Prevalence, characterization and antimicrobial resistance of non-O157 Shiga toxin-producing Escherichia coli isolates from healthy cattle in Tunisia

As a continuation of our previous work, here we examined the occurrence, virulence factors and antibiotic resistance of non-O157 Shiga toxin-producing Escherichia coli (STEC) bacteria in faecal samples of healthy cattle in Tunisia. From 260 faecal samples, 236 E. coli isolates were obtained, of which 30 (12.7%) proved to be non-O157:H7 STEC. The presence of STEC-serogroup virulence genes stx1, stx2, eaeA and ehxA was detected by PCR. Further virulence genes and other genes used for phylogenetic grouping were also examined among the STEC isolates. The most dominant serogroup was O145, followed by O103 and O45. Shiga toxin gene (stx1) was found in 70% of the STEC strains, stx2 and ehxA were detected in 17 isolates (56.7%). Other virulence genes, including fimH, traT, sfa/focDE, iutA, cdt3, hly, fyuA and ibeA, were detected in 100%, 60%, 46.7%, 46.7%, 36.7%, 10%, 6.7% and 3.3%, of the strains, respectively. More than 70% of the isolates were susceptible to most of the tested antibiotics. We concluded that the presence of STEC O145, O103 and O45 (12.7%), together with the earlier described STEC O157:H7 (4.2%) in cattle, intended for slaughter, may represent a threat to public health. Efficient control measures are needed in the farms and slaughterhouses in Tunisia.