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Updated: Jun 6, 2025
Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes
Published on: March 3, 2023
Aeromonas and mcr-3: A Critical Juncture for Transferable Polymyxin Resistance in Gram-Negative Bacteria
Nathan L McDonald1, David W Wareham2, David C Bean1
1Microbiology Research Group, Institute of Innovation, Science and Sustainability, Federation University Australia, Mount Helen Campus, P.O. Box 663, Ballarat, VIC 3353, Australia.
Abstract:
Polymyxin antibiotics B and colistin are considered drugs of last resort for the treatment of multi-drug and carbapenem-resistant Gram-negative bacteria. With the emergence and dissemination of multi-drug resistance, monitoring the use and resistance to polymyxins imparted by mobilised colistin resistance genes (mcr) is becoming increasingly important. The Aeromonas genus is widely disseminated throughout the environment and serves as a reservoir of mcr-3, posing a significant risk for the spread of resistance to polymyxins. Recent phylogenetic studies and the identification of insertion elements associated with mcr-3 support the notion that Aeromonas spp. may be the evolutionary origin of the resistance gene. Furthermore, mcr-3-related genes have been shown to impart resistance in naïve E. coli and can increase the polymyxin MIC by up to 64-fold (with an MIC of 64 mg/L) in members of Aeromonas spp. This review will describe the genetic background of the mcr gene, the epidemiology of mcr-positive isolates, and the relationship between intrinsic and transferable mcr resistance genes, focusing on mcr-3 and mcr-3-related genes.
Insights
Mobilised colistin resistance (mcr) genes, particularly mcr-3, found in Aeromonas bacteria pose a significant risk for polymyxin resistance spread. Aeromonas may be the evolutionary origin of these critical resistance genes.
Area of Science:
- Microbiology
- Genetics
- Antimicrobial Resistance
Background:
- Polymyxins (e.g., colistin) are last-resort antibiotics against multidrug-resistant Gram-negative bacteria.
- Emerging resistance to polymyxins, driven by mobilised colistin resistance (mcr) genes, necessitates enhanced monitoring.
- The environmental bacterium Aeromonas harbors mcr-3, acting as a potential reservoir for polymyxin resistance.
Purpose of the Study:
- To review the genetic basis and epidemiology of mcr genes, focusing on mcr-3 and related genes.
- To explore the role of Aeromonas spp. as a potential origin and reservoir for mcr-3.
- To understand the implications of mcr-3 transfer on polymyxin resistance in clinically relevant bacteria.
Main Methods:
- Review of existing phylogenetic studies on mcr gene evolution.
- Analysis of the association between mcr-3 and insertion elements in Aeromonas.
- Examination of studies demonstrating mcr-3 mediated resistance in E. coli and Aeromonas.
Main Results:
- Aeromonas spp. may represent the evolutionary origin of the mcr-3 gene, supported by phylogenetic data and associated insertion elements.
- mcr-3 and related genes confer significant polymyxin resistance, increasing minimum inhibitory concentrations (MICs) up to 64-fold in Aeromonas.
- Transferable mcr-3 genes can impart resistance in naive E. coli strains.
Conclusions:
- Aeromonas spp. are a significant reservoir and potential evolutionary origin for mcr-3, posing a threat to polymyxin efficacy.
- Understanding the intrinsic and transferable nature of mcr-3 is crucial for combating polymyxin resistance.
- Continued surveillance of mcr genes in environmental bacteria like Aeromonas is vital.
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