Prevalence, Serogroups, Shiga-toxin Genes and Pulsed Field Gel Electrophoresis Analyses of Escherichia coli Isolated from Bovine Milk

Shiga toxin-producing Escherichia coli (STEC) including non-O157 strains have been linked to outbreaks and sporadic cases of illness worldwide. A total of 647 milk samples were collected at different levels of collection and processing (udder, milking utensils, milk collection centres and receiving dock) within West Coast region of India. The milk samples were screened for the presence of E. coli and further tested for the Shiga-toxin ( stx ) genes by PCR. The isolates were characterized for their serogroups and Xba I digestion patterns of total DNA separated by pulsed-field gel electrophoresis (PFGE). A total of 77 (11.90 %) isolates were confirmed as having E. coli . The serogroups reported were O4, O60, O112, O56, O159, O120, O2, O83, O88, O95, O141, O21, O25, O80, O140, O97, O24, O166, O146, O51, O169, O147, O103, O18, O100, O15, O69, O43, O7, O3, O45, O124, O110, O84, and O114. Out of the 77 E. coli isolates, 25 (32.46 %) could be classified as Shiga-toxigenic based on PCR results. Of these 11, 3 and 11 isolates were positive for stx 1, stx 2, and both stx 1 and stx 2, respectively. PFGE profiles indicated genetic diversity of E. coli strains. Much variation was observed among isolates recovered at different levels of collection. Further research is needed to uncover unique characteristics and resistance of non-O157 STEC strains.