AUTHOR=Chopjitt Peechanika , Boueroy Parichart , Morita Masatomo , Iida Tetsuya , Akeda Yukihiro , Hamada Sihigeyuki , Kerdsin Anusak 

TITLE=Genetic characterization of multidrug-resistant Escherichia coli harboring colistin-resistant gene isolated from food animals in food supply chain

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=14

YEAR=2024

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2024.1289134

DOI=10.3389/fcimb.2024.1289134

ISSN=2235-2988

ABSTRACT=<p>Colistin is widely used for the prophylaxis and treatment of infectious disease in humans and livestock. However, the global food chain may actively promote the dissemination of colistin-resistant bacteria in the world. Mobile colistin-resistant (<italic>mcr</italic>) genes have spread globally, in both communities and hospitals. This study sought to genomically characterize <italic>mcr</italic>-mediated colistin resistance in 16 <italic>Escherichia coli</italic> strains isolated from retail meat samples using whole genome sequencing with short-read and long-read platforms. To assess colistin resistance and the transferability of <italic>mcr</italic> genes, antimicrobial susceptibility testing and conjugation experiments were conducted. Among the 16 isolates, 11 contained <italic>mcr-1</italic>, whereas three carried <italic>mcr-3</italic> and two contained <italic>mcr-1</italic> and <italic>mcr-3</italic>. All isolates had minimum inhibitory concentration (MIC) for colistin in the range 1–64 μg/mL. Notably, 15 out of the 16 isolates demonstrated successful transfer of <italic>mcr</italic> genes via conjugation, indicative of their presence on plasmids. In contrast, the KK3 strain did not exhibit such transferability. Replicon types of <italic>mcr-1</italic>-containing plasmids included IncI2 and IncX4, while IncFIB, IncFII, and IncP1 contained <italic>mcr-3</italic>. Another single strain carried <italic>mcr</italic>-<italic>1.1</italic> on IncX4 and <italic>mcr</italic>-<italic>3.5</italic> on IncP1. Notably, one isolate contained <italic>mcr-1.1</italic> located on a chromosome and carrying <italic>mcr</italic>-<italic>3.1</italic> on the IncFIB plasmid. The chromosomal location of the <italic>mcr</italic> gene may ensure a steady spread of resistance in the absence of selective pressure. Retail meat products may act as critical reservoirs of plasmid-mediated colistin resistance that has been transmitted to humans.</p>