Isolation, molecular characterization and antibiotic resistance of Shiga ToxinProducing Escherichia coli (STEC) from buffalo in India

In total, 363 Escherichia coli were isolated from 165 faecal samples of healthy buffaloes in West Bengal, India. Twenty-four of these isolates (6 center dot 61%) were found to carry at least one gene characteristic for Shiga toxinproducing Escherichia coli (STEC). These STEC strains belonged to 13 different O-serogroups. The stx1 gene was present in 23 (95 center dot 8%) of total STEC isolates, whereas 20 (83 center dot 3%) STEC isolates carried the gene stx2. Twelve strains of E.coli (50% of total STEC isolates) possessed enterohaemolysin (ehxA) gene in combination with others. Fourteen (58 center dot 33%) isolates found to possess saa gene. However, no E.coli was detected harbouring gene for intimin protein (eaeA). Of 23 stx1-positive isolates, seven (30 center dot 43%) were positive for genes of the stx1C subtype. Of the 20 isolates with the stx2 gene, 25% (5/20) possessed stx2C and 10% (2/20) possessed stx2d gene. The phylogenetic analysis after RAPD of STEC strains revealed six major clusters. The isolated STEC strains were resistant most frequently to erythromycin (95 center dot 83%), cephalothin (62 center dot 5%), amikacin (54 center dot 17%), kanamycin (45 center dot 83%) and gentamicin (41 center dot 67%) group of antibiotics. No ESBL-producing (blaCTXM, blaTEM, blaSHV) or quinolone resistance gene (qnrA) was detected in the STEC isolates.