see also:

• clinically important bacteria
• antibiotics for Rx of Staph. aureus

• Gram +ve, spherical, often in clusters, non-motile, non-sporing;
• Catalase +ve; fermentative (cf. micrococcus oxidative);
• Some have capsules; aerobic & facultative anaerobes;
• Grow easily on most media, best at 37°C;
• Usually cream-yellow on blood agar within 24hrs; usually odourless;

• coagulase +ve (converts fibrinogen→fibrin coats bacteria);
• DNAase +ve; reside mainly in ant. nares (40-80% adults);
• Some produce:
  • enterotoxin (heat stable; in food poisoning);
  • alpha-toxin (hemolysin & leucocidin);
  • Panton-Valentine leucocidin;
  • exfoliatin (group II only);
  • toxic-shock toxin (group I only1);
  • penicillinase (group III);
  • eryhthrogenic toxin (→scarlet fever-like rash);
  • staphylokinase (lyses fibrin via activ. plasmin);
  • hyaluronidase;
• Grouped by phage typing into 3 main groups:
  • I - incl. many endemic hosp. strains;
  • II - incl. many cause minor sepsis/impetigo/exfoliatin;
  • III - incl. most enterotoxin strains & antib.res.strains;
• Lesions:
  • impetigo - pustule beneath stratum corneum epidermis;
  • superficial folliculitis - superficial part hair follicle only;
  • boil (furuncle) - entire hair follicle → s/c;
  • carbuncle - pockets in s/c tissue due to fibrous septae, with communication b/n boils;
  • abscesses of pulp spaces/palmar spaces/etc.
  • mastitis from newborn via cracked nipples;
  • pneumonia
  • pseudomembranous enterocolitis;
  • osteomyelitis if bacteraemia + trauma or compound #;
  • renal carbuncle due to bacteraemia;
  • lymphadenitis;
  • septicaemia/pyaemia;
• in over 80% of cases of S. aureus bacteraemia, the Staph strain can be detected in the anterior nares of the patient which is presumably the site of endogenous colonisation ¹⁾

• (coagulase -ve) grouped via:
  • Novobiocin sens. → S.epidermidis
  • resist. → S.saprophyticus