Background: The emergence of carbapenem and colistin co-resistant Escherichia coli poses a huge challenge to infection control. The purpose of this study was to clarify the mechanism of the carbapenems and colistin co-resistance in E. coli strains.
Methods: Antimicrobial susceptibility test was carried out by agar dilution methods and colistin resistance was confirmed by broth microdilution methods. Whole genome sequencing was carried out, and resistance genes, sequence types and virulence genes of carbapenems and colistin co-resistance E. coli isolates were analyzed.
Results: The results showed that among the 176 carbapenem-resistant Enterobacteriaceae strains, 5 multidrug resistant E. coli strains exhibiting coresistance to carbapenem and colistin. The main mechanism of 5 E. coli strains in this study was generating carbapenem. Four E. coli strains were mcr- positive, while one mcr -negative strain had a new MgrB mutation. The bla NDM-5, bla CTX-M-65, bla OXA-10, bla TEM-1 and mcr-1.1 genes were simultaneously detected in E. coli 20IR1127 strain belonging to ST156 lineage. Other antimicrobial resistance genes encoding aminoglycosides-, sulfonamide-, chloramphenicol-, tetracyclines- and macrolides resistance were also detected.
Conclusion: The main mechanisms of carbapenem and colistin resistance were encoded by bla _NDM and mcr1.1 , meanwhile mgrB mutations also contribute to colistin resistance. To our knowledge, this study is the first to report of E. coli ST156 strain in which the bla _NDM-5, bla _CTX-M-65, bla _OXA-10, bla _TEM-1 and mcr1.1 genes coexist. In addition, there is also an E. coli ST457 strain, which carries bla _TEM-1, bla _NDM-9, bla _CTX-M-199 and is positive for mcr1.1 gene.
Keywords: Escherichia coli , carbapenem, colistin, co-resistance, WGS