Assessment of a plasmid conjugation procedure to monitor horizontal transfer of an extended-spectrum ?-lactamase resistance gene under food chain scenarios

Plasmids are relevant reservoirs of antimicrobial resistance genes (ARGs) which confer adaptive advantages to their host and can be horizontally transferred. The aims of this study were to develop a conjugation procedure to monitor the horizontal transfer of a 193 kb plasmid containing the extended-spectrum beta-lactamase production gene blaCTX-M-14 between two Escherichia coli strains under a range of food chain-related scenarios, including temperature (20-37 degrees C), pH (5.0-9.0) or the presence of some biocidal agents (benzalkonium chloride, sodium hypochlorite or peracetic acid). The average conjugation rate in LB broth after 18 h at 37 degrees C was 2.09e-04 and similar rates were observed in a food matrix (cow's milk). The conjugation was reduced at temperatures below 37 degrees C, at alkaline pH (especially at pH 9.0) or in the presence of benzalkonium chloride. Peracetic acid and sodium hypochlorite slightly increased conjugation rates, which reached 5.59e-04 and 6.77e-03, respectively. The conjugation procedure described can be used to identify risk scenarios leading to an enhanced ARGs transmission via plasmid conjugation, as well as to identify novel intervention strategies impairing plasmid conjugation and tackling antimicrobial resistance.

Automated summary

Plasmids containing antimicrobial resistance genes (ARGs) are important for the horizontal transfer of resistance between bacteria. This study developed a conjugation procedure to monitor the transfer of a specific plasmid in different food chain-related scenarios. The results showed that temperature, pH, and the presence of certain biocidal agents can affect the conjugation rate. This procedure can be used to identify risk scenarios and develop strategies to combat antimicrobial resistance.