Molecular Genetic Characteristics of Plasmid-Borne mcr-9 in Salmonella enterica Serotype Typhimurium and Thompson in Zhejiang, China

Abstract

Salmonella enterica is a zoonotic food-borne pathogen threatening public health around the world. As is the case with many other pathogens, the spread of mobilized colistin resistance (mcr) alleles is of grave concern. In this study, totally 689 clinical Salmonella isolates were collected from a local hospital in Hangzhou, Zhejiang Province, China between 2009 and 2018. Resistance genes were screen by PCR. Two mcr-9-positive Salmonella strains S15 and S639 were identified which belong to serotype Typhimurium and Thompson, respectively. We observed that both mcr-9 genes were located on conjugative IncHI2 plasmids which encoded numerous resistance genes, likely facilitating the dissemination of mcr-9 by co-resistance mechanisms. The mcr-9 cassettes encoded on the two plasmids were not identical: downstream of the mcr-9 genes, we found IS1 on one plasmid (pS15), while the other had a WbuC-IS26 (pS639). Despite the presence of mcr-9 cassettes, the strains were not rendered colistin resistant. Yet, it is of epidemiological importance to implement surveillance to be able to observe and possibly control the spread of mcr-9 due to its potential to mediate resistance to the last-resort antibiotic colistin.

Plasmid-encoded lactose metabolism and mobilized colistin resistance (mcr-9) genes in Salmonella enterica serovars isolated from dairy facilities in the 1980s

“…Our results highlight the problematic nature of measuring colistin resistance in the lab, consistent with several studies that found that the presence of mcr-9 gene is not sufficient to confer colistin resistance [50,74,75]. Nevertheless, over-expression of mcr-9 consistently generates clinically relevant resistance in E. coli [44].…”

Oxford nanopore long-read sequencing enables the generation of complete bacterial and plasmid genomes without short-read sequencing

“…Three MDR Salmonella strains were recovered from the strain bank and isolated with Salmonella agar (CHROMagar Company, Paris, France); strains were identified using the Vitek-II system (bioMérieux, Lyon, France). The genomic DNA from each strains was extracted by boiling and freeze-thawing processes, and the resulting supernatant was recovered for use as the PCR template ( Doyle et al, 2012 ; Ding et al, 2020 ; Fan et al, 2022 ).…”

Genomic characterization of Salmonella isolated from retail chicken and humans with diarrhea in Qingdao, China

“…However, selective pressure from the overuse or misuse of both antimicrobials has resulted in the emergence of carbapenem- and colistin-resistant Enterobacteriaceae (CRE) ( Nang et al, 2019 ; Octavia et al, 2020 ). Regarding Salmonella isolates, recent studies have demonstrated their resistance to these critical antimicrobial drugs ( Wang et al, 2017 ; Fan et al, 2022 ; Zhang et al, 2022b ).…”