nTwo notable pathogens belong to the genus <em>Bacillus. B. anthracis<\/em> is the pathogen that causes <strong>anthrax<\/strong>, a severe disease that affects wild and domesticated animals and can spread from infected animals to humans. Anthrax manifests in humans as charcoal-black ulcers on the skin, severe enterocolitis, pneumonia, and brain damage due to swelling. If untreated, anthrax is lethal. <em>B. cereus<\/em>, a closely related species, is a pathogen that may cause food poisoning. It is a rod-shaped species that forms chains. Colonies appear milky white with irregular shapes when cultured on blood agar (Figure\u00a04). One other important species is <em>B. thuringiensis<\/em>. This bacterium produces a number of substances used as insecticides because they are toxic for insects.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1100\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154157\/OSC_Microbio_04_04_Bacillus.jpg\" alt=\"a) A micrograph of rod shaped cells in a chain. B) A photograph of colonies on agar. The agar is red and the colonies are white and fluffy looking.\" width=\"1100\" height=\"489\" \/> Figure\u00a04. (a) In this gram-stained specimen, the violet rod-shaped cells forming chains are the gram-positive bacteria <strong><em>Bacillus cereus<\/em><\/strong>. The small, pink cells are the gram-negative bacteria <strong><em>Escherichia coli<\/em><\/strong>. (b) In this culture, white colonies of <em>B. cereus<\/em> have been grown on sheep blood agar. (credit a: modification of work by \"Bibliomaniac 15\"\/Wikimedia Commons; credit b: modification of work by Centers for Disease Control and Prevention)[\/caption]\r\n\r\n[caption id=\"\" align=\"alignright\" width=\"400\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154201\/OSC_Microbio_04_04_SAureus.jpg\" alt=\"A micrograph of clusters of spherical cells.\" width=\"400\" height=\"270\" \/> Figure\u00a05. This SEM of <strong><em>Staphylococcus aureus<\/em><\/strong> illustrates the typical \"grape-like\" clustering of cells. (credit: modification of work by Centers for Disease Control and Prevention)[\/caption]\r\n\r\nThe genus <em>Staphylococcus<\/em> also belongs to the class Bacilli, even though its shape is coccus rather than a bacillus. The name <em>Staphylococcus<\/em> comes from a Greek word for <em>bunches of grapes<\/em>, which describes their microscopic appearance in culture (Figure\u00a05). <em>Staphylococcus<\/em> spp. are facultative anaerobic, halophilic, and nonmotile. The two best-studied species of this genus are <em>S. epidermidis<\/em> and <em>S. aureus<\/em>.\r\n\r\n<em>S. epidermidis<\/em>, whose main habitat is the human skin, is thought to be nonpathogenic for humans with healthy immune systems, but in patients with immunodeficiency, it may cause infections in skin wounds and prostheses (e.g., artificial joints, heart valves)<em>. S. epidermidis<\/em> is also an important cause of infections associated with intravenous catheters. This makes it a dangerous pathogen in hospital settings, where many patients may be immunocompromised.\r\n\r\nStrains of <em>S. aureus<\/em> cause a wide variety of infections in humans, including skin infections that produce boils, carbuncles, cellulitis, or impetigo. Certain strains of <em>S. aureus<\/em> produce a substance called <strong>enterotoxin<\/strong>, which can cause severe enteritis, often called staph food poisoning. Some strains of <em>S. aureus<\/em> produce the toxin responsible for <strong>toxic shock syndrome<\/strong>, which can result in cardiovascular collapse and death.\r\n\r\nMany strains of <em>S. aureus<\/em> have developed resistance to antibiotics. Some antibiotic-resistant strains are designated as <strong>methicillin-resistant <em>S. aureus<\/em> (MRSA)<\/strong> and <strong>vancomycin-resistant <em>S. aureus<\/em> (VRSA)<\/strong>. These strains are some of the most difficult to treat because they exhibit resistance to nearly all available antibiotics, not just methicillin and vancomycin. Because they are difficult to treat with antibiotics, infections can be lethal. MRSA and VRSA are also contagious, posing a serious threat in hospitals, nursing homes, dialysis facilities, and other places where there are large populations of elderly, bedridden, and\/or immunocompromised patients.\u00a0<a href=\"https:\/\/courses.lumenlearning.com\/microbiology\/chapter\/proteobacteria\/chapter\/taxonomy-of-clinically-relevant-microorganisms\/\" target=\"_blank\" rel=\"noopener\">Taxonomy of Clinically Relevant Microorganisms<\/a>\u00a0lists the genera, species, and related diseases for bacilli.\r\n<h3>Mycoplasmas<\/h3>\r\nAlthough <strong><em>Mycoplasma<\/em><\/strong> spp. do not possess a cell wall and, therefore, are not stained by Gram-stain reagents, this genus is still included with the low G+C gram-positive bacteria. The genus <em>Mycoplasma<\/em> includes more than 100 species, which share several unique characteristics. They are very small cells, some with a diameter of about 0.2 \u03bcm, which is smaller than some large viruses. They have no cell walls and, therefore, are <strong>pleomorphic<\/strong>, meaning that they may take on a variety of shapes and can even resemble very small animal cells. Because they lack a characteristic shape, they can be difficult to identify. One species, <em>M. pneumoniae<\/em>, causes the mild form of <strong>pneumonia<\/strong> known as \"<strong>walking pneumonia<\/strong>\" or \"<strong>atypical pneumonia<\/strong>.\" This form of pneumonia is typically less severe than forms caused by other bacteria or viruses.\r\n\r\nTable 3 summarizes the characteristics of notable genera low G+C Gram-positive bacteria.\r\n<table id=\"fs-id1172100547469\" class=\"span-all\" summary=\"Table titled Class Actinobacteria: Low G+C Gram-Positive. Three columns: Genus, Microscopic Morphology and Unique Characteristics. Genus Bacillus: Large, gram-positive bacillus. Characteristics: Aerobes or facultative anaerobes; form endospores; B. anthracis causes anthrax in cattle and humans, B. cereus may cause food poisoning. Genus Clostridium: Gram-positive bacillus. Characteristics: Strict anaerobes; form endospores; all known species are pathogenic, causing tetanus, gas gangrene, botulism, and colitis. Genus Enterococcus: Gram-positive coccus; forms microscopic pairs in culture (resembling Streptococcus pneumoniae). Characteristics: Anaerobic aerotolerant bacteria, abundant in the human gut, may cause urinary tract and other infections in the nosocomial environment. Genus Lactobacillus: Gram-positive bacillus. Characteristics: Facultative anaerobes; ferment sugars into lactic acid; part of the vaginal microbiota; used as probiotics. Genus Leuconostoc: Gram-positive coccus; may form microscopic chains in culture. Characteristics: Fermenter, used in food industry to produce sauerkraut and kefir . Genus Mycoplasma: The smallest bacteria; appear pleomorphic under electron microscope. Characteristics: Have no cell wall; classified as low G+C Gram-positive bacteria because of their genome; M. pneumoniae causes \">\r\n<thead>\r\n<tr>\r\n<th colspan=\"3\">Table 3. Bacilli: Low G+C Gram-Positive Bacteria<\/th>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<th>Example Genus<\/th>\r\n<th>Microscopic Morphology<\/th>\r\n<th>Unique Characteristics<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td><em>Bacillus<\/em><\/td>\r\n<td>Large, gram-positive bacillus<\/td>\r\n<td>Aerobes or facultative anaerobes; form endospores; <em>B. anthracis<\/em> causes anthrax in cattle and humans, <em>B. cereus<\/em> may cause food poisoning<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Clostridium<\/em><\/td>\r\n<td>Gram-positive bacillus<\/td>\r\n<td>Strict anaerobes; form endospores; all known species are pathogenic, causing tetanus, gas gangrene, botulism, and colitis<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Enterococcus<\/em><\/td>\r\n<td>Gram-positive coccus; forms microscopic pairs in culture (resembling <em>Streptococcus pneumoniae<\/em>)<\/td>\r\n<td>Anaerobic aerotolerant bacteria, abundant in the human gut, may cause urinary tract and other infections in the nosocomial environment<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Lactobacillus<\/em><\/td>\r\n<td>Gram-positive bacillus<\/td>\r\n<td>Facultative anaerobes; ferment sugars into lactic acid; part of the vaginal microbiota; used as probiotics<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Leuconostoc<\/em><\/td>\r\n<td>Gram-positive coccus; may form microscopic chains in culture<\/td>\r\n<td>Fermenter, used in food industry to produce sauerkraut and kefir<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Mycoplasma<\/em><\/td>\r\n<td>The smallest bacteria; appear pleomorphic under electron microscope<\/td>\r\n<td>Have no cell wall; classified as low G+C Gram-positive bacteria because of their genome; <em>M. pneumoniae<\/em> causes \"walking\" pneumonia<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Staphylococcus<\/em><\/td>\r\n<td>Gram-positive coccus; forms microscopic clusters in culture that resemble bunches of grapes<\/td>\r\n<td>Tolerate high salt concentration; facultative anaerobes; produce catalase; <em>S. aureus<\/em> can also produce coagulase and toxins responsible for local (skin) and generalized infections<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Streptococcus<\/em><\/td>\r\n<td>Gram-positive coccus; forms chains or pairs in culture<\/td>\r\n<td>Diverse genus; classified into groups based on sharing certain antigens; some species cause hemolysis and may produce toxins responsible for human local (throat) and generalized disease<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><em>Ureaplasma<\/em><\/td>\r\n<td>Similar to <em>Mycoplasma<\/em><\/td>\r\n<td>Part of the human vaginal and lower urinary tract microbiota; may cause inflammation, sometimes leading to internal scarring and infertility<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ul>\r\n \t<li>Name some ways in which streptococci are classified.<\/li>\r\n \t<li>Name one pathogenic low G+C gram-positive bacterium and a disease it causes.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Biopiracy and Bioprospecting<\/h3>\r\nIn 1969, an employee of a Swiss pharmaceutical company was vacationing in Norway and decided to collect some soil samples. He took them back to his lab, and the Swiss company subsequently used the fungus <em>Tolypocladium<\/em> <em>inflatum<\/em> in those samples to develop cyclosporine A, a drug widely used in patients who undergo tissue or organ transplantation. The Swiss company earns more than $1 billion a year for production of cyclosporine A, yet Norway receives nothing in return\u2014no payment to the government or benefit for the Norwegian people. Despite the fact the cyclosporine A saves numerous lives, many consider the means by which the soil samples were obtained to be an act of \"biopiracy,\" essentially a form of theft. Do the ends justify the means in a case like this?\r\n\r\nNature is full of as-yet-undiscovered bacteria and other microorganisms that could one day be used to develop new life-saving drugs or treatments.[footnote]J. Andre. <em>Bioethics as Practice<\/em>. Chapel Hill, NC: University of North Carolina Press, 2002.[\/footnote] Pharmaceutical and biotechnology companies stand to reap huge profits from such discoveries, but ethical questions remain. To whom do biological resources belong? Should companies who invest (and risk) millions of dollars in research and development be required to share revenue or royalties for the right to access biological resources?\r\n\r\nCompensation is not the only issue when it comes to bioprospecting. Some communities and cultures are philosophically opposed to bioprospecting, fearing unforeseen consequences of collecting genetic or biological material. Native Hawaiians, for example, are very protective of their unique biological resources.\r\n\r\nFor many years, it was unclear what rights government agencies, private corporations, and citizens had when it came to collecting samples of microorganisms from public land. Then, in 1993, the Convention on Biological Diversity granted each nation the rights to any genetic and biological material found on their own land. Scientists can no longer collect samples without a prior arrangement with the land owner for compensation. This convention now ensures that companies act ethically in obtaining the samples they use to create their products.\r\n\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Key Concepts and Summary<\/h3>\r\n<ul>\r\n \t<li>Gram-positive bacteria are a very large and diverse group of microorganisms. Understanding their taxonomy and knowing their unique features is important for diagnostics and treatment of infectious diseases.<\/li>\r\n \t<li>Gram-positive bacteria are classified into <strong>high G+C gram-positive<\/strong> and <strong>low G+C gram-positive<\/strong> bacteria, based on the prevalence of guanine and cytosine nucleotides in their genome<\/li>\r\n \t<li>Actinobacteria is the taxonomic name of the class of high G+C gram-positive bacteria. This class includes the genera <em>Actinomyces, Arthrobacter, Corynebacterium, Frankia, Gardnerella, Micrococcus, Mycobacterium, Nocardia<\/em>, <em>Propionibacterium, Rhodococcus,<\/em> and <em>Streptomyces<\/em>. Some representatives of these genera are used in industry; others are human or animal pathogens.<\/li>\r\n \t<li>Examples of high G+C gram-positive bacteria that are human pathogens include <em>Mycobacterium<\/em> <em>tuberculosis<\/em>, which causes tuberculosis; <em>M. leprae<\/em>, which causes leprosy (Hansen\u2019s disease); and <em>Corynebacterium<\/em> <em>diphtheriae<\/em>, which causes diphtheria.<\/li>\r\n \t<li><em>Clostridia<\/em> spp. are low G+C gram-positive bacteria that are generally obligate anaerobes and can form endospores. Pathogens in this genus include <em>C.<\/em> <em>perfringens<\/em> (gas gangrene), <em>C. tetani<\/em> (tetanus), and <em>C. botulinum<\/em> (botulism).<\/li>\r\n \t<li>Lactobacillales include the genera <em>Enterococcus<\/em>, <em>Lactobacillus<\/em>, <em>Leuconostoc<\/em>, and <em>Streptococcus. Streptococcus<\/em> is responsible for many human diseases, including pharyngitis (strep throat), scarlet fever, rheumatic fever, glomerulonephritis, pneumonia, and other respiratory infections.<\/li>\r\n \t<li>Bacilli is a taxonomic class of low G+C gram-positive bacteria that include rod-shaped and coccus-shaped species, including the genera <em>Bacillus<\/em> and <em>Staphylococcus<\/em>. <em>B. anthracis<\/em> causes anthrax, <em>B. cereus<\/em> may cause opportunistic infections of the gastrointestinal tract, and <em>S.<\/em> <em>aureus<\/em> strains can cause a wide range of infections and diseases, many of which are highly resistant to antibiotics.<\/li>\r\n \t<li><em>Mycoplasma<\/em> spp. are very small, <strong>pleomorphic<\/strong> low G+C gram-positive bacteria that lack cell walls. <em>M. pneumoniae<\/em> causes atypical pneumonia.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Multiple Choice<\/h3>\r\nWhich of the following bacterial species is classified as high G+C gram-positive?\r\n<ol style=\"list-style-type: lower-alpha\">\r\n \t<li><em>Corynebacterium diphtheriae<\/em><\/li>\r\n \t<li><em>Staphylococcus aureus<\/em><\/li>\r\n \t<li><em>Bacillus anthracis<\/em><\/li>\r\n \t<li><em>Streptococcus pneumonia<\/em><\/li>\r\n<\/ol>\r\n[reveal-answer q=\"246698\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"246698\"]Answer a.\u00a0<em>Corynebacterium diphtheriae<\/em>\u00a0 is classified as high G+C gram-positive.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Fill in the Blank<\/h3>\r\n<em>Streptococcus<\/em> is the ________ of bacteria that is responsible for many human diseases.\r\n\r\n[reveal-answer q=\"938587\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"938587\"]<em>Streptococcus<\/em> is the <strong>genus<\/strong> of bacteria that is responsible for many human diseases.[\/hidden-answer]\r\n\r\nOne species of <em>Streptococcus<\/em>, <em>S<\/em>. <em>pyogenes<\/em>, is a classified as a ________ pathogen due to the characteristic production of pus in infections it causes.\r\n\r\n[reveal-answer q=\"640648\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"640648\"]One species of <em>Streptococcus<\/em>, <em>S. pyogenes<\/em>, is a classified as a <strong>pyogenic<\/strong> pathogen due to the characteristic production of pus in infections it causes.[\/hidden-answer]\r\n\r\n<em>Propionibacterium<\/em> belongs to ________ G+C gram-positive bacteria. One of its species is used in the food industry and another causes acne.\r\n\r\n[reveal-answer q=\"718674\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"718674\"]<em>Propionibacterium<\/em> belongs to <strong>high<\/strong> G+C gram-positive bacteria. One of its species is used in the food industry and another causes acne.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ol>\r\n \t<li>Name and describe two types of <em>S. aureus<\/em> that show multiple antibiotic resistance.<\/li>\r\n \t<li>The microscopic growth pattern shown is characteristic of which genus of bacteria?<\/li>\r\n<\/ol>\r\n[caption id=\"\" align=\"aligncenter\" width=\"599\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154206\/OSC_Microbio_04_04_ArtConn2_img.jpg\" alt=\"A micrograph showing clusters of spherical cells.\" width=\"599\" height=\"393\" \/> (credit: modification of work by Janice Haney Carr\/Centers for Disease Control and Prevention)[\/caption]\r\n\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<ul>\n<li>Describe the unique features of each category of high G+C and low G+C gram-positive bacteria<\/li>\n<li>Identify similarities and differences between high G+C and low G+C bacterial groups<\/li>\n<li>Give an example of a bacterium of high G+C and low G+C group commonly associated with each category<\/li>\n<\/ul>\n<\/div>\n<p>Prokaryotes are identified as gram-positive if they have a multiple layer matrix of peptidoglycan forming the cell wall. Crystal violet, the primary stain of the Gram stain procedure, is readily retained and stabilized within this matrix, causing gram-positive <strong>prokaryotes<\/strong> to appear purple under a brightfield microscope after Gram staining. For many years, the retention of Gram stain was one of the main criteria used to classify prokaryotes, even though some prokaryotes did not readily stain with either the primary or secondary stains used in the Gram stain procedure.<\/p>\n<p>Advances in nucleic acid biochemistry have revealed additional characteristics that can be used to classify gram-positive prokaryotes, namely the guanine to cytosine ratios (G+C) in DNA and the composition of 16S rRNA subunits. Microbiologists currently recognize two distinct groups of gram-positive, or weakly staining gram-positive, prokaryotes. The class <strong>Actinobacteria<\/strong> comprises the <strong>high G+C gram-positive bacteria<\/strong>, which have more than 50% guanine and cytosine nucleotides in their DNA. The class <strong>Bacilli<\/strong> comprises <strong>low G+C gram-positive bacteria<\/strong>, which have less than 50% of guanine and cytosine nucleotides in their DNA.<\/p>\n<h2>Actinobacteria: High G+C Gram-Positive Bacteria<\/h2>\n<p>The name Actinobacteria comes from the Greek words for <em>rays<\/em> and <em>small rod<\/em>, but Actinobacteria are very diverse. Their microscopic appearance can range from thin filamentous branching rods to coccobacilli. Some Actinobacteria are very large and complex, whereas others are among the smallest independently living organisms. Most Actinobacteria live in the soil, but some are aquatic. The vast majority are aerobic. One distinctive feature of this group is the presence of several different peptidoglycans in the cell wall.<\/p>\n<p>The genus <strong><em>Actinomyces<\/em><\/strong> is a much studied representative of Actinobacteria. <em>Actinomyces<\/em> spp. play an important role in soil ecology, and some species are human pathogens. A number of <em>Actinomyces<\/em> spp. inhabit the human mouth and are opportunistic pathogens, causing infectious diseases like <strong>periodontitis<\/strong> (inflammation of the gums) and oral abscesses. The species <em>A. israelii<\/em> is an anaerobe notorious for causing <strong>endocarditis<\/strong> (inflammation of the inner lining of the heart) (Figure\u00a01).<\/p>\n<div style=\"width: 1310px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154148\/OSC_Microbio_04_04_Actinobac.jpg\" alt=\"a) A micrograph of branched cells. B) A micrograph of cells arranged in a V-shape \u2013 these are labeled palisades. C) A micrograph of corn-flake shaped cells with a nucleus. Smaller cells outside of these are identified with an arrow.\" width=\"1300\" height=\"372\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a01. (a) <em>Actinomyces israelii<\/em> (false-color scanning electron micrograph [SEM]) has a branched structure. (b) <em>Corynebacterium diphtheria<\/em> causes the deadly disease diphtheria. Note the distinctive palisades. (c) The gram-variable bacterium <em>Gardnerella vaginalis<\/em> causes bacterial vaginosis in women. This micrograph shows a Pap smear from a woman with vaginosis. (credit a: modification of work by &#8220;GrahamColm&#8221;\/Wikimedia Commons; credit b: modification of work by Centers for Disease Control and Prevention; credit c: modification of work by Mwakigonja AR, Torres LM, Mwakyoma HA, Kaaya EE)<\/p>\n<\/div>\n<p>The genus <strong><em>Mycobacterium<\/em><\/strong> is represented by bacilli covered with a mycolic acid coat. This waxy coat protects the bacteria from some antibiotics, prevents them from drying out, and blocks penetration by Gram stain reagents (see <a href=\".\/chapter\/staining-microscopic-specimens\/\" target=\"_blank\" rel=\"noopener\">Staining Microscopic Specimens<\/a>). Because of this, a special acid-fast staining procedure is used to visualize these bacteria. The genus <em>Mycobacterium<\/em> is an important cause of a diverse group of infectious diseases. <em>M. tuberculosis<\/em> is the causative agent of <strong>tuberculosis<\/strong>, a disease that primarily impacts the lungs but can infect other parts of the body as well. It has been estimated that one-third of the world\u2019s population has been infected with <em>M. tuberculosis<\/em> and millions of new infections occur each year. Treatment of <em>M. tuberculosis<\/em> is challenging and requires patients to take a combination of drugs for an extended time. Complicating treatment even further is the development and spread of multidrug-resistant strains of this pathogen.<\/p>\n<p>Another pathogenic species, <em>M. leprae<\/em>, is the cause of <strong>Hansen\u2019s disease (leprosy)<\/strong>, a chronic disease that impacts peripheral nerves and the integrity of the skin and mucosal surface of the respiratory tract. Loss of pain sensation and the presence of skin lesions increase susceptibility to secondary injuries and infections with other pathogens.<\/p>\n<p>Bacteria in the genus <strong><em>Corynebacterium<\/em><\/strong> contain diaminopimelic acid in their cell walls, and microscopically often form <strong><em>palisades<\/em><\/strong>, or pairs of rod-shaped cells resembling the letter V. Cells may contain metachromatic <strong>granules<\/strong>, intracellular storage of inorganic phosphates that are useful for identification of <em>Corynebacterium<\/em>. The vast majority of <em>Corynebacterium<\/em> spp. are nonpathogenic; however, <em>C. diphtheria<\/em> is the causative agent of <strong>diphtheria<\/strong>, a disease that can be fatal, especially in children (Figure\u00a01b). <em>C. diphtheria<\/em> produces a toxin that forms a pseudomembrane in the patient\u2019s throat, causing swelling, difficulty breathing, and other symptoms that can become serious if untreated.<\/p>\n<p>The genus <strong><em>Bifidobacterium<\/em><\/strong> consists of filamentous anaerobes, many of which are commonly found in the gastrointestinal tract, vagina, and mouth. In fact, <em>Bifidobacterium<\/em> spp. constitute a substantial part of the human gut microbiota and are frequently used as probiotics and in yogurt production.<\/p>\n<p>The genus <strong><em>Gardnerella<\/em><\/strong>, contains only one species, <em>G. vaginalis<\/em>. This species is defined as &#8220;gram-variable&#8221; because its small coccobacilli do not show consistent results when Gram stained (Figure\u00a01c). Based on its genome, it is placed into the high G+C gram-positive group. <em>G. vaginalis<\/em> can cause bacterial vaginosis in women; symptoms are typically mild or even undetectable, but can lead to complications during pregnancy.<\/p>\n<p>Table 1 summarizes the characteristics of some important genera of Actinobacteria. Additional information on Actinobacteria appears in\u00a0<a href=\"https:\/\/courses.lumenlearning.com\/microbiology\/chapter\/proteobacteria\/chapter\/taxonomy-of-clinically-relevant-microorganisms\/\" target=\"_blank\" rel=\"noopener\">Taxonomy of Clinically Relevant Microorganisms<\/a>.<\/p>\n<table id=\"fs-id1172100595032\" class=\"span-all\" summary=\"Table titled Class Actinobacteria: High G+C Gram-Positive. Three columns: Genus, Microscopic Morphology and Unique Characteristics. Genus Actinomyces: Gram-positive bacillus; in colonies, shows fungus-like threads (hyphae). Characteristics: Facultative anaerobes; in soil, decompose organic matter; in the human mouth, may cause gum disease. Genus Arthrobacter: Gram-positive bacillus (at the exponential stage of growth) or coccus (in stationary phase). Characteristics: Obligate aerobes; divide by\">\n<thead>\n<tr>\n<th colspan=\"3\">Table 1. Actinobacteria: High G+C Gram-Positive<\/th>\n<\/tr>\n<tr valign=\"top\">\n<th>Example Genus<\/th>\n<th>Microscopic Morphology<\/th>\n<th>Unique Characteristics<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr valign=\"top\">\n<td><em>Actinomyces<\/em><\/td>\n<td>Gram-positive bacillus; in colonies, shows fungus-like threads (hyphae)<\/td>\n<td>Facultative anaerobes; in soil, decompose organic matter; in the human mouth, may cause gum disease<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Arthrobacter<\/em><\/td>\n<td>Gram-positive bacillus (at the exponential stage of growth) or coccus (in stationary phase)<\/td>\n<td>Obligate aerobes; divide by &#8220;snapping,&#8221; forming V-like pairs of daughter cells; degrade phenol, can be used in bioremediation<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Bifidobacterium<\/em><\/td>\n<td>Gram-positive, filamentous actinobacterium<\/td>\n<td>Anaerobes commonly found in human gut microbiota<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Corynebacterium<\/em><\/td>\n<td>Gram-positive bacillus<\/td>\n<td>Aerobes or facultative anaerobes; form palisades; grow slowly; require enriched media in culture; <em>C. diphtheriae<\/em> causes diphtheria<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Frankia<\/em><\/td>\n<td>Gram-positive, fungus-like (filamentous) bacillus<\/td>\n<td>Nitrogen-fixing bacteria; live in symbiosis with legumes<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Gardnerella<\/em><\/td>\n<td>Gram-variable coccobacillus<\/td>\n<td>Colonize the human vagina, may alter the microbial ecology, thus leading to vaginosis<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Micrococcus<\/em><\/td>\n<td>Gram-positive coccus, form microscopic clusters<\/td>\n<td>Ubiquitous in the environment and on the human skin; oxidase-positive (as opposed to morphologically similar <em>S. aureus<\/em>); some are opportunistic pathogens<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Mycobacterium<\/em><\/td>\n<td>Gram-positive, acid-fast bacillus<\/td>\n<td>Slow growing, aerobic, resistant to drying and phagocytosis; covered with a waxy coat made of mycolic acid; <em>M. tuberculosis<\/em> causes tuberculosis; <em>M. leprae<\/em> causes leprosy<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Nocardia<\/em><\/td>\n<td>Weakly gram-positive bacillus; forms acid-fast branches<\/td>\n<td>May colonize the human gingiva; may cause severe pneumonia and inflammation of the skin<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Propionibacterium<\/em><\/td>\n<td>Gram-positive bacillus<\/td>\n<td>Aerotolerant anaerobe; slow-growing; <em>P. acnes<\/em> reproduces in the human sebaceous glands and may cause or contribute to acne<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Rhodococcus<\/em><\/td>\n<td>Gram-positive bacillus<\/td>\n<td>Strict aerobe; used in industry for biodegradation of pollutants; <em>R. fascians<\/em> is a plant pathogen, and <em>R. equi<\/em> causes pneumonia in foals<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Streptomyces<\/em><\/td>\n<td>Gram-positive, fungus-like (filamentous) bacillus<\/td>\n<td>Very diverse genus (&gt;500 species); aerobic, spore-forming bacteria; scavengers, decomposers found in soil (give the soil its &#8220;earthy&#8221; odor); used in pharmaceutical industry as antibiotic producers (more than two-thirds of clinically useful antibiotics)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>\nLow G+C Gram-positive Bacteria<\/h2>\n<p>The <strong>low G+C gram-positive bacteria<\/strong> have less than 50% guanine and cytosine in their DNA, and this group of bacteria includes a number of genera of bacteria that are pathogenic.<\/p>\n<h3>Clostridia<\/h3>\n<p>One large and diverse class of <strong>low G+C gram-positive bacteria<\/strong> is Clostridia. The best studied genus of this class is <strong><em>Clostridium<\/em><\/strong>. These rod-shaped bacteria are generally obligate anaerobes that produce endospores and can be found in anaerobic habitats like soil and aquatic sediments rich in organic nutrients. The endospores may survive for many years.<\/p>\n<div style=\"width: 409px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154151\/OSC_Microbio_04_04_Clostridia.jpg\" alt=\"A micrograph of many rod shaped cells.\" width=\"399\" height=\"236\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a02. <strong><em>Clostridium difficile<\/em><\/strong>, a gram-positive, rod-shaped bacterium, causes severe colitis and diarrhea, often after the normal gut microbiota is eradicated by antibiotics. (credit: modification of work by Centers for Disease Control and Prevention)<\/p>\n<\/div>\n<p><em>Clostridium<\/em> spp. produce more kinds of protein toxins than any other bacterial genus, and several species are human pathogens. <em>C. perfringens<\/em> is the third most common cause of food poisoning in the United States and is the causative agent of an even more serious disease called <strong>gas gangrene<\/strong>. Gas gangrene occurs when <em>C. perfringens<\/em> endospores enter a wound and germinate, becoming viable bacterial cells and producing a toxin that can cause the necrosis (death) of tissue. <em>C. tetani<\/em>, which causes <strong>tetanus<\/strong>, produces a neurotoxin that is able to enter neurons, travel to regions of the central nervous system where it blocks the inhibition of nerve impulses involved in muscle contractions, and cause a life-threatening spastic paralysis. <em>C. botulinum<\/em> produces <strong>botulinum neurotoxin<\/strong>, the most lethal biological toxin known. Botulinum toxin is responsible for rare but frequently fatal cases of <strong>botulism<\/strong>. The toxin blocks the release of acetylcholine in neuromuscular junctions, causing flaccid paralysis. In very small concentrations, botulinum toxin has been used to treat muscle pathologies in humans and in a cosmetic procedure to eliminate wrinkles. <em>C. difficile<\/em> is a common source of hospital-acquired infections (Figure\u00a02) that can result in serious and even fatal cases of colitis (inflammation of the large intestine). Infections often occur in patients who are immunosuppressed or undergoing antibiotic therapy that alters the normal microbiota of the gastrointestinal tract.\u00a0<a href=\"https:\/\/courses.lumenlearning.com\/microbiology\/chapter\/proteobacteria\/chapter\/taxonomy-of-clinically-relevant-microorganisms\/\" target=\"_blank\" rel=\"noopener\">Taxonomy of Clinically Relevant Microorganisms<\/a>\u00a0lists the genera, species, and related diseases for Clostridia.<\/p>\n<h3>Lactobacillales<\/h3>\n<p>The order <strong>Lactobacillales<\/strong> comprises low G+C gram-positive bacteria that include both <strong>bacilli<\/strong> and <strong>cocci<\/strong> in the genera <strong><em>Lactobacillus<\/em><\/strong>, <strong><em>Leuconostoc<\/em><\/strong>, <strong><em>Enterococcus<\/em><\/strong>, and <strong><em>Streptococcus<\/em><\/strong>. Bacteria of the latter three genera typically are spherical or ovoid and often form chains.<\/p>\n<p><em>Streptococcus<\/em>, the name of which comes from the Greek word for <em>twisted chain<\/em>, is responsible for many types of infectious diseases in humans. Species from this genus, often referred to as <strong>streptococci<\/strong>, are usually classified by serotypes called Lancefield groups, and by their ability to lyse red blood cells when grown on blood agar.<\/p>\n<p><em>S. pyogenes<\/em> belongs to the <strong>Lancefield group<\/strong> A, \u03b2-hemolytic <em>Streptococcus<\/em>. This species is considered a pyogenic pathogen because of the associated pus production observed with infections it causes (Figure\u00a03). <em>S. pyogenes<\/em> is the most common cause of bacterial pharyngitis (<strong>strep throat<\/strong>); it is also an important cause of various skin infections that can be relatively mild (e.g., <strong>impetigo<\/strong>) or life threatening (e.g., <strong>necrotizing fasciitis<\/strong>, also known as flesh eating disease), life threatening.<\/p>\n<div style=\"width: 824px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154154\/OSC_Microbio_04_04_Strep.jpg\" alt=\"a) A micrograph of spherical cells in a chain. B) A photograph of colonies on agar. The agar is red, and there is a clearing around each colony.\" width=\"814\" height=\"408\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a03. (a) A gram-stained specimen of <em>Streptococcus pyogenes<\/em> shows the chains of cocci characteristic of this organism\u2019s morphology. (b) <em>S. pyogenes<\/em> on blood agar shows characteristic lysis of red blood cells, indicated by the halo of clearing around colonies. (credit a, b: modification of work by American Society for Microbiology)<\/p>\n<\/div>\n<p>The nonpyogenic (i.e., not associated with pus production) streptococci are a group of streptococcal species that are not a taxon but are grouped together because they inhabit the human mouth. The <strong>nonpyogenic streptococci<\/strong> do not belong to any of the Lancefield groups. Most are commensals, but a few, such as <em>S. mutans<\/em>, are implicated in the development of dental caries.<\/p>\n<p><em>S. pneumoniae<\/em> (commonly referred to as pneumococcus), is a <strong><em>Streptococcus<\/em><\/strong> species that also does not belong to any <strong>Lancefield group<\/strong>. <em>S. pneumoniae<\/em> cells appear microscopically as diplococci, pairs of cells, rather than the long chains typical of most streptococci. Scientists have known since the 19th century that <em>S. pneumoniae<\/em> causes <strong>pneumonia<\/strong> and other respiratory infections. However, this bacterium can also cause a wide range of other diseases, including meningitis, septicemia, osteomyelitis, and endocarditis, especially in newborns, the elderly, and patients with immunodeficiency.<\/p>\n<h3>Bacilli<\/h3>\n<p>The name of the class <strong>Bacilli<\/strong> suggests that it is made up of bacteria that are bacillus in shape, but it is a morphologically diverse class that includes bacillus-shaped and cocccus-shaped genera. Among the many genera in this class are two that are very important clinically: <strong><em>Bacillus<\/em><\/strong> and <strong><em>Staphylococcus<\/em><\/strong>.<\/p>\n<p>Bacteria in the genus <em>Bacillus<\/em> are bacillus in shape and can produce <strong>endospores<\/strong>. They include aerobes or facultative anaerobes. A number of <em>Bacillus<\/em> spp. are used in various industries, including the production of antibiotics (e.g., barnase), enzymes (e.g., alpha-amylase, BamH1 restriction endonuclease), and detergents (e.g., subtilisin).<\/p>\n<p>Two notable pathogens belong to the genus <em>Bacillus. B. anthracis<\/em> is the pathogen that causes <strong>anthrax<\/strong>, a severe disease that affects wild and domesticated animals and can spread from infected animals to humans. Anthrax manifests in humans as charcoal-black ulcers on the skin, severe enterocolitis, pneumonia, and brain damage due to swelling. If untreated, anthrax is lethal. <em>B. cereus<\/em>, a closely related species, is a pathogen that may cause food poisoning. It is a rod-shaped species that forms chains. Colonies appear milky white with irregular shapes when cultured on blood agar (Figure\u00a04). One other important species is <em>B. thuringiensis<\/em>. This bacterium produces a number of substances used as insecticides because they are toxic for insects.<\/p>\n<div style=\"width: 1110px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154157\/OSC_Microbio_04_04_Bacillus.jpg\" alt=\"a) A micrograph of rod shaped cells in a chain. B) A photograph of colonies on agar. The agar is red and the colonies are white and fluffy looking.\" width=\"1100\" height=\"489\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a04. (a) In this gram-stained specimen, the violet rod-shaped cells forming chains are the gram-positive bacteria <strong><em>Bacillus cereus<\/em><\/strong>. The small, pink cells are the gram-negative bacteria <strong><em>Escherichia coli<\/em><\/strong>. (b) In this culture, white colonies of <em>B. cereus<\/em> have been grown on sheep blood agar. (credit a: modification of work by &#8220;Bibliomaniac 15&#8243;\/Wikimedia Commons; credit b: modification of work by Centers for Disease Control and Prevention)<\/p>\n<\/div>\n<div style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154201\/OSC_Microbio_04_04_SAureus.jpg\" alt=\"A micrograph of clusters of spherical cells.\" width=\"400\" height=\"270\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a05. This SEM of <strong><em>Staphylococcus aureus<\/em><\/strong> illustrates the typical &#8220;grape-like&#8221; clustering of cells. (credit: modification of work by Centers for Disease Control and Prevention)<\/p>\n<\/div>\n<p>The genus <em>Staphylococcus<\/em> also belongs to the class Bacilli, even though its shape is coccus rather than a bacillus. The name <em>Staphylococcus<\/em> comes from a Greek word for <em>bunches of grapes<\/em>, which describes their microscopic appearance in culture (Figure\u00a05). <em>Staphylococcus<\/em> spp. are facultative anaerobic, halophilic, and nonmotile. The two best-studied species of this genus are <em>S. epidermidis<\/em> and <em>S. aureus<\/em>.<\/p>\n<p><em>S. epidermidis<\/em>, whose main habitat is the human skin, is thought to be nonpathogenic for humans with healthy immune systems, but in patients with immunodeficiency, it may cause infections in skin wounds and prostheses (e.g., artificial joints, heart valves)<em>. S. epidermidis<\/em> is also an important cause of infections associated with intravenous catheters. This makes it a dangerous pathogen in hospital settings, where many patients may be immunocompromised.<\/p>\n<p>Strains of <em>S. aureus<\/em> cause a wide variety of infections in humans, including skin infections that produce boils, carbuncles, cellulitis, or impetigo. Certain strains of <em>S. aureus<\/em> produce a substance called <strong>enterotoxin<\/strong>, which can cause severe enteritis, often called staph food poisoning. Some strains of <em>S. aureus<\/em> produce the toxin responsible for <strong>toxic shock syndrome<\/strong>, which can result in cardiovascular collapse and death.<\/p>\n<p>Many strains of <em>S. aureus<\/em> have developed resistance to antibiotics. Some antibiotic-resistant strains are designated as <strong>methicillin-resistant <em>S. aureus<\/em> (MRSA)<\/strong> and <strong>vancomycin-resistant <em>S. aureus<\/em> (VRSA)<\/strong>. These strains are some of the most difficult to treat because they exhibit resistance to nearly all available antibiotics, not just methicillin and vancomycin. Because they are difficult to treat with antibiotics, infections can be lethal. MRSA and VRSA are also contagious, posing a serious threat in hospitals, nursing homes, dialysis facilities, and other places where there are large populations of elderly, bedridden, and\/or immunocompromised patients.\u00a0<a href=\"https:\/\/courses.lumenlearning.com\/microbiology\/chapter\/proteobacteria\/chapter\/taxonomy-of-clinically-relevant-microorganisms\/\" target=\"_blank\" rel=\"noopener\">Taxonomy of Clinically Relevant Microorganisms<\/a>\u00a0lists the genera, species, and related diseases for bacilli.<\/p>\n<h3>Mycoplasmas<\/h3>\n<p>Although <strong><em>Mycoplasma<\/em><\/strong> spp. do not possess a cell wall and, therefore, are not stained by Gram-stain reagents, this genus is still included with the low G+C gram-positive bacteria. The genus <em>Mycoplasma<\/em> includes more than 100 species, which share several unique characteristics. They are very small cells, some with a diameter of about 0.2 \u03bcm, which is smaller than some large viruses. They have no cell walls and, therefore, are <strong>pleomorphic<\/strong>, meaning that they may take on a variety of shapes and can even resemble very small animal cells. Because they lack a characteristic shape, they can be difficult to identify. One species, <em>M. pneumoniae<\/em>, causes the mild form of <strong>pneumonia<\/strong> known as &#8220;<strong>walking pneumonia<\/strong>&#8221; or &#8220;<strong>atypical pneumonia<\/strong>.&#8221; This form of pneumonia is typically less severe than forms caused by other bacteria or viruses.<\/p>\n<p>Table 3 summarizes the characteristics of notable genera low G+C Gram-positive bacteria.<\/p>\n<table id=\"fs-id1172100547469\" class=\"span-all\" summary=\"Table titled Class Actinobacteria: Low G+C Gram-Positive. Three columns: Genus, Microscopic Morphology and Unique Characteristics. Genus Bacillus: Large, gram-positive bacillus. Characteristics: Aerobes or facultative anaerobes; form endospores; B. anthracis causes anthrax in cattle and humans, B. cereus may cause food poisoning. Genus Clostridium: Gram-positive bacillus. Characteristics: Strict anaerobes; form endospores; all known species are pathogenic, causing tetanus, gas gangrene, botulism, and colitis. Genus Enterococcus: Gram-positive coccus; forms microscopic pairs in culture (resembling Streptococcus pneumoniae). Characteristics: Anaerobic aerotolerant bacteria, abundant in the human gut, may cause urinary tract and other infections in the nosocomial environment. Genus Lactobacillus: Gram-positive bacillus. Characteristics: Facultative anaerobes; ferment sugars into lactic acid; part of the vaginal microbiota; used as probiotics. Genus Leuconostoc: Gram-positive coccus; may form microscopic chains in culture. Characteristics: Fermenter, used in food industry to produce sauerkraut and kefir . Genus Mycoplasma: The smallest bacteria; appear pleomorphic under electron microscope. Characteristics: Have no cell wall; classified as low G+C Gram-positive bacteria because of their genome; M. pneumoniae causes\">\n<thead>\n<tr>\n<th colspan=\"3\">Table 3. Bacilli: Low G+C Gram-Positive Bacteria<\/th>\n<\/tr>\n<tr valign=\"top\">\n<th>Example Genus<\/th>\n<th>Microscopic Morphology<\/th>\n<th>Unique Characteristics<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr valign=\"top\">\n<td><em>Bacillus<\/em><\/td>\n<td>Large, gram-positive bacillus<\/td>\n<td>Aerobes or facultative anaerobes; form endospores; <em>B. anthracis<\/em> causes anthrax in cattle and humans, <em>B. cereus<\/em> may cause food poisoning<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Clostridium<\/em><\/td>\n<td>Gram-positive bacillus<\/td>\n<td>Strict anaerobes; form endospores; all known species are pathogenic, causing tetanus, gas gangrene, botulism, and colitis<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Enterococcus<\/em><\/td>\n<td>Gram-positive coccus; forms microscopic pairs in culture (resembling <em>Streptococcus pneumoniae<\/em>)<\/td>\n<td>Anaerobic aerotolerant bacteria, abundant in the human gut, may cause urinary tract and other infections in the nosocomial environment<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Lactobacillus<\/em><\/td>\n<td>Gram-positive bacillus<\/td>\n<td>Facultative anaerobes; ferment sugars into lactic acid; part of the vaginal microbiota; used as probiotics<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Leuconostoc<\/em><\/td>\n<td>Gram-positive coccus; may form microscopic chains in culture<\/td>\n<td>Fermenter, used in food industry to produce sauerkraut and kefir<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Mycoplasma<\/em><\/td>\n<td>The smallest bacteria; appear pleomorphic under electron microscope<\/td>\n<td>Have no cell wall; classified as low G+C Gram-positive bacteria because of their genome; <em>M. pneumoniae<\/em> causes &#8220;walking&#8221; pneumonia<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Staphylococcus<\/em><\/td>\n<td>Gram-positive coccus; forms microscopic clusters in culture that resemble bunches of grapes<\/td>\n<td>Tolerate high salt concentration; facultative anaerobes; produce catalase; <em>S. aureus<\/em> can also produce coagulase and toxins responsible for local (skin) and generalized infections<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Streptococcus<\/em><\/td>\n<td>Gram-positive coccus; forms chains or pairs in culture<\/td>\n<td>Diverse genus; classified into groups based on sharing certain antigens; some species cause hemolysis and may produce toxins responsible for human local (throat) and generalized disease<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><em>Ureaplasma<\/em><\/td>\n<td>Similar to <em>Mycoplasma<\/em><\/td>\n<td>Part of the human vaginal and lower urinary tract microbiota; may cause inflammation, sometimes leading to internal scarring and infertility<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ul>\n<li>Name some ways in which streptococci are classified.<\/li>\n<li>Name one pathogenic low G+C gram-positive bacterium and a disease it causes.<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Biopiracy and Bioprospecting<\/h3>\n<p>In 1969, an employee of a Swiss pharmaceutical company was vacationing in Norway and decided to collect some soil samples. He took them back to his lab, and the Swiss company subsequently used the fungus <em>Tolypocladium<\/em> <em>inflatum<\/em> in those samples to develop cyclosporine A, a drug widely used in patients who undergo tissue or organ transplantation. The Swiss company earns more than $1 billion a year for production of cyclosporine A, yet Norway receives nothing in return\u2014no payment to the government or benefit for the Norwegian people. Despite the fact the cyclosporine A saves numerous lives, many consider the means by which the soil samples were obtained to be an act of &#8220;biopiracy,&#8221; essentially a form of theft. Do the ends justify the means in a case like this?<\/p>\n<p>Nature is full of as-yet-undiscovered bacteria and other microorganisms that could one day be used to develop new life-saving drugs or treatments.<a class=\"footnote\" title=\"J. Andre. Bioethics as Practice. Chapel Hill, NC: University of North Carolina Press, 2002.\" id=\"return-footnote-229-1\" href=\"#footnote-229-1\" aria-label=\"Footnote 1\"><sup class=\"footnote\">[1]<\/sup><\/a> Pharmaceutical and biotechnology companies stand to reap huge profits from such discoveries, but ethical questions remain. To whom do biological resources belong? Should companies who invest (and risk) millions of dollars in research and development be required to share revenue or royalties for the right to access biological resources?<\/p>\n<p>Compensation is not the only issue when it comes to bioprospecting. Some communities and cultures are philosophically opposed to bioprospecting, fearing unforeseen consequences of collecting genetic or biological material. Native Hawaiians, for example, are very protective of their unique biological resources.<\/p>\n<p>For many years, it was unclear what rights government agencies, private corporations, and citizens had when it came to collecting samples of microorganisms from public land. Then, in 1993, the Convention on Biological Diversity granted each nation the rights to any genetic and biological material found on their own land. Scientists can no longer collect samples without a prior arrangement with the land owner for compensation. This convention now ensures that companies act ethically in obtaining the samples they use to create their products.<\/p>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Key Concepts and Summary<\/h3>\n<ul>\n<li>Gram-positive bacteria are a very large and diverse group of microorganisms. Understanding their taxonomy and knowing their unique features is important for diagnostics and treatment of infectious diseases.<\/li>\n<li>Gram-positive bacteria are classified into <strong>high G+C gram-positive<\/strong> and <strong>low G+C gram-positive<\/strong> bacteria, based on the prevalence of guanine and cytosine nucleotides in their genome<\/li>\n<li>Actinobacteria is the taxonomic name of the class of high G+C gram-positive bacteria. This class includes the genera <em>Actinomyces, Arthrobacter, Corynebacterium, Frankia, Gardnerella, Micrococcus, Mycobacterium, Nocardia<\/em>, <em>Propionibacterium, Rhodococcus,<\/em> and <em>Streptomyces<\/em>. Some representatives of these genera are used in industry; others are human or animal pathogens.<\/li>\n<li>Examples of high G+C gram-positive bacteria that are human pathogens include <em>Mycobacterium<\/em> <em>tuberculosis<\/em>, which causes tuberculosis; <em>M. leprae<\/em>, which causes leprosy (Hansen\u2019s disease); and <em>Corynebacterium<\/em> <em>diphtheriae<\/em>, which causes diphtheria.<\/li>\n<li><em>Clostridia<\/em> spp. are low G+C gram-positive bacteria that are generally obligate anaerobes and can form endospores. Pathogens in this genus include <em>C.<\/em> <em>perfringens<\/em> (gas gangrene), <em>C. tetani<\/em> (tetanus), and <em>C. botulinum<\/em> (botulism).<\/li>\n<li>Lactobacillales include the genera <em>Enterococcus<\/em>, <em>Lactobacillus<\/em>, <em>Leuconostoc<\/em>, and <em>Streptococcus. Streptococcus<\/em> is responsible for many human diseases, including pharyngitis (strep throat), scarlet fever, rheumatic fever, glomerulonephritis, pneumonia, and other respiratory infections.<\/li>\n<li>Bacilli is a taxonomic class of low G+C gram-positive bacteria that include rod-shaped and coccus-shaped species, including the genera <em>Bacillus<\/em> and <em>Staphylococcus<\/em>. <em>B. anthracis<\/em> causes anthrax, <em>B. cereus<\/em> may cause opportunistic infections of the gastrointestinal tract, and <em>S.<\/em> <em>aureus<\/em> strains can cause a wide range of infections and diseases, many of which are highly resistant to antibiotics.<\/li>\n<li><em>Mycoplasma<\/em> spp. are very small, <strong>pleomorphic<\/strong> low G+C gram-positive bacteria that lack cell walls. <em>M. pneumoniae<\/em> causes atypical pneumonia.<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Multiple Choice<\/h3>\n<p>Which of the following bacterial species is classified as high G+C gram-positive?<\/p>\n<ol style=\"list-style-type: lower-alpha\">\n<li><em>Corynebacterium diphtheriae<\/em><\/li>\n<li><em>Staphylococcus aureus<\/em><\/li>\n<li><em>Bacillus anthracis<\/em><\/li>\n<li><em>Streptococcus pneumonia<\/em><\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q246698\">Show Answer<\/span><\/p>\n<div id=\"q246698\" class=\"hidden-answer\" style=\"display: none\">Answer a.\u00a0<em>Corynebacterium diphtheriae<\/em>\u00a0 is classified as high G+C gram-positive.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Fill in the Blank<\/h3>\n<p><em>Streptococcus<\/em> is the ________ of bacteria that is responsible for many human diseases.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q938587\">Show Answer<\/span><\/p>\n<div id=\"q938587\" class=\"hidden-answer\" style=\"display: none\"><em>Streptococcus<\/em> is the <strong>genus<\/strong> of bacteria that is responsible for many human diseases.<\/div>\n<\/div>\n<p>One species of <em>Streptococcus<\/em>, <em>S<\/em>. <em>pyogenes<\/em>, is a classified as a ________ pathogen due to the characteristic production of pus in infections it causes.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q640648\">Show Answer<\/span><\/p>\n<div id=\"q640648\" class=\"hidden-answer\" style=\"display: none\">One species of <em>Streptococcus<\/em>, <em>S. pyogenes<\/em>, is a classified as a <strong>pyogenic<\/strong> pathogen due to the characteristic production of pus in infections it causes.<\/div>\n<\/div>\n<p><em>Propionibacterium<\/em> belongs to ________ G+C gram-positive bacteria. One of its species is used in the food industry and another causes acne.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q718674\">Show Answer<\/span><\/p>\n<div id=\"q718674\" class=\"hidden-answer\" style=\"display: none\"><em>Propionibacterium<\/em> belongs to <strong>high<\/strong> G+C gram-positive bacteria. One of its species is used in the food industry and another causes acne.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ol>\n<li>Name and describe two types of <em>S. aureus<\/em> that show multiple antibiotic resistance.<\/li>\n<li>The microscopic growth pattern shown is characteristic of which genus of bacteria?<\/li>\n<\/ol>\n<div style=\"width: 609px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154206\/OSC_Microbio_04_04_ArtConn2_img.jpg\" alt=\"A micrograph showing clusters of spherical cells.\" width=\"599\" height=\"393\" \/><\/p>\n<p class=\"wp-caption-text\">(credit: modification of work by Janice Haney Carr\/Centers for Disease Control and Prevention)<\/p>\n<\/div>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-229\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>OpenStax Microbiology. <strong>Provided by<\/strong>: OpenStax CNX. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\">http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section><hr class=\"before-footnotes clear\" \/><div class=\"footnotes\"><ol><li id=\"footnote-229-1\">J. Andre. <em>Bioethics as Practice<\/em>. Chapel Hill, NC: University of North Carolina Press, 2002. <a href=\"#return-footnote-229-1\" class=\"return-footnote\" aria-label=\"Return to footnote 1\">&crarr;<\/a><\/li><\/ol><\/div>","protected":false},"author":17,"menu_order":5,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"OpenStax Microbiology\",\"author\":\"\",\"organization\":\"OpenStax CNX\",\"url\":\"http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-229","chapter","type-chapter","status-publish","hentry"],"part":198,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/229","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":7,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/229\/revisions"}],"predecessor-version":[{"id":2145,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/229\/revisions\/2145"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/parts\/198"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/229\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/media?parent=229"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapter-type?post=229"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/contributor?post=229"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/license?post=229"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}