Colistin resistance prevalence in Escherichia coli from domestic animals in intensive breeding farms of Jiangsu Province, China

The global dissemination of colistin resistance has received a great deal of attention. Recently, the plasmid-mediated colistin resistance encoded by mcr -1 and mcr -2 genes in Escherichia coli ( E.coli ) strains from animals, food, and patients in China have been reported continuously. To make clear the colisin resistance and mcr gene spread in domestic animals in Jiangsu Province, we collected fecael swabs from pigs, chicken and cattle at different age distributed in intensive feeding farms. The selected chromogenic agar and mcr -PCR were used to screen the colisin resistance and mcr gene carriage. Colistin resistant E.coli colonies were identified from 54.25 % (440/811) pig faecal swabs, from 35.96 % (443/1232) chicken faecal swabs, and 26.92 % (42/156) from cattle faecal swabs. Of all the colisin resistant E.coli colonies, the positive amplifications of mcr -1 were significantly higher than mcr -2. The mcr -1 prevalence was 68.86 % (303/440) in pigs, 87.58 % (388/443) in chicken, and 71.43 % (30/42), compared with 46.82 % (206/440) in pigs, 14.90 % (66/443) in chicken, and 19.05 % (8/42) in cattle of prevalence of mcr -2. Co-occurrence of mcr -1 and mcr -2 was identified in 20 % (88/440) in pigs, 7.22 % (32/443) in chickens, and in 9.52 % (4/42) cattle. These data indicate that mcr was the most important colistin resistance mechanism. Interventions and alternative options are necessary to minimise further dissemination of mcr between food-producing animals and human. IMPORTANCE Colistin is recognized one of the last defence lines for the treatment of highly resistant bacteria, but the emergence of resistance that conferred by a transferable plasmid-mediated mcr genes to this vital antibiotic is extremely disturbing. Here, we used E. coli as an index to monitor drug resistance in domestic animals (pigs, chicken and cattle). It was found that the colistin resistance widely occurred at all ages of domestic animals and the mcr -dependent mechanism dominated in E.coli . We also found that the elder and adult animals were a reservoir of resistant strains, suggesting a potential food safety issue and greater public health problems.