Isolation, Identification, and Molecular Characterisation of Shiga Toxin-producing Escherichia coli from Raw Beef

Abstract

Shiga toxin-producing Escherichia coli (STEC) is a foodborne pathogen associated with contaminated animal-derived foods. This study investigated the occurrence of E. coli and the presence of Shiga toxin-associated genes in raw beef collected in the Chittoor district of Andhra Pradesh. Seventy-two raw beef samples were obtained from slaughterhouses and retail meat shops and examined using conventional microbiological and molecular methods. Samples were enriched in MacConkey broth and cultured on Eosin Methylene Blue agar. Presumptive E. coli colonies were purified and confirmed by biochemical testing. Genomic DNA was extracted from the confirmed isolates, and polymerase chain reaction assays were used to detect the stx1 and stx2 genes. Of the 72 samples examined, 35 yielded presumptive E. coli, corresponding to a prevalence of 48.61%. Among the 35 isolates, four carried stx1 and three carried stx2, representing 11.42% and 8.57% of the isolates, respectively. These findings confirm the presence of Shiga toxin-associated genes among E. coli isolates recovered from raw beef in the study area. The results indicate the need for consistent hygienic practices during slaughter, meat handling, processing, and distribution. Continued microbiological surveillance across the meat supply chain may support the early detection of STEC contamination and inform locally appropriate food-safety measures.