First Identification and Limited Dissemination of mcr-1 Colistin Resistance in Salmonella Isolates from Jiaxing

Area of Science:

• Foodborne pathogen research
• Antimicrobial resistance
• Molecular epidemiology

Background:

• Salmonella is a significant global foodborne pathogen causing illness in humans and animals.
• The emergence of colistin resistance, mediated by the mcr-1 gene, is a critical public health concern.
• Plasmid-mediated antimicrobial resistance in bacteria poses a substantial threat to effective treatment strategies.

Purpose of the Study:

• To report the first identification of mcr-1-mediated colistin resistance in a foodborne Salmonella isolate from Jiaxing, China.
• To characterize the genetic features of the plasmid carrying the mcr-1 gene.
• To assess the dissemination of transferable colistin resistance in local foodborne pathogens.

Main Methods:

• Analysis of 355 Salmonella isolates collected from 2015 to 2019 for foodborne pathogen monitoring.
• Antimicrobial susceptibility testing, including resistance to colistin and other agents.
• Plasmid profiling and sequencing to identify resistance genes and their genetic context (e.g., IncX4 and IncHI2 plasmids).

Main Results:

• One multidrug-resistant Salmonella isolate (16062) exhibited resistance to colistin.
• The mcr-1 gene was located on an IncX4 plasmid (p16062-MCR), sharing structural similarity with other mcr-IncX4 plasmids.
• Additional antimicrobial resistance genes were identified on an atypical IncHI2 plasmid (p16062-cmlA).

Conclusions:

• This study provides the first evidence of transferable colistin resistance in a foodborne Salmonella isolate in Jiaxing City.
• The genetic characterization of the mcr-1-carrying plasmid enhances understanding of transferable resistance mechanisms.
• Limited dissemination was observed during a 5-year monitoring period, but continued surveillance is crucial.