AUTHOR=Zhou Lin , Zhang Tie-Jun , Zhang Weicheng , Xie Chengjiang , Yang Ye , Chen Xuan , Wang Qin , Wang Hong-Ning , Lei Chang-Wei 

TITLE=Prevalence and genetic diversity of multidrug-resistant Salmonella Typhimurium monophasic variant in a swine farm from China

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1200088

DOI=10.3389/fmicb.2023.1200088

ISSN=1664-302X

ABSTRACT=<p><italic>Salmonella</italic> 4,[5],12:i:-, a monophasic variant of <italic>S</italic>. Typhimurium, has become a global serovar causing animal and human infections since its first emergence in the late 1980's. Several previous studies showed the increasing prevalence of <italic>S</italic>. 4,[5],12:i:- in China, most of which were from swine with multidrug resistance (MDR) profiles. However, the molecular characteristic and evolution of <italic>S</italic>. 4,[5],12:i:- in the same swine farm are still unknown. In this study, a total of 54 <italic>S. enterica</italic> strains were isolated from different fattening pigs aged 1, 3, and 6 months, most of which belonged to <italic>S</italic>. 4,[5],12:i:-. Whole-genome sequencing revealed that all 45 <italic>S</italic>. 4,[5],12:i:- strains belonged to ST34 and were further divided into two different ribosomal STs and nine different core-genome STs. Phylogenetic analysis of 286 <italic>S</italic>. 4,[5],12:i:- strains in China, including 241 from the EnteroBase <italic>Salmonella</italic> database, revealed the genetic diversity of <italic>S</italic>. 4,[5],12:i:- and indicated that <italic>S</italic>. 4,[5],12:i:- in this swine farm might have multiple origins. Three different IncHI2 plasmids carrying various resistance genes were characterized by nanopore sequencing and could be conjugated to <italic>Escherichia coli</italic>. The colistin resistance gene <italic>mcr-1</italic> and ESBLs gene <italic>bla</italic><sub>CTX − M−14</sub> were co-located on the chromosome of one strain. The dynamic changes in antimicrobial resistance regions and transferability of IncHI2 plasmids, as well as the chromosomal location of resistance genes, facilitated the diversity of the antimicrobial resistance characteristics in <italic>S</italic>. 4,[5],12:i:-. Since the swine farm is regarded as the important reservoir of MDR <italic>S</italic>. 4,[5],12:i:-, the prevalence and evolution of <italic>S</italic>. 4,[5],12:i:- from swine farms to pig products and humans should be continually monitored.</p>