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Questions and Answers
The outer portion of the skin, the epidermis, contains keratin, which provides a waterproof coating.
The outer portion of the skin, the epidermis, contains keratin, which provides a waterproof coating.
True
Sebum and perspiration provide nutrients for all microorganisms.
Sebum and perspiration provide nutrients for all microorganisms.
False
Which of the following is NOT a type of lesion described in Microbial Diseases of the Skin?
Which of the following is NOT a type of lesion described in Microbial Diseases of the Skin?
What is the name of the bacterial species that is the primary component of the majority of skin microbiota?
What is the name of the bacterial species that is the primary component of the majority of skin microbiota?
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All pathogenic strains of Staphylococcus aureus produce coagulase.
All pathogenic strains of Staphylococcus aureus produce coagulase.
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Which of the following is NOT a toxin that pathogenic Staphylococcus aureus can produce?
Which of the following is NOT a toxin that pathogenic Staphylococcus aureus can produce?
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Impetigo is a contagious superficial skin infection caused by Staphylococcus aureus.
Impetigo is a contagious superficial skin infection caused by Staphylococcus aureus.
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Which of the following is NOT a characteristic of Group A beta-hemolytic streptococci?
Which of the following is NOT a characteristic of Group A beta-hemolytic streptococci?
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Pseudomonas aeruginosa is a common cause of skin infections.
Pseudomonas aeruginosa is a common cause of skin infections.
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What is the name of the pigment that gives P. aeruginosa infections a characteristic blue-green pus?
What is the name of the pigment that gives P. aeruginosa infections a characteristic blue-green pus?
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What type of viral infection can cause a benign growth called a wart or papilloma?
What type of viral infection can cause a benign growth called a wart or papilloma?
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Warts are always contagious and cannot be removed.
Warts are always contagious and cannot be removed.
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Variola virus can cause either variola major or variola minor infections.
Variola virus can cause either variola major or variola minor infections.
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Smallpox has been eradicated from the world.
Smallpox has been eradicated from the world.
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What is the name of the skin lesion that is associated with chickenpox?
What is the name of the skin lesion that is associated with chickenpox?
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Which of the following complications is NOT associated with chickenpox?
Which of the following complications is NOT associated with chickenpox?
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After someone has had chickenpox, the varicella-zoster virus can remain latent in nerve cells and later reactivate as shingles.
After someone has had chickenpox, the varicella-zoster virus can remain latent in nerve cells and later reactivate as shingles.
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Herpes simplex infection causes a characteristic skin rash.
Herpes simplex infection causes a characteristic skin rash.
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Herpes simplex virus infections can be triggered by periods of stress or illness.
Herpes simplex virus infections can be triggered by periods of stress or illness.
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Measles is transmitted through the respiratory route.
Measles is transmitted through the respiratory route.
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A characteristic symptom of measles is the appearance of Koplik's spots on the oral mucosa.
A characteristic symptom of measles is the appearance of Koplik's spots on the oral mucosa.
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Which of the following is NOT a complication associated with measles?
Which of the following is NOT a complication associated with measles?
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The rubella virus is transmitted through the respiratory route.
The rubella virus is transmitted through the respiratory route.
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Congenital rubella syndrome can occur if a woman contracts rubella during any trimester of pregnancy, but is most severe during the second trimester.
Congenital rubella syndrome can occur if a woman contracts rubella during any trimester of pregnancy, but is most severe during the second trimester.
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Human parvovirus B19 causes fifth disease.
Human parvovirus B19 causes fifth disease.
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Hand-foot-and-mouth disease is caused by a single type of enterovirus.
Hand-foot-and-mouth disease is caused by a single type of enterovirus.
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Fungi that colonize only the outer layer of the epidermis cause dermatomycoses.
Fungi that colonize only the outer layer of the epidermis cause dermatomycoses.
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Which of the following is NOT a genus of fungus that can cause dermatomycoses?
Which of the following is NOT a genus of fungus that can cause dermatomycoses?
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Dermatomycoses are often diagnosed by microscopic examination of skin scrapings or fungal culture.
Dermatomycoses are often diagnosed by microscopic examination of skin scrapings or fungal culture.
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Sporotrichosis results from a soil fungus that penetrates the skin through a wound.
Sporotrichosis results from a soil fungus that penetrates the skin through a wound.
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Scabies is caused by a mite burrowing and laying eggs in the skin.
Scabies is caused by a mite burrowing and laying eggs in the skin.
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Pediculosis is an infestation by a type of louse.
Pediculosis is an infestation by a type of louse.
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Conjunctivitis, an inflammation of the conjunctiva, can be caused by bacteria or viruses.
Conjunctivitis, an inflammation of the conjunctiva, can be caused by bacteria or viruses.
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Bacteria that cause conjunctivitis usually originate from the skin or mucous membranes.
Bacteria that cause conjunctivitis usually originate from the skin or mucous membranes.
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Ophthalmia neonatorum is a type of conjunctivitis that is usually transmitted to newborns through the birth canal.
Ophthalmia neonatorum is a type of conjunctivitis that is usually transmitted to newborns through the birth canal.
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Inclusion conjunctivitis is an infection of the conjunctiva caused by Chlamydia trachomatis and is primarily transmitted through direct contact.
Inclusion conjunctivitis is an infection of the conjunctiva caused by Chlamydia trachomatis and is primarily transmitted through direct contact.
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Trachoma, an infection of the conjunctiva, is primarily transmitted by flies.
Trachoma, an infection of the conjunctiva, is primarily transmitted by flies.
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Study Notes
Introduction
- Skin acts as a physical barrier against microorganisms
- Moist skin areas have larger bacterial populations compared to dry areas
Structure and Function of the Skin
- Outer skin layer (epidermis) contains keratin, a waterproof material
- Inner skin layer (dermis) contains hair follicles, sweat ducts, and oil glands allowing microorganisms to pass through
- Sebum and perspiration inhibit microbial growth, but also provide nutrients to some microorganisms
- Epithelial cells lining body cavities secrete mucus, forming a mucous membrane
Normal Microbiota of the Skin
- Skin microorganisms tolerate desiccation and high salt concentrations
- Gram-positive cocci are predominant skin microbes
- Normal skin microbiota is not fully removed by washing
- Cutibacterium metabolizes oil and colonizes hair follicles
- Malassezia furfur yeast grows on oily secretions, and may cause dandruff
Microbial Diseases of the Skin
- Vesicles are small fluid-filled lesions; bullae are larger than 1 cm, macules are flat, reddened lesions, papules are raised lesions, and pustules are raised lesions that contain pus
- Most skin microbiota consists of coagulase-negative Staphylococcus epidermidis
- Almost all pathogenic S. aureus strains produce coagulase
- Pathogenic S. aureus produces enterotoxins, leukocidins, and exfoliative toxin
- Localized infections, impetigo, toxemia, and staphylococcal toxemias (e.g., scalded skin syndrome, toxic shock syndrome) can result from skin infections
- Group A beta-hemolytic streptococci produce virulence factors like M protein, deoxyribonuclease, streptokinases, and hyaluronidase, causing tissue destruction
- Pseudomonas aeruginosa produces endotoxins and several exotoxins causing otitis externa, respiratory infections, burn infections, and dermatitis; characterized by blue-green pus
- Mycobacterium ulcerans causes deep-tissue ulceration
- Cutibacterium acnes metabolites cause inflammatory acne
Viral Diseases of the Skin
- Papillomaviruses cause skin cell proliferation, forming warts (papillomas)
- Warts spread through direct contact and can regress spontaneously or be removed
- Variola virus causes variola major and minor skin infections
- Smallpox is transmitted via the respiratory route and bloodstream; eradicated
- HHV-3 (varicella-zoster virus) causes chickenpox and shingles. Chickenpox can cause complications such as encephalitis and Reye's syndrome
- Shingles is a reactivation of varicella-zoster virus, characterized by a vesicular rash along the affected cutaneous sensory nerves
Herpes Simplex Virus Infections
- Herpes simplex virus (HSV-1) infection of mucosal cells results in cold sores and, less commonly, encephalitis; transmitted primarily through oral and respiratory routes
- Herpes encephalitis occurs when herpes simplex viruses infect the brain, with acyclovir showing successful treatment
- Herpes simplex virus remains latent in nerve cells, allowing recurrences of cold sores
Measles
- Measles virus causes measles infection, is transmitted by respiratory route
- Macular lesions appear on the skin after the incubation period in the upper respiratory tract.
- Complications of measles include middle ear infections, pneumonia, encephalitis, and secondary bacterial infections
Rubella
- Rubella virus transmitted by the respiratory route, leading to a red rash and mild fever
- Congenital rubella syndrome can result if a woman contracts rubella during the first trimester of pregnancy
Fungal Diseases of the Skin and Nails
- Microsporum, Trichophyton, and Epidermophyton cause dermatomycoses (e.g., ringworm, tinea)
- Fungi colonize keratin-containing structures (hair, skin, nails)
- Diagnosis involves microscopic examination of scrapings or fungal cultures
- Sporotrichosis results from soil fungi penetrating the skin through wounds
- Candida albicans causes oral thrush and vaginitis
Parasitic Diseases of the Skin
- Scabies is caused by mites burrowing and laying eggs in the skin
- Pediculosis involves infestation by Pediculus humanus
Microbial Diseases of the Eye
- Conjunctivitis is caused by bacterial transmission from skin and upper respiratory tract, or through contact lenses
- Ophthalmia neonatorum is caused by Neisseria gonorrhoeae transmission from mother to infant during birth
- Inclusion conjunctivitis results from Chlamydia trachomatis infection , often transmitted through unchlorinated water during birth,
- Trachoma is transmitted by hands, fomites (inanimate objects), and perhaps flies
- Fusarium and Aspergillus fungi, herpes simplex virus (HSV-1), and Acanthamoeba protozoa can also infect the eye, potentially causing corneal ulcers, and other forms of keratitis.
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