{"id":452,"date":"2016-11-04T03:33:30","date_gmt":"2016-11-04T03:33:30","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/microbiology\/?post_type=chapter&#038;p=452"},"modified":"2016-11-10T02:29:56","modified_gmt":"2016-11-10T02:29:56","slug":"oxygen-requirements-for-microbial-growth","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/chapter\/oxygen-requirements-for-microbial-growth\/","title":{"raw":"Oxygen Requirements for Microbial Growth","rendered":"Oxygen Requirements for Microbial Growth"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\n<ul>\r\n \t<li>Interpret visual data demonstrating minimum, optimum, and maximum oxygen or carbon dioxide requirements for growth<\/li>\r\n \t<li>Identify and describe different categories of microbes with requirements for growth with or without oxygen: obligate aerobe, obligate anaerobe, facultative anaerobe, aerotolerant anaerobe, microaerophile, and capnophile<\/li>\r\n \t<li>Give examples of microorganisms for each category of growth requirements<\/li>\r\n<\/ul>\r\n<\/div>\r\nAsk most people \"What are the major requirements for life?\" and the answers are likely to include water and oxygen. Few would argue about the need for water, but what about oxygen? Can there be life without oxygen?\r\n\r\nThe answer is that molecular oxygen (O<sub>2<\/sub>) is not always needed. The earliest signs of life are dated to a period when conditions on earth were highly reducing and free oxygen gas was essentially nonexistent. Only after cyanobacteria started releasing oxygen as a byproduct of photosynthesis and the capacity of iron in the oceans for taking up oxygen was exhausted did oxygen levels increase in the atmosphere. This event, often referred to as the <strong>Great Oxygenation Event<\/strong> or the <strong>Oxygen Revolution<\/strong>, caused a massive extinction. Most organisms could not survive the powerful oxidative properties of <strong>reactive oxygen species (ROS)<\/strong>, highly unstable ions and molecules derived from partial reduction of oxygen that can damage virtually any macromolecule or structure with which they come in contact. Singlet oxygen (O<sub>2<\/sub>\u2022), superoxide [latex]\\left({\\text{O}}_{2}^{-}\\right)[\/latex], peroxides (H<sub>2<\/sub>O<sub>2<\/sub>), hydroxyl radical (OH\u2022), and hypochlorite ion (OCl<sup>\u2212<\/sup>), the active ingredient of household bleach, are all examples of ROS. The organisms that were able to detoxify reactive oxygen species harnessed the high electronegativity of oxygen to produce free energy for their metabolism and thrived in the new environment.\r\n<h2>Oxygen Requirements of Microorganisms<\/h2>\r\nMany ecosystems are still free of molecular oxygen. Some are found in extreme locations, such as deep in the ocean or in earth\u2019s crust; others are part of our everyday landscape, such as marshes, bogs, and sewers. Within the bodies of humans and other animals, regions with little or no oxygen provide an anaerobic environment for microorganisms (Figure\u00a01).\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\/03164315\/OSC_Microbio_09_02_bog.jpg\" alt=\"a) A photograph of a bog. B) A photograph of cows.\" width=\"1100\" height=\"400\" data-media-type=\"image\/jpeg\" \/> Figure\u00a01. Anaerobic environments are still common on earth. They include environments like (a) a bog where undisturbed dense sediments are virtually devoid of oxygen, and (b) the rumen (the first compartment of a cow\u2019s stomach), which provides an oxygen-free incubator for methanogens and other obligate anaerobic bacteria. (credit a: modification of work by National Park Service; credit b: modification of work by US Department of Agriculture)[\/caption]\r\n\r\nWe can easily observe different requirements for molecular oxygen by growing bacteria in <strong>thioglycolate tube cultures<\/strong>. A test-tube culture starts with autoclaved <strong>thioglycolate medium<\/strong> containing a low percentage of agar to allow motile bacteria to move throughout the medium. Thioglycolate has strong reducing properties and autoclaving flushes out most of the oxygen. The tubes are inoculated with the bacterial cultures to be tested and incubated at an appropriate temperature. Over time, oxygen slowly diffuses throughout the thioglycolate tube culture from the top. Bacterial density increases in the area where oxygen concentration is best suited for the growth of that particular organism.\r\n\r\nThe growth of bacteria with varying oxygen requirements in thioglycolate tubes is illustrated in Figure\u00a02. In tube A, all the growth is seen at the top of the tube. The bacteria are <strong>obligate (strict) aerobes<\/strong> that cannot grow without an abundant supply of oxygen. Tube B looks like the opposite of tube A. Bacteria grow at the bottom of tube B. Those are <strong>obligate anaerobes<\/strong>, which are killed by oxygen. Tube C shows heavy growth at the top of the tube and growth throughout the tube, a typical result with <strong>facultative anaerobes<\/strong>. Facultative anaerobes are organisms that thrive in the presence of oxygen but also grow in its absence by relying on fermentation or anaerobic respiration, if there is a suitable electron acceptor other than oxygen and the organism is able to perform anaerobic respiration. The <strong>aerotolerant anaerobes<\/strong> in tube D are indifferent to the presence of oxygen. They do not use oxygen because they usually have a fermentative metabolism, but they are not harmed by the presence of oxygen as obligate anaerobes are. Tube E on the right shows a \"Goldilocks\" culture. The oxygen level has to be just right for growth, not too much and not too little. These <strong>microaerophiles<\/strong> are bacteria that require a minimum level of oxygen for growth, about 1%\u201310%, well below the 21% found in the atmosphere.\r\n\r\nExamples of obligate aerobes are <strong><em>Mycobacterium tuberculosis<\/em><\/strong>, the causative agent of tuberculosis and <strong><em>Micrococcus luteus<\/em><\/strong>, a gram-positive bacterium that colonizes the skin. <strong><em>Neisseria meningitidis<\/em><\/strong>, the causative agent of severe <strong>bacterial meningitis<\/strong>, and <em>N. gonorrheae<\/em>, the causative agent of sexually transmitted <strong>gonorrhea<\/strong>, are also obligate aerobes.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"701\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03164318\/OSC_Microbio_09_02_tubO.jpg\" alt=\"A diagram of bacterial distribution in tubes. Tube A shows obligate aerobes which grow at the top of the tube. Tube B shows obligate anaerobes which grow at the bottom of the tube. Tube C shows facultative anaerobes which grow best at the top but also grow throughout the tube. Tube D shows aerotolerant anaerobes which grow equally well throughout. Tube E shows microaerophiles which grow just below the top of the tube.\" width=\"701\" height=\"344\" data-media-type=\"image\/jpeg\" \/> Figure\u00a02. Diagram of bacterial cell distribution in thioglycolate tubes.[\/caption]\r\n\r\nMany obligate anaerobes are found in the environment where anaerobic conditions exist, such as in deep sediments of soil, still waters, and at the bottom of the deep ocean where there is no photosynthetic life. Anaerobic conditions also exist naturally in the intestinal tract of animals. Obligate anaerobes, mainly <strong><em>Bacteroidetes<\/em><\/strong>, represent a large fraction of the microbes in the human gut. Transient anaerobic conditions exist when tissues are not supplied with blood circulation; they die and become an ideal breeding ground for obligate anaerobes. Another type of obligate anaerobe encountered in the human body is the gram-positive, rod-shaped <strong><em>Clostridium<\/em><\/strong> spp. Their ability to form endospores allows them to survive in the presence of oxygen. One of the major causes of health-acquired infections is <em>C. difficile<\/em>, known as C. diff. Prolonged use of antibiotics for other infections increases the probability of a patient developing a secondary <em>C. difficile<\/em> infection. Antibiotic treatment disrupts the balance of microorganisms in the intestine and allows the colonization of the gut by <em>C. difficile<\/em>, causing a significant inflammation of the colon.\r\n\r\nOther clostridia responsible for serious infections include <em>C. tetani<\/em>, the agent of tetanus, and <em>C. perfringens<\/em>, which causes <strong>gas gangrene<\/strong>. In both cases, the infection starts in necrotic tissue (dead tissue that is not supplied with oxygen by blood circulation). This is the reason that deep puncture wounds are associated with tetanus. When tissue death is accompanied by lack of circulation, gangrene is always a danger.\r\n\r\nThe study of obligate anaerobes requires special equipment. Obligate anaerobic bacteria must be grown under conditions devoid of oxygen. The most common approach is culture in an <strong>anaerobic jar<\/strong> (Figure\u00a03). Anaerobic jars include chemical packs that remove oxygen and release carbon dioxide (CO<sub>2<\/sub>). An <strong>anaerobic chamber<\/strong> is an enclosed box from which all oxygen is removed. Gloves sealed to openings in the box allow handling of the cultures without exposing the culture to air (Figure\u00a03).\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\/03164321\/OSC_Microbio_09_02_jar.jpg\" alt=\"a) A photo of a stack of agar plates in a chamber. B) A photo of a chamber with sleeves for arms.\" width=\"1100\" height=\"414\" data-media-type=\"image\/jpeg\" \/> Figure\u00a03. (a) An anaerobic jar is pictured that is holding nine Petri plates supporting cultures. (b) Openings in the side of an anaerobic box are sealed by glove-like sleeves that allow for the handling of cultures inside the box. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by NIST)[\/caption]\r\n\r\nStaphylococci and <strong>Enterobacteriaceae<\/strong> are examples of facultative anaerobes. Staphylococci are found on the skin and upper respiratory tract. Enterobacteriaceae are found primarily in the gut and upper respiratory tract but can sometimes spread to the urinary tract, where they are capable of causing infections. It is not unusual to see mixed bacterial infections in which the facultative anaerobes use up the oxygen, creating an environment for the obligate anaerobes to flourish.\r\n\r\nExamples of aerotolerant anaerobes include lactobacilli and streptococci, both found in the oral microbiota. <strong><em>Campylobacter jejuni<\/em><\/strong>, which causes gastrointestinal infections, is an example of a microaerophile and is grown under low-oxygen conditions.\r\n\r\nThe <strong>optimum oxygen concentration<\/strong>, as the name implies, is the ideal concentration of oxygen for a particular microorganism. The lowest concentration of oxygen that allows growth is called the <strong>minimum permissive oxygen concentration<\/strong>. The highest tolerated concentration of oxygen is the maximum permissive oxygen concentration. The organism will not grow outside the range of oxygen levels found between the minimum and maximum permissive oxygen concentrations.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ul>\r\n \t<li>Would you expect the oldest bacterial lineages to be aerobic or anaerobic?<\/li>\r\n \t<li>Which bacteria grow at the top of a thioglycolate tube, and which grow at the bottom of the tube?<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>An Unwelcome Anaerobe<\/h3>\r\n[caption id=\"\" align=\"alignright\" width=\"449\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03164324\/OSC_Microbio_09_02_foot.jpg\" alt=\"A swollen foot with peeling skin and black regions under the skin.\" width=\"449\" height=\"292\" data-media-type=\"image\/jpeg\" \/> Figure\u00a04. This clinical photo depicts ulcers on the foot of a diabetic patient. Dead tissue accumulating in ulcers can provide an ideal growth environment for the anaerobe <em>C. perfringens<\/em>, a causative agent of gas gangrene. (credit: Shigeo Kono, Reiko Nakagawachi, Jun Arata, Benjamin A Lipsky)[\/caption]\r\n\r\nCharles is a retired bus driver who developed type 2 <strong>diabetes<\/strong> over 10 years ago. Since his retirement, his lifestyle has become very sedentary and he has put on a substantial amount of weight. Although he has felt tingling and numbness in his left foot for a while, he has not been worried because he thought his foot was simply \"falling asleep.\" Recently, a scratch on his foot does not seem to be healing and is becoming increasingly ugly. Because the sore did not bother him much, Charles figured it could not be serious until his daughter noticed a purplish discoloration spreading on the skin and oozing (Figure\u00a04). When he was finally seen by his physician, Charles was rushed to the operating room. His open sore, or ulcer, is the result of a <strong>diabetic foot<\/strong>.\r\n\r\nThe concern here is that <strong>gas gangrene<\/strong> may have taken hold in the dead tissue. The most likely agent of gas gangrene is <strong><em>Clostridium perfringens<\/em><\/strong>, an endospore-forming, gram-positive bacterium. It is an obligate anaerobe that grows in tissue devoid of oxygen. Since dead tissue is no longer supplied with oxygen by the circulatory system, the dead tissue provides pockets of ideal environment for the growth of <em>C. perfringens<\/em>.\r\n\r\nA surgeon examines the ulcer and radiographs of Charles\u2019s foot and determines that the bone is not yet infected. The wound will have to be surgically debrided (debridement refers to the removal of dead and infected tissue) and a sample sent for microbiological lab analysis, but Charles will not have to have his foot amputated. Many diabetic patients are not so lucky. In 2008, nearly 70,000 diabetic patients in the United States lost a foot or limb to amputation, according to statistics from the Centers for Disease Control and Prevention.[footnote]Centers for Disease Control and Prevention. \"Living With Diabetes: Keep Your Feet Healthy.\" http:\/\/www.cdc.gov\/Features\/DiabetesFootHealth\/[\/footnote]\r\n<ul>\r\n \t<li>Which growth conditions would you recommend for the detection of <em>C. perfringens<\/em>?<\/li>\r\n<\/ul>\r\n<\/div>\r\n<h2>Detoxification of Reactive Oxygen Species<\/h2>\r\nAerobic respiration constantly generates reactive oxygen species (ROS), byproducts that must be detoxified. Even organisms that do not use aerobic respiration need some way to break down some of the ROS that may form from atmospheric oxygen. Three main enzymes break down those toxic byproducts: superoxide dismutase, peroxidase, and catalase. Each one catalyzes a different reaction. Reactions of type seen in Reaction 1 are catalyzed by peroxidases.\r\n<p style=\"text-align: center;\">[latex]\\left(1\\right)\\text{X}-\\left(2{\\text{H}}^{\\text{+}}\\right)+{\\text{H}}_{2}{\\text{O}}_{2}\\to \\text{oxidized-X}+2{\\text{H}}_{2}\\text{O}[\/latex]<\/p>\r\nIn these reactions, an electron donor (reduced compound; e.g., reduced nicotinamide adenine dinucleotide [NADH]) oxidizes <strong>hydrogen peroxide<\/strong>, or other peroxides, to water. The enzymes play an important role by limiting the damage caused by peroxidation of membrane lipids. Reaction 2 is mediated by the enzyme superoxide dismutase (SOD) and breaks down the powerful superoxide anions generated by aerobic metabolism:\r\n<p style=\"text-align: center;\">[latex]\\left(2\\right)2{\\text{O}}^{2\\text{-}}+2{\\text{H}}^{+}\\to {\\text{H}}_{2}{\\text{O}}_{2}+{\\text{O}}_{2}[\/latex]<\/p>\r\nThe enzyme catalase converts hydrogen peroxide to water and oxygen as shown in Reaction 3.\r\n<p style=\"text-align: center;\">[latex]\\left(3\\right)2{\\text{H}}_{2}{\\text{O}}_{2}\\to 2{\\text{H}}_{2}\\text{O}+{\\text{O}}_{2}[\/latex]<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignright\" width=\"449\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03164326\/OSC_Microbio_09_01_cat.jpg\" alt=\"A slide with two drops of clear liquid. The left drop is not bubbling and is labeled catalase negative. The right drop is bubbling and is labeled catalase positive.\" width=\"449\" height=\"272\" data-media-type=\"image\/jpeg\" \/> Figure\u00a05. The catalase test detects the presence of the enzyme catalase by noting whether bubbles are released when hydrogen peroxide is added to a culture sample. Compare the positive result (right) with the negative result (left). (credit: Centers for Disease Control and Prevention)[\/caption]\r\n\r\nObligate anaerobes usually lack all three enzymes. Aerotolerant anaerobes do have SOD but no catalase. Reaction 3, shown occurring in Figure\u00a05, is the basis of a useful and rapid test to distinguish streptococci, which are aerotolerant and do not possess catalase, from staphylococci, which are facultative anaerobes. A sample of culture rapidly mixed in a drop of 3% hydrogen peroxide will release bubbles if the culture is catalase positive.\r\n\r\nBacteria that grow best in a higher concentration of CO<sub>2<\/sub> and a lower concentration of oxygen than present in the atmosphere are called capnophiles. One common approach to grow capnophiles is to use a candle jar. A candle jar consists of a jar with a tight-fitting lid that can accommodate the cultures and a candle. After the cultures are added to the jar, the candle is lit and the lid closed. As the candle burns, it consumes most of the oxygen present and releases CO<sub>2<\/sub>.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ul>\r\n \t<li>What substance is added to a sample to detect catalase?<\/li>\r\n \t<li>What is the function of the candle in a candle jar?<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox examples\">\r\n<h3>Clinical Focus: Nataliya, Part 2<\/h3>\r\nThis example continues Nataliya\u2019s story that started in <a href=\".\/chapter\/how-microbes-grow\/\" target=\"_blank\">How Microbes Grow<\/a>.\r\n\r\nThe health-care provider who saw Nataliya was concerned primarily because of her pregnancy. Her condition enhances the risk for infections and makes her more vulnerable to those infections. The immune system is downregulated during pregnancy, and pathogens that cross the placenta can be very dangerous for the fetus. A note on the provider\u2019s order to the microbiology lab mentions a suspicion of infection by <strong><em>Listeria monocytogenes<\/em><\/strong>, based on the signs and symptoms exhibited by the patient.\r\n\r\nNataliya\u2019s blood samples are streaked directly on <strong>sheep blood agar<\/strong>, a medium containing tryptic soy agar enriched with 5% sheep blood. (Blood is considered sterile; therefore, competing microorganisms are not expected in the medium.) The inoculated plates are incubated at 37 \u00b0C for 24 to 48 hours. Small grayish colonies surrounded by a clear zone emerge. Such colonies are typical of <em>Listeria<\/em> and other pathogens such as streptococci; the clear zone surrounding the colonies indicates complete lysis of blood in the medium, referred to as beta-hemolysis (Figure\u00a06). When tested for the presence of catalase, the colonies give a positive response, eliminating <em>Streptococcus<\/em> as a possible cause. Furthermore, a Gram stain shows short gram-positive bacilli. Cells from a broth culture grown at room temperature displayed the tumbling motility characteristic of <em>Listeria<\/em> (Figure\u00a06). All of these clues lead the lab to positively confirm the presence of <em>Listeria<\/em> in Nataliya\u2019s blood samples.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1200\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03164329\/OSC_Microbio_09_02_listumbrel.jpg\" alt=\"a) Two blood agar plates which have a red color. The left plate is labeled alpha hemolysis and shows slight clearings around the colonies. The right plate is labeled beta hemolysis and shows complete clearings around the colonies. B) Two tubes. The left tube is positive and shows cloudiness spreading out from the central line down the middle of the tube. The right tube is negative and shows no cloudiness spreading out from this central line.\" width=\"1200\" height=\"509\" data-media-type=\"image\/jpeg\" \/> Figure\u00a06. (a) A sample blood agar test showing beta-hemolysis. (b) A sample motility test showing both positive and negative results. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by \"VeeDunn\"\/Flickr)[\/caption]\r\n<ul>\r\n \t<li>How serious is Nataliya\u2019s condition and what is the appropriate treatment?<\/li>\r\n<\/ul>\r\nWe\u2019ll return to Nataliya\u2019s example in later pages.\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>Aerobic and anaerobic environments can be found in diverse niches throughout nature, including different sites within and on the human body.<\/li>\r\n \t<li>Microorganisms vary in their requirements for molecular oxygen. <strong>Obligate aerobes<\/strong> depend on aerobic respiration and use oxygen as a terminal electron acceptor. They cannot grow without oxygen.<\/li>\r\n \t<li><strong>Obligate anaerobes<\/strong> cannot grow in the presence of oxygen. They depend on fermentation and anaerobic respiration using a final electron acceptor other than oxygen.<\/li>\r\n \t<li><strong>Facultative anaerobes<\/strong> show better growth in the presence of oxygen but will also grow without it.<\/li>\r\n \t<li>Although <strong>aerotolerant anaerobes<\/strong> do not perform aerobic respiration, they can grow in the presence of oxygen. Most aerotolerant anaerobes test negative for the enzyme <strong>catalase<\/strong>.<\/li>\r\n \t<li><strong>Microaerophiles<\/strong> need oxygen to grow, albeit at a lower concentration than 21% oxygen in air.<\/li>\r\n \t<li><strong>Optimum oxygen concentration<\/strong> for an organism is the oxygen level that promotes the fastest growth rate. The <strong>minimum permissive oxygen concentration<\/strong> and the <strong>maximum permissive oxygen concentration<\/strong> are, respectively, the lowest and the highest oxygen levels that the organism will tolerate.<\/li>\r\n \t<li><strong>Peroxidase<\/strong>, <strong>superoxide dismutase<\/strong>, and <strong>catalase<\/strong> are the main enzymes involved in the detoxification of the <strong>reactive oxygen species<\/strong>. Superoxide dismutase is usually present in a cell that can tolerate oxygen. All three enzymes are usually detectable in cells that perform aerobic respiration and produce more ROS.<\/li>\r\n \t<li>A <strong>capnophile<\/strong> is an organism that requires a higher than atmospheric concentration of CO<sub>2<\/sub> to grow.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Multiple Choice<\/h3>\r\nAn inoculated thioglycolate medium culture tube shows dense growth at the surface and turbidity throughout the rest of the tube. What is your conclusion?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>The organisms die in the presence of oxygen<\/li>\r\n \t<li>The organisms are facultative anaerobes.<\/li>\r\n \t<li>The organisms should be grown in an anaerobic chamber.<\/li>\r\n \t<li>The organisms are obligate aerobes.<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"859236\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"859236\"]Answer b. The organisms are facultative anaerobes.[\/hidden-answer]\r\n\r\nAn inoculated thioglycolate medium culture tube is clear throughout the tube except for dense growth at the bottom of the tube. What is your conclusion?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>The organisms are obligate anaerobes.<\/li>\r\n \t<li>The organisms are facultative anaerobes.<\/li>\r\n \t<li>The organisms are aerotolerant.<\/li>\r\n \t<li>The organisms are obligate aerobes.<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"424438\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"424438\"]Answer a. The organisms are obligate anaerobes.[\/hidden-answer]\r\n\r\n<em>Pseudomonas aeruginosa<\/em> is a common pathogen that infects the airways of patients with cystic fibrosis. It does not grow in the absence of oxygen. The bacterium is probably which of the following?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>an aerotolerant anaerobe<\/li>\r\n \t<li>an obligate aerobe<\/li>\r\n \t<li>an obligate anaerobe<\/li>\r\n \t<li>a facultative anaerobe<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"688845\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"688845\"]Answer b. The bacterium is probably\u00a0an obligate aerobe.[\/hidden-answer]\r\n\r\n<em>Streptococcus mutans<\/em> is a major cause of cavities. It resides in the gum pockets, does not have catalase activity, and can be grown outside of an anaerobic chamber. The bacterium is probably which of the following?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>a facultative anaerobe<\/li>\r\n \t<li>an obligate aerobe<\/li>\r\n \t<li>an obligate anaerobe<\/li>\r\n \t<li>an aerotolerant anaerobe<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"332806\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"332806\"]Answer d. The bacterium is probably\u00a0an aerotolerant anaerobe.[\/hidden-answer]\r\n\r\nWhy do the instructions for the growth of <em>Neisseria gonorrheae<\/em> recommend a CO<sub>2<\/sub>-enriched atmosphere?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>It uses CO<sub>2<\/sub> as a final electron acceptor in respiration.<\/li>\r\n \t<li>It is an obligate anaerobe.<\/li>\r\n \t<li>It is a capnophile.<\/li>\r\n \t<li>It fixes CO<sub>2<\/sub> through photosynthesis.<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"635999\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"635999\"]Answer c. It is a capnophile.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Matching<\/h3>\r\nFour tubes are illustrated with cultures grown in a medium that slows oxygen diffusion. Match the culture tube with the correct type of bacteria from the following list: facultative anaerobe, obligate anaerobe, microaerophile, aerotolerant anaerobe, obligate aerobe.\r\n\r\n<img class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03164331\/OSC_Microbio_09_02_tubO_img.jpg\" alt=\"A) Cells are all at the bottom of the tube. b) Cells are all at the top of the tube. C) Cells are all just under the top of the tube. D) Cells are throughout the tube but more prominent at the top.\" width=\"683\" height=\"402\" data-media-type=\"image\/jpeg\" \/>\r\n[reveal-answer q=\"876008\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"876008\"]Tube a is an obligate anaerobe. Tube b is an obligate aerobe. Tube c is a microaerophile. Tube d is a facultative anaerobe[\/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>Why are some obligate anaerobes able to grow in tissues (e.g., gum pockets) that are not completely free of oxygen?<\/li>\r\n \t<li>Why should <em>Haemophilus influenzae<\/em> be grown in a candle jar?<\/li>\r\n \t<li>In terms of oxygen requirements, what type of organism would most likely be responsible for a foodborne illness associated with canned foods?<\/li>\r\n \t<li>A microbiology instructor prepares cultures for a gram-staining practical laboratory by inoculating growth medium with a gram-positive coccus (nonmotile) and a gram-negative rod (motile). The goal is to demonstrate staining of a mixed culture. The flask is incubated at 35 \u00b0C for 24 hours without aeration. A sample is stained and reveals only gram-negative rods. Both cultures are known facultative anaerobes. Give a likely reason for success of the gram-negative rod. Assume that the cultures have comparable intrinsic growth rates.<\/li>\r\n<\/ol>\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<ul>\n<li>Interpret visual data demonstrating minimum, optimum, and maximum oxygen or carbon dioxide requirements for growth<\/li>\n<li>Identify and describe different categories of microbes with requirements for growth with or without oxygen: obligate aerobe, obligate anaerobe, facultative anaerobe, aerotolerant anaerobe, microaerophile, and capnophile<\/li>\n<li>Give examples of microorganisms for each category of growth requirements<\/li>\n<\/ul>\n<\/div>\n<p>Ask most people &#8220;What are the major requirements for life?&#8221; and the answers are likely to include water and oxygen. Few would argue about the need for water, but what about oxygen? Can there be life without oxygen?<\/p>\n<p>The answer is that molecular oxygen (O<sub>2<\/sub>) is not always needed. The earliest signs of life are dated to a period when conditions on earth were highly reducing and free oxygen gas was essentially nonexistent. Only after cyanobacteria started releasing oxygen as a byproduct of photosynthesis and the capacity of iron in the oceans for taking up oxygen was exhausted did oxygen levels increase in the atmosphere. This event, often referred to as the <strong>Great Oxygenation Event<\/strong> or the <strong>Oxygen Revolution<\/strong>, caused a massive extinction. Most organisms could not survive the powerful oxidative properties of <strong>reactive oxygen species (ROS)<\/strong>, highly unstable ions and molecules derived from partial reduction of oxygen that can damage virtually any macromolecule or structure with which they come in contact. Singlet oxygen (O<sub>2<\/sub>\u2022), superoxide [latex]\\left({\\text{O}}_{2}^{-}\\right)[\/latex], peroxides (H<sub>2<\/sub>O<sub>2<\/sub>), hydroxyl radical (OH\u2022), and hypochlorite ion (OCl<sup>\u2212<\/sup>), the active ingredient of household bleach, are all examples of ROS. The organisms that were able to detoxify reactive oxygen species harnessed the high electronegativity of oxygen to produce free energy for their metabolism and thrived in the new environment.<\/p>\n<h2>Oxygen Requirements of Microorganisms<\/h2>\n<p>Many ecosystems are still free of molecular oxygen. Some are found in extreme locations, such as deep in the ocean or in earth\u2019s crust; others are part of our everyday landscape, such as marshes, bogs, and sewers. Within the bodies of humans and other animals, regions with little or no oxygen provide an anaerobic environment for microorganisms (Figure\u00a01).<\/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\/03164315\/OSC_Microbio_09_02_bog.jpg\" alt=\"a) A photograph of a bog. B) A photograph of cows.\" width=\"1100\" height=\"400\" data-media-type=\"image\/jpeg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a01. Anaerobic environments are still common on earth. They include environments like (a) a bog where undisturbed dense sediments are virtually devoid of oxygen, and (b) the rumen (the first compartment of a cow\u2019s stomach), which provides an oxygen-free incubator for methanogens and other obligate anaerobic bacteria. (credit a: modification of work by National Park Service; credit b: modification of work by US Department of Agriculture)<\/p>\n<\/div>\n<p>We can easily observe different requirements for molecular oxygen by growing bacteria in <strong>thioglycolate tube cultures<\/strong>. A test-tube culture starts with autoclaved <strong>thioglycolate medium<\/strong> containing a low percentage of agar to allow motile bacteria to move throughout the medium. Thioglycolate has strong reducing properties and autoclaving flushes out most of the oxygen. The tubes are inoculated with the bacterial cultures to be tested and incubated at an appropriate temperature. Over time, oxygen slowly diffuses throughout the thioglycolate tube culture from the top. Bacterial density increases in the area where oxygen concentration is best suited for the growth of that particular organism.<\/p>\n<p>The growth of bacteria with varying oxygen requirements in thioglycolate tubes is illustrated in Figure\u00a02. In tube A, all the growth is seen at the top of the tube. The bacteria are <strong>obligate (strict) aerobes<\/strong> that cannot grow without an abundant supply of oxygen. Tube B looks like the opposite of tube A. Bacteria grow at the bottom of tube B. Those are <strong>obligate anaerobes<\/strong>, which are killed by oxygen. Tube C shows heavy growth at the top of the tube and growth throughout the tube, a typical result with <strong>facultative anaerobes<\/strong>. Facultative anaerobes are organisms that thrive in the presence of oxygen but also grow in its absence by relying on fermentation or anaerobic respiration, if there is a suitable electron acceptor other than oxygen and the organism is able to perform anaerobic respiration. The <strong>aerotolerant anaerobes<\/strong> in tube D are indifferent to the presence of oxygen. They do not use oxygen because they usually have a fermentative metabolism, but they are not harmed by the presence of oxygen as obligate anaerobes are. Tube E on the right shows a &#8220;Goldilocks&#8221; culture. The oxygen level has to be just right for growth, not too much and not too little. These <strong>microaerophiles<\/strong> are bacteria that require a minimum level of oxygen for growth, about 1%\u201310%, well below the 21% found in the atmosphere.<\/p>\n<p>Examples of obligate aerobes are <strong><em>Mycobacterium tuberculosis<\/em><\/strong>, the causative agent of tuberculosis and <strong><em>Micrococcus luteus<\/em><\/strong>, a gram-positive bacterium that colonizes the skin. <strong><em>Neisseria meningitidis<\/em><\/strong>, the causative agent of severe <strong>bacterial meningitis<\/strong>, and <em>N. gonorrheae<\/em>, the causative agent of sexually transmitted <strong>gonorrhea<\/strong>, are also obligate aerobes.<\/p>\n<div style=\"width: 711px\" 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\/03164318\/OSC_Microbio_09_02_tubO.jpg\" alt=\"A diagram of bacterial distribution in tubes. Tube A shows obligate aerobes which grow at the top of the tube. Tube B shows obligate anaerobes which grow at the bottom of the tube. Tube C shows facultative anaerobes which grow best at the top but also grow throughout the tube. Tube D shows aerotolerant anaerobes which grow equally well throughout. Tube E shows microaerophiles which grow just below the top of the tube.\" width=\"701\" height=\"344\" data-media-type=\"image\/jpeg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a02. Diagram of bacterial cell distribution in thioglycolate tubes.<\/p>\n<\/div>\n<p>Many obligate anaerobes are found in the environment where anaerobic conditions exist, such as in deep sediments of soil, still waters, and at the bottom of the deep ocean where there is no photosynthetic life. Anaerobic conditions also exist naturally in the intestinal tract of animals. Obligate anaerobes, mainly <strong><em>Bacteroidetes<\/em><\/strong>, represent a large fraction of the microbes in the human gut. Transient anaerobic conditions exist when tissues are not supplied with blood circulation; they die and become an ideal breeding ground for obligate anaerobes. Another type of obligate anaerobe encountered in the human body is the gram-positive, rod-shaped <strong><em>Clostridium<\/em><\/strong> spp. Their ability to form endospores allows them to survive in the presence of oxygen. One of the major causes of health-acquired infections is <em>C. difficile<\/em>, known as C. diff. Prolonged use of antibiotics for other infections increases the probability of a patient developing a secondary <em>C. difficile<\/em> infection. Antibiotic treatment disrupts the balance of microorganisms in the intestine and allows the colonization of the gut by <em>C. difficile<\/em>, causing a significant inflammation of the colon.<\/p>\n<p>Other clostridia responsible for serious infections include <em>C. tetani<\/em>, the agent of tetanus, and <em>C. perfringens<\/em>, which causes <strong>gas gangrene<\/strong>. In both cases, the infection starts in necrotic tissue (dead tissue that is not supplied with oxygen by blood circulation). This is the reason that deep puncture wounds are associated with tetanus. When tissue death is accompanied by lack of circulation, gangrene is always a danger.<\/p>\n<p>The study of obligate anaerobes requires special equipment. Obligate anaerobic bacteria must be grown under conditions devoid of oxygen. The most common approach is culture in an <strong>anaerobic jar<\/strong> (Figure\u00a03). Anaerobic jars include chemical packs that remove oxygen and release carbon dioxide (CO<sub>2<\/sub>). An <strong>anaerobic chamber<\/strong> is an enclosed box from which all oxygen is removed. Gloves sealed to openings in the box allow handling of the cultures without exposing the culture to air (Figure\u00a03).<\/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\/03164321\/OSC_Microbio_09_02_jar.jpg\" alt=\"a) A photo of a stack of agar plates in a chamber. B) A photo of a chamber with sleeves for arms.\" width=\"1100\" height=\"414\" data-media-type=\"image\/jpeg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a03. (a) An anaerobic jar is pictured that is holding nine Petri plates supporting cultures. (b) Openings in the side of an anaerobic box are sealed by glove-like sleeves that allow for the handling of cultures inside the box. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by NIST)<\/p>\n<\/div>\n<p>Staphylococci and <strong>Enterobacteriaceae<\/strong> are examples of facultative anaerobes. Staphylococci are found on the skin and upper respiratory tract. Enterobacteriaceae are found primarily in the gut and upper respiratory tract but can sometimes spread to the urinary tract, where they are capable of causing infections. It is not unusual to see mixed bacterial infections in which the facultative anaerobes use up the oxygen, creating an environment for the obligate anaerobes to flourish.<\/p>\n<p>Examples of aerotolerant anaerobes include lactobacilli and streptococci, both found in the oral microbiota. <strong><em>Campylobacter jejuni<\/em><\/strong>, which causes gastrointestinal infections, is an example of a microaerophile and is grown under low-oxygen conditions.<\/p>\n<p>The <strong>optimum oxygen concentration<\/strong>, as the name implies, is the ideal concentration of oxygen for a particular microorganism. The lowest concentration of oxygen that allows growth is called the <strong>minimum permissive oxygen concentration<\/strong>. The highest tolerated concentration of oxygen is the maximum permissive oxygen concentration. The organism will not grow outside the range of oxygen levels found between the minimum and maximum permissive oxygen concentrations.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ul>\n<li>Would you expect the oldest bacterial lineages to be aerobic or anaerobic?<\/li>\n<li>Which bacteria grow at the top of a thioglycolate tube, and which grow at the bottom of the tube?<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>An Unwelcome Anaerobe<\/h3>\n<div style=\"width: 459px\" 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\/03164324\/OSC_Microbio_09_02_foot.jpg\" alt=\"A swollen foot with peeling skin and black regions under the skin.\" width=\"449\" height=\"292\" data-media-type=\"image\/jpeg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a04. This clinical photo depicts ulcers on the foot of a diabetic patient. Dead tissue accumulating in ulcers can provide an ideal growth environment for the anaerobe <em>C. perfringens<\/em>, a causative agent of gas gangrene. (credit: Shigeo Kono, Reiko Nakagawachi, Jun Arata, Benjamin A Lipsky)<\/p>\n<\/div>\n<p>Charles is a retired bus driver who developed type 2 <strong>diabetes<\/strong> over 10 years ago. Since his retirement, his lifestyle has become very sedentary and he has put on a substantial amount of weight. Although he has felt tingling and numbness in his left foot for a while, he has not been worried because he thought his foot was simply &#8220;falling asleep.&#8221; Recently, a scratch on his foot does not seem to be healing and is becoming increasingly ugly. Because the sore did not bother him much, Charles figured it could not be serious until his daughter noticed a purplish discoloration spreading on the skin and oozing (Figure\u00a04). When he was finally seen by his physician, Charles was rushed to the operating room. His open sore, or ulcer, is the result of a <strong>diabetic foot<\/strong>.<\/p>\n<p>The concern here is that <strong>gas gangrene<\/strong> may have taken hold in the dead tissue. The most likely agent of gas gangrene is <strong><em>Clostridium perfringens<\/em><\/strong>, an endospore-forming, gram-positive bacterium. It is an obligate anaerobe that grows in tissue devoid of oxygen. Since dead tissue is no longer supplied with oxygen by the circulatory system, the dead tissue provides pockets of ideal environment for the growth of <em>C. perfringens<\/em>.<\/p>\n<p>A surgeon examines the ulcer and radiographs of Charles\u2019s foot and determines that the bone is not yet infected. The wound will have to be surgically debrided (debridement refers to the removal of dead and infected tissue) and a sample sent for microbiological lab analysis, but Charles will not have to have his foot amputated. Many diabetic patients are not so lucky. In 2008, nearly 70,000 diabetic patients in the United States lost a foot or limb to amputation, according to statistics from the Centers for Disease Control and Prevention.<a class=\"footnote\" title=\"Centers for Disease Control and Prevention. &quot;Living With Diabetes: Keep Your Feet Healthy.&quot; http:\/\/www.cdc.gov\/Features\/DiabetesFootHealth\/\" id=\"return-footnote-452-1\" href=\"#footnote-452-1\" aria-label=\"Footnote 1\"><sup class=\"footnote\">[1]<\/sup><\/a><\/p>\n<ul>\n<li>Which growth conditions would you recommend for the detection of <em>C. perfringens<\/em>?<\/li>\n<\/ul>\n<\/div>\n<h2>Detoxification of Reactive Oxygen Species<\/h2>\n<p>Aerobic respiration constantly generates reactive oxygen species (ROS), byproducts that must be detoxified. Even organisms that do not use aerobic respiration need some way to break down some of the ROS that may form from atmospheric oxygen. Three main enzymes break down those toxic byproducts: superoxide dismutase, peroxidase, and catalase. Each one catalyzes a different reaction. Reactions of type seen in Reaction 1 are catalyzed by peroxidases.<\/p>\n<p style=\"text-align: center;\">[latex]\\left(1\\right)\\text{X}-\\left(2{\\text{H}}^{\\text{+}}\\right)+{\\text{H}}_{2}{\\text{O}}_{2}\\to \\text{oxidized-X}+2{\\text{H}}_{2}\\text{O}[\/latex]<\/p>\n<p>In these reactions, an electron donor (reduced compound; e.g., reduced nicotinamide adenine dinucleotide [NADH]) oxidizes <strong>hydrogen peroxide<\/strong>, or other peroxides, to water. The enzymes play an important role by limiting the damage caused by peroxidation of membrane lipids. Reaction 2 is mediated by the enzyme superoxide dismutase (SOD) and breaks down the powerful superoxide anions generated by aerobic metabolism:<\/p>\n<p style=\"text-align: center;\">[latex]\\left(2\\right)2{\\text{O}}^{2\\text{-}}+2{\\text{H}}^{+}\\to {\\text{H}}_{2}{\\text{O}}_{2}+{\\text{O}}_{2}[\/latex]<\/p>\n<p>The enzyme catalase converts hydrogen peroxide to water and oxygen as shown in Reaction 3.<\/p>\n<p style=\"text-align: center;\">[latex]\\left(3\\right)2{\\text{H}}_{2}{\\text{O}}_{2}\\to 2{\\text{H}}_{2}\\text{O}+{\\text{O}}_{2}[\/latex]<\/p>\n<div style=\"width: 459px\" 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\/03164326\/OSC_Microbio_09_01_cat.jpg\" alt=\"A slide with two drops of clear liquid. The left drop is not bubbling and is labeled catalase negative. The right drop is bubbling and is labeled catalase positive.\" width=\"449\" height=\"272\" data-media-type=\"image\/jpeg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a05. The catalase test detects the presence of the enzyme catalase by noting whether bubbles are released when hydrogen peroxide is added to a culture sample. Compare the positive result (right) with the negative result (left). (credit: Centers for Disease Control and Prevention)<\/p>\n<\/div>\n<p>Obligate anaerobes usually lack all three enzymes. Aerotolerant anaerobes do have SOD but no catalase. Reaction 3, shown occurring in Figure\u00a05, is the basis of a useful and rapid test to distinguish streptococci, which are aerotolerant and do not possess catalase, from staphylococci, which are facultative anaerobes. A sample of culture rapidly mixed in a drop of 3% hydrogen peroxide will release bubbles if the culture is catalase positive.<\/p>\n<p>Bacteria that grow best in a higher concentration of CO<sub>2<\/sub> and a lower concentration of oxygen than present in the atmosphere are called capnophiles. One common approach to grow capnophiles is to use a candle jar. A candle jar consists of a jar with a tight-fitting lid that can accommodate the cultures and a candle. After the cultures are added to the jar, the candle is lit and the lid closed. As the candle burns, it consumes most of the oxygen present and releases CO<sub>2<\/sub>.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ul>\n<li>What substance is added to a sample to detect catalase?<\/li>\n<li>What is the function of the candle in a candle jar?<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox examples\">\n<h3>Clinical Focus: Nataliya, Part 2<\/h3>\n<p>This example continues Nataliya\u2019s story that started in <a href=\".\/chapter\/how-microbes-grow\/\" target=\"_blank\">How Microbes Grow<\/a>.<\/p>\n<p>The health-care provider who saw Nataliya was concerned primarily because of her pregnancy. Her condition enhances the risk for infections and makes her more vulnerable to those infections. The immune system is downregulated during pregnancy, and pathogens that cross the placenta can be very dangerous for the fetus. A note on the provider\u2019s order to the microbiology lab mentions a suspicion of infection by <strong><em>Listeria monocytogenes<\/em><\/strong>, based on the signs and symptoms exhibited by the patient.<\/p>\n<p>Nataliya\u2019s blood samples are streaked directly on <strong>sheep blood agar<\/strong>, a medium containing tryptic soy agar enriched with 5% sheep blood. (Blood is considered sterile; therefore, competing microorganisms are not expected in the medium.) The inoculated plates are incubated at 37 \u00b0C for 24 to 48 hours. Small grayish colonies surrounded by a clear zone emerge. Such colonies are typical of <em>Listeria<\/em> and other pathogens such as streptococci; the clear zone surrounding the colonies indicates complete lysis of blood in the medium, referred to as beta-hemolysis (Figure\u00a06). When tested for the presence of catalase, the colonies give a positive response, eliminating <em>Streptococcus<\/em> as a possible cause. Furthermore, a Gram stain shows short gram-positive bacilli. Cells from a broth culture grown at room temperature displayed the tumbling motility characteristic of <em>Listeria<\/em> (Figure\u00a06). All of these clues lead the lab to positively confirm the presence of <em>Listeria<\/em> in Nataliya\u2019s blood samples.<\/p>\n<div style=\"width: 1210px\" 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\/03164329\/OSC_Microbio_09_02_listumbrel.jpg\" alt=\"a) Two blood agar plates which have a red color. The left plate is labeled alpha hemolysis and shows slight clearings around the colonies. The right plate is labeled beta hemolysis and shows complete clearings around the colonies. B) Two tubes. The left tube is positive and shows cloudiness spreading out from the central line down the middle of the tube. The right tube is negative and shows no cloudiness spreading out from this central line.\" width=\"1200\" height=\"509\" data-media-type=\"image\/jpeg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a06. (a) A sample blood agar test showing beta-hemolysis. (b) A sample motility test showing both positive and negative results. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by &#8220;VeeDunn&#8221;\/Flickr)<\/p>\n<\/div>\n<ul>\n<li>How serious is Nataliya\u2019s condition and what is the appropriate treatment?<\/li>\n<\/ul>\n<p>We\u2019ll return to Nataliya\u2019s example in later pages.<\/p>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Key Concepts and Summary<\/h3>\n<ul>\n<li>Aerobic and anaerobic environments can be found in diverse niches throughout nature, including different sites within and on the human body.<\/li>\n<li>Microorganisms vary in their requirements for molecular oxygen. <strong>Obligate aerobes<\/strong> depend on aerobic respiration and use oxygen as a terminal electron acceptor. They cannot grow without oxygen.<\/li>\n<li><strong>Obligate anaerobes<\/strong> cannot grow in the presence of oxygen. They depend on fermentation and anaerobic respiration using a final electron acceptor other than oxygen.<\/li>\n<li><strong>Facultative anaerobes<\/strong> show better growth in the presence of oxygen but will also grow without it.<\/li>\n<li>Although <strong>aerotolerant anaerobes<\/strong> do not perform aerobic respiration, they can grow in the presence of oxygen. Most aerotolerant anaerobes test negative for the enzyme <strong>catalase<\/strong>.<\/li>\n<li><strong>Microaerophiles<\/strong> need oxygen to grow, albeit at a lower concentration than 21% oxygen in air.<\/li>\n<li><strong>Optimum oxygen concentration<\/strong> for an organism is the oxygen level that promotes the fastest growth rate. The <strong>minimum permissive oxygen concentration<\/strong> and the <strong>maximum permissive oxygen concentration<\/strong> are, respectively, the lowest and the highest oxygen levels that the organism will tolerate.<\/li>\n<li><strong>Peroxidase<\/strong>, <strong>superoxide dismutase<\/strong>, and <strong>catalase<\/strong> are the main enzymes involved in the detoxification of the <strong>reactive oxygen species<\/strong>. Superoxide dismutase is usually present in a cell that can tolerate oxygen. All three enzymes are usually detectable in cells that perform aerobic respiration and produce more ROS.<\/li>\n<li>A <strong>capnophile<\/strong> is an organism that requires a higher than atmospheric concentration of CO<sub>2<\/sub> to grow.<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Multiple Choice<\/h3>\n<p>An inoculated thioglycolate medium culture tube shows dense growth at the surface and turbidity throughout the rest of the tube. What is your conclusion?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>The organisms die in the presence of oxygen<\/li>\n<li>The organisms are facultative anaerobes.<\/li>\n<li>The organisms should be grown in an anaerobic chamber.<\/li>\n<li>The organisms are obligate aerobes.<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q859236\">Show Answer<\/span><\/p>\n<div id=\"q859236\" class=\"hidden-answer\" style=\"display: none\">Answer b. The organisms are facultative anaerobes.<\/div>\n<\/div>\n<p>An inoculated thioglycolate medium culture tube is clear throughout the tube except for dense growth at the bottom of the tube. What is your conclusion?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>The organisms are obligate anaerobes.<\/li>\n<li>The organisms are facultative anaerobes.<\/li>\n<li>The organisms are aerotolerant.<\/li>\n<li>The organisms are obligate aerobes.<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q424438\">Show Answer<\/span><\/p>\n<div id=\"q424438\" class=\"hidden-answer\" style=\"display: none\">Answer a. The organisms are obligate anaerobes.<\/div>\n<\/div>\n<p><em>Pseudomonas aeruginosa<\/em> is a common pathogen that infects the airways of patients with cystic fibrosis. It does not grow in the absence of oxygen. The bacterium is probably which of the following?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>an aerotolerant anaerobe<\/li>\n<li>an obligate aerobe<\/li>\n<li>an obligate anaerobe<\/li>\n<li>a facultative anaerobe<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q688845\">Show Answer<\/span><\/p>\n<div id=\"q688845\" class=\"hidden-answer\" style=\"display: none\">Answer b. The bacterium is probably\u00a0an obligate aerobe.<\/div>\n<\/div>\n<p><em>Streptococcus mutans<\/em> is a major cause of cavities. It resides in the gum pockets, does not have catalase activity, and can be grown outside of an anaerobic chamber. The bacterium is probably which of the following?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>a facultative anaerobe<\/li>\n<li>an obligate aerobe<\/li>\n<li>an obligate anaerobe<\/li>\n<li>an aerotolerant anaerobe<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q332806\">Show Answer<\/span><\/p>\n<div id=\"q332806\" class=\"hidden-answer\" style=\"display: none\">Answer d. The bacterium is probably\u00a0an aerotolerant anaerobe.<\/div>\n<\/div>\n<p>Why do the instructions for the growth of <em>Neisseria gonorrheae<\/em> recommend a CO<sub>2<\/sub>-enriched atmosphere?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>It uses CO<sub>2<\/sub> as a final electron acceptor in respiration.<\/li>\n<li>It is an obligate anaerobe.<\/li>\n<li>It is a capnophile.<\/li>\n<li>It fixes CO<sub>2<\/sub> through photosynthesis.<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q635999\">Show Answer<\/span><\/p>\n<div id=\"q635999\" class=\"hidden-answer\" style=\"display: none\">Answer c. It is a capnophile.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Matching<\/h3>\n<p>Four tubes are illustrated with cultures grown in a medium that slows oxygen diffusion. Match the culture tube with the correct type of bacteria from the following list: facultative anaerobe, obligate anaerobe, microaerophile, aerotolerant anaerobe, obligate aerobe.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03164331\/OSC_Microbio_09_02_tubO_img.jpg\" alt=\"A) Cells are all at the bottom of the tube. b) Cells are all at the top of the tube. C) Cells are all just under the top of the tube. D) Cells are throughout the tube but more prominent at the top.\" width=\"683\" height=\"402\" data-media-type=\"image\/jpeg\" \/><\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q876008\">Show Answer<\/span><\/p>\n<div id=\"q876008\" class=\"hidden-answer\" style=\"display: none\">Tube a is an obligate anaerobe. Tube b is an obligate aerobe. Tube c is a microaerophile. Tube d is a facultative anaerobe<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ol>\n<li>Why are some obligate anaerobes able to grow in tissues (e.g., gum pockets) that are not completely free of oxygen?<\/li>\n<li>Why should <em>Haemophilus influenzae<\/em> be grown in a candle jar?<\/li>\n<li>In terms of oxygen requirements, what type of organism would most likely be responsible for a foodborne illness associated with canned foods?<\/li>\n<li>A microbiology instructor prepares cultures for a gram-staining practical laboratory by inoculating growth medium with a gram-positive coccus (nonmotile) and a gram-negative rod (motile). The goal is to demonstrate staining of a mixed culture. The flask is incubated at 35 \u00b0C for 24 hours without aeration. A sample is stained and reveals only gram-negative rods. Both cultures are known facultative anaerobes. Give a likely reason for success of the gram-negative rod. Assume that the cultures have comparable intrinsic growth rates.<\/li>\n<\/ol>\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-452\">\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-452-1\">Centers for Disease Control and Prevention. \"Living With Diabetes: Keep Your Feet Healthy.\" http:\/\/www.cdc.gov\/Features\/DiabetesFootHealth\/ <a href=\"#return-footnote-452-1\" class=\"return-footnote\" aria-label=\"Return to footnote 1\">&crarr;<\/a><\/li><\/ol><\/div>","protected":false},"author":17,"menu_order":3,"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-452","chapter","type-chapter","status-publish","hentry"],"part":421,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapters\/452","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":4,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapters\/452\/revisions"}],"predecessor-version":[{"id":1589,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapters\/452\/revisions\/1589"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/parts\/421"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapters\/452\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/wp\/v2\/media?parent=452"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/pressbooks\/v2\/chapter-type?post=452"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/wp\/v2\/contributor?post=452"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-microbiology\/wp-json\/wp\/v2\/license?post=452"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}