Staphylococcosis
The disease is caused by the ingestion of preformed toxin released by Staphylococcus aureus.
Epidemiology: Staphylococci grow in meat, dairy and bakery products and produce enterotoxins. In food microbiology, detection of S. aureus is of interest as it indicates the mishandling of the product, due to poor hygiene during processing. Sources of staphylococci contaminations may be animals, human carriers and contaminated processing equipment. Pathogenic strains of Staphylococcus species produce several toxins and enzymes, viz. coagulase, hyaluronidase, phosphatase, fibrinolysin, haemolysin (á, â and ä haemolysin), necrotoxin, lethal toxin, leucocidin and enterotoxin.
Clinical features: The incubation period is short usually ranges from 1–8 hours and rarely up to 18 hours. Enterotoxin acts on receptors in gut that transmits impulse to medullary center. Abrupt and intense vomiting occurs for up to 24 hours. It takes 24-48 hours to recover.
Diagnosis: For isolation, enrichment can be done in staphylococcal enrichment broth or alternatively in trypticase soy broth with 10% sodium chloride and 1% sodium pyruvate. Baird Parker agar is the medium of choice on which shiny, jet black colonies appears showing zone of precipitation around the colony or halo around the colony with white precipitation beneath the colony or no zone or halo but only precipitation beneath the colony. The nuc-gene, encoding the thermostable nuclease (TNase) is used for PCR based detection of S. aureus. Use of PCR is also described to screen S. aurues for the presence of enterotoxin genes. Some of the enterotoxin genes detected by PCR in S. aurues are entA, entB, entC1, entD, entE, toxic shock syndrome (tst) and exfoliative toxin A & B (eta, etb).