Characterization of resistance mechanisms of Enterobacter cloacae Complex Co-resistant to Carbapenem and Colistin
Abstract Background: The emergence of carbapenem-resistant and colistin-resistant ECC pose a huge challenge to infection control. The purpose of this study was to clarify the mechanism of the carbapenems and colistin co-resistance in Enterobacter cloacae Complex (ECC) strains.Methods: Nineteen ECC isolates co-resistant to carbapenems and colistin were collected from a regional medical center in China. Carbapenemase gene, extended-spectrum β-lactamase gene, AmpC cephalosporinase gene ampC, mcr series genes, and ecr gene were detected by PCR. Expression levels of outer membrane protein OmpC/OmpF and efflux pump protein AcrA/AcrB were investigated. And the structural modification of lipid A of 19 ECC strains was analyzed.Results: This study showed that the mechanisms of carbapenem resistance in this study are: 1. Generating carbapenemase (7 of 19); 2. The production of AmpC or ESBLs combined with decreased expression of out membrane protein (12 of 19). And the mechanism of colistin resistance is increaseing expression of acrA in the efflux pump AcrAB-TolC alone (5 of 19) or accompanied by a decrease of affinity between colistin and outer membrane caused by the modification of lipid A (14 of 19). Moreover, an ECC strain co-harboring plasmid-mediated mcr-4.3 and blaNDM-1 has been found.Conclusions: This study suggested that there is no overlap between the resistance mechanism of co-resistant ECC strains to carbapenem and colistin. However, the emergence of strain co-harboring plasmid-mediated resistance genes indicated that ECC is a potential carrier for the horizontal spread of carbapenems and colistin resistance.