Identification of enterotoxigenic Staphylococcus aureus strains from meat and dairy products by multiplex PCR and reverse passive latex agglutination test in Nairobi, Kenya
Gicheru, M. M.
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Background: Foods of animal origin, especially meat and dairy products, are sometimes associated with food borne diseases. In many countries, Staphylococcus aureus is considered the second or third most common pathogen responsible for outbreaks of food poisoning. In Kenya enterotoxigenic staphylococcal food poisoning poses a potential health hazard to the consumers of meat and dairy products but little data is available about the strains involved in food poisoning. Objective: The primary objective of this study were to investigate the occurrence of different strains of Staphylococcus aureus in meat and milk products and to determine the existence of gene coding, the classical staphylococcal enterotoxins. Methodology: The survey was a crosssectional descriptive study targeting meat, dairy products and meat processing plant. The study was confined in randomly selected meat and milk outlets in the Central Business District of Nairobi (CBDN) and its surroundings. Four hundred and twenty food samples of animal origin, comprising of meat and dairy products, were randomly sampled. Genes coding classical staphylococcal enterotoxins were profiled using multiplex Polymerase Chain Reaction (PCR) and the production by Reversed Passive Latex Agglutination (RPLA). Two hundred and fifty one samples of raw pork and packed pork products from a local processing factory were similarly tested. Results: Data from a total 671 samples were examined and 37.4% of them were contaminated with S. aureus in which the contamination rate was higher in meat products than in the milk products. Enterotoxin production was detected in 74.5% of the isolated strains of S. aureus. Staphylococcal enterotoxin genes (ses) were detected in 77.3% of the total isolates. The most frequent gene was sea (61.8%) followed by see (33.1%), sed (17.5%) and see (15.9%) respectively. Staphylococcal enterotoxin B (seb) was the least occurring gene in the S. aureus isolates examined (13.9%). Genes occurring in pairs included Sea/See (21.2%), Sea/Sed (9.8%), Sed/See (2.1 %), Sea/See (0.7%) and Seb/Sec (0.5%) among others. A relatively low number 4 (2.1 %) of discrepancies between the results of multiplex PCR and RPLA were found where by the sed genes were expressed by PCR but the corresponding toxins were not detected by RPLA. Conclusions: The study clearly indicated that meat and milk products marketed in and around Nairobi, Kenya were contaminated with enterotoxigenic S. aureus posing a high risk of food poisoning to the consumers. Equally, these data demonstrated that multiplex PCR and RPLA are useful methods for detection of enterotoxigenic potential of S. aureus. There is need for strict hygienic and preventive measures to the manufacturer, distributors and consumers of meat and milk products since the contamination of S. aureus is greater than other pathogenic bacteria previously reported.