Staphylococci

Staphylococci are Gram-positive cocci which are arranged in grape-like clusters. They are aerobic or facultative anaerobes which normally inhabit the human skin. They are nutritionally undemanding and are catalase positive.

Two forms of classification are used (most common first):

• coagulase test:
  • coagulase positive:
    • Staph. aureus
      
      
• coagulase negative:
  • Staph. epidermidis (novobiocin sensitive)
  • Staph. saprophyticus (novobiocin resistant)
    
    
• biochemical:
  • 26 species recognised, many of which rarely occur in human infections, e.g. Staph. haemolyticus
  • includes micrococcus spp. - similar to coagulase -ve staphs. and rare causes of similar infection

Staphs. multiply rapidly at 37 deg. C and can be isolated from swabs, pus etc. in 24 hours. Blood cultures become positive after 24-48 hours incubation.