Metal complexes and conjugation: Harnessing the power of cobalt complexes to curtail plasmid transfer

BackgroundAntimicrobial resistance genes (ARG), such as extended spectrum {beta}-lactamase (ESBL) and carbapenemase genes, are commonly carried on plasmids. Plasmids can transmit between bacteria, disseminate globally, and cause clinically important resistance. Therefore, targeting plasmids could reduce ARG prevalence, and restore the efficacy of existing antibiotics. Here, we assessed the effect of four previously characterised bis(N-picolinamido)cobalt(II) complexes on the conjugative transfer of plasmids in Escherichia coli and Klebsiella pneumoniae. MethodsLiquid broth and solid agar conjugation assays were used to measure complex activity on four plasmids in E. coli. Additionally, the effect of cobalt complexes was tested on the transmission of the fluorescently tagged extended spectrum {beta}-lactamase encoding pCTgfp plasmid in E. coli and carbapenemase encoding pKpQILgfp plasmid in K. pneumoniae, using flow cytometry. ResultsAntimicrobial susceptibility testing of cobalt complexes revealed no antibacterial activity. The cobalt complexes significantly reduced conjugative transfer of RP4, R6K, and R388 plasmids on solid agar in E. coli and pKpQILgfp transmission in K. pneumoniae. None affected conjugative transfer of pKM101 or transmission of fluorescently tagged pCT in E. coli. The cobalt complexes had no effect on plasmid persistence, suggesting that they target conjugation rather than plasmid prevalence. ConclusionsTo the best of our knowledge, this is the first study to report reduced transmission of clinically relevant plasmids with cobalt complexes. These cobalt complexes are not cytotoxic towards mammalian cells and are not antibacterial, therefore they could be optimised and employed as conjugation inhibitors to reduce prevalence of AMR and/or virulence genes in animals and humans. SignificanceAntimicrobial resistance is a growing problem that poses a significant threat to modern medicine. Some of the most problematic resistance genes are carried on genetic elements, called plasmids, that can spread between bacteria. While our understanding of the mechanisms and drivers of gene transfer amongst bacteria is increasing, we lack effective tools to slow down/control these processes. Here we demonstrate for the first time that novel cobalt-based compounds have anti-plasmid activity on a subset of E. coli plasmids, and are extremely potent in K. pneumoniae carrying a clinical carbapenem-resistance plasmid, without impacting plasmid maintenance. This finding forms the foundations of a potential strategy to control the transfer of genes within Gram-negative bacteria, which has implications for AMR and virulence.