Natural products from food sources can alter the spread of antimicrobial resistance plasmids in Enterobacterales.

Antimicrobial resistance (AMR) poses a significant threat to global public health. Notably, resistance to carbapenem and extended-spectrum ß-lactam antibiotics in Gram-negative bacteria is a major impediment to treating infections. Genes responsible for antibiotic resistance are frequently carried on plasmids, which can transfer between bacteria. Therefore, exploring strategies to prevent this transfer and the prevalence of AMR plasmids is timely and pertinent. Here, we show that certain natural product extracts and associated pure compounds can reduce the conjugation of AMR plasmids into new bacterial hosts. Using our established high-throughput fluorescence-based flow cytometry assay, we found that the natural products were more active in reducing transmission of the IncK extended-spectrum ß-lactamase-encoding plasmid pCT in Escherichia coli EC958c, compared to Klebsiella pneumoniae Ecl8 carrying the IncFII carbapenemase-encoding plasmid pKpQIL. The exception was the natural product rottlerin, also active in K. pneumoniae. In classical conjugation assays, rottlerin also reduced the conjugation frequency of the IncFII bla NDM-1 carrying plasmid pCPE16_3 from a clinical K. pneumoniae isolate. Our data indicate that the natural products tested here, in their current molecular structure, reduced conjugation by a small amount, which is unlikely to achieve a large-scale reduction in AMR in bacterial populations. However, certain natural products like rottlerin could provide a foundation for further research into compounds with effective anti-plasmid activity.

Cobalt complexes modulate plasmid conjugation in Escherichia coli and Klebsiella pneumoniae.

Antimicrobial resistance genes (ARG), such as extended-spectrum ß-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. Cobalt complexes possess diverse biological activities, including antimicrobial and anticancer properties. However, their effect on plasmid conjugation has not been explored yet. Here, we assessed the effect of four previously characterised bis(N-picolinamido)cobalt(II) complexes lacking antibacterial activity on plasmid conjugation in Escherichia coli and Klebsiella pneumoniae. Antimicrobial susceptibility testing of these cobalt complexes confirmed the lack of antibacterial activity in E. coli and K. pneumoniae. Liquid broth and solid agar conjugation assays were used to screen the activity of the complexes on four archetypical plasmids in E. coli J53. The cobalt complexes significantly reduced the conjugation of RP4, R6K, and R388 plasmids, but not pKM101, on solid agar in E. coli J53. Owing to their promising activity, the impact of cobalt complexes was tested on the conjugation of fluorescently tagged extended-spectrum ß-lactamase encoding pCTgfp plasmid in E. coli and carbapenemase encoding pKpQILgfp plasmid in K. pneumoniae, using flow cytometry. The complexes significantly reduced the conjugation of pKpQILgfp in K. pneumoniae but had no impact on pCTgfp conjugation in E. coli. The cobalt complexes did not have plasmid-curing activity, suggesting that they target conjugation rather than plasmid stability. To our knowledge, this is the first study to report reduced conjugation 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 inhibitors of plasmid conjugation.