Abstract
ABSTRACTAntimicrobial resistance associated with colistin has emerged as a significant concern worldwide, threatening the use of one of the most important antimicrobials for treating human disease. This study aimed to investigate the prevalence of colistin-resistant avian-pathogenic Escherichia coli (APEC) and shed light on the possibility of transmission of mcr-1 (mobilized colistin resistance)-positive APEC. A total of 72 APEC isolates from Anhui Province in China were collected between March 2017 and December 2018 and screened for the mcr-1 gene. Antimicrobial susceptibility testing was performed using the broth dilution method. Pulsed-field gel electrophoresis, Southern blot analysis, and conjugation assay were performed to determine the location and conjugative ability of the mcr-1 gene. Whole-genome sequencing and analysis were performed using Illumina MiSeq and Nanopore MinION platforms. Three APEC isolates (AH25, AH62, and AH65) were found to be positive for the mcr-1 gene and showed multidrug resistance. The mcr-1 genes were located on IncI2 plasmids, and conjugation assays revealed that these plasmids were transferrable. Notably, strains AH62 and AH65, both belonging to ST1788, were collected from different places but carried the same drug resistance genes and shared highly similar plasmids. This study highlights the potential for a possible epidemic of mcr-1-positive APEC and the urgent need for continuous active monitoring.IMPORTANCE In this study, three plasmids carrying mcr-1 were isolated and characterized from APEC isolates from Anhui Province in China. The mcr-1 genes were located on IncI2 plasmids, and these plasmids were transferrable. These three IncI2 plasmids had high homology with the plasmids harbored by pathogenic bacteria isolated from other species. This finding showed that IncI2 plasmids poses a risk for the exchange of genetic material between different niches. Although colistin has been banned for use in food-producing animals in China, the coexistence of the broad-spectrum β-lactamase and mcr-1 genes on a plasmid can also lead to the stable existence of mcr-1 genes. The findings illustrated the need to improve the monitoring of drug resistance in poultry systems so as to curb the transmission or persistence of multidrug-resistant bacteria.
Highlights
Antimicrobial resistance associated with colistin has emerged as a significant concern worldwide, threatening the use of one of the most important antimicrobials for treating human disease
All the mcr-1-positive transconjugants in this study belonged to IncI2, consistent with the results of previous studies showing that the mcr-1-carrying IncI2 plasmid had the advantages of suitability and was more beneficial for the isolation of the host E. coli than either IncHI2 or IncX4 plasmid [14]
Liu et al found that IncI2 plasmids harbored the blaCTX-M-64 gene, which was widely distributed among members of the Enterobacteriaceae in different animals and different regions in China [16]
Summary
Antimicrobial resistance associated with colistin has emerged as a significant concern worldwide, threatening the use of one of the most important antimicrobials for treating human disease. The mcr-1 genes were located on IncI2 plasmids, and these plasmids were transferrable These three IncI2 plasmids had high homology with the plasmids harbored by pathogenic bacteria isolated from other species. Before 2016, colistin was generally used as a feed additive in farms to prevent diseases caused by members of the Enterobacteriaceae This resulted in a significant increase in the rate of resistance to colistin among organisms isolated from livestock and poultry farms, threatening public health [2]. The present study aimed to characterize three avian-pathogenic Escherichia coli (APEC) isolates by Illumina short-read and MinION long-read whole-genome sequencing (WGS) and identify the genetic features of plasmids containing the mcr-1 genes. A total of 72 APEC isolates were collected from diseased chickens in Anhui Province in China between March 2017 and December 2018 and screened for the mcr-1 gene
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