AUTHOR=Elbediwi Mohammed , Wu Beibei , Pan Hang , Jiang Zenghai , Biswas Silpak , Li Yan , Yue Min 

TITLE=Genomic Characterization of mcr-1-carrying Salmonella enterica Serovar 4,[5],12:i:- ST 34 Clone Isolated From Pigs in China

JOURNAL=Frontiers in Bioengineering and Biotechnology

VOLUME=8

YEAR=2020

URL=https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2020.00663

DOI=10.3389/fbioe.2020.00663

ISSN=2296-4185

ABSTRACT=<p><italic>Salmonella enterica</italic> serovar 4,[5],12:i:-, so-called Typhimurium monophasic variant, has become one of the most frequently isolated serovars both in humans and in animals all over the world. The increasing prevalence of <italic>mcr</italic>-1-carrying <italic>Salmonella</italic> poses significant global health concerns. However, the potential role of <italic>Salmonella</italic> 4,[5],12:i:- in <italic>mcr</italic>-<italic>1</italic> gene migration through the food chain to the human remains obscure. Here, we investigated 337 <italic>Salmonella</italic> isolates from apparently healthy finishing pigs, which is rarely studied, obtained from pig farms and slaughterhouses in China. The <italic>mcr</italic>-<italic>1</italic> gene was found in four colistin-resistant <italic>S. enterica</italic> 4,[5],12:i:- isolates. Notably, all four isolates belonged to sequence type 34 (ST34) with multidrug resistance phenotype. Further genomic sequencing and antimicrobial resistance characterization confirmed that <italic>mcr</italic> was responsible for the colistin resistance, and the conjugation assay demonstrated that three of four isolates carried <italic>mcr</italic>-<italic>1</italic> in IncHI2 plasmid. Importantly, <italic>mcr</italic>-<italic>1</italic> and class-1 integron were found to co-localize in two strains with IncHI2 plasmid. By collecting all the <italic>mcr</italic>-<italic>1</italic>-carrying Typhimurium and monophasic variant strains across the food chain (farm animals, animal-origin food, and humans), our phylogenomic analysis of available 66 genomes, including four strains in this study, demonstrated an independent phylogenetic cluster of all eight Chinese swine-originated isolates and one human isolate. Together, this study provides direct evidence for clonal and pork-borne transmission of <italic>mcr-1</italic> by <italic>Salmonella</italic> 4,[5],12:i:- ST34 in China and highlighted a domestication pathway by acquisition of additional antimicrobial resistance determinants in Chinese ST34 isolates.</p>