Virulence characterization and phylogenetic analysis of non-O157 vero toxin producing Escherichia coli (VTEC) isolated from cattle in India

Abstract

The virulence potential and phylogenetic analysis of non-O157 Vero toxin-producing Escherichia coli (VTEC) serogroups isolates was studied. A total of 540 samples comprise of cattle faeces (378 samples), cow raw milk (108 samples) and farm soil (54 samples) were processed for the isolation of E. coli and characterized phenotypically by Vero cell cytotoxicity assay (VCA). The positive isolates subjected to serotyping and molecular characterization carried out by multiplex PCR followed by phylogenetic analysis. The sixty VCA positive isolates were serotyped into 18 different serogroups of non-O157 VTEC with prevalence of 11.11% (60/540) while none of isolates belonged to O157 serogroup. The two serogroups (O26 and O121) members of Top-6 non-O157 VTEC were also reported in serotyping. The five different gene combinations of virulent genes were revealed in 48.33% (26/60) isolates while rest were single verotoxin gene bearer in virulence profile. The dominance of vt2 gene (43.33%, 26/60) was noticed over the vt1 (35%, 21/60), hlyA (33.33%, 20/60) and eaeA (18.33%, 11/60) genes while, coexistence of verotoxin genes (vt1 and vt2) was revealed in 21.66% (13/60) isolates. Phylogenetic analysis showed the 100% identity and least divergence among the sequences of vt1 gene in comparison with other studied genes, therefore, the vt1 moiety can be used as diagnostic tool. Thus, findings provide the genetic diversity profile of non-O157 VTEC from cattle of Indian region that may be valuable in diagnostic strategies for control of these serogroups around the globe.