Detection of staphylococcal enterotoxins among foods using the reverse passive latex agglutination and enzyme linked immunosorbent assays
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Date
2011-12-29
Authors
Mathenge, John Mureithi
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Abstract
Staphyloccus aureus is a cause of food poisoning in humans. Vomiting, headache, abdominal pain, and diarrhoea that occur 1-6 hours following consumption of contaminated food characterize the poisoning. The illness is caused by five serologically distinct enterotoxins produced by organisms while growing in food. A number of methods have been used to detect Staphylococcal enterotoxins in foods and in S. aureus culture filtrates. These include biological assays and immunological methods. Biological methods have varied sensitivities and suffer from cross reactivity problems. This study was carried to determine the rate of contamination of milk and meat products with enterotoxigenic S. aureus and compare sensitivity of the two immunological techniques: RPLA and ELISA techniques for detection of enterotoxigenic strains of Staphylococcus aureus. A total of 400 milk and meat products were collected around Nairobi. The samples included 200 raw milk, 100 beef carcass swabs, 50 minced meat and 50 chicken carcass. Mannitol salt agar was used as selective and indicator medium for isolation of S. aureus from food samples. S. aureus were identified using a number of different and diagnostic tests which included oxidative fermentation, mannitol fermentation, coagulase production and deoxyribonucIease (DNase) production assays. Enterotoxin production was dectected using RPLA and ELISA techniques, Staphylococcal enterotoxins reverse passive latex agglutination SET RPLA kit and Staphylococcal enterotoxin enzyme immunoassay SETEIA Kit. (Labour Dr. W. Bommeli, Bern). S. aureus was isolated from a total of 101 (25.4 %) food samples. Of these, 22 were from chicken, 16 minced meat, 55 raw milk and 8 beef carcass. The prevalence of S. aureus in the various foods ranged from 8% in beef carcasses to 44% in chicken. A total of 67 S. aureus were enterotoxigenic as detected using ELISA, while 62 S. aureus were enterotoxigenic using RPLA. There was no significant difference in the number of enterotoxigenic S. aureus detected by the two techniques among the food stuffs (t = 1.324; df =3, P = 0.277). Staphylococcal enterotoxins SEA, SEB, SEC and SED were tested for, and SEC was the most frequent accounting for 59 (88 %) of the 67 enterotoxigenic S. aureus identified using ELISA and 61 (98.4 %) of the 62 identified by RPLA. There was however no significant difference in the prevalence of SEC as identified by the two techniques (t = 0.815, df = 100, P = 0.417). SEA was found in 41 (61.2%) of 67 enterotoxigenic S. aureus while SEB was found in 31 (46.3 %), and SED in 26 (38.8 %) isolates as identified using ELISA. SEA was detected in 32 (51.6 %), SEB in 21 (33.9 %) and SED in 13 (21 %) of the 62 enterotoxigenic S. aureus as identified by RPLA. S. aureus strains were found to produce one or more of the enterotoxins types. Twenty four (38.5 %) of the enterotoxigenic S. aureus produced a single enterotoxins while 44 (67.7 %) produced one or more with 21 (32.3 %) producing all the four enterotoxins type as identified by ELISA. The results showed that there was a high prevalence of enterotoxigenic S. aureus in raw foodstuffs of animal origin with SEC producing strains as the most prevalent, and that RPLA and ELISA were comparable techniques for detection of staphylococcal enterotoxins.
Description
The QR 82.M5M3
Keywords
Staphylococaus aureus//Food poisoning//Enterotoxins