Emergence of Transferable Plasmid Coharboring mcr-1.1 and bla_CTX-M-55 Genes in Multidrug-Resistant Escherichia coli...

Area of Science:

• Microbiology
• Genomics
• Veterinary Medicine

Background:

• Multidrug-resistant (MDR) bacteria pose a significant threat to public health, limiting treatment options.
• Antimicrobial resistance (AMR) in animal-derived Escherichia coli (E. coli) is a growing concern, yet data on mink isolates are scarce.
• Understanding the genomic basis of AMR in E. coli from mink is crucial for One Health approaches.

Purpose of the Study:

• To characterize the antimicrobial resistance profile and genomic features of an MDR E. coli strain isolated from a farmed mink.
• To investigate the presence and transferability of resistance genes within this mink-associated E. coli strain.
• To assess the potential role of mink-derived E. coli in the broader AMR transmission network.

Main Methods:

• Antimicrobial susceptibility testing was performed on the isolated E. coli strain EC0D1.
• Whole genome sequencing was conducted to identify resistance genes and plasmids.
• Phylogenetic and comparative genomic analyses were used to understand genetic relationships and plasmid origins.
• Conjugation assays were performed to assess the transferability of resistance plasmids.

Main Results:

• A MDR E. coli strain (EC0D1) was isolated from mink lung tissue, showing resistance to multiple antimicrobial classes (β-lactams, fluoroquinolones, aminoglycosides, tetracyclines, polymyxins).
• Whole genome sequencing identified key resistance genes (bla_CTX-M-55, mcr-1.1, tet(A), floR) located on transferable plasmids (pEC0D1-2, pEC0D1-3).
• Phylogenetic analysis placed EC0D1 within ST457, closely related to human clinical isolates, and its plasmids showed similarity to those from avian and human sources.

Conclusions:

• The identified MDR E. coli strain from mink harbors transferable resistance genes, including critical ones like mcr-1.1.
• The genetic relatedness to human isolates and plasmid similarities suggest potential inter-species transmission pathways for AMR.
• Mink farming environments may serve as a reservoir and potential bridge for the dissemination of MDR E. coli and resistance genes between animal and human populations.