Genome Characterization of mcr-1 -Positive Escherichia coli Isolated From Pigs With Postweaning Diarrhea in China.

DiarrheagenicEscherichia coliis the causative agent of diarrhea in infants and animals worldwide. Many isolated strains recovered from pigs with postweaning diarrhea are multidrug resistance (MDR), and hybrids ofE. coliare potentially more virulent, as enterotoxigenicE. coli(ETEC)/Shiga-toxigenicE. coli(STEC) hybrids. Here, we used whole-genome sequencing to analyze clinical isolates of the five colistin-resistantE. coli. TheE. coliCAU15104, CAU15134, and CAU16060 belonged to ETEC/STEC hybrids, displaying the same serotype O3:H45 and sequence type ST4214. TheE. coliCAU16175 and CAU16177 belonged to atypical enteropathogenicE. coli(aEPEC), display O4:H11 and O103:H2, ST29, and ST20, respectively. TheE. coliCAU16175 carries six plasmids. An IncHI2-type plasmid, pCAU16175_1, harbors an IS26-enriched MDR region, which includes 16 antimicrobial-resistant genes. An IncFII-type plasmid, pCAU16175_3, harborsmcr-1.1, tet(M), andbla(TEM-1B), whereasmcr-1.1is located within a Tn2derivative. Our findings indicate that the ETEC/STEC strains of the O3:H45 serotype as well as the aEPEC strains of the O4:H11 and O103:H2 serotypes are associated with postweaning diarrhea in swine and that some of diarrheagenicE. colicontains IS26-enriched MDR region and themcr-1gene located within a Tn2derivative on IncFII plasmid.