Abstract
Colistin is used to treat infectious diseases in humans and livestock; it has also been used as a feed additive for livestock for approximately 50 years. Since the mcr-1 plasmid-mediated colistin resistance gene was discovered in China in 2015, it has been detected worldwide, mainly in livestock. In this study, we investigated the prevalence and characteristics of mcr-mediated colistin-resistant Escherichia coli in livestock and farmers in Japan. We collected fecal samples from 295 healthy livestock (202 cattle and 93 swine) and 62 healthy farmers from 72 livestock farms (58 cattle farms and 14 swine farms) between 2013 and 2015. Twenty-eight mcr-1-harboring E. coli strains were isolated from 25 livestock (six cattle and 19 swine) and three farmers (two cattle farmers and one swine farmer). The prevalence rates of mcr-1-harboring E. coli in livestock and farmers were 8.47 and 4.84%, respectively. Of the 28 strains, the resistance genes of three were transferable via the mcr-1-coding plasmids to E. coli J53 at low frequencies (10−7–10−8). Six strains coharbored mcr-1 with CTX-M β-lactamases (CTX-M-14, CTX-M-27, or CTX-M-156). Of the isolates obtained from livestock and farmers in four farms (farms C, I, N, and P), nine strains had the same genotypical characteristics (sequence types and pulsed-field gel electrophoresis band patterns), plasmid characteristics (incompatibility group and plasmid transferability), and minimum inhibitory concentrations. Thus, the findings suggested that clonal strains could spread among livestock and farmers within farms. To our knowledge, this is the first study to detect clonal relatedness of mcr-1-mediated colistin-resistant E. coli in livestock and farmers. It is suggested that farmers are at a higher risk of acquiring mcr-1-harboring strains, calling for our attention based on the One Health concept.
Highlights
Colistin is a cationic antimicrobial peptide that damages bacterial cell membranes by targeting the lipid A moiety of lipopolysaccharides (LPSs), which are present in the outer cell membrane of Gram-negative bacteria
To evaluate the relatedness of mcr-1-harboring E. coli isolated from livestock and farmers, we identified and compared the characteristics [sequence types (STs), pulsed-field gel electrophoresis (PFGE) band patterns, plasmid incompatibility (Inc) groups, plasmid transferability, and minimum inhibitory concentrations (MICs)] of the isolates
We investigated the prevalence, characteristics, and relatedness of mcr-mediated colistin-resistant E. coli in livestock and farmers in Japan
Summary
Colistin is a cationic antimicrobial peptide that damages bacterial cell membranes by targeting the lipid A moiety of lipopolysaccharides (LPSs), which are present in the outer cell membrane of Gram-negative bacteria. The most common mechanism of chromosomally mediated colistin resistance is mainly through modification of the bacterial outer membrane through alteration of LPSs, by the addition of 4-amino4-deoxy-l-arabinose and/or phosphoethanolamine, via amino acid changes in the PmrA/PmrB and PhoP/PhoQ two-component regulatory systems (Olaitan et al, 2014; Poirel et al, 2017; Aghapour et al, 2019). Plasmidmediated colistin resistance is attributable to the transmissible gene mcr-1, which is a phosphoethanolamine transferase, leading to a more cationic LPS structure and resistance to polymyxins (Liu et al, 2016) It was first discovered in swine in China in 2015; subsequently, mcr-1-harboring Escherichia coli has been reported worldwide, mainly in livestock and meat and even in humans (Nang et al, 2019). The clonal spread and relatedness of isolates of mcr-harboring E. coli from other spheres (e.g., among humans, livestock, and environment) remain unclear. We investigated the prevalence, characteristics, and relatedness of mcr-mediated colistin-resistant E. coli in livestock (cattle and swine) and farmers in Japan
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