Skin Infections and Diseases PDF

# Introduction (p. 590) 1. The skin is a physical barrier against microorganisms. 2. Moist areas of the skin support larger populations of bacteria than dry areas. # Structure and Function of the Skin (p. 591) 1. The outer portion of the skin (epidermis) contains keratin, a waterproof coating. 2....

# Introduction (p. 590) 1. The skin is a physical barrier against microorganisms. 2. Moist areas of the skin support larger populations of bacteria than dry areas. # Structure and Function of the Skin (p. 591) 1. The outer portion of the skin (epidermis) contains keratin, a waterproof coating. 2. The inner portion of the skin, the dermis, contains hair follicles, sweat ducts, and oil glands that provide passageways for microorganisms. 3. Sebum and perspiration are secretions of the skin that can inhibit the growth of microorganisms. 4. Sebum and perspiration provide nutrients for some microorganisms. 5. Body cavities are lined with epithelial cells. When these cells secrete mucus, they constitute the mucous membrane. # Normal Microbiota of the Skin (p. 592) 1. Microorganisms that live on skin are resistant to desiccation and high concentrations of salt. 2. Gram-positive cocci predominate on the skin. 3. Washing does not completely remove the normal skin microbiota. 4. Members of the genus Cutibacterium metabolize oil from the oil glands and colonize hair follicles. 5. Malassezia furfur yeast grows on oily secretions and may be the cause of dandruff. # Microbial Diseases of the Skin (pp. 592-602) 1. Vesicles are small fluid-filled lesions; bullae are vesicles larger than 1 cm; macules are flat, reddened lesions; papules are raised lesions; and pustules are raised lesions containing pus. # Bacterial Diseases of the Skin (pp. 592-611) 2. The majority of skin microbiota consist of coagulase-negative Staphylococcus epidermidis. 3. Almost all pathogenic strains of *S. aureus* produce coagulase. 4. Pathogenic *S. aureus* can produce enterotoxins, leukocidins, and exfoliative toxin. 5. Localized infections (sties, pimples, and carbuncles) result from entry of *S. aureus* through openings in the skin. 6. Impetigo is a highly contagious superficial skin infection caused by *S. aureus*. 7. Toxemia occurs when toxins enter the bloodstream; staphylococcal toxemias include scalded skin syndrome and toxic shock syndrome. 8. Streptococci are classified according to their hemolytic enzymes and cell wall antigens. 9. Group A beta-hemolytic streptococci produce a number of virulence factors: M protein, deoxyribonuclease, streptokinases, and hyaluronidase. 10. Invasive group A beta-hemolytic streptococci cause severe and rapid tissue destruction. 11. *Pseudomonas aeruginosa* produces an endotoxin and several exotoxins. 12. Diseases caused by *P. aeruginosa* include otitis externa, respiratory infections, burn infections, and dermatitis. 13. *P. aeruginosa* infections have a characteristic blue-green pus caused by the pigment pyocyanin. # Viral Diseases of the Skin (pp. 602-607) 14. *Mycobacterium ulcerans* causes deep-tissue ulceration. 15. Metabolic products (fatty acids) of *Cutibacterium acnes* cause inflammatory acne. 16. Papillomaviruses cause skin cells to proliferate and produce a benign growth called a wart or papilloma. 17. Warts are spread by direct contact. 18. Warts may regress spontaneously or be removed chemically or physically. 19. Variola virus causes two types of skin infections: variola major and variola minor. 20. Smallpox is transmitted by the respiratory route, and the virus is moved to the skin via the bloodstream. 21. Smallpox has been eradicated as a result of a vaccination effort by the World Health Organization. 22. HHV-3 is transmitted by the respiratory route and is localized in skin cells, causing a vesicular rash. 23. Complications of chickenpox include encephalitis and Reye's syndrome. 24. After chickenpox, the virus can remain latent in nerve cells and subsequently activate as shingles.. 25. Shingles is characterized by a vesicular rash along the affected cutaneous sensory nerves. 26. HHV-3 can be treated with acyclovir. An attenuated live vaccine is available. 27. Herpes simplex infection of mucosal cells results in cold sores and occasionally encephalitis. 28. The virus remains latent in nerve cells, and cold sores can recur when the virus is activated. 29. HSV-1 is transmitted primarily by oral and respiratory routes. 30. Herpes encephalitis occurs when herpes simplex viruses infect the brain. 31. Acyclovir has proven successful in treating herpes encephalitis. 32. Measles is caused by measles virus and is transmitted by the respiratory route. 33. Vaccination against measles provides effective long-term immunity. 34. After the measles virus has incubated in the upper respiratory tract, macular lesions appear on the skin, and Koplik's spots appear on the oral mucosa. 35. Complications of measles include middle ear infections, pneumonia, encephalitis, and secondary bacterial infections. 36. The rubella virus is transmitted by the respiratory route and causes a red rash and light fever. 37. Congenital rubella syndrome can affect a fetus when a woman contracts rubella during the first trimester of her pregnancy. 38. Vaccination with live, attenuated rubella virus provides immunity of unknown duration. 39. Human parvovirus B19 causes fifth disease, and HHV-6 and HHV-7 cause roseola. 40. Hand-foot-and-mouth disease is an infection in young children caused by several enteroviruses. # Fungal Diseases of the Skin and Nails (pp. 607-609) 41. Fungi that colonize the outer layer of the epidermis cause dermatomycoses. 42. *Microsporum*, *Trichophyton*, and *Epidermophyton* cause dermatomycoses called ringworm, or tinea. 43. These fungi grow on keratin-containing epidermis, such as hair, skin, and nails. 44. Diagnosis is based on the microscopic examination of skin scrapings or fungal culture. 45. Sporotrichosis results from a soil fungus that penetrates the skin through a wound. 46. The fungi grow and produce subcutaneous nodules along the lymphatic vessels. 47. *Candida albicans* causes infections of mucous membranes and is a common cause of thrush (in oral mucosa) and vaginitis. 48. Topical antifungal chemicals may be used to treat fungal diseases of the skin. # Parasitic Infestation of the Skin (pp. 609–611) 49. Scabies is caused by a mite burrowing and laying eggs in the skin. 50. Pediculosis is an infestation by *Pediculus humanus*. # Microbial Diseases of the Eye (pp. 612–613) 1. The mucous membrane lining the eyelid and covering the eyeball is the conjunctiva. # Inflammation of the Eye Membranes: Conjunctivitis (p. 612) 2. Conjunctivitis is caused by several bacteria and can be transmitted by improperly disinfected contact lenses. # Bacterial Diseases of the Eye (p. 612) 3. Bacterial microbiota of the eye usually originate from the skin and upper respiratory tract.. 4. Ophthalmia neonatorum is caused by the transmission of *Neisseria gonorrhoeae* from an infected mother to an infant during its passage through the birth canal. 5. Inclusion conjunctivitis is an infection of the conjunctiva caused by *Chlamydia trachomatis*. It is transmitted to infants during birth and is transmitted in unchlorinated swimming water. 6. Trachoma is transmitted by hands, fomites, and perhaps flies. # Other Infectious Diseases of the Eye (p. 613) 7. *Fusarium* and *Aspergillus* fungi can infect the eye. 8. Herpetic keratitis causes corneal ulcers. The etiology is HSV-1 that invades the central nervous system and can recur. 9. *Acanthamoeba* protozoa, transmitted via water, can cause a serious form of keratitis.