# P02 Horizontal transfer of antimicrobial resistance genes from Aeromonas salmonicida to Escherichia coli via conjugation

## TL;DR

This study shows that antibiotic resistance genes from a fish pathogen can be transferred to E. coli through conjugation, highlighting a risk for spreading drug resistance.

## Contribution

Demonstrates horizontal transfer of AMR genes from Aeromonas salmonicida to E. coli via conjugation using a transferable R plasmid.

## Key findings

- E. coli acquired resistance to sulfamethoxazole, tetracycline, and trimethoprim through conjugation with A. salmonicida.
- PCR and sequencing confirmed the transfer of sul1, tet(A), dfr16, and a class 1 integron to E. coli.
- The study emphasizes the role of conjugation in spreading AMR between environmental and clinical bacteria.

## Abstract

Furunculosis, a bacterial infectious disease affecting salmonid fish species, is caused by the water-borne Gram-negative bacterium Aeromonas salmonicida subspecies salmonicida capable of hosting drug resistance plasmids carrying various antimicrobial resistance genes and genetic structures as integrons with ability to adapt the contents of the antibiotic resistance genes in the genome. The spread of antimicrobial resistance (AMR) genes among bacterial species poses a significant threat to both animal and public health.

In this study, we investigated the horizontal transfer of AMR genes from Aeromonas salmonicida to Escherichia coli (DH5α) through conjugation.

Three strains of A. salmonicida (1711/93, 1995/91 and 2402/89) harbouring the resistance genes sul1, tet(A), dfr16 and the class 1 integron on the transferable R plasmid pRAS1were used as donors, while E. coli DH5α, lacking antibiotic resistance genes and integrons, served as the recipient. Antimicrobial susceptibility testing using the disc diffusion method confirmed resistance in A. salmonicida to sulfamethoxazole, tetracycline and trimethoprim. Conjugation experiments were performed at room temperature for 24 h, and transconjugants were selected on Mueller–Hinton agar supplemented with the respective antibiotics.

Growth in the inhibition zones around sulfamethoxazole, tetracycline and trimethoprim discs indicated the acquisition of resistance by E. coli. PCR amplification and Sanger sequencing confirmed the presence of sul1, tet(A), dfr16 and the integron in the transconjugants, demonstrating the successful transfer of pRAS1 with its AMR genes.

This study highlights the role of conjugation in the dissemination of antibiotic resistance and underscores the potential for AMR gene transfer between environmental and clinically relevant bacteria, emphasizing the need for continued surveillance and control of AMR spread.