High antimicrobial resistance and plasmid-carrying resistance genes in swine-origin mcr-1-positive Escherichia coli in Guangxi, South China

Abstract Background The discovery of mcr-1-positive Escherichia coli (MCRPEC), a notable superbug, attracted great attention worldwide. Swine-origin multi-drug resistance MCRPEC is a potential threat to public health and safety. To date, few detailed studies regarding swine-origin MCRPEC in Guangxi, South China, have been reported. Results In this study, thirty-three MCRPEC harbored mcr-1 genes were identified from 142 E. coli strains isolated from swine droppings and entrails in Guangxi in 2018. All MCRPEC isolates were assigned to 8 unique STs, including ST10, ST224 and ST410, which overlapped with the human-origin MCRPEC. Additionally, a total of six plasmid replicon types (IncFI, IncHI1, IncY, IncN, IncI1 and IncX1) were found. Moreover, the drug susceptibility of the MCRPEC isolates was tested with 27 antimicrobial agents belonging to 17 antimicrobial categories that are usually used in hospitals. There were 19 extended spectrum beta lactamase (ESBL) E. coli and 12 carbapenem resistant E. coli among the 33 MCRPEC strains. Importantly, the MCRPEC showed a high rate of resistance against two broad-spectrum carbapenem antibiotics, imipenem and meropenem, which are forbidden in livestock production use. Three MCRPEC strains were further identified to be extensively drug-resistant (XDR), and other isolates were recognized as multi-drug-resistant (MDR). Meanwhile, to detect whether plasmid-carrying antimicrobial resistance genes coexisted with the mcr-1 gene in the MCRPEC isolates, a total of 22 plasmid-carrying antimicrobial resistance genes were tested for. The results showed that four ESBL genes and one pAmpC gene were identified. Eight of the MCRPEC isolates also contained the carbapenem gene blaNDM-5, which could cause untreatable infections. Moreover, ten non-lactamase genes were also detected. Conclusion This study indicated that swine-origin MCRPEC isolated in Guangxi seemed to have a high rate of resistance to both regular and final line of defense drugs as well as drug resistance genes, which pose a great threat to human public safety and health.