The emergence and dissemination of mcr-1 have become a public concern worldwide. And food animal production has been singled out as responsible for amplification and spread of mcr-1 . Herein, a total of 249 porcine Escherichia coli ( E. coli ) were isolated from the 300 fecal samples in Heilongjiang province of China. Susceptibility testing revealed 186 (74.70%) E. coli were colistin-resistant. And a total of 86 mcr-1 -positive E. coli were detected. The mcr-1 -positive E. coli showed extensive antimicrobial resistance profiles with the presence of additional resistance genes, including TEM1 , CTX-M , aac3-IV , tetA , flor , sul1 , sul2 , sul3 , oqxAB . No mutations in pmrA, pmrB and mgrB were found to be associated with colistin resistance. By phylogenetic group classification, the distribution of all mcr-1 -positive E. coli belonging to group A, B1, B2 and D was 52.33%, 33.72%, 5.81%, 8.14%, respectively. The presence of virulence-associated genes iutA, iron, fimH, vat, ompA and traT was at moderate frequencies. And 7 mcr -positive E. coli belonged to ExPEC. Among 20 representative mcr-1 -positive E. coli, MLST showed that the most common ST was ST 10 (n=5). The conjugation assays showed that the majority of mcr-1 were transferable at frequencies of 7.05×10 −7 to 7.57×10 −4 . Therefore, the results of this study revealed the necessity of monitoring and minimizing the further dissemination of mcr-1 in food animals, particular in swine.

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