Chapter 21

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Chapter 21

  1. 1. Ch. 21: Microbial Diseases ofCh. 21: Microbial Diseases of the Skin and Eyethe Skin and Eye  Structure and function of SkinStructure and function of Skin  Normal microbiota of skinNormal microbiota of skin  Diseases of the skinDiseases of the skin BacterialBacterial ViralViral FungalFungal  Diseases of the eyeDiseases of the eye
  2. 2. Structure and function of SkinStructure and function of Skin  Epidermis: outerEpidermis: outer layer of most deadlayer of most dead cellscells Stratum corneumStratum corneum consists keratinconsists keratin  Dermis: inner layerDermis: inner layer composed of c.t.p.composed of c.t.p. Contains hair follicles,Contains hair follicles, exocrine glands, andexocrine glands, and nailsnails
  3. 3. Normal microbiota of skinNormal microbiota of skin  Gram positive cocciGram positive cocci staphylococci and micrococcistaphylococci and micrococci  Gram positive pleomorphic rodsGram positive pleomorphic rods Propionibacterium acnesPropionibacterium acnes Cornybacterium xerosisCornybacterium xerosis  YeastYeast Pityrosporum ovalePityrosporum ovale
  4. 4. Staphylococcal skin infectionsStaphylococcal skin infections  CharacteristicsCharacteristics  MorphologyMorphology  Virulence FactorsVirulence Factors  DiseasesDiseases caused bycaused by Staphylococcus aureusStaphylococcus aureus  Folliculitis: Hair follicle infectionsFolliculitis: Hair follicle infections  Scalded skin syndromeScalded skin syndrome  Toxic shock syndromeToxic shock syndrome  ImpetigoImpetigo
  5. 5. MorphologyMorphology  Gram-positive cocciGram-positive cocci  Facultative anaerobeFacultative anaerobe  Non-spore formingNon-spore forming  Agar appearanceAgar appearance Round, raised, yellow colorRound, raised, yellow color  Blood agar differentiationBlood agar differentiation Secretes coagulaseSecretes coagulase
  6. 6. Virulence factors ofVirulence factors of Staphylococcus aureusStaphylococcus aureus
  7. 7. Hair follicle infections: BoilsHair follicle infections: Boils
  8. 8. Scalded skin syndromeScalded skin syndrome
  9. 9. Features of scalded skin syndromeFeatures of scalded skin syndrome
  10. 10. Toxic shock syndromeToxic shock syndrome  Produce a variety of toxinsProduce a variety of toxins ExotoxinsExotoxins EnterotoxinsEnterotoxins  Toxins absorb into bloodstreamToxins absorb into bloodstream
  11. 11. Features toxic shock syndromeFeatures toxic shock syndrome
  12. 12. ImpetigoImpetigo
  13. 13. Features of impetigoFeatures of impetigo
  14. 14. Streptococcal skin infectionsStreptococcal skin infections  CharacteristicsCharacteristics  MorphologyMorphology  ClassificationClassification  Virulence FactorsVirulence Factors  Diseases caused byDiseases caused by Streptococcus pyogenes  ImpetigoImpetigo  Necrotizing fasciitis: flesh-eating diseaseNecrotizing fasciitis: flesh-eating disease
  15. 15. MorphologyMorphology  Gram-positive cocciGram-positive cocci  Facultative anaerobeFacultative anaerobe  Non-spore formingNon-spore forming  Blood agar differentiationBlood agar differentiation Secretes hemolysinsSecretes hemolysins ββ-hemolytic streptococci: clear halo around the-hemolytic streptococci: clear halo around the colonycolony αα-hemolytic streptococci: green halo around the-hemolytic streptococci: green halo around the colonycolony
  16. 16. ClassificationClassification  Hemolytic patternsHemolytic patterns  αα-hemolysis: incomplete destruction of RBCs-hemolysis: incomplete destruction of RBCs  ββ-hemolysis: complete destruction of RBCs-hemolysis: complete destruction of RBCs  γγ: no hemolysis of RBCs: no hemolysis of RBCs  Lancefield system – most currentLancefield system – most current Based on cell wall carbohydratesBased on cell wall carbohydrates  20 major groups (alphabet, minus I & J)20 major groups (alphabet, minus I & J) Better predictor of pathogenic potentialBetter predictor of pathogenic potential Group A: most human infectionsGroup A: most human infections
  17. 17. Virulence factors ofVirulence factors of S. pyogenesS. pyogenes
  18. 18. Necrotizing fasciitis (“flesh-eating” disease)Necrotizing fasciitis (“flesh-eating” disease)
  19. 19. Features ofFeatures of “flesh-eating” disease“flesh-eating” disease Symptoms Severe pain, swelling, fever, confusion, skin becomes tense and discolored; shock and death occur if not immediately treated Incubation period 3 to 7 days Causative Agent Streptococcus pyogenes Pathogenesis Produce toxic products in the mass of dead tissue, using the breakdown products as nutrients; cause shock by releasing cytokines Epidemiology Underlying conditions that increase risk include diabetes, cancer, alcoholism, drug abuse, AIDS, surgery, abortion, childbirth, chickenpox Prevention and No proven preventive measures; treatment immediate surgery is mandatory; amputation sometimes necessary
  20. 20. Other Bacterial skin infectionsOther Bacterial skin infections  Clostridium perfringensClostridium perfringens Gram-positive rods, spore forming, obligateGram-positive rods, spore forming, obligate anaerobesanaerobes Clostridial myonecrosis (Gas gangrene)Clostridial myonecrosis (Gas gangrene)  Pseudomonas aeruginosaPseudomonas aeruginosa  Gram-negative, aerobic rod, pyocyanin produces a blue-green pus  Pseudomonas dermatitis Otitis externa (swimmer’s ear) Post-burn infections
  21. 21. Clostridial myonecrosis (Gas gangrene)Clostridial myonecrosis (Gas gangrene)
  22. 22. Features of Clostridial myonecrosisFeatures of Clostridial myonecrosis
  23. 23. Viral diseases of the skinViral diseases of the skin Papillomaviruses: Warts Poxviruses Smallpox (Variola) Chickenpox (Varicella) and Shingles (Herpes Zoster) Measles Rubeola Rubella (German Measles)
  24. 24. Chickenpox and ShinglesChickenpox and Shingles
  25. 25. Rubeola and RubellaRubeola and Rubella
  26. 26. Fungal diseases of the skinFungal diseases of the skin  Caused by dermatophytesCaused by dermatophytes  Tinea capitis: ringworm of the scalpTinea capitis: ringworm of the scalp Associated with elementary childrenAssociated with elementary children  Tinea cruris: ringworm of the groinTinea cruris: ringworm of the groin Associated with jock itchAssociated with jock itch  Tinea pedis: ringworm of the feetTinea pedis: ringworm of the feet Associated with athlete’s footAssociated with athlete’s foot
  27. 27. Fungal diseases of the skinFungal diseases of the skin
  28. 28. Diseases of the eyeDiseases of the eye Conjunctivitis (pinkeye) Haemophilus influenzae Various microbes Associated with unsanitary contact lenses Neonatal gonorrheal ophthalmia Neisseria gonorrhoeae Transmitted to newborn's eyes during passage through the birth canal Prevented by treatment newborn's eyes with antibiotics

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