Abstract
A third plasmid-mediated colistin resistance gene, mcr-3, is increasingly being reported in Enterobacteriaceae and Aeromonas spp. from animals and humans. To investigate the molecular epidemiology of mcr in the gut flora of Chinese outpatients, 152 stool specimens were randomly collected from outpatients in our hospital from May to June, 2017. Stool specimens enriched in alkaline peptone water or Luria-Bertani (LB) broth were screened for mcr-1, mcr-2, and mcr-3 using polymerase chain reaction (PCR)-based assays. Overall, 19.1% (29/152) and 5.3% (8/152) of the stool samples enriched in alkaline peptone water were PCR-positive for mcr-1 and mcr-3, respectively, while 2.7% (4/152) of samples were positive for both mcr-1 and mcr-3. Strains isolated from the samples that were both mcr-1- and mcr-3-positive were subjected to antimicrobial susceptibility testing by broth microdilution. They were also screened for the presence of other resistance genes by PCR, while multilocus sequence typing and whole-genome sequencing were used to investigate the molecular epidemiology and genetic environment, respectively, of the resistance genes. mcr-3-positive Aeromonas veronii strain 126-14, containing a mcr-3.8-mcr-3-like2 segment, and mcr-1-positive Escherichia coli strain 126-1, belonging to sequence type 1485, were isolated from the sample from a diarrheic butcher with no history of colistin treatment. A. veronii 126-14 had a colistin minimum inhibitory concentration (MIC) of 2 µg/mL and was susceptible to antibiotics in common use, while E. coli 126-1 produced TEM-1, CTX-M-55, and CTX-M-14 β-lactamases and was resistant to colistin, ceftazidime, and cefotaxime. Overall, there was a higher detection rate of mcr-3-carrying strains with low colistin MICs from the samples enriched in alkaline peptone water than from samples grown in LB broth.
Highlights
Since the identification of a third plasmid-mediated colistin resistance gene, mcr-3, in a porcine Escherichia coli isolate from China in 2017 [1], several mcr-3 variants have been detected in clinical E. coli and Salmonella isolates from Denmark, Spain, and China [2,3,4,5]
Following enrichment in alkaline peptone water, 19.1% (29/152) and 5.3% (8/152) of the stool samples were polymerase chain reaction (PCR)-positive for mcr1 and mcr-3, respectively, while 18.4% (28/152) of the samples enriched in LB broth were positive for mcr-1
None of the LB enrichment samples tested positive for mcr-3 (Table 1), and none mcr-3 in Diarrheic Outpatient Guts of the samples from either enrichment method were positive for mcr-2
Summary
Since the identification of a third plasmid-mediated colistin resistance gene, mcr-3, in a porcine Escherichia coli isolate from China in 2017 [1], several mcr-3 variants have been detected in clinical E. coli and Salmonella isolates from Denmark, Spain, and China [2,3,4,5]. Ling et al reported that chromosomally located mcr-3 variants, including mcr-3.3 and mcr-3-like, which were identified in Aeromonas veronii from chicken meat, showed 95.2 and 84.2% nucleotide sequence identity, respectively, to mcr-3 from E. coli of porcine origin [6]. The reported minimum inhibitory concentration (MIC) of colistin for the mcr-3-carrying A. veronii isolate from chicken meat was 2 μg/mL while colistin MICs for the mcr-3-positive Enterobacteriaceae were in the range of 4–8 μg/mL. Mcr-3-positive Aeromonas spp. strains are likely to go undetected by routine clinical tests. Our previous studies have established an optimized enrichment method for the screening of mcr-1 from human gut and environmental water sources [7, 8], in which the mcr-1-carrying strains demonstrated MICs for colistin of 1–32 μg/mL. We used the newly developed enrichment method to investigate the epidemiology of mcr in the gut flora of outpatients treated in our hospital
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
