Mobile colistin resistance gene mcr-5 in porcine Aeromonas hydrophila

Area of Science:

• Microbiology
• Antimicrobial Resistance
• Genetics

Background:

• Colistin is a critical antibiotic for treating multidrug-resistant Gram-negative bacterial infections.
• The emergence and spread of colistin resistance genes, such as mcr-5, pose a significant threat to public health.
• Aeromonas hydrophila is an opportunistic pathogen found in various environments, including livestock.

Purpose of the Study:

• To characterize the mobile colistin resistance gene mcr-5 in Aeromonas hydrophila isolates from backyard pigs in China.
• To investigate the genetic location, transferability, and stability of the mcr-5 gene and its associated plasmid.

Main Methods:

• Polymerase Chain Reaction (PCR) was used to detect the mcr-5 gene in pig fecal samples.
• Antimicrobial susceptibility testing (broth dilution) determined the phenotypic resistance profiles.
• S1-PFGE with Southern blotting, DNA hybridization, and natural transformation were employed to analyze plasmid location and transferability.
• Whole Genome Sequencing (WGS) and subculturing were used to examine plasmid stability.

Main Results:

• One mcr-5-positive Aeromonas hydrophila isolate was identified, exhibiting colistin resistance (MIC of 4 mg/L).
• The mcr-5 gene was located on a plasmid (pI064-2) that could be naturally transformed into other A. hydrophila strains, mediating colistin resistance.
• The plasmid backbone showed similarity to known ColE2-type plasmids, with related replication primases found in other bacterial species.

Conclusions:

• This study reports the first identification of the mcr-5 gene in Aeromonas hydrophila from backyard pig feces.
• The findings indicate that mcr-5 can be mobilized on plasmids and has the potential for dissemination among diverse bacterial species and genera.
• The presence of mcr-5 in A. hydrophila from livestock underscores the need for continued surveillance of antimicrobial resistance in food-producing animals.