Skin Infection Bugs

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  1. Staphylococcus aureus
    coagulase +, b-hemolysis, golden colonies, mannitol +

    Direct invasion w/ abscess formation causes folliculitis, furuncles, carbuncles, impetigo. Coagulase and clumping factor convert fibrinogen to a fibrin clot --> abscess formation. Protein A- binds Fc receptor of IgG. Enzymes- Lipases, Cytolytic toxins: alpha toxin pore forming

    • Production of exotoxin causes toxin-mediated disease: scalded skin syndrome and toxic shock syndrome
    • Scalded skin syndrome: exfoliative Toxins A and B. Proteases- cleave desmoglein on suface of epidermal cells. Involve exfoliative dermatitis. Cutaneus blisters- clear fluid w/ no organisms or leukocytes
    • Toxic shock syndrome Toxin 1 (TSST-1): superantigens binds directly to MHCII on macrophages --> nonspecific proliferation of T cells and massive release of cytokines. Sudden onset of fever, vomiting, diarrhea. Red rash resembling a sunburn and desquamation 1-2 wks later. Hypotensive shock, impaired renal and hepatic function, occasional deaths
  2. Streptococcus pyogens
    • b-hemolytic, Group A strep, bacitracin sensitive
    • wound infections, impetigo, erysipelas, cellulitis, necrotizing fasciitis, pharyngitis, scarlet fever, rheumatic fever, glomerulonephritis
    • Protection: hyaluronic acid capsule (non-immunogenic), M protein (antiphagocytic), C5a peptidase
    • Adhesion: M and F proteins
    • Spreading factors and damage: streptolysins (pore forming), streptokinase (lysis of clots and fibrin deposition facilitate spread)
    • exo-enzymes: hyaluronidase, DNAase
    • Virulence factors: Pyrogenic or erythrogenic exotoxins. Phage coded superantigens --> massive release of cytokines. Scarlet fever (diffuse erythematous rash, strawberry tongue), streptococcal toxic shock syndrome
    • Rx: penicillin
  3. Vibrio vulnificus
    • curved gram - rods, facultative anaerobe, polar flagella, oxidase +
    • Halophilic- requires salt for growth
    • found in salt water and known for contaminating oysters
    • Virulence factors: polysaccharide capsule
    • wound infections after exposure to contaminated seawater --> necrotic cellulitis
  4. P. aeruginosa
    • Hot tub folliculitis: skin rash in healthy persons
    • infection of burn wounds: blue green pus, grape-like odor
  5. Mycobacterium Leprae
    • Acid fast bacillus
    • no growth in artificial medium or tissue culture
    • Causes Leprosy: chronic granulomatous disease of the peripheral nerves and superficial tissues
    • incubation period: 2-7 yrs
    • obligate intracellular parasite of macrophages and Schwann cells
    • doesn't produce toxins; damage from host response
    • Paucibacillary (tuberculoid) leprosy: Macules or large flattened plaques; raised erythematous edges w/ dry, pale, hairless centers (healing). Loss of sensation. low infectivity- few or no acid-fast rods. Dapsone + refampin 6 months
    • Multibacillary (lepromatous) leprosy: multiple erythematous nodules, extensive tissue destruction, sensory loss, highly infectious, numerous acid-fast rods in lesions, deficient cell immunity. Dapsone + rifampin + clofazimine. 2 yrs
  6. Bacillus anthracis
    • gram + in box car chains, polypeptide capsule,
    • EF= adenylate cyclase --> inc intracellular cAMP --> inc efflux of fluids and ions --> edema
    • LF= mitogen-activated protein kinase kinase (MAPKK) protease --> disrupts cell signaling --> cell death and tissue necrosis
    • Cutaneous anthrax:forarm or hands. starts from erythematous papules --> progresses through vesicular and ulcerative stages --> black eschar surrounded by edema
    • Rx: fluoroquinolones (ciprofloxacin)
Card Set:
Skin Infection Bugs
2012-04-21 02:57:31

micro skin
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