staphylococcus
Table of Contents
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