Isolation and molecular epidemiology analysis of Gram-negative bacilli carrying mcr-1 gene in fecal specimens / 中华微生物学和免疫学杂志

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 1263 and 750 fecal specimens were col-lected 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 1263 samples from inpatients(7. 3％, 92/1263) 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 colistin8 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 detec-ted 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.