Staphylococcus aureus ("Golden staph")
General: Certainly the best known and arguably the most significant human bacterial pathogen.
Clinical: Five cytolytic or membrane damaging toxins (alpha, beta, gamma, delta, and Panton-Valentine (P-V) leukocidin), two exfoliative toxins (A and
, eight enterotoxins (A to E, G to I), and toxic shock syndrome toxin-1 (TSST-1). Of those, enterotoxin A is most commonly associated with disease; enterotoxin B causes staphylococcal pseudomembranous colitis; enterotoxins C & D are found in contaminated milk products; less is known about the remaining. Gastrointestinal illness is by way of a toxin, with abrupt onset of vomiting, watery diarrhea, abdominal pain, nausea 2~8hrs post-ingestion and lasting <24hrs.- Normal: Skin & mucosa, and especially the anterior nares, sometimes only transient colonization.
- Abnormal: Staphylococcal scalded skin syndrome (SSSS, Ritter's disease), toxic shock syndrome (TSS), endocarditis, osteomyelitis, joints, pneumonia, wounds, catheters, blood; processed meats, potato salad, custard-filled pastries, and ice-cream (all contaminated by way of a human carrier).
Resistance: Most are penicillinase+ (beta-lactamase). Major developing problem with methicillin-resistant (MRSA) strains, usually due to a specific alteration in penicillin binding protein (PBP2a) encoded by mecA gene, and only rarely due to excessive production of penicillinase. There are increasing reports of vancomycin intermediate strains (VISA)/glycopeptide intermediate (GISA).
Morphology: Gram+ cocci seen in clusters, single cells, or possibly short chains.
Growth characteristics: Coagulase+, catalase+, lipase+, and nuclease+; virtually all are fibrinolysin+; most strains hyaluronidase+ and penicillinase+ (beta-lactamase+). Eleven capsular serotypes; 1 and 2 are associated with thick capsules and mucoid colonies, but 5 and 7 are associated with the majority of infections. Also produce a water-soluble "slime layer," composed of monosaccharides, proteins, and peptides, which varies depending on the strain and growth conditions; this helps bind bacteria to tissues or foreign bodies but is more important in the virulence of other staphylococci. May survive on dry surfaces for long periods.
Common/important pathogens: