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 attracted worldwide attention. Swine-origin multi-drug resistant MCRPEC is a potential threat to public health and safety. To date, few detailed studies have been reported on swine MCRPEC in Guangxi, South China. Results: In this study, thirty-three MCRPEC strains were identified from 142 E. coli strains isolated from 116 samples in Guangxi in 2018. All MCRPEC isolates were classified into eight unique STs and a total of six incompatibility plasmid groups (IncFI, IncHI1, IncY, IncN, IncI1 and IncX1) were found. Then, susceptibility of MCRPEC isolates to 27 antimicrobial agents belonging to 17 antimicrobial categories was tested. There were nineteen 3rd and 4th generation cephalosporins resistant E. coli and twelve carbapenem resistant E. coli among the 33 MCRPEC strains. Importantly, the MCRPEC were highly resistant to two carbapenem antibiotics, imipenem and meropenem, which were not permitted for use in livestock production. Three MCRPEC strains were further identified to be extensively drug-resistant (XDR), and the other isolates were recognized as multi-drug-resistant (MDR). Moreover, we detected whether the plasmid-carrying resistance genes coexist with the mcr-1 gene of the MCRPEC isolates. At last, β-lactamase antimicrobial resistance genes such as ESBL genes ( bla CTX-M14 , bla CTX-M24 , bla CTX-M123 , bla OXA-1 ), plasmid-mediated AmpC (pAmpC) gene ( bla CMY-2 ), and the carbapenem gene bla NDM-5 were detected. In addition, non-β-lactamase antimicrobial resistance genes such as qnrA , qnrB , qnrS , aac(6’)-Ib-cr , tetA , tetB , sul1 , sul2 , floR , aadA were also detected. Conclusion: Thirty-three mcr-1 -positive E. coli isolates in Guangxi had a wide range 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.