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

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

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.852434

DOI=10.3389/fmicb.2022.852434

ISSN=1664-302X

ABSTRACT=<p><italic>Salmonella enterica</italic> 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 (<italic>mcr</italic>) alleles is of grave concern. In this study, totally 689 clinical <italic>Salmonella</italic> isolates were collected from a local hospital in Hangzhou, Zhejiang Province, China between 2009 and 2018. Resistance genes were screen by PCR. Two <italic>mcr-9-</italic>positive <italic>Salmonella</italic> strains S15 and S639 were identified which belong to serotype Typhimurium and Thompson, respectively. We observed that both <italic>mcr-9</italic> genes were located on conjugative IncHI2 plasmids which encoded numerous resistance genes, likely facilitating the dissemination of <italic>mcr-9</italic> by co-resistance mechanisms. The <italic>mcr-9</italic> cassettes encoded on the two plasmids were not identical: downstream of the <italic>mcr-9</italic> genes, we found IS<italic>1</italic> on one plasmid (pS15), while the other had a <italic>WbuC</italic>-IS<italic>26</italic> (pS639). Despite the presence of <italic>mcr-9</italic> 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 <italic>mcr-9</italic> due to its potential to mediate resistance to the last-resort antibiotic colistin.</p>