Colistin resistance gene mcr-1 in gut flora of children

- Targeted, specific screening approach to investigate the prevalence of mcr-1 in faecal samples.
- This approach increases the detection rate of mcr-1.
- First discovery of mcr-1 in Citrobacter freundii.
- Until now, few studies have addressed the prevalence of mcr-1 in children.
- Prevalence and transmission mechanism of mcr-1 in children's gut flora was investigated.

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.