Prevalence of toxicogenic bacteria in some foods and detection of Bacillus cereus and Staphylococcus aureus enterotoxin genes using multiplex PCR

Abstract

Thirty-three food samples representing seven different food products were collected from the market in Sharkia Governorate (Egypt) and analyzed for their bacterial burden, including total mesophilic bacteria, spore formers, Staphylococcus aureus, and Bacillus cereus, using specific and selective nutrient media. The identified strains were screened for their virulence factors using the agar diffusion method. B. cereus strains CH, GT1, LB3, and G8 were found to be the most potent isolates, with four S. aureus showing nearly equal potency in terms of the virulence factors investigated. Separation of the extracellular proteins of the four most potent B. cereus strains by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the presence of protein bands with molecular weights ranging from 30 to 53 kDa that were suspected to be hemolytic enterotoxins. Protein bands having molecular weights between 22 and 33 kDa were also observed in three strains (S1, S2, and S3) of the S. aureus strains examined. Applying the multiplex PCR technique, we used two pairs of primers (FHblC and RHblC; FCytK and R2Cytk) to detect the toxin genes (hblC and cytK) in the suspected toxic B. cereus strains and five pairs of primers (SEA-3 and SEA-4; SEB-1 and SEB-2; SEC-5 and SEC-6; SED-1 and SED-2; SEE-1and SEE-2) to detect the five enterotoxins in the S. aureus strains. Our results indicate that the multiplex PCR amplification enabled the rapid detection and identification of enterotoxin genes in food-borne bacteria. © Springer-Verlag and the University of Milan 2011.