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

Jianzhong Fan; Heng Cai; Youhong Fang; Jintao He; Linghong Zhang; Qingye Xu; Yunxing Yang; Sebastian Leptihn; Yunsong Yu; Dongdong Zhao; Xiaoting Hua

doi:10.3389/fmicb.2022.852434

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

Front Microbiol. 2022 Mar 17:13:852434. doi: 10.3389/fmicb.2022.852434. eCollection 2022.

Authors

Jianzhong Fan¹, Heng Cai^{2

3

4}, Youhong Fang⁵, Jintao He^{2

3

4}, Linghong Zhang^{2

3

4}, Qingye Xu¹, Yunxing Yang¹, Sebastian Leptihn^{2

6}, Yunsong Yu^{2

3

4}, Dongdong Zhao^{2

3

4}, Xiaoting Hua^{2

3

4}

Affiliations

¹ Department of Laboratory Medicine, Affiliated Hangzhou First People's Hospital, Zhejiang University School of Medicine, Hangzhou, China.
² Department of Infectious Diseases, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China.
³ Key Laboratory of Microbial Technology and Bioinformatics of Zhejiang Province, Hangzhou, China.
⁴ Regional Medical Center for National Institute of Respiratory Diseases, Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
⁵ Department of Gastroenterology, The Children's Hospital, Zhejiang University School of Medicine, National Clinical Research Center for Child Health, Hangzhou, China.
⁶ Zhejiang University-University of Edinburgh (ZJU-UoE) Institute, Zhejiang University, Haining, 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.

Keywords: IncHI2 plasmid; Salmonella Thompson; Salmonella Typhimurium; colistin; mcr-9.