{"id":888,"date":"2016-11-04T03:35:38","date_gmt":"2016-11-04T03:35:38","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/microbiology\/?post_type=chapter&#038;p=888"},"modified":"2018-07-12T11:25:37","modified_gmt":"2018-07-12T11:25:37","slug":"anatomy-and-normal-microbiota-of-the-skin-and-eyes","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/chapter\/anatomy-and-normal-microbiota-of-the-skin-and-eyes\/","title":{"raw":"Anatomy and Normal Microbiota of the Skin and Eyes","rendered":"Anatomy and Normal Microbiota of the Skin and Eyes"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\n<ul>\r\n \t<li>Describe the major anatomical features of the skin and eyes<\/li>\r\n \t<li>Compare and contrast the microbiomes of various body sites, such as the hands, back, feet, and eyes<\/li>\r\n \t<li>Explain how microorganisms overcome defenses of skin and eyes in order to cause infection<\/li>\r\n \t<li>Describe general signs and symptoms of disease associated with infections of the skin and eyes<\/li>\r\n<\/ul>\r\n<\/div>\r\nHuman skin is an important part of the innate immune system. In addition to serving a wide range of other functions, the skin serves as an important barrier to microbial invasion. Not only is it a physical barrier to penetration of deeper tissues by potential pathogens, but it also provides an inhospitable environment for the growth of many pathogens. In this section, we will provide a brief overview of the anatomy and normal microbiota of the skin and eyes, along with general symptoms associated with skin and eye infections.\r\n<h2>Layers of the Skin<\/h2>\r\nHuman skin is made up of several layers and sublayers. The two main layers are the <strong>epidermis<\/strong> and the <strong>dermis<\/strong>. These layers cover a third layer of tissue called the <strong>hypodermis<\/strong>, which consists of fibrous and adipose connective tissue (Figure\u00a01).\r\n\r\nThe epidermis is the outermost layer of the skin, and it is relatively thin. The exterior surface of the epidermis, called the <strong>stratum corneum<\/strong>, primarily consists of dead skin cells. This layer of dead cells limits direct contact between the outside world and live cells. The stratum corneum is rich in <strong>keratin<\/strong>, a tough, fibrous protein that is also found in hair and nails. Keratin helps make the outer surface of the skin relatively tough and waterproof. It also helps to keep the surface of the skin dry, which reduces microbial growth. However, some microbes are still able to live on the surface of the skin, and some of these can be shed with dead skin cells in the process of <strong>desquamation<\/strong>, which is the shedding and peeling of skin that occurs as a normal process but that may be accelerated when infection is present.\r\n\r\nBeneath the epidermis lies a thicker skin layer called the <strong>dermis<\/strong>. The dermis contains connective tissue and embedded structures such as blood vessels, nerves, and muscles. Structures called <strong>hair follicles<\/strong> (from which hair grows) are located within the dermis, even though much of their structure consists of epidermal tissue. The dermis also contains the two major types of glands found in human skin: <strong>sweat glands<\/strong> (tubular glands that produce sweat) and <strong>sebaceous glands<\/strong> (which are associated with hair follicles and produce <strong>sebum<\/strong>, a lipid-rich substance containing proteins and minerals).\r\n\r\nPerspiration (sweat) provides some moisture to the epidermis, which can increase the potential for microbial growth. For this reason, more microbes are found on the regions of the skin that produce the most sweat, such as the skin of the underarms and groin. However, in addition to water, sweat also contains substances that inhibit microbial growth, such as salts, <strong>lysozyme<\/strong>, and <strong>antimicrobial peptides<\/strong>. Sebum also serves to protect the skin and reduce water loss. Although some of the lipids and fatty acids in sebum inhibit microbial growth, sebum contains compounds that provide nutrition for certain microbes.\r\n\r\n[caption id=\"attachment_1754\" align=\"aligncenter\" width=\"1024\"]<img class=\"size-large wp-image-1754\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/11170513\/OSC_Microbio_21_01_skinlayers1-1024x572.jpg\" alt=\"a) A micrograph of a large light pink region labeled dermis, a thinner dark pink region on top of that labeled epidermis, and a thin region of clear cells. The division between the dermis and epidermis is wavy; with areas where one projects into the other. B) A diagram of skin. The top layer is dark and is labeled epidermis. The next layer is lighter and much thicker; this is the dermis. Inside the dermis are vase-shaped hair follicles with hairs projecting out of the skin. Next to the hair follicle is a smaller vase-shape labeled sebaceous gland; this empties into the space of the hair follicle. There are also coiled shapes labeled receptor and a variety of long tubes labeled: nerve, lymph vessel and blood vessels. A coiled blob is labeled sweat gland; this leads to a tube that opens at the surface called a sweat pore. Below the dermis is a yellow bubbly-looking layer labeled fatty tissue; this is the hypodermis.\" width=\"1024\" height=\"572\" \/> Figure\u00a01. (a) A micrograph of a section through human skin shows the epidermis and dermis. (b) The major layers of human skin are the epidermis, dermis, and hypodermis. (credit b: modification of work by National Cancer Institute)[\/caption]\r\n<h2>Normal Microbiota of the Skin<\/h2>\r\nThe skin is home to a wide variety of normal microbiota, consisting of commensal organisms that derive nutrition from skin cells and secretions such as sweat and sebum. The normal microbiota of skin tends to inhibit transient-microbe colonization by producing antimicrobial substances and outcompeting other microbes that land on the surface of the skin. This helps to protect the skin from pathogenic infection.\r\n\r\nThe skin\u2019s properties differ from one region of the body to another, as does the composition of the skin\u2019s microbiota. The availability of nutrients and moisture partly dictates which microorganisms will thrive in a particular region of the skin. Relatively moist skin, such as that of the nares (nostrils) and underarms, has a much different microbiota than the dryer skin on the arms, legs, hands, and top of the feet. Some areas of the skin have higher densities of <strong>sebaceous glands<\/strong>. These <strong>sebum<\/strong>-rich areas, which include the back, the folds at the side of the nose, and the back of the neck, harbor distinct microbial communities that are less diverse than those found on other parts of the body.\r\n\r\nDifferent types of bacteria dominate the dry, moist, and sebum-rich regions of the skin. The most abundant microbes typically found in the dry and sebaceous regions are <strong>Betaproteobacteria<\/strong> and <strong>Propionibacteria<\/strong>, respectively. In the moist regions, <strong><em>Corynebacterium<\/em><\/strong> and <strong><em>Staphylococcus<\/em><\/strong> are most commonly found (Figure\u00a02). Viruses and fungi are also found on the skin, with <strong><em>Malassezia<\/em><\/strong> being the most common type of fungus found as part of the normal microbiota. The role and populations of viruses in the microbiota, known as <strong>viromes<\/strong>, are still not well understood, and there are limitations to the techniques used to identify them. However, <strong>Circoviridae<\/strong>, <strong>Papillomaviridae<\/strong>, and <strong>Polyomaviridae<\/strong> appear to be the most common residents in the healthy skin virome.[footnote]Belkaid, Y., and J.A. Segre. \"Dialogue Between Skin Microbiota and Immunity,\" <em>Science<\/em> 346 (2014) 6212:954\u2013959.[\/footnote] [footnote]Foulongne, Vincent, et al. \"Human Skin Microbiota: High Diversity of DNA Viruses Identified on the Human Skin by High Throughput Sequencing.\" <em>PLoS ONE<\/em> (2012) 7(6): e38499. doi: 10.1371\/journal.pone.0038499.[\/footnote] [footnote]Robinson, C.M., and J.K. Pfeiffer. \"Viruses and the Microbiota.\" <em>Annual Review of Virology<\/em> (2014) 1:55\u201359. doi: 10.1146\/annurev-virology-031413-085550.[\/footnote]\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\/03173051\/OSC_Microbio_21_01_microbiota.jpg\" alt=\"A diagram showing different regions of the body. Each region has a pie chart that shows which bacteria are most prevalent. The most common bacterium in each region: Glabella (corynebacterineae), Alar Crease (propionibacterineae), External auditory canal (propionibacterineae), Nare (other actinobacteria), manubrioum (propionibacterineae), Axillary vault (proteobacteria), antecubital fossa (proteobacteria), Volar forearm (proteobacteria), interdigital web space (proteobacteria), hypothenar palm (proteobacteria), inguinal crease (corynebacterineae), umbilicus (corynebacterineae), toe web space (corynebacterineae, , propionibacterineae, and staphylococcaceae), reticular crease (propionibacterineae), occiput (staphylococcaceae, back (propionibacterineae), buttock (proteobacteria), gluteal crease (corynebacterineae), popliteal fossa (staphylococcaceae), plantar heel (staphylococcaceae). Second part of the image shows that different subjects have different bacterial percentages and that these percentages change over time.\" width=\"1300\" height=\"812\" \/> Figure\u00a02. The normal microbiota varies on different regions of the skin, especially in dry versus moist areas. The figure shows the major organisms commonly found in different locations of a healthy individual\u2019s skin and external mucosa. Note that there is significant variation among individuals. (credit: modification of work by National Human Genome Research Institute)[\/caption]\r\n<h2>Infections of the Skin<\/h2>\r\nWhile the microbiota of the skin can play a protective role, it can also cause harm in certain cases. Often, an opportunistic pathogen residing in the skin microbiota of one individual may be transmitted to another individual more susceptible to an infection. For example, methicillin-resistant <em>Staphylococcus aureus<\/em> (<strong>MRSA<\/strong>) can often take up residence in the nares of health care workers and hospital patients; though harmless on intact, healthy skin, MRSA can cause infections if introduced into other parts of the body, as might occur during surgery or via a post-surgical incision or wound. This is one reason why clean surgical sites are so important.\r\n\r\nInjury or damage to the skin can allow microbes to enter deeper tissues, where nutrients are more abundant and the environment is more conducive to bacterial growth. Wound infections are common after a puncture or laceration that damages the physical barrier of the skin. Microbes may infect structures in the <strong>dermis<\/strong>, such as <strong>hair follicles<\/strong> and <strong>glands<\/strong>, causing a localized infection, or they may reach the bloodstream, which can lead to a systemic infection.\r\n\r\nIn some cases, infectious microbes can cause a variety of rashes or lesions that differ in their physical characteristics. These rashes can be the result of inflammation reactions or direct responses to toxins produced by the microbes. Table 1\u00a0lists some of the medical terminology used to describe skin <strong>lesions<\/strong> and <strong>rashes<\/strong> based on their characteristics; Figure\u00a03\u00a0and Figure\u00a04\u00a0illustrate some of the various types of skin lesions. It is important to note that many different diseases can lead to skin conditions of very similar appearance; thus the terms used in the table are generally not exclusive to a particular type of infection or disease.\r\n<table id=\"fs-id1167662552650\" class=\"span-all\" summary=\"Table labeled: some medical terms associated with skin lesions and rashes. Abscess means localized collection of pus. Bulla (pl., bullae) means fluid-filled blister no more than 5 mm in diameter. Carbuncle means deep, pus-filled abscess generally formed from multiple furuncles. Crust means dried fluids from a lesion on the surface of the skin. Cyst means encapsulated, fluid-filled sac, typically just below the upper layers of skin. Folliculitis means a localized rash due to inflammation of hair follicles. Furuncle (boil) means pus-filled abscess due to infection of a hair follicle. Macules means smooth spots of discoloration on the skin. Papules means small raised bumps on the skin. Pseudocyst means lesion that resembles a cyst but with a less defined boundary. Purulent means pus-producing; suppurative. Pustules means fluid- or pus-filled bumps on the skin. Pyoderma means any suppurative (pus-producing) infection of the skin. Suppurative means producing pus; purulent. Ulcer means break in the skin; open sore. Vesicle means small, fluid-filled lesion. Wheal means swollen, inflamed skin that itches or burns, such as from an insect bite.\">\r\n<thead>\r\n<tr>\r\n<th colspan=\"2\">Table 1. Some Medical Terms Associated with Skin Lesions and Rashes<\/th>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<th>Term<\/th>\r\n<th>Definition<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td><strong>abscess<\/strong><\/td>\r\n<td>localized collection of <strong>pus<\/strong><\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>bulla<\/strong> (pl., <strong>bullae<\/strong>)<\/td>\r\n<td>fluid-filled blister no more than 5 mm in diameter<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>carbuncle<\/strong><\/td>\r\n<td>deep, pus-filled abscess generally formed from multiple furuncles<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>crust<\/strong><\/td>\r\n<td>dried fluids from a lesion on the surface of the skin<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>cyst<\/strong><\/td>\r\n<td>encapsulated sac filled with fluid, semi-solid matter, or gas, typically located just below the upper layers of skin<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>folliculitis<\/strong><\/td>\r\n<td>a localized rash due to inflammation of <strong>hair follicles<\/strong><\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>furuncle<\/strong> (<strong>boil<\/strong>)<\/td>\r\n<td>pus-filled abscess due to infection of a hair follicle<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>macules<\/strong><\/td>\r\n<td>smooth spots of discoloration on the skin<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>papules<\/strong><\/td>\r\n<td>small raised bumps on the skin<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>pseudocyst<\/strong><\/td>\r\n<td>lesion that resembles a cyst but with a less defined boundary<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>purulent<\/strong><\/td>\r\n<td>pus-producing; suppurative<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>pustules<\/strong><\/td>\r\n<td>fluid- or pus-filled bumps on the skin<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>pyoderma<\/strong><\/td>\r\n<td>any suppurative (pus-producing) infection of the skin<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>suppurative<\/strong><\/td>\r\n<td>producing pus; purulent<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>ulcer<\/strong><\/td>\r\n<td>break in the skin; open sore<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>vesicle<\/strong><\/td>\r\n<td>small, fluid-filled lesion<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td><strong>wheal<\/strong><\/td>\r\n<td>swollen, inflamed skin that itches or burns, such as from an insect bite<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n[caption id=\"attachment_1755\" align=\"aligncenter\" width=\"1024\"]<img class=\"size-large wp-image-1755\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/11170716\/OSC_Microbio_21_01_Lesion1-1024x446.jpg\" alt=\" a) Acne (labeled whitehead) on a person\u2019s cheek. B) A drawing of skin with a yellow bubble labeled pus. This is below a raised region on the skin.\" width=\"1024\" height=\"446\" \/> Figure\u00a03. (a) Acne is a bacterial infection of the skin that manifests as a rash of inflamed hair follicles (folliculitis). The large whitehead near the center of the cheek is an infected hair follicle that has become purulent (or suppurative), leading to the formation of a furuncle. (b) An abscess is a pus-filled lesion. (credit b: modification of work by Bruce Blaus)[\/caption]\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\/03173059\/OSC_Microbio_21_01_LesionLine.jpg\" alt=\"A table labeled types of skin lesions. Crust is shown as a raised region on the surface of the skin. Cyst is shown as a large white sphere in the upper layers of the skin. Macule is shown as a dark mark on the surface. Papule is shown as a raised bubble on the surface. Pusture is shown as a large yellow sphere in the upper layers of the skin. Ulcer is a large cavity in the skin. Vesicle is a small blue bubble in the upper regions of the skin. Wheal is a small blue bubble on the surface of the skin.\" width=\"1100\" height=\"584\" \/> Figure\u00a04. Numerous causes can lead to skin lesions of various types, some of which are very similar in appearance. (credit: modification of work by Bruce Blaus)[\/caption]\r\n\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ul>\r\n \t<li>How can asymptomatic health care workers transmit bacteria such as MRSA to patients?<\/li>\r\n<\/ul>\r\n<\/div>\r\n<h2>Anatomy and Microbiota of the Eye<\/h2>\r\n[caption id=\"\" align=\"alignright\" width=\"450\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03173102\/OSC_Microbio_21_01_lacrimapp.jpg\" alt=\"Diagram of an eye. Above the eye is the lacrimal gland. At the point nearest the nose is the punctums and tubes leading to the lacrimal sac and nasolacrimal duct.\" width=\"450\" height=\"245\" \/> Figure\u00a05. The lacrimal apparatus includes the structures of the eye associated with tear production and drainage. (credit: modification of work by \"Evidence Based Medical Educator Inc.\"\/YouTube)[\/caption]\r\n\r\nAlthough the <strong>eye<\/strong> and skin have distinct anatomy, they are both in direct contact with the external environment. An important component of the eye is the nasolacrimal drainage system, which serves as a conduit for the fluid of the eye, called <strong>tears<\/strong>. Tears flow from the external eye to the nasal cavity by the lacrimal apparatus, which is composed of the structures involved in tear production (Figure\u00a05). The <strong>lacrimal gland<\/strong>, above the eye, secretes tears to keep the eye moist. There are two small openings, one on the inside edge of the upper eyelid and one on the inside edge of the lower eyelid, near the nose. Each of these openings is called a <strong>lacrimal punctum<\/strong>. Together, these lacrimal puncta collect tears from the eye that are then conveyed through <strong>lacrimal ducts<\/strong> to a reservoir for tears called the <strong>lacrimal sac<\/strong><strong>,<\/strong> also known as the <strong>dacrocyst<\/strong> or <strong>tear sac<\/strong>.\r\n\r\nFrom the sac, tear fluid flows via a <strong>nasolacrimal duct<\/strong> to the inner nose. Each nasolacrimal duct is located underneath the skin and passes through the bones of the face into the nose. Chemicals in tears, such as <strong>defensins<\/strong>, <strong>lactoferrin<\/strong>, and <strong>lysozyme<\/strong>, help to prevent colonization by pathogens. In addition, <strong>mucins<\/strong> facilitate removal of microbes from the surface of the eye.\r\n\r\nThe surfaces of the eyeball and inner eyelid are mucous membranes called <strong>conjunctiva<\/strong>. The normal conjunctival microbiota has not been well characterized, but does exist. One small study (part of the Ocular Microbiome project) found twelve genera that were consistently present in the conjunctiva.[footnote]Abelson, M.B., Lane, K., and Slocum, C.. \"The Secrets of Ocular Microbiomes.\" <em>Review of Ophthalmology<\/em> June 8, 2015. http:\/\/www.reviewofophthalmology.com\/content\/t\/ocular_disease\/c\/55178. Accessed Sept 14, 2016.[\/footnote] These microbes are thought to help defend the membranes against pathogens. However, it is still unclear which microbes may be transient and which may form a stable microbiota.[footnote]Shaikh-Lesko, R. \"Visualizing the Ocular Microbiome.\" <em>The Scientist<\/em> May 12, 2014. http:\/\/www.the-scientist.com\/?articles.view\/articleNo\/39945\/title\/Visualizing-the-Ocular-Microbiome. Accessed Sept 14, 2016.[\/footnote]\r\n\r\nUse of <strong>contact lenses<\/strong> can cause changes in the normal microbiota of the conjunctiva by introducing another surface into the natural anatomy of the eye. Research is currently underway to better understand how contact lenses may impact the normal microbiota and contribute to eye disease.\r\n\r\nThe watery material inside of the eyeball is called the <strong>vitreous humor<\/strong>. Unlike the conjunctiva, it is protected from contact with the environment and is almost always sterile, with no normal microbiota (Figure\u00a06).\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"600\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03173105\/OSC_Microbio_21_01_eyeball.jpg\" alt=\"A cross section of the eye. The large spherical center is the vitreous humor. The layer surrounding this is the retina. A projection out of the back of the eye is the optic nerve. A region on the retina just above the optic nerve is the fovea. At the front of the eye is the lens. In front of this is a space labeled pupil. The colored region around the pupil is the iris. The cornea is the covering in front of the iris and pupil. The conjunctiva is a mucous membrane on the eye.\" width=\"600\" height=\"443\" \/> Figure\u00a06. Some microbes live on the conjunctiva of the human eye, but the vitreous humor is sterile.[\/caption]\r\n<h2>Infections of the Eye<\/h2>\r\nThe conjunctiva is a frequent site of infection of the eye; like other mucous membranes, it is also a common portal of entry for pathogens. Inflammation of the conjunctiva is called <strong>conjunctivitis<\/strong>, although it is commonly known as <strong>pinkeye<\/strong> because of the pink appearance in the eye. Infections of deeper structures, beneath the cornea, are less common (Figure\u00a07). Conjunctivitis occurs in multiple forms. It may be acute or chronic. Acute purulent conjunctivitis is associated with pus formation, while acute hemorrhagic conjunctivitis is associated with bleeding in the conjunctiva. The term <strong>blepharitis<\/strong> refers to an inflammation of the eyelids, while <strong>keratitis<\/strong> refers to an inflammation of the cornea (Figure\u00a07); <strong>keratoconjunctivitis<\/strong> is an inflammation of both the cornea and the conjunctiva, and <strong>dacryocystitis<\/strong> is an inflammation of the <strong>lacrimal sac<\/strong> that can often occur when a <strong>nasolacrimal duct<\/strong> is blocked.\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\/03173108\/OSC_Microbio_21_01_ConjBleph.jpg\" alt=\"a) photo of an eyelid being pulled back to show a red are. B) A photo of inflamed eyelids. C)A photo of an eye with a cloudy cornea.\" width=\"1300\" height=\"308\" \/> Figure\u00a07. (a) Conjunctivitis is inflammation of the conjunctiva. (b) Blepharitis is inflammation of the eyelids. (c) Keratitis is inflammation of the cornea. (credit a: modification of work by Lopez-Prats MJ, Sanz Marco E, Hidalgo-Mora JJ, Garcia-Delpech S, Diaz-Llopis M; credit b, c: modification of work by Centers for Disease Control and Prevention)[\/caption]\r\n\r\nInfections leading to conjunctivitis, blepharitis, keratoconjunctivitis, or dacryocystitis may be caused by bacteria or viruses, but allergens, pollutants, or chemicals can also irritate the eye and cause inflammation of various structures. Viral infection is a more likely cause of conjunctivitis in cases with symptoms such as fever and watery discharge that occurs with upper respiratory infection and itchy eyes. Table 2\u00a0summarizes some common forms of conjunctivitis and blepharitis.\r\n<table id=\"fs-id1167660218530\" class=\"span-all\" summary=\"A table titled: Types of conjunctivitis and blepharitis. Each condition has a description and sample causative agents. Acute purulent conjunctivitis is conjunctivitis with purulent discharge and is caused by bacteria (Haemophilus, Staphylococcus). Acute hemorrhagic conjunctivitis involves subconjunctival hemorrhages and is caused by viruses (Picornaviradae). Acute ulcerative blepharitis is an infection involving eyelids; pustules and ulcers may develop and is caused by bacteria (Staphylococcal) or virus (herpes simplex, varicella zoster, etc.). Follicular conjunctivitis is inflammation of the conjunctiva with nodules (dome-shaped structures that are red at the base and pale on top) and is caused by viruses (adenovirus and others); and environmental irritants. Dacryocystitis is inflammation of the lacrimal sac often associated with a plugged nasolacrimal duct and is caused by bacteria (Haemophilus, Staphylococcus, Streptococcus). Keratitis is inflammation of cornea and is caused by bacteria, viruses, protozoa or environmental irritants. Keratoconjunctivitis is inflammation of cornea and conjunctiva and is caused by bacteria, viruses (adenoviruses), or other causes (including dryness of the eye). Nonulcerative blepharitis is inflammation, irritation, redness of the eyelids without ulceration and is caused by environmental irritants; allergens.Papillary conjunctivitis is inflammation of the conjunctiva; nodules and papillae with red tops develop and is caused by environmental irritants; allergens.\">\r\n<thead>\r\n<tr>\r\n<th colspan=\"3\">Table 2. Types of Conjunctivities and Blepharitis<\/th>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<th>Condition<\/th>\r\n<th>Description<\/th>\r\n<th>Causative Agent(s)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr valign=\"top\">\r\n<td>Acute purulent conjunctivitis<\/td>\r\n<td>Conjunctivitis with purulent discharge<\/td>\r\n<td>Bacterial (<strong><em>Haemophilus<\/em><\/strong>, <strong><em>Staphylococcus<\/em><\/strong>)<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>Acute hemorrhagic conjunctivitis<\/td>\r\n<td>Involves subconjunctival hemorrhages<\/td>\r\n<td>Viral (<strong>Picornaviradae<\/strong>)<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>Acute ulcerative blepharitis<\/td>\r\n<td>Infection involving eyelids; pustules and ulcers may develop<\/td>\r\n<td>Bacterial (<em>Staphylococcal<\/em>) or viral (herpes simplex, varicella-zoster, etc.)<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>Follicular conjunctivitis<\/td>\r\n<td>Inflammation of the conjunctiva with nodules (dome-shaped structures that are red at the base and pale on top)<\/td>\r\n<td>Viral (<strong>adenovirus<\/strong> and others); environmental irritants<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>Dacryocystitis<\/td>\r\n<td>Inflammation of the lacrimal sac often associated with a plugged nasolacrimal duct<\/td>\r\n<td>Bacterial (<em>Haemophilus, Staphylococcus<\/em>, <strong><em>Streptococcus<\/em><\/strong>)<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>Keratitis<\/td>\r\n<td>Inflammation of cornea<\/td>\r\n<td>Bacterial, viral, or protozoal; environmental irritants<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>Keratoconjunctivitis<\/td>\r\n<td>Inflammation of cornea and conjunctiva<\/td>\r\n<td>Bacterial, viral (adenoviruses), or other causes (including dryness of the eye)<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>Nonulcerative blepharitis<\/td>\r\n<td>Inflammation, irritation, redness of the eyelids without ulceration<\/td>\r\n<td>Environmental irritants; allergens<\/td>\r\n<\/tr>\r\n<tr valign=\"top\">\r\n<td>Papillary conjunctivitis<\/td>\r\n<td>Inflammation of the conjunctiva; nodules and papillae with red tops develop<\/td>\r\n<td>Environmental irritants; allergens<\/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>How does the lacrimal apparatus help to prevent eye infections?<\/li>\r\n<\/ul>\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>Human skin consists of two main layers, the <strong>epidermis<\/strong> and <strong>dermis<\/strong>, which are situated on top of the <strong>hypodermis<\/strong>, a layer of connective tissue.<\/li>\r\n \t<li>The skin is an effective physical barrier against microbial invasion.<\/li>\r\n \t<li>The skin\u2019s relatively dry environment and normal microbiota discourage colonization by transient microbes.<\/li>\r\n \t<li>The skin\u2019s normal microbiota varies from one region of the body to another.<\/li>\r\n \t<li>The <strong>conjunctiva<\/strong> of the eye is a frequent site for microbial infection, but deeper eye infections are less common; multiple types of conjunctivitis exist.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Multiple Choice<\/h3>\r\n_____________ glands produce a lipid-rich substance that contains proteins and minerals and protects the skin.\r\n<ol style=\"list-style-type: lower-alpha\">\r\n \t<li>Sweat<\/li>\r\n \t<li>Mammary<\/li>\r\n \t<li>Sebaceous<\/li>\r\n \t<li>Endocrine<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"830731\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"830731\"]Answer c. Sweat\u00a0glands produce a lipid-rich substance that contains proteins and minerals and protects the skin.[\/hidden-answer]\r\n\r\nWhich layer of skin contains living cells, is vascularized, and lies directly above the hypodermis?\r\n<ol style=\"list-style-type: lower-alpha\">\r\n \t<li>the stratum corneum<\/li>\r\n \t<li>the dermis<\/li>\r\n \t<li>the epidermis<\/li>\r\n \t<li>the conjunctiva<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"775134\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"775134\"]Answer b. The dermis contains living cells, is vascularized, and lies directly above the hypodermis.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Fill in the Blank<\/h3>\r\nThe ________ is the outermost layer of the epidermis.\r\n\r\n[reveal-answer q=\"936879\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"936879\"]The <strong>stratum corneum<\/strong> is the outermost layer of the epidermis.[\/hidden-answer]\r\n\r\nThe mucous membrane that covers the surface of the eyeball and inner eyelid is called the ________.\r\n\r\n[reveal-answer q=\"31099\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"31099\"]The mucous membrane that covers the surface of the eyeball and inner eyelid is called the <strong>conjunctiva<\/strong>.[\/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>What is the role of keratin in the skin?<\/li>\r\n \t<li>What are two ways in which tears help to prevent microbial colonization?<\/li>\r\n \t<li>Which label indicates a sweat gland?\r\n\r\n[caption id=\"attachment_1756\" align=\"aligncenter\" width=\"376\"]<img class=\" wp-image-1756\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/11171251\/OSC_Microbio_21_01_ArtConnect_img1.jpg\" alt=\"A diagram of skin. i \u2013 a vase shape in the center of skin with a long projection out the top. iv \u2013 the long projection from i. iii \u2013 a small vase shape attached to i. ii \u2013 a coiled structure in the center with a tube leading out.\" width=\"376\" height=\"474\" \/> (credit: modification of work by National Cancer Institute)[\/caption]<\/li>\r\n \t<li>Explain why it is important to understand the normal microbiota of the skin.<\/li>\r\n \t<li>Besides the presence or absence of ulceration, how do acute ulcerative and nonulcerative blepharitis differ?<\/li>\r\n<\/ol>\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<ul>\n<li>Describe the major anatomical features of the skin and eyes<\/li>\n<li>Compare and contrast the microbiomes of various body sites, such as the hands, back, feet, and eyes<\/li>\n<li>Explain how microorganisms overcome defenses of skin and eyes in order to cause infection<\/li>\n<li>Describe general signs and symptoms of disease associated with infections of the skin and eyes<\/li>\n<\/ul>\n<\/div>\n<p>Human skin is an important part of the innate immune system. In addition to serving a wide range of other functions, the skin serves as an important barrier to microbial invasion. Not only is it a physical barrier to penetration of deeper tissues by potential pathogens, but it also provides an inhospitable environment for the growth of many pathogens. In this section, we will provide a brief overview of the anatomy and normal microbiota of the skin and eyes, along with general symptoms associated with skin and eye infections.<\/p>\n<h2>Layers of the Skin<\/h2>\n<p>Human skin is made up of several layers and sublayers. The two main layers are the <strong>epidermis<\/strong> and the <strong>dermis<\/strong>. These layers cover a third layer of tissue called the <strong>hypodermis<\/strong>, which consists of fibrous and adipose connective tissue (Figure\u00a01).<\/p>\n<p>The epidermis is the outermost layer of the skin, and it is relatively thin. The exterior surface of the epidermis, called the <strong>stratum corneum<\/strong>, primarily consists of dead skin cells. This layer of dead cells limits direct contact between the outside world and live cells. The stratum corneum is rich in <strong>keratin<\/strong>, a tough, fibrous protein that is also found in hair and nails. Keratin helps make the outer surface of the skin relatively tough and waterproof. It also helps to keep the surface of the skin dry, which reduces microbial growth. However, some microbes are still able to live on the surface of the skin, and some of these can be shed with dead skin cells in the process of <strong>desquamation<\/strong>, which is the shedding and peeling of skin that occurs as a normal process but that may be accelerated when infection is present.<\/p>\n<p>Beneath the epidermis lies a thicker skin layer called the <strong>dermis<\/strong>. The dermis contains connective tissue and embedded structures such as blood vessels, nerves, and muscles. Structures called <strong>hair follicles<\/strong> (from which hair grows) are located within the dermis, even though much of their structure consists of epidermal tissue. The dermis also contains the two major types of glands found in human skin: <strong>sweat glands<\/strong> (tubular glands that produce sweat) and <strong>sebaceous glands<\/strong> (which are associated with hair follicles and produce <strong>sebum<\/strong>, a lipid-rich substance containing proteins and minerals).<\/p>\n<p>Perspiration (sweat) provides some moisture to the epidermis, which can increase the potential for microbial growth. For this reason, more microbes are found on the regions of the skin that produce the most sweat, such as the skin of the underarms and groin. However, in addition to water, sweat also contains substances that inhibit microbial growth, such as salts, <strong>lysozyme<\/strong>, and <strong>antimicrobial peptides<\/strong>. Sebum also serves to protect the skin and reduce water loss. Although some of the lipids and fatty acids in sebum inhibit microbial growth, sebum contains compounds that provide nutrition for certain microbes.<\/p>\n<div id=\"attachment_1754\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1754\" class=\"size-large wp-image-1754\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/11170513\/OSC_Microbio_21_01_skinlayers1-1024x572.jpg\" alt=\"a) A micrograph of a large light pink region labeled dermis, a thinner dark pink region on top of that labeled epidermis, and a thin region of clear cells. The division between the dermis and epidermis is wavy; with areas where one projects into the other. B) A diagram of skin. The top layer is dark and is labeled epidermis. The next layer is lighter and much thicker; this is the dermis. Inside the dermis are vase-shaped hair follicles with hairs projecting out of the skin. Next to the hair follicle is a smaller vase-shape labeled sebaceous gland; this empties into the space of the hair follicle. There are also coiled shapes labeled receptor and a variety of long tubes labeled: nerve, lymph vessel and blood vessels. A coiled blob is labeled sweat gland; this leads to a tube that opens at the surface called a sweat pore. Below the dermis is a yellow bubbly-looking layer labeled fatty tissue; this is the hypodermis.\" width=\"1024\" height=\"572\" \/><\/p>\n<p id=\"caption-attachment-1754\" class=\"wp-caption-text\">Figure\u00a01. (a) A micrograph of a section through human skin shows the epidermis and dermis. (b) The major layers of human skin are the epidermis, dermis, and hypodermis. (credit b: modification of work by National Cancer Institute)<\/p>\n<\/div>\n<h2>Normal Microbiota of the Skin<\/h2>\n<p>The skin is home to a wide variety of normal microbiota, consisting of commensal organisms that derive nutrition from skin cells and secretions such as sweat and sebum. The normal microbiota of skin tends to inhibit transient-microbe colonization by producing antimicrobial substances and outcompeting other microbes that land on the surface of the skin. This helps to protect the skin from pathogenic infection.<\/p>\n<p>The skin\u2019s properties differ from one region of the body to another, as does the composition of the skin\u2019s microbiota. The availability of nutrients and moisture partly dictates which microorganisms will thrive in a particular region of the skin. Relatively moist skin, such as that of the nares (nostrils) and underarms, has a much different microbiota than the dryer skin on the arms, legs, hands, and top of the feet. Some areas of the skin have higher densities of <strong>sebaceous glands<\/strong>. These <strong>sebum<\/strong>-rich areas, which include the back, the folds at the side of the nose, and the back of the neck, harbor distinct microbial communities that are less diverse than those found on other parts of the body.<\/p>\n<p>Different types of bacteria dominate the dry, moist, and sebum-rich regions of the skin. The most abundant microbes typically found in the dry and sebaceous regions are <strong>Betaproteobacteria<\/strong> and <strong>Propionibacteria<\/strong>, respectively. In the moist regions, <strong><em>Corynebacterium<\/em><\/strong> and <strong><em>Staphylococcus<\/em><\/strong> are most commonly found (Figure\u00a02). Viruses and fungi are also found on the skin, with <strong><em>Malassezia<\/em><\/strong> being the most common type of fungus found as part of the normal microbiota. The role and populations of viruses in the microbiota, known as <strong>viromes<\/strong>, are still not well understood, and there are limitations to the techniques used to identify them. However, <strong>Circoviridae<\/strong>, <strong>Papillomaviridae<\/strong>, and <strong>Polyomaviridae<\/strong> appear to be the most common residents in the healthy skin virome.<a class=\"footnote\" title=\"Belkaid, Y., and J.A. Segre. &quot;Dialogue Between Skin Microbiota and Immunity,&quot; Science 346 (2014) 6212:954\u2013959.\" id=\"return-footnote-888-1\" href=\"#footnote-888-1\" aria-label=\"Footnote 1\"><sup class=\"footnote\">[1]<\/sup><\/a> <a class=\"footnote\" title=\"Foulongne, Vincent, et al. &quot;Human Skin Microbiota: High Diversity of DNA Viruses Identified on the Human Skin by High Throughput Sequencing.&quot; PLoS ONE (2012) 7(6): e38499. doi: 10.1371\/journal.pone.0038499.\" id=\"return-footnote-888-2\" href=\"#footnote-888-2\" aria-label=\"Footnote 2\"><sup class=\"footnote\">[2]<\/sup><\/a> <a class=\"footnote\" title=\"Robinson, C.M., and J.K. Pfeiffer. &quot;Viruses and the Microbiota.&quot; Annual Review of Virology (2014) 1:55\u201359. doi: 10.1146\/annurev-virology-031413-085550.\" id=\"return-footnote-888-3\" href=\"#footnote-888-3\" aria-label=\"Footnote 3\"><sup class=\"footnote\">[3]<\/sup><\/a><\/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\/03173051\/OSC_Microbio_21_01_microbiota.jpg\" alt=\"A diagram showing different regions of the body. Each region has a pie chart that shows which bacteria are most prevalent. The most common bacterium in each region: Glabella (corynebacterineae), Alar Crease (propionibacterineae), External auditory canal (propionibacterineae), Nare (other actinobacteria), manubrioum (propionibacterineae), Axillary vault (proteobacteria), antecubital fossa (proteobacteria), Volar forearm (proteobacteria), interdigital web space (proteobacteria), hypothenar palm (proteobacteria), inguinal crease (corynebacterineae), umbilicus (corynebacterineae), toe web space (corynebacterineae, , propionibacterineae, and staphylococcaceae), reticular crease (propionibacterineae), occiput (staphylococcaceae, back (propionibacterineae), buttock (proteobacteria), gluteal crease (corynebacterineae), popliteal fossa (staphylococcaceae), plantar heel (staphylococcaceae). Second part of the image shows that different subjects have different bacterial percentages and that these percentages change over time.\" width=\"1300\" height=\"812\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a02. The normal microbiota varies on different regions of the skin, especially in dry versus moist areas. The figure shows the major organisms commonly found in different locations of a healthy individual\u2019s skin and external mucosa. Note that there is significant variation among individuals. (credit: modification of work by National Human Genome Research Institute)<\/p>\n<\/div>\n<h2>Infections of the Skin<\/h2>\n<p>While the microbiota of the skin can play a protective role, it can also cause harm in certain cases. Often, an opportunistic pathogen residing in the skin microbiota of one individual may be transmitted to another individual more susceptible to an infection. For example, methicillin-resistant <em>Staphylococcus aureus<\/em> (<strong>MRSA<\/strong>) can often take up residence in the nares of health care workers and hospital patients; though harmless on intact, healthy skin, MRSA can cause infections if introduced into other parts of the body, as might occur during surgery or via a post-surgical incision or wound. This is one reason why clean surgical sites are so important.<\/p>\n<p>Injury or damage to the skin can allow microbes to enter deeper tissues, where nutrients are more abundant and the environment is more conducive to bacterial growth. Wound infections are common after a puncture or laceration that damages the physical barrier of the skin. Microbes may infect structures in the <strong>dermis<\/strong>, such as <strong>hair follicles<\/strong> and <strong>glands<\/strong>, causing a localized infection, or they may reach the bloodstream, which can lead to a systemic infection.<\/p>\n<p>In some cases, infectious microbes can cause a variety of rashes or lesions that differ in their physical characteristics. These rashes can be the result of inflammation reactions or direct responses to toxins produced by the microbes. Table 1\u00a0lists some of the medical terminology used to describe skin <strong>lesions<\/strong> and <strong>rashes<\/strong> based on their characteristics; Figure\u00a03\u00a0and Figure\u00a04\u00a0illustrate some of the various types of skin lesions. It is important to note that many different diseases can lead to skin conditions of very similar appearance; thus the terms used in the table are generally not exclusive to a particular type of infection or disease.<\/p>\n<table id=\"fs-id1167662552650\" class=\"span-all\" summary=\"Table labeled: some medical terms associated with skin lesions and rashes. Abscess means localized collection of pus. Bulla (pl., bullae) means fluid-filled blister no more than 5 mm in diameter. Carbuncle means deep, pus-filled abscess generally formed from multiple furuncles. Crust means dried fluids from a lesion on the surface of the skin. Cyst means encapsulated, fluid-filled sac, typically just below the upper layers of skin. Folliculitis means a localized rash due to inflammation of hair follicles. Furuncle (boil) means pus-filled abscess due to infection of a hair follicle. Macules means smooth spots of discoloration on the skin. Papules means small raised bumps on the skin. Pseudocyst means lesion that resembles a cyst but with a less defined boundary. Purulent means pus-producing; suppurative. Pustules means fluid- or pus-filled bumps on the skin. Pyoderma means any suppurative (pus-producing) infection of the skin. Suppurative means producing pus; purulent. Ulcer means break in the skin; open sore. Vesicle means small, fluid-filled lesion. Wheal means swollen, inflamed skin that itches or burns, such as from an insect bite.\">\n<thead>\n<tr>\n<th colspan=\"2\">Table 1. Some Medical Terms Associated with Skin Lesions and Rashes<\/th>\n<\/tr>\n<tr valign=\"top\">\n<th>Term<\/th>\n<th>Definition<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr valign=\"top\">\n<td><strong>abscess<\/strong><\/td>\n<td>localized collection of <strong>pus<\/strong><\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>bulla<\/strong> (pl., <strong>bullae<\/strong>)<\/td>\n<td>fluid-filled blister no more than 5 mm in diameter<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>carbuncle<\/strong><\/td>\n<td>deep, pus-filled abscess generally formed from multiple furuncles<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>crust<\/strong><\/td>\n<td>dried fluids from a lesion on the surface of the skin<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>cyst<\/strong><\/td>\n<td>encapsulated sac filled with fluid, semi-solid matter, or gas, typically located just below the upper layers of skin<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>folliculitis<\/strong><\/td>\n<td>a localized rash due to inflammation of <strong>hair follicles<\/strong><\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>furuncle<\/strong> (<strong>boil<\/strong>)<\/td>\n<td>pus-filled abscess due to infection of a hair follicle<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>macules<\/strong><\/td>\n<td>smooth spots of discoloration on the skin<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>papules<\/strong><\/td>\n<td>small raised bumps on the skin<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>pseudocyst<\/strong><\/td>\n<td>lesion that resembles a cyst but with a less defined boundary<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>purulent<\/strong><\/td>\n<td>pus-producing; suppurative<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>pustules<\/strong><\/td>\n<td>fluid- or pus-filled bumps on the skin<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>pyoderma<\/strong><\/td>\n<td>any suppurative (pus-producing) infection of the skin<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>suppurative<\/strong><\/td>\n<td>producing pus; purulent<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>ulcer<\/strong><\/td>\n<td>break in the skin; open sore<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>vesicle<\/strong><\/td>\n<td>small, fluid-filled lesion<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td><strong>wheal<\/strong><\/td>\n<td>swollen, inflamed skin that itches or burns, such as from an insect bite<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div id=\"attachment_1755\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1755\" class=\"size-large wp-image-1755\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/11170716\/OSC_Microbio_21_01_Lesion1-1024x446.jpg\" alt=\"a) Acne (labeled whitehead) on a person\u2019s cheek. B) A drawing of skin with a yellow bubble labeled pus. This is below a raised region on the skin.\" width=\"1024\" height=\"446\" \/><\/p>\n<p id=\"caption-attachment-1755\" class=\"wp-caption-text\">Figure\u00a03. (a) Acne is a bacterial infection of the skin that manifests as a rash of inflamed hair follicles (folliculitis). The large whitehead near the center of the cheek is an infected hair follicle that has become purulent (or suppurative), leading to the formation of a furuncle. (b) An abscess is a pus-filled lesion. (credit b: modification of work by Bruce Blaus)<\/p>\n<\/div>\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\/03173059\/OSC_Microbio_21_01_LesionLine.jpg\" alt=\"A table labeled types of skin lesions. Crust is shown as a raised region on the surface of the skin. Cyst is shown as a large white sphere in the upper layers of the skin. Macule is shown as a dark mark on the surface. Papule is shown as a raised bubble on the surface. Pusture is shown as a large yellow sphere in the upper layers of the skin. Ulcer is a large cavity in the skin. Vesicle is a small blue bubble in the upper regions of the skin. Wheal is a small blue bubble on the surface of the skin.\" width=\"1100\" height=\"584\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a04. Numerous causes can lead to skin lesions of various types, some of which are very similar in appearance. (credit: modification of work by Bruce Blaus)<\/p>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ul>\n<li>How can asymptomatic health care workers transmit bacteria such as MRSA to patients?<\/li>\n<\/ul>\n<\/div>\n<h2>Anatomy and Microbiota of the Eye<\/h2>\n<div style=\"width: 460px\" 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\/03173102\/OSC_Microbio_21_01_lacrimapp.jpg\" alt=\"Diagram of an eye. Above the eye is the lacrimal gland. At the point nearest the nose is the punctums and tubes leading to the lacrimal sac and nasolacrimal duct.\" width=\"450\" height=\"245\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a05. The lacrimal apparatus includes the structures of the eye associated with tear production and drainage. (credit: modification of work by &#8220;Evidence Based Medical Educator Inc.&#8221;\/YouTube)<\/p>\n<\/div>\n<p>Although the <strong>eye<\/strong> and skin have distinct anatomy, they are both in direct contact with the external environment. An important component of the eye is the nasolacrimal drainage system, which serves as a conduit for the fluid of the eye, called <strong>tears<\/strong>. Tears flow from the external eye to the nasal cavity by the lacrimal apparatus, which is composed of the structures involved in tear production (Figure\u00a05). The <strong>lacrimal gland<\/strong>, above the eye, secretes tears to keep the eye moist. There are two small openings, one on the inside edge of the upper eyelid and one on the inside edge of the lower eyelid, near the nose. Each of these openings is called a <strong>lacrimal punctum<\/strong>. Together, these lacrimal puncta collect tears from the eye that are then conveyed through <strong>lacrimal ducts<\/strong> to a reservoir for tears called the <strong>lacrimal sac<\/strong><strong>,<\/strong> also known as the <strong>dacrocyst<\/strong> or <strong>tear sac<\/strong>.<\/p>\n<p>From the sac, tear fluid flows via a <strong>nasolacrimal duct<\/strong> to the inner nose. Each nasolacrimal duct is located underneath the skin and passes through the bones of the face into the nose. Chemicals in tears, such as <strong>defensins<\/strong>, <strong>lactoferrin<\/strong>, and <strong>lysozyme<\/strong>, help to prevent colonization by pathogens. In addition, <strong>mucins<\/strong> facilitate removal of microbes from the surface of the eye.<\/p>\n<p>The surfaces of the eyeball and inner eyelid are mucous membranes called <strong>conjunctiva<\/strong>. The normal conjunctival microbiota has not been well characterized, but does exist. One small study (part of the Ocular Microbiome project) found twelve genera that were consistently present in the conjunctiva.<a class=\"footnote\" title=\"Abelson, M.B., Lane, K., and Slocum, C.. &quot;The Secrets of Ocular Microbiomes.&quot; Review of Ophthalmology June 8, 2015. http:\/\/www.reviewofophthalmology.com\/content\/t\/ocular_disease\/c\/55178. Accessed Sept 14, 2016.\" id=\"return-footnote-888-4\" href=\"#footnote-888-4\" aria-label=\"Footnote 4\"><sup class=\"footnote\">[4]<\/sup><\/a> These microbes are thought to help defend the membranes against pathogens. However, it is still unclear which microbes may be transient and which may form a stable microbiota.<a class=\"footnote\" title=\"Shaikh-Lesko, R. &quot;Visualizing the Ocular Microbiome.&quot; The Scientist May 12, 2014. http:\/\/www.the-scientist.com\/?articles.view\/articleNo\/39945\/title\/Visualizing-the-Ocular-Microbiome. Accessed Sept 14, 2016.\" id=\"return-footnote-888-5\" href=\"#footnote-888-5\" aria-label=\"Footnote 5\"><sup class=\"footnote\">[5]<\/sup><\/a><\/p>\n<p>Use of <strong>contact lenses<\/strong> can cause changes in the normal microbiota of the conjunctiva by introducing another surface into the natural anatomy of the eye. Research is currently underway to better understand how contact lenses may impact the normal microbiota and contribute to eye disease.<\/p>\n<p>The watery material inside of the eyeball is called the <strong>vitreous humor<\/strong>. Unlike the conjunctiva, it is protected from contact with the environment and is almost always sterile, with no normal microbiota (Figure\u00a06).<\/p>\n<div style=\"width: 610px\" 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\/03173105\/OSC_Microbio_21_01_eyeball.jpg\" alt=\"A cross section of the eye. The large spherical center is the vitreous humor. The layer surrounding this is the retina. A projection out of the back of the eye is the optic nerve. A region on the retina just above the optic nerve is the fovea. At the front of the eye is the lens. In front of this is a space labeled pupil. The colored region around the pupil is the iris. The cornea is the covering in front of the iris and pupil. The conjunctiva is a mucous membrane on the eye.\" width=\"600\" height=\"443\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a06. Some microbes live on the conjunctiva of the human eye, but the vitreous humor is sterile.<\/p>\n<\/div>\n<h2>Infections of the Eye<\/h2>\n<p>The conjunctiva is a frequent site of infection of the eye; like other mucous membranes, it is also a common portal of entry for pathogens. Inflammation of the conjunctiva is called <strong>conjunctivitis<\/strong>, although it is commonly known as <strong>pinkeye<\/strong> because of the pink appearance in the eye. Infections of deeper structures, beneath the cornea, are less common (Figure\u00a07). Conjunctivitis occurs in multiple forms. It may be acute or chronic. Acute purulent conjunctivitis is associated with pus formation, while acute hemorrhagic conjunctivitis is associated with bleeding in the conjunctiva. The term <strong>blepharitis<\/strong> refers to an inflammation of the eyelids, while <strong>keratitis<\/strong> refers to an inflammation of the cornea (Figure\u00a07); <strong>keratoconjunctivitis<\/strong> is an inflammation of both the cornea and the conjunctiva, and <strong>dacryocystitis<\/strong> is an inflammation of the <strong>lacrimal sac<\/strong> that can often occur when a <strong>nasolacrimal duct<\/strong> is blocked.<\/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\/03173108\/OSC_Microbio_21_01_ConjBleph.jpg\" alt=\"a) photo of an eyelid being pulled back to show a red are. B) A photo of inflamed eyelids. C)A photo of an eye with a cloudy cornea.\" width=\"1300\" height=\"308\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a07. (a) Conjunctivitis is inflammation of the conjunctiva. (b) Blepharitis is inflammation of the eyelids. (c) Keratitis is inflammation of the cornea. (credit a: modification of work by Lopez-Prats MJ, Sanz Marco E, Hidalgo-Mora JJ, Garcia-Delpech S, Diaz-Llopis M; credit b, c: modification of work by Centers for Disease Control and Prevention)<\/p>\n<\/div>\n<p>Infections leading to conjunctivitis, blepharitis, keratoconjunctivitis, or dacryocystitis may be caused by bacteria or viruses, but allergens, pollutants, or chemicals can also irritate the eye and cause inflammation of various structures. Viral infection is a more likely cause of conjunctivitis in cases with symptoms such as fever and watery discharge that occurs with upper respiratory infection and itchy eyes. Table 2\u00a0summarizes some common forms of conjunctivitis and blepharitis.<\/p>\n<table id=\"fs-id1167660218530\" class=\"span-all\" summary=\"A table titled: Types of conjunctivitis and blepharitis. Each condition has a description and sample causative agents. Acute purulent conjunctivitis is conjunctivitis with purulent discharge and is caused by bacteria (Haemophilus, Staphylococcus). Acute hemorrhagic conjunctivitis involves subconjunctival hemorrhages and is caused by viruses (Picornaviradae). Acute ulcerative blepharitis is an infection involving eyelids; pustules and ulcers may develop and is caused by bacteria (Staphylococcal) or virus (herpes simplex, varicella zoster, etc.). Follicular conjunctivitis is inflammation of the conjunctiva with nodules (dome-shaped structures that are red at the base and pale on top) and is caused by viruses (adenovirus and others); and environmental irritants. Dacryocystitis is inflammation of the lacrimal sac often associated with a plugged nasolacrimal duct and is caused by bacteria (Haemophilus, Staphylococcus, Streptococcus). Keratitis is inflammation of cornea and is caused by bacteria, viruses, protozoa or environmental irritants. Keratoconjunctivitis is inflammation of cornea and conjunctiva and is caused by bacteria, viruses (adenoviruses), or other causes (including dryness of the eye). Nonulcerative blepharitis is inflammation, irritation, redness of the eyelids without ulceration and is caused by environmental irritants; allergens.Papillary conjunctivitis is inflammation of the conjunctiva; nodules and papillae with red tops develop and is caused by environmental irritants; allergens.\">\n<thead>\n<tr>\n<th colspan=\"3\">Table 2. Types of Conjunctivities and Blepharitis<\/th>\n<\/tr>\n<tr valign=\"top\">\n<th>Condition<\/th>\n<th>Description<\/th>\n<th>Causative Agent(s)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr valign=\"top\">\n<td>Acute purulent conjunctivitis<\/td>\n<td>Conjunctivitis with purulent discharge<\/td>\n<td>Bacterial (<strong><em>Haemophilus<\/em><\/strong>, <strong><em>Staphylococcus<\/em><\/strong>)<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>Acute hemorrhagic conjunctivitis<\/td>\n<td>Involves subconjunctival hemorrhages<\/td>\n<td>Viral (<strong>Picornaviradae<\/strong>)<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>Acute ulcerative blepharitis<\/td>\n<td>Infection involving eyelids; pustules and ulcers may develop<\/td>\n<td>Bacterial (<em>Staphylococcal<\/em>) or viral (herpes simplex, varicella-zoster, etc.)<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>Follicular conjunctivitis<\/td>\n<td>Inflammation of the conjunctiva with nodules (dome-shaped structures that are red at the base and pale on top)<\/td>\n<td>Viral (<strong>adenovirus<\/strong> and others); environmental irritants<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>Dacryocystitis<\/td>\n<td>Inflammation of the lacrimal sac often associated with a plugged nasolacrimal duct<\/td>\n<td>Bacterial (<em>Haemophilus, Staphylococcus<\/em>, <strong><em>Streptococcus<\/em><\/strong>)<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>Keratitis<\/td>\n<td>Inflammation of cornea<\/td>\n<td>Bacterial, viral, or protozoal; environmental irritants<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>Keratoconjunctivitis<\/td>\n<td>Inflammation of cornea and conjunctiva<\/td>\n<td>Bacterial, viral (adenoviruses), or other causes (including dryness of the eye)<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>Nonulcerative blepharitis<\/td>\n<td>Inflammation, irritation, redness of the eyelids without ulceration<\/td>\n<td>Environmental irritants; allergens<\/td>\n<\/tr>\n<tr valign=\"top\">\n<td>Papillary conjunctivitis<\/td>\n<td>Inflammation of the conjunctiva; nodules and papillae with red tops develop<\/td>\n<td>Environmental irritants; allergens<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ul>\n<li>How does the lacrimal apparatus help to prevent eye infections?<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Key Concepts and Summary<\/h3>\n<ul>\n<li>Human skin consists of two main layers, the <strong>epidermis<\/strong> and <strong>dermis<\/strong>, which are situated on top of the <strong>hypodermis<\/strong>, a layer of connective tissue.<\/li>\n<li>The skin is an effective physical barrier against microbial invasion.<\/li>\n<li>The skin\u2019s relatively dry environment and normal microbiota discourage colonization by transient microbes.<\/li>\n<li>The skin\u2019s normal microbiota varies from one region of the body to another.<\/li>\n<li>The <strong>conjunctiva<\/strong> of the eye is a frequent site for microbial infection, but deeper eye infections are less common; multiple types of conjunctivitis exist.<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Multiple Choice<\/h3>\n<p>_____________ glands produce a lipid-rich substance that contains proteins and minerals and protects the skin.<\/p>\n<ol style=\"list-style-type: lower-alpha\">\n<li>Sweat<\/li>\n<li>Mammary<\/li>\n<li>Sebaceous<\/li>\n<li>Endocrine<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q830731\">Show Answer<\/span><\/p>\n<div id=\"q830731\" class=\"hidden-answer\" style=\"display: none\">Answer c. Sweat\u00a0glands produce a lipid-rich substance that contains proteins and minerals and protects the skin.<\/div>\n<\/div>\n<p>Which layer of skin contains living cells, is vascularized, and lies directly above the hypodermis?<\/p>\n<ol style=\"list-style-type: lower-alpha\">\n<li>the stratum corneum<\/li>\n<li>the dermis<\/li>\n<li>the epidermis<\/li>\n<li>the conjunctiva<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q775134\">Show Answer<\/span><\/p>\n<div id=\"q775134\" class=\"hidden-answer\" style=\"display: none\">Answer b. The dermis contains living cells, is vascularized, and lies directly above the hypodermis.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Fill in the Blank<\/h3>\n<p>The ________ is the outermost layer of the epidermis.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q936879\">Show Answer<\/span><\/p>\n<div id=\"q936879\" class=\"hidden-answer\" style=\"display: none\">The <strong>stratum corneum<\/strong> is the outermost layer of the epidermis.<\/div>\n<\/div>\n<p>The mucous membrane that covers the surface of the eyeball and inner eyelid is called the ________.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q31099\">Show Answer<\/span><\/p>\n<div id=\"q31099\" class=\"hidden-answer\" style=\"display: none\">The mucous membrane that covers the surface of the eyeball and inner eyelid is called the <strong>conjunctiva<\/strong>.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ol>\n<li>What is the role of keratin in the skin?<\/li>\n<li>What are two ways in which tears help to prevent microbial colonization?<\/li>\n<li>Which label indicates a sweat gland?\n<div id=\"attachment_1756\" style=\"width: 386px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1756\" class=\"wp-image-1756\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/11171251\/OSC_Microbio_21_01_ArtConnect_img1.jpg\" alt=\"A diagram of skin. i \u2013 a vase shape in the center of skin with a long projection out the top. iv \u2013 the long projection from i. iii \u2013 a small vase shape attached to i. ii \u2013 a coiled structure in the center with a tube leading out.\" width=\"376\" height=\"474\" \/><\/p>\n<p id=\"caption-attachment-1756\" class=\"wp-caption-text\">(credit: modification of work by National Cancer Institute)<\/p>\n<\/div>\n<\/li>\n<li>Explain why it is important to understand the normal microbiota of the skin.<\/li>\n<li>Besides the presence or absence of ulceration, how do acute ulcerative and nonulcerative blepharitis differ?<\/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-888\">\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-888-1\">Belkaid, Y., and J.A. Segre. \"Dialogue Between Skin Microbiota and Immunity,\" <em>Science<\/em> 346 (2014) 6212:954\u2013959. <a href=\"#return-footnote-888-1\" class=\"return-footnote\" aria-label=\"Return to footnote 1\">&crarr;<\/a><\/li><li id=\"footnote-888-2\">Foulongne, Vincent, et al. \"Human Skin Microbiota: High Diversity of DNA Viruses Identified on the Human Skin by High Throughput Sequencing.\" <em>PLoS ONE<\/em> (2012) 7(6): e38499. doi: 10.1371\/journal.pone.0038499. <a href=\"#return-footnote-888-2\" class=\"return-footnote\" aria-label=\"Return to footnote 2\">&crarr;<\/a><\/li><li id=\"footnote-888-3\">Robinson, C.M., and J.K. Pfeiffer. \"Viruses and the Microbiota.\" <em>Annual Review of Virology<\/em> (2014) 1:55\u201359. doi: 10.1146\/annurev-virology-031413-085550. <a href=\"#return-footnote-888-3\" class=\"return-footnote\" aria-label=\"Return to footnote 3\">&crarr;<\/a><\/li><li id=\"footnote-888-4\">Abelson, M.B., Lane, K., and Slocum, C.. \"The Secrets of Ocular Microbiomes.\" <em>Review of Ophthalmology<\/em> June 8, 2015. http:\/\/www.reviewofophthalmology.com\/content\/t\/ocular_disease\/c\/55178. Accessed Sept 14, 2016. <a href=\"#return-footnote-888-4\" class=\"return-footnote\" aria-label=\"Return to footnote 4\">&crarr;<\/a><\/li><li id=\"footnote-888-5\">Shaikh-Lesko, R. \"Visualizing the Ocular Microbiome.\" <em>The Scientist<\/em> May 12, 2014. http:\/\/www.the-scientist.com\/?articles.view\/articleNo\/39945\/title\/Visualizing-the-Ocular-Microbiome. Accessed Sept 14, 2016. <a href=\"#return-footnote-888-5\" class=\"return-footnote\" aria-label=\"Return to footnote 5\">&crarr;<\/a><\/li><\/ol><\/div>","protected":false},"author":17,"menu_order":2,"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-888","chapter","type-chapter","status-publish","hentry"],"part":877,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/888","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":4,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/888\/revisions"}],"predecessor-version":[{"id":2219,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/888\/revisions\/2219"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/parts\/877"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/888\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/media?parent=888"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapter-type?post=888"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/contributor?post=888"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/license?post=888"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}