High prevalence of colistin resistance and mcr-9/10 genes in Enterobacter spp. in a tertiary hospital over a decade

Enterobacter spp . are members of the 'ESKAPE' group of pathogens, which which are recognised as the leading cause of multidrug-resistant (MDR) hospital-acquired infections. Colistin is usually regarded as a last-line therapeutic option for MDR Gram-negative bacilli infections. However, colistin-resistant Enterobacter spp . have emerged in the last decade. Here we investigated the prevalence of colistin resistance and mcr genes in Enterobacter spp . of clinical origin between 2011 and 2020 in a tertiary hospital in China. Colistin resistance rates ranged between 17.1% and 34.5%, with an overall prevalence of 22.2% (190/854). No mcr-1 to mcr-8 genes were identified in the colistin-resistant Enterobacter spp . isolates, while mcr9 and mcr-10 were detected at rates of 8.4% (16/190) and 12.6% (24/190), respectively. All of the mcr9/10 -positive Enterobacter isolates belonged to the Enterobacter cloacae complex (ECC). Meanwhile, 14.8% (98/664) and 6.0% (40/664) of non-colistin-resistant Enterobacter spp. isolates carried mcr-9 and mcr-10 genes, respectively. For the 40 mcr-9/10- positive colistin-resistant ECC isolates, mcr-9- positive ECC isolates usually co-produced extended-spectrum ,B-lactamases (ESBLs) or carbapenemases, while mcr-10 -positive ECC isolates produced neither. Most mcr-9/10 genes were located on plasmids. The backbone of mcr-9harbouring plasmids was conserved, while that of mcr-10- harbouring plasmids was diverse. Our findings revealed a high prevalence of colistin resistance and a silent distribution of mcr - 9/10 genes in clinical Enterobacter spp . isolates in China. It is urgent to take steps and interventions to control the prevalence of colistin resistance and prevent the dissemination of mcr - 9/10 genes. (c) 2022 The Authors. Published by Elsevier Ltd.

Automated summary

This study investigated the prevalence of colistin resistance and mcr genes in clinical Enterobacter spp. isolates in a tertiary hospital in China between 2011 and 2020. The results showed a high prevalence of colistin resistance, with a range of 17.1% to 34.5% and an overall prevalence of 22.2%. No mcr-1 to mcr-8 genes were identified in the colistin-resistant Enterobacter spp. isolates, but mcr-9 and mcr-10 were detected at rates of 8.4% and 12.6%, respectively. Most mcr-9/10 genes were located on plasmids, and the plasmid backbones differed between mcr-9 and mcr-10. This study highlights the urgent need to control the prevalence of colistin resistance and prevent the dissemination of mcr-9/10 genes in clinical Enterobacter spp. isolates.