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Staph epidermidis

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  • Staphylococcus epidermidis 
    • Gram + cocci in clusters
    • Catalase +
      • First test to differentiate staph vs. strep (catalase negative)
    • Coagulase –
      • Second test to differentiate from staph aureus (coagulase positive)
    • Novobiocin sensitive
      • Third test to differentiate vs. staph saprophyticus (novobiocin-resistant), by exposure to the antibiotic novobiocin
    • Urease +
      • Enzyme that hydrolyzes urea into ammonia and carbon dioxide
      • Urease broth is less frequently used in labs
        • Cannot distinguish between saprophyticus and epidermidis
    • Does not ferment mannitol
      • Compare vs. staph aureus (ferments mannitol)
    • Produces adherent biofilms made of extracellular polysaccharide
      • Infects prosthetic devices (e.g. hip implants, heart valves) and IV catheters
      • Biofilm serves as a barrier that protects the bacteria from antibiotics and host defense mechanisms (opsonization, neutrophil migration, and T-lymphocyte activation) 
    • Component of normal skin flora
      • Contaminates blood cultures