User Tools

Site Tools


staphylococcus

staphylococcus

Staphylococci:

  • 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;

S. aureus:

  • 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)

Other Staphylococci:

  • (coagulase -ve) grouped via:
    • Novobiocin sens. → S.epidermidis
    • resist. → S.saprophyticus
1)
NEJM Journal Watch. Emergency Medicine (Feb 28, 2001) Adams, J G.
staphylococcus.txt · Last modified: 2014/08/27 04:58 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki