Prevalence of colistin resistance gene (mcr-1) containing Enterobacteriaceae in feces of patients attending a tertiary care hospital and detection of a mcr-1 containing, colistin susceptible E. coli.

The emergence of the plasmid-mediated mcr colistin resistance gene in the community poses a potential threat for treatment of patients, especially when hospitalized. The aim of this study was to determine the prevalence of all currently known mcr mediated colistin resistance gene in fecal samples of patients attending a tertiary care hospital. From November 2014 until July 2015, fecal samples of patients attending the Leiden University Medical Center were collected and screened for presence of mcr using real-time PCR. Two of 576 patients were positive for mcr-1, resulting in a prevalence of 0.35%, whereas no mcr-2 was found. One of these samples was culture negative, the second sample contained a blaCMY-2 and mcr-1 containing E.coli. This strain belonged to Sequence Type 359 and serotype O177:H21. The mcr-1 containing E.coli was phenotypically susceptible to colistin with a MIC of ≤ 0.25mg/l, due to a 1329bp transposon IS10R inserted into the mcr-1 gene as identified by WGS. This prevalence study shows that mcr-1 is present in low levels patients out of the community attending a hospital. Furthermore the study underlines the importance of phenotypical confirmation of molecular detection of a mcr-1 gene.