Abstract
Colistin is considered the last resort for the treatment of multi-drug resistant Gram-negative bacterial infections. We studied colistin resistance and the mcr-1 gene carriage in Salmonella isolates recovered from food animals in South Korea between 2010 and 2018. Colistin resistance was found in 277 isolates, predominantly in Salmonella Enteritidis (57.1%) and Salmonella Gallinarum (41.9%). However, the mcr-1 gene was identified in only one colistin-resistant Salmonella Typhimurium (MIC = 16 µg/mL) isolated from a healthy pig. The mcr-1 carrying isolate presented additional resistance to multiple antimicrobials. The strain belonged to sequence type (ST)19 and carried various virulence factor genes that are associated with adhesion and invasion of Salmonella into intestinal epithelial cells, as well as its survival in macrophages. The mcr-1 gene was identified on an IncI2 plasmid and it was also transferred to the E. coli J53 recipient strain. The mcr-1-carrying plasmid (pK18JST013) in this study was closely related to that previously reported in S. Indiana (pCFSA664-3) from chicken in China. This is the first report of mcr-1 carrying S. Typhimurium in South Korea. The finding indicates the importance of regular screening for the presence of the mcr-1 gene in S. Typhimurium in food animals to prevent the spread to humans.
Highlights
Accepted: 12 February 2021Non-typhoidal Salmonella serovars are common causes of foodborne diseases, especially in the elderly, children, and immunocompromised individuals [1]
The mcr genes encode phosphoethanolamine transferases that modify the lipopolysaccharides of the outer membrane in Gram-negative bacteria, which leads to reduced susceptibility or resistance to colistin [5]
In view of the concerning horizontal spread of the mcr-1 gene among Enterobacteriaceae in food animals and its significant public health impacts, we performed a retrospective evaluation of colistin resistance and investigated the mcr-1-carrying plasmid in Salmonella isolated from food animals between 2010 and 2018 in Korea
Summary
Non-typhoidal Salmonella serovars are common causes of foodborne diseases, especially in the elderly, children, and immunocompromised individuals [1]. Colistin belongs to the group of polymyxins and has been used for the treatment and prevention of gut infections in food animals poultry and pigs In humans, their parenteral usage has been limited because of concerns of toxicity, it is the last resort treatment for severe infections caused by multi-drug resistant (MDR) Gram-negative bacteria, carbapenem-resistant Enterobacteriaceae [4]. In Korea, this gene has been detected only in E. coli and Enterobacter aerogenes isolated from humans, food and companion animals, and fresh vegetables [8,19,20,21]. In view of the concerning horizontal spread of the mcr-1 gene among Enterobacteriaceae in food animals and its significant public health impacts, we performed a retrospective evaluation of colistin resistance and investigated the mcr-1-carrying plasmid in Salmonella isolated from food animals between 2010 and 2018 in Korea
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