21: Microbial Diseases of the Skin and Eyes Learning Objectives 1. Describe the structure of the skin and mucous membranes and the ways pathogens can invade the skin. 2. Provide examples of normal skin microbiota, and state their locations and ecological roles of its members. 3. Differentiate staphylococci from streptococci, and name several skin infections caused by each. 4. List the causative agent, method of transmission, and clinical symptoms of Pseudomonas, dermatitis, otitis externa, acne. 5. List the causative agent, method of transmission, and clinical symptoms of these skin infections: warts, smallpox, chickenpox, shingles, cold sores, measles, rubella, fifth disease, roseola. 6. Differentiate cutaneous from subcutaneous mycoses, and provide an example of each. 7. List the causative agent of and predisposing factors for candidiasis. 8. List the causative agent, method of transmission, clinical symptoms, and treatment for scabies and pediculosis. 9. Define conjunctivitis. 10. List the causative agent, method of transmission, and clinical symptoms of these eye infections: neonatal gonorrheal ophthalmia, inclusion conjunctivitis, trachoma. 11. List the causative agent, method of transmission, and clinical symptoms of these eye infections: herpetic keratitis, Acanthamoeba keratitis. New in this Edition • The new discussion of the causes of toxic shock syndrome makes a clear distinction between staphylococci and streptococci. • The new Clinical Problem Solving box describes infections in the gym. Chapter Summary Introduction (p. 613) 1. The skin is a physical barrier against microorganisms. 2. Moist areas of the skin (such as the armpit) support larger populations of bacteria than dry areas (such as the scalp). 3. Human skin produces antibiotics called defensins. Structure and Function of the Skin (pp. 614–615) 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 (pp. 615–634) 1. Microorganisms that live on skin are resistant to desiccation and high concentrations of salt. 2. Gram-positive cocci predominate on the skin. 3. The normal skin microbiota are not completely removed by washing. 4. Members of the genus Propionibacterium 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 (p. 615) 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. 615–623) Staphylococcal Skin Infections (pp. 615–620) 2. Staphylococci are gram-positive bacteria that often grow in clusters. 3. The majority of skin microbiota consist of coagulase-negative Staphylococcus epidermidis. 4. Almost all pathogenic strains of S. aureus produce coagulase. 5. Pathogenic S. aureus can produce enterotoxins, leukocidins, and exfoliative toxin. 6. Many strains of S. aureus produce penicillinase; these are treated with vancomycin. 7. Localized infections (sties, pimples, and carbuncles) result from S. aureus entering openings in the skin. 8. Impetigo of the newborn is a highly contagious superficial skin infection caused by S. aureus. 9. Toxemia occurs when toxins enter the bloodstream; staphylococcal toxemias include scalded skin syndrome and toxic shock syndrome. Streptococcal Skin Infections (pp. 620–622) 10. Streptococci are gram-positive cocci that often grow in chains. 11. Streptococci are classified according to their hemolytic enzymes and cell wall antigens. 12. Group A beta-hemolytic streptococci (including Streptococcus pyogenes) are the pathogens most important to humans. 13. Group A beta-hemolytic streptococci produce a number of virulence factors: M protein, erythrogenic toxin, deoxyribonuclease, streptokinases, and hyaluronidase. 14. Erysipelas (reddish patches) and impetigo (isolated pustules) are skin infections caused by S. pyogenes. 15. Invasive group A beta-hemolytic streptococci cause severe and rapid tissue destruction. Infections by Pseudomonads (p. 622) 16. Pseudomonads are gram-negative rods. They are aerobes found primarily in soil and water that are resistant to many disinfectants and antibiotics. 17. Pseudomonas aeruginosa produces an endotoxin and several exotoxins. 18. Diseases caused by P. aeruginosa include otitis externa, respiratory infections, burn infections, and dermatitis. 19. Infections have a characteristic blue-green pus caused by the pigment pyocyanin. 20. Quinolones are useful in treating P. aeruginosa infections. Acne (pp. 622–623) 21. Propionibacterium acnes can metabolize sebum trapped in hair follicles. 22. Metabolic end-products (fatty acids) cause inflammatory acne. 23. Tretinoin, benzoyl peroxide, erythromycin, and Accutane are used to treat acne. Viral Diseases of the Skin (pp. 623–629) Warts (p. 623) 24. Papillomaviruses cause skin cells to proliferate and produce a benign growth called a wart or papilloma. 25. Warts are spread by direct contact. 26. Warts may regress spontaneously or be removed chemically or physically. Smallpox (Variola) (pp. 623–624) 27. Variola virus causes two types of skin infections: variola major and variola minor. 28. Smallpox is transmitted by the respiratory route, and the virus is moved to the skin via the bloodstream. 29. The only host for smallpox is humans. 30. Smallpox has been eradicated as a result of a vaccination effort by the WHO. Chickenpox (Varicella) and Shingles (Herpes Zoster) (pp. 624–626) 31. Varicella-zoster virus is transmitted by the respiratory route and is localized in skin cells, causing a vesicular rash. 32. Complications of chickenpox include encephalitis and Reye’s syndrome. 33. After chickenpox, the virus can remain latent in nerve cells and subsequently activate as shingles. 34. Shingles (herpes zoster) is characterized by a vesicular rash along the affected cutaneous sensory nerves. 35. The virus can be treated with acyclovir. An attenuated live vaccine is available. Herpes Simplex (pp. 626–627) 36. Herpes simplex infection of mucosal cells results in cold sores and occasionally encephalitis. 37. The virus remains latent in nerve cells, and cold sores can recur when the virus is activated. 38. HSV-1 is transmitted primarily by oral and respiratory routes. 39. Herpes encephalitis occurs when herpes simplex viruses infect the brain. 40. Acyclovir has proven successful in treating herpes encephalitis. Measles (Rubeola) (p. 627) 41. Measles is caused by measles virus and transmitted by the respiratory route. 42. Vaccination provides effective long-term immunity. 43. After the virus has incubated in the upper respiratory tract, macular lesions appear on the skin, and Koplik’s spots appear on the oral mucosa. 44. Complications of measles include middle ear infections, pneumonia, encephalitis, and secondary bacterial infections. Rubella (pp. 627–628) 45. The rubella virus is transmitted by the respiratory route. 46. A red rash and light fever might occur in an infected individual; the disease can be asymptomatic. 47. Congenital rubella syndrome can affect a fetus when a woman contracts rubella during the first trimester of her pregnancy. 48. Damage from congenital rubella syndrome includes stillbirth, deafness, eye cataracts, heart defects, and mental retardation. 49. Vaccination with live rubella virus provides immunity of unknown duration. Other Viral Rashes (pp. 628–629) 50. Human parvovirus B19 causes fifth disease, and HHV-6 causes roseola. Fungal Diseases of the Skin and Nails (pp. 629–631) Cutaneous Mycoses (pp. 629–630) 51. Fungi that colonize the outer layer of the epidermis cause dermatomycoses. 52. Microsporum, Trichophyton, and Epidermophyton cause dermatomycoses called ringworm, or tinea. 53. These fungi grow on keratin-containing epidermis, such as hair, skin, and nails. 54. Ringworm and athlete’s foot are usually treated with topical antifungal chemicals. 55. Diagnosis is based on the microscopic examination of skin scrapings or fungal culture. Subcutaneous Mycoses (p. 630) 56. Sporotrichosis results from a soil fungus that penetrates the skin through a wound. 57. The fungi grow and produce subcutaneous nodules along the lymphatic vessels. Candidiasis (pp. 630–631) 58. Candida albicans causes infections of mucous membranes and is a common cause of thrush (in oral mucosa) and vaginitis. 59. C. albicans is an opportunistic pathogen that may proliferate when the normal bacterial microbiota are suppressed. 60. Topical antifungal chemicals may be used to treat candidiasis. Parasitic Infestation of the Skin (pp. 631–634) 61. Scabies is caused by a mite burrowing and laying eggs in the skin. 62. Pediculosis is an infestation by Pediculus humanus. Microbial Diseases of the Eye (pp. 634–637) 1. The mucous membrane lining the eyelid and covering the eyeball is the conjunctiva. Inflammation of the Eye Membranes: Conjunctivitis (pp. 634– 635) 2. Conjunctivitis is caused by several bacteria and can be transmitted by improperly disinfected contact lenses. Bacterial Diseases of the Eye (pp. 635–636) 3. Bacterial microbiota of the eye usually originate from the skin and upper respiratory tract. 4. Neonatal gonorrheal ophthalmia is caused by the transmission of Neisseria gonorrhoeae from an infected mother to an infant during its passage through the birth canal. 5. All newborn infants are treated with an antibiotic to prevent Neisseria and Chlamydia infection. 6. 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. 7. In trachoma, which is caused by C. trachomatis, scar tissue forms on the cornea. 8. Trachoma is transmitted by hands, fomites, and perhaps flies. Other Infectious Diseases of the Eye (pp. 636–637) 9. Inflammation of the cornea is called keratitis. 10. Herpetic keratitis causes corneal ulcers. The etiology is HSV-1 that invades the central nervous system and can recur. 11. Acanthamoeba protozoa, transmitted via water, can cause a serious form of keratitis. The Loop For a taxonomic approach, pages can be assigned as follows: Bacterial diseases of the skin pp. 615–623 Bacterial diseases of the eye pp. 634–635 Viral diseases of the skin pp. 623–629, 633 Viral disease of the eye p. 637 Fungal diseases of the skin pp. 629–631 Protozoan disease of the eye p. 637 Arthropod infestations of the skin pp. 631–633 Answers Review 1. Bacteria usually enter through inapparent openings in the skin. Fungal pathogens (except subcutaneous) often grow on the skin itself. Viral infections of the skin (except warts and herpes simplex) most often gain access to the body through the respiratory tract. 2. Staphylococcus aureus; Streptococcus pyogenes. 3. Disease Etiology Symptoms Treatment Notes Impetigo Staphylococcus aureus Vesicles that Hexachlorophene May be rupture and epidemic crust over Erysipelas Streptococcus pyogenes Thickened red Penicillin May be patches, swollen endogenous at margins 4. Etiological Method of Disease Agent Clinical Symptoms Transmission Acne P. acnes Infected oil glands Direct contact Pimples S. aureus Infected hair follicles Direct contact Warts Papovavirus Benign tumor Direct contact Chickenpox Herpesvirus Vesicular rash Respiratory route Fever blisters Herpesvirus Recurrent ―blisters‖ Direct contact Measles Paramyxovirus Papular rash, Koplik’s spots Respiratory route Rubella Togavirus Macular rash Respiratory route 5. Both are fungal infections. Sporotrichosis is a subcutaneous mycosis; athlete’s foot is a cutaneous mycosis. 6. a. Conjunctivitis is inflammation of the conjunctiva, and keratitis is inflammation of the cornea. b. Table 21.2. 7. Candidiasis is caused by Candida albicans. The yeast is able to grow when the normal microbiota are suppressed or when the immune system is suppressed. The yeast can be transferred from another person or be transient microbiota. White patches in the mouth or bright red areas of the skin and mucous membranes are signs of infection. Antifungal agents such as miconazole are used to treat candidiasis. Systemic infections are treated with oral ketoconazole. 8. The test determines the woman’s susceptibility to rubella. If the test is negative, she is susceptible to the disease. If she acquires the disease during pregnancy the fetus could become infected. A susceptible woman should be vaccinated. 9. Symptoms Disease Koplik’s spots Measles Macular rash Measles Vesicular rash Chickenpox Small, spotted rash German measles ―Blisters‖ Cold sore Corneal ulcer Keratoconjunctivitis 10. The central nervous system can be invaded following keratoconjunctivitis; this results in encephalitis. 11. Attenuated measles, mumps, and rubella viruses. 12. Varicella-zoster virus appears to remain latent in nerve cells following recovery from a childhood infection of chickenpox. Later, the virus may be activated and cause a vesicular rash (shingles) in the area of the nerve. 13. To prevent neonatal gonorrheal ophthalmia. This is caused by N. gonorrhoeae contracted by the newborn during passage through the birth canal. 14. Trachoma. 15. Scabies is an infestation of mites in the skin. It is treated with permethrin insecticide or gamma benzene hexachloride. The presence of a six-legged arthropod (insect) indicates pediculosis (lice). Critical Thinking 1. S. aureus is adapted for surviving on the human skin, which has a high concentration of NaCl. Microorganisms that are not adapted to this hypertonic environment will not be able to tolerate the 7.5% NaCl in mannitol salt agar. 2. Most warts regress spontaneously. Removal of warts is usually for cosmetic reasons. Occasionally warts are painful when they are located where pressure is placed on them (e.g., plantar warts on the sole of the foot). 3. The infections were transmitted by the contact lenses or cosmetics. Cosmetics are inoculated with microbes each time they are used. Some of the microbes grow, resulting in large inoculations of the eyes. Contact lenses can be improperly cleaned (i.e., not using an antiseptic) or contaminated by fingers. 4. The virus had one host—humans. It was not found in soil, water, or nonhuman organisms. Polio and measles meet this criterion. Clinical Applications 1. Pseudomonas aeruginosa. This bacterium is common in soil and is resistant to many antibiotics. 2. Toxic shock syndrome due to growth of Staphylococcus at the injection site. 3. The symptoms of toxic shock syndrome were caused by toxins produced from the secondary infection (S. aureus). Case History: Wrestling with Skin Infections Background A wrestling camp held July 2 through July 28 was attended by 175 male high school wrestlers from throughout the United States. On July 19, seven wrestlers were referred to a local urgent care facility because of complaints of painful vesicles on various parts of their bodies [head or neck (3), extremities (2), trunk (1)] and conjunctiva (1). Bacterial and fungal cultures from the skin lesions were negative. A questionnaire was administered to wrestlers by telephone following the conclusion of camp. Sixty-one wrestlers met the case definition of the presence of cutaneous vesicles. The athletes had onset during the camp session or within one week after leaving camp (see the figure). Athletes who reported wrestling with a participant with a rash were more likely to have the infection. Thirty-eight wrestlers interviewed reported a past history of oral cold sores. The attack rate was 24% for wrestlers who reported a past history of oral cold sores and 38% for wrestlers without a history of oral cold sores. Questions 1. What diseases do you suspect? 2. How was this disease transmitted? 3. How is this disease treated? 4. Provide a possible explanation of the lower attack rate in wrestlers with a history of oral cold sores. 5. How can such outbreaks be prevented? The Solution 1. Herpes gladiatorum 2. Direct contact 3. Acyclovir 4. Individuals with a history of oral herpes may have circulating antibodies that will prevent a new infection or recurrence. 5. Control methods should include education of athletes and trainers regarding herpes gladiatorum, routine skin examinations before wrestling contact, and exclusion of wrestlers with suspicious skin lesions. This outbreak might have been prevented if athletes with such lesions had been promptly excluded from contact competition.