Abstract
Objective To investigate the colonization of Gram-negative bacilli carrying mcr-1 gene in intestinal tracts of inpatients and people having physical examination for further elucidating the molecular and epidemiological features of mcr-1 gene. Methods A total of 1 263 and 750 fecal specimens were collected from inpatients in the First Affiliated Hospital of Guangzhou Medical University and people having physical examination in the Kingmed Physical Examination Centre, respectively. Drug-resistant bacteria were isolated using Maconkey agar supplemented with colistin. PCR was performed to detect the bacteria carrying mcr-1 gene. Multilocus sequence typing (MLST) and enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR) were used for homology analysis. The transferability of mcr-1 gene was verified by plasmid transfer assays. Plasmids of mcr-1-carrying strains were typed by PCR-based replicon typing techniques. Twelve virulence-related genes were also detected by PCR. Results Ninety-two colistin-resistant strains were isolated from the 1 263 samples from inpatients(7.3%, 92/1 263) and two of them were positive for mcr-1 gene (one strain also carried the blaNDM-5 gene). Thirty-six colistin-resistant strains were isolated from the 750 samples of physical examination group (4.8%, 36/750) and one of them carried the mcr-1 gene. MLST analysis showed that three mcr-1-carrying Escherichia coli strains (minimum inhibitory concentration of colistin: 8 μg/ml) belonged to three different sequence types. Moreover, they exhibited different banding patterns in ERIC-PCR analysis. All of the mcr-1-carrying isolates could transfer mcr-1 gene to the recipient strains successfully. Six types of incompatibility plasmids were detected in the mcr-1-carrying isolates (IncFⅡ, IncX2, IncHI2, IncFIB, IncX4 and IncX1). Virulence-related genes fimH, iutA and fyuA were detected in all mcr-1-carrying Escherichia coli strains. Conclusions Colistin-resistant strains and mcr-1 gene are prevalent in inpatients and people having physical examination, which brings potential risk for the control of clinical infections. Key words: mcr-1; Gut microbiota; Plasmid typing
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