Occurrence of shiga toxin producing Escherichia coli (STEC) in healthy cattle of organized farms in West Bengal

Among the emerging zoonosis, Shiga toxin producing Escherichia coli (STEC) is the predominant one. Ruminants act as major reservoir of these organisms, which can be transmitted by direct or indirect means. Healthy ruminants can also shed the organisms in the surrounding environment causing transmission of the infection. Present study was undertaken to investigate the occurrence of STEC in cattle faecal samples collected from organized farms of Kolkata and Bankura districts in West Bengal, India. Out of 84 samples examined total 77 samples (92%) were found positive for E. coli. In specific, from Kolkata out of 48 samples 45 samples (94%) and from Bankura out of 36 samples 32 (89%) were positive for E. coli. Of the 77 strains of E. coli isolated from cattle, 14 were untypable, 11 were rough and 52 strains were typed into 24 different serogroups. O25 serogroup was isolated from maximum number of cattle (12%), followed by O60 serogroup (7%). All the E. coli isolates were subjected to multiplex PCR for detection of shiga toxin genes (stx₁, stx₂), intimin gene (eaeA), and enterohaemolysin gene (ehx). STEC was detected in 40 (48%) of the 84 cattle samples in the present study. These STEC strains belonged to 17 different serogroups and seven could not be typed. This study detected little more number of stx₂ positive isolates than stx₁ (95% and 92%, respectively). No Escherichia coli harboring gene for only intimin i.e. eaeA (Enteropathogenic E. Coli) was detected. However, five strains of Escherichia coli harboring only gene for enterohaemolysin i.e. ehx were detected. These strains belonged to three different serogroups and one could not be typed. The present study detects the occurrence of STEC from apparently healthy cattle of West Bengal, India.