Plasmid-Mediated Colistin Resistance in O157:H7 Cattle and Sheep Isolates and Whole-Genome Sequence of a Colistin-Resistant Sorbitol Fermentative O157:H7.

The aims of this study were to investigate the plasmid-mediated colistin resistance genes (, , , , and ), phenotypic colistin resistance in O157:H7/H7 strains isolated from cattle and sheep, and whole-genome sequence (WGS) analysis of colistin-resistant sorbitol fermentative O157:H7. According to the results, 5 of the 49 isolates were found to harbor and/or genes. Three isolates, including a sorbitol fermentative O157:H7, were found phenotypically resistant to colistin with a minimum inhibitory concentration value of 128 μg/mL. The genome of sorbitol fermentative O157:H7 did not show 100% similarity to any of the other genome sequences found in the universal genome database. It has also been determined that this isolate carried 62 different antimicrobial resistance genes. This is the first report of plasmid-mediated and genes carrying O157:H7 from cattle and sheep isolates and WGS of a colistin-resistant sorbitol fermentative O157:H7. Findings of this study indicate that cattle and sheep can be an important source of colistin resistance in O157:H7, and slaughterhouse wastewater might be a significant route for dissemination of the plasmid-mediated colistin genes. Therefore, the use of colistin in veterinary medicine should be restricted to reduce the development of resistance. Also it may be necessary to review the non-sorbitol fermentation-based isolation protocol for not missing the sorbitol fermentative O157:H7 in epidemiological studies.