Conjugation-driven horizontal gene transfer in bacteria on antimicrobial surfaces

Abstract

Conjugation is the main mechanism of horizontal gene transfer of antibiotic resistance genes between bacteria. There is evidence that the presence of trace amounts of antimicrobials in the environment may increase the conjugation frequency between bacteria and thus, potential spread of antibiotic resistance genes. However, to date the effect of stress conditions, including the presence of antimicrobials, on conjugation is relatively modestly studied and almost no studies are available about the effect of antimicrobial surfaces on conjugation frequency. This study first constructed an optimized conjugation protocol for solid surfaces. For that, a chromosomally marked strain of Pseudomonas putida KT2440 to be used as recipient strain in conjugation, was constructed. As a donor strain, Escherichia coli CSH26 with conjugative plasmid pKJK5 was used. The optimal experimental conditions: organic content, conjugation time, and donor-to-recipient ratio on conjugation frequency, were studied. For the conjugation experiments, a series of copper- silver- and quaternary ammonium- based surfaces that were expected to show an antimicrobial effect, were selected. Plastic and stainless-steel surfaces served as controls with no expected antimicrobial activity. Prior to conjugation, viability of donor and recipient on test surfaces was analyzed and the most toxic surfaces were not included in conjugation assay. On selected surfaces, conjugation experiments were carried out for 24 h and conjugation frequencies were calculated for each surface. The results showed that the presence of low level of copper on surface may promote conjugation while silver- and quaternary ammonium compounds-based surfaces did not significantly affect conjugation frequency.