AUTHOR=Sun Xinran , Zhang Lin , Meng Jiantong , Peng Kai , Huang Weifeng , Lei Gaopeng , Wang Zhiqiang , Li Ruichao , Yang Xiaorong 

TITLE=The characteristics of mcr-bearing plasmids in clinical Salmonella enterica in Sichuan, China, 2014 to 2017

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2023.1240580

DOI=10.3389/fcimb.2023.1240580

ISSN=2235-2988

ABSTRACT=<p><italic>Salmonella</italic> is one of the most important zoonotic pathogens and a major cause of foodborne illnesses, posing a serious global public health hazard. The emergence of plasmid-mediated <italic>mcr</italic> genes in <italic>Salmonella</italic> has greatly reduced the clinical choice of salmonellosis treatment. The aim of this study was to investigate the plasmid characteristics of <italic>mcr</italic>-positive Salmonella identified from patients in Sichuan, China during 2014 to 2017 by whole genomes sequencing. In this study, a total of 12 <italic>mcr</italic>-positive isolates (1.15%, ; <italic>mcr</italic>-1, n=10; <italic>mcr</italic>-3, n=2) were identified from 1046 Salmonella isolates using PCR. Further characterization of these isolates was performed through antimicrobial susceptibility testing, conjugation assays, whole genome sequencing, and bioinformatics analysis. The <italic>mcr-1</italic> gene in these isolates were carried by three types of typical <italic>mcr-1</italic>-bearing plasmids widely distributed in Enterobacteriaceae (IncX4, IncI2 and IncHI2). Of note, two mcr-1-harboring IncHI2 plasmids were integrated into chromosomes by insertion sequences. Two <italic>mcr-3</italic>-bearing plasmids were IncC and IncFIB broad-host-range plasmids respectively. Genetic context analysis found that <italic>mcr-1</italic> was mainly located in Tn<italic>6330</italic> or truncated Tn<italic>6300</italic>, and <italic>mcr-3</italic> shared a common genetic structure <italic>tnpA-mcr-3-dgkA-ISKpn40</italic>. Overall, we found that <italic>mcr</italic> gene in clinical <italic>Salmonella</italic> were commonly carried by broad-host plasmids and have potential to transfer into other bacteria by these plasmids. Continuous surveillance of MDR <italic>Salmonella</italic> in humans and investigation the underlying transmission mechanisms of ARGs are vital to curb the current severe AMR concern.</p>