Phenotypic variations among strains of Escherichia coli O157 isolated from raw milk samples collected in Kerala, South India

Abstract

Entero-haemorrhagic Escherichia coli (EHEC) constitutes a heterogeneous group of foodborne pathogens. We characterize 60 E. coli O157 serotypes isolated from 97 raw milk samples collected from local milk retailers. The biochemical analysis of the indigenous strains revealed a significant variation from their global counterparts. The study identifies a distinct phenotypic variant of E. coli O157 that ferments sorbitol, is urease-positive and produces hydrogen sulphide. The observed heterogeneity points to the inconsistency in the current screening approaches, which mostly depend on biochemical features, and justifies the demand for a universally inclusive standard procedure.