Genomic characteristics of mcr-1 and bla(CTX-M-type) in a single multidrug-resistant Escherichia coli ST93 from chicken in China

This study was undertaken to discern the transmission characteristics of mcr-1 and bla(CTX-M-type) in one multidrug-resistant Escherichia coli LWY24 from chicken in China. The genetic profiles of LWY24 isolate were determined by conjugation, S1-pulsed-field gel electrophoresis, southern blot hybridization, and whole genome sequencing analysis. Meanwhile, co-transfer of plasmids in LWY24 isolate was screened by dual conjugation assays. The LWY24 isolate was identified as ST93, and harbored 3 conjugative plasmids, pLWY24J-3 (bla(CTX-M-55)-bearing IncFⅡ), pLWY24J-mcr-1 (mcr-1-carrying IncI2), and pLWY24J-4 (non-resistance-conferring IncI1), and one nonconjugative plasmid pLWY24 (bla(CTX-M-14)-containing IncHI2/IncHI2A). Numerous resistance genes, insertion sequences (especially IS26), and transposons were found in the 4 plasmids, suggesting that horizontal transmission have occurred by plasmid mating, homologous recombination, and transpositions. Under the selection pressure of cefotaxime and colistin or cefotaxime alone, the mcr-1-bearing plasmid and the bla(CTX-M-55)-harboring plasmid could be co-transferred at a similar frequency, with 8.00 × 10(−4) or 9.00 × 10(−4) transconjugants per donor cell, respectively. The specific shufflon region in mcr-1-encoding plasmid could generate up to 6 diverse PilV structures, which may further accelerate the horizontal transfer of plasmid. In conclusion, the transmission characteristics of mcr-1 and bla(CTX-M-type) in LWY24 isolate could due to clonal spread of ST93, selective pressure of cefotaxime, IS26-mediate homologous recombination and transposition, and the specific shufflon region.