Skin Infection Bugs

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

• 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

• 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

• Hot tub folliculitis: skin rash in healthy persons
• infection of burn wounds: blue green pus, grape-like odor

• 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

• 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)