Chromosome-Mediated mcr-3 Variants in Aeromonas veronii from Chicken Meat

Area of Science:

• Microbiology
• Genetics
• Food Safety

Background:

• Colistin is a crucial antibiotic for treating multidrug-resistant Gram-negative bacterial infections.
• The emergence of colistin resistance genes, such as the mobile colistin resistance (mcr) genes, poses a significant threat to public health.
• Aeromonas species are increasingly recognized as opportunistic pathogens and potential reservoirs for antimicrobial resistance genes.

Purpose of the Study:

• To identify and characterize novel colistin resistance gene variants in Aeromonas species.
• To determine the functional polymyxin resistance conferred by these variants.
• To investigate the presence of these variants in other Aeromonas species.

Main Methods:

• Whole-genome sequencing of an Aeromonas veronii isolate from retail chicken meat.
• Bioinformatic analysis to identify gene variants and compare nucleotide sequences.
• Functional cloning and expression in Escherichia coli and Aeromonas salmonicida to assess polymyxin resistance.
• Comparative analysis of gene presence across different Aeromonas species.

Main Results:

• Two adjacent colistin resistance gene variants, mcr-3.3 and mcr-3-like, were identified in the chromosome of an Aeromonas veronii isolate.
• mcr-3.3 and mcr-3-like showed 95.20% and 84.19% nucleotide sequence identity to mcr-3, respectively.
• Functional cloning confirmed that only mcr-3.3 conferred polymyxin resistance in both E. coli and A. salmonicida.
• The mcr-3.3-mcr-3-like segment was detected in other Aeromonas species, including A. media, A. caviae, and A. hydrophila.

Conclusions:

• Novel colistin resistance gene variants, mcr-3.3 and mcr-3-like, are present in Aeromonas veronii from food sources.
• The mcr-3.3 gene variant is functional and confers polymyxin resistance, highlighting a potential mechanism for resistance spread.
• The widespread presence of the mcr-3.3-mcr-3-like segment in various Aeromonas species suggests a broader dissemination of these resistance determinants within this genus.