Isolation and Characterization of Shiga-toxigenic Escherichia Coli Isolated from Various Food Samples

Shiga toxigenic Escherichia coli (STEC) is a food-borne pathogen associated with community health concern. Contamination of food by STEC and toxin causes infectious diseases. Escherichia coli isolated from food samples such as yogurt, apples, tomatoes and milk by applying violet-red bile glucose agar, Triphenyl tetrazolium chloride agar (TTC) and eosin-methylene blue agar (EMB) test after pre-enrichment of food samples in buffered peptone water. Escherichia coli isolates were screened for the existence of shiga toxin genes Stx1 and Stx2 through Polymerase Chain Reaction (PCR). Apples (17%), tomatoes (26%) and milk (1%) of the samples examined showed positive results for Stx genes. Yoghurt samples examined in this study had no Stx1 or Stx2 gene. The presence of Shiga toxin that is protein in nature was confirmed by SDS-PAGE in milk sample. The present study has shown that foods from densely populated areas i.e. Harbanspura, Lahore could be sources of STEC.