Colistin resistance gene mcr-1 in gut flora of children

Abstract The aim of this study was to determine the prevalence and transmission mechanism(s) of mcr-1 in the gut flora of children. Faecal samples ( n  = 173) were obtained from non-diarrhoea patients at the Children's Hospital of Zhejiang University (Hangzhou, China). PCR-based analysis indicated that 17 isolates from 9.8% of the samples were positive for mcr-1 , comprising 16 Escherichia coli and 1 Citrobacter freundii . Nine mcr-1- bearing isolates co-expressed extended-spectrum β-lactamase (ESBL) genes, but plasmid-mediated quinolone resistance (PMQR) genes were not detected. Transconjugation followed by Southern hybridisation analysis revealed that 14 of the E. coli isolates were able to transfer their colistin-resistant phenotype to E. coli EC600. All 14 of these E. coli strains contained a major mcr-1 -containing conjugative plasmid with a size of ca. 33 kb or 55 kb. All but two of the E. coli isolates presented distinct pulsed-field gel electrophoresis (PFGE) patterns. Multilocus sequence typing (MLST) analysis revealed 11 sequence types (STs) among the E. coli 16 isolates, with ST117 being the most common. The finding of a high prevalence of mcr-1 in the intestinal flora of children, with the majority of mcr-1 -positive isolates being E. coli , highlights the need for more rational use of polymyxins to prevent polymyxin resistance from becoming disseminated among different microbial pathogens. Given the high detection rate of mcr-1 in children, we recommend that polymyxin is no longer used as a last-resort antimicrobial agent and that alternative strategies are developed to treat infections caused by such pathogens.