Pathogenicity of Staphylococci Infection





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.


Laboratory Diagnosis


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.