Extensive antimicrobial resistance and plasmid-carrying resistance genes in mcr-1-positive E. coli sampled in swine, in Guangxi, South China

Abstract Background: The discovery of the superbug mcr-1-positive Escherichia coli (MCRPEC) has drew greet attention. Swine-origin multi-drug resistant MCRPEC has been a potential threat to public health and safety. However, there were few detailed studies have been reported on swine MCRPEC in Guangxi, South China.Results: In this study, thirty-three MCRPEC strains were detected from 142 E. coli strains from 116 samples in Guangxi in 2018. Which could be classified into eight unique STs and a total of six incompatibility plasmid groups (IncFI, IncHI1, IncY, IncN, IncI1 and IncX1). After that, the susceptibility of MCRPEC isolates to 27 antimicrobial agents belonging to 17 antimicrobial categories was tested. There were nineteen E. coli resistant to 3rd and 4th generation cephalosporins and twelve E. coli resistant to carbapenem resistan. Importantly, the MCRPEC showed high resistance highly resistance for imipenem and meropenem, which were forbidden to use in livestock production. Three MCRPEC strains were further proved to be extensively drug-resistant (XDR), and the other isolates were multi-drug-resistant (MDR). Furthermore, we found that the plasmid-carrying resistance genes coexisted with the mcr-1 gene of the MCRPEC isolates. Which were listed as follows: β-lactamase antimicrobial resistance genes e.g. ESBL genes (blaCTX-M14, blaCTX-M24, blaCTX-M123, blaOXA-1), plasmid-mediated AmpC (pAmpC) gene (blaCMY-2), the carbapenem resistance gene (blaNDM-5), and non-β-lactamase antimicrobial resistance genes (qnrA, qnrB, qnrS, aac(6’)-Ib-cr, tetA, tetB, sul1, sul2, floR, aadA).Conclusion: Thirty-three mcr-1-positive E. coli isolates in Guangxi displayed a wide profile of antimicrobial resistance. Plasmid-carrying resistance genes might be the main cause of MCRPEC multidrug resistance. This study highlighted the necessity for long-term surveillance of mcr-1-positive E. coli in pigs.