Staphylococci were first recognized as causative agents of distinct diseases by Koch in 1878. Until recently, Staphylococci were classified as two distinct species: S. aureus, whose colonies are golden-yellow and coagulase-positive, and S. albus, whose colonies are white and coagulase-negative. Now, at least 20 biotypes of S. albus are known although there is far from general agreement on the speciation of staphylococci.
growth in irregular clusters
genome consists of one chromosome plus plasmids, transposons, and prophages
pentaglycine cross-bridge in the peptidoglycan,
Most specimens are natural inhabitants of the mamalian skin
Other gram-positive cluster-forming cocci such as micrococcus, planococcus, peptococcus, and peptostreptococci differ mainly from Staphylococci in that they have no pentaglycine in their peptoglycan.
The following cellular antigens are present: (1) virtually all S. aureus strains possess protein A which is covalently linked to peptidoglycan. (2) Polysacharride A is a species-specifc surface antigen of S. Aureus and S. epidermidis. Staphylococci are among the hardiest of all non-spore-forming bacteria.
S. Aureus isolates differ widely in their patterns of exoprotein production, antibiotic resistance, surface antigens, phage sensitivity, and other traits. A number of typing schemes are available of which the most important is phage typing. Besides coagulase production, S. aureus is the only staphylococci specimen that ferments mannitol anaerobically. S. aureus also has a high salt tolerance.
S. aureus is responsible for a wide variety of suppurative disease in humans, including superficial and deep abscesses, wound infections, and infections of various internal organs. They also cause several toxinoses, including food poisoning, toxic epidermal necrolysis, and the toxic shock syndrome.
S. aureus is one of the commonest causes of food poisoning, which is due to preformed enterotoxin in the food. The victim typically presents with nausea, cramps, vomiting, and diarrhoea 1 to 6 hours after ingestion of contaminated food. Foods which are commonly implicated include pastries, custards, salad dressing, sliced meats, and meat products. The food is usually contaminated by food handlers. Staphylococcal enterotoxins are heat-stable (100oC for 30 minutes). It is essential to prevent multiplication of the organisms by refrigerating food before as well as after cooking.
Most coagulase-negative staphylococci are non-pathogenic or are opportunistic pathogens. S. epidermidis is by far the most frequent cause of infection from intravacular catheters and prosthesis. S. saprophyticus is an important cause of urinary infection in young women.
Aureus should be grown under aerobic conditions. On blood agar, S. aureus colonies are typically golden-yellow in colour, and a zone of B-haemolysis may be present. Fermentation of mannitol and growth in high salt concentration provide further suggestive evidence. S. Aureus can only be definitively identified by the presence of coagulase.
Minor lesions do not generally require anti-microbial treatment. Localized abscesses should be drained. Antibiotics can be used to inhibit dissemination. Systemic disease must be treated vigorously with an appropriate antibiotic. Penicillin is the drug of choice should the strain responsible be sensitive to it. Otherwise, in the absence of sensitivity data, empirical treatment may be started with a penicilinase-resistant agent such as ampicillin. In certain hospital settings throughout the world, serious nosocomial epidemics are cause by S. aureus strains resistant to all antibiotics except vancomycin.