Prevalence rate and presence of virulence genes of Escherichia coli O157: H7 in raw milk and traditional cheese at Marand retails

The aim of this study was to estimate the prevalence rate of Escherichia coli O157: H7 in raw milk and traditional cheese at Marand retails. Moreover, the isolates were assessed for the presence of virulence gene of stx1, stx2, eaeA and hly. For this reason, 100 traditional cheese and 50 raw milk samples were collected randomly. The samples were enriched in EC broth containing novobiocin and were isolated on sorbitol MacConkey agar with cefixime and tellurite. The isolates were further assayed by VRBA, tryptone broth and Escherichia coli Chromogenic agar for the lactose fermentation, indole production and beta-glucuronidase activity, respectively. The selected colonies were confirmed by E. coli O157: H7 antiserum and finally the isolates were analyzed for the presence of virulence genes. According to the results, 9% (9/100) of cheese and 10% (5/50) of raw milk samples were found contaminated with sorbitol-negative E. coli. Using the anti-E. coli antiserum, 1 isolate (2%) among the milk samples was confirmed and the presence of virulence genes of eaeA and stx1 were determined by multiplex PCR. With respect to the occurrence of E. coli O157: H7 in raw milk and its high persistence to acidic environment, it was concluded that raw milks and traditional cheeses marketed at Marand could be considered as the potential source of infection to humans.