Abstract
A number of studies from different countries have characterized mcr-1-harboring plasmids isolated from food; however, nothing has been reported about it in South Korea. In this study, we report the characterization of mcr-1 plasmids from pan drug-resistant (PDR) Escherichia coli strains isolated from retail food in the country. Colistin-resistant E. coli strains were isolated from retail raw chicken, and PCR was carried out to detect the mcr-1 gene. Whole genome sequencing of the mcr-1-positive strains was performed for further characterization. The results of whole genome sequencing revealed that all mcr-1 plasmids belonged to the IncI2 type. In addition to the mcr-1 plasmids, all of the isolates also carried additional plasmids possessing multiple antibiotic resistance genes, and the PDR was mediated by resistant plasmids except for fluoroquinolone resistance resulting from mutations in gyrA and parC. Interestingly, the mcr-1 plasmids were transferred by conjugation to other pathogenic strains including enterohemorrhagic E. coli (EHEC), enterotoxigenic E. coli (ETEC), enteroaggregative E. coli (EAEC), Salmonella, and Klebsiella at the frequencies of 10−3−10−6, 10−2−10−5, 10−4−10−5, 10−4−10−6, and 10−5−10−6, respectively. The results showed that mcr-1 plasmids can be easily transmitted to pathogenic bacteria by conjugation.
Highlights
The emergence of multidrug-resistant (MDR) pathogens, such as ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumonia, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp., or recently Enterobacteriaceae) and the lack of effective antimicrobials are a serious issue in public health [1]
Since the first discovery of the mobilized colistin resistance-1 gene on plasmids in Escherichia coli by Liu et al in China, 2016 [4], E. coli strains harboring mcr-1 have been reported in many countries throughout America, Asia, and Europe [4,9,10] and have been isolated from various sources, such as animals, humans, environmental samples, and food [10,11,12]
The results of whole genome sequencing revealed that the three mcr-1-postive E. coli strains possessed multiple plasmids and some of the plasmids harbored a number of antibiotic resistance genes (Table 1 and Figure S1)
Summary
The emergence of multidrug-resistant (MDR) pathogens, such as ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumonia, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp., or recently Enterobacteriaceae) and the lack of effective antimicrobials are a serious issue in public health [1]. Colistin is one of the last-resort antibiotics to treat MDR Gram-negative bacteria, and its binding to the lipid A moiety of lipopolysaccharide (LPS) destabilizes the outer membrane and results in cell death [2]. Colistin resistance is mainly associated with the modification of LPS, such as phosphoethanolamine modification of lipid A [3,4,5], and causes serous clinical problems in the control of Gram-negative pathogens in ESKAPE [6,7,8]. In South Korea, mcr-1-positive E. coli strains have been isolated in livestock and humans [13,14]. There have been no studies about mcr-1-positive E. coli from retail food in the country
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