Investigating the impact of bisphosphonates and structurally related compounds on bacteria containing conjugative plasmids

Bacterial plasmids propagate through microbial populations via the directed process of conjugative plasmid transfer (CPT). Because conjugative plasmids often encode antibiotic resistance genes and virulence factors, several approaches to inhibit CPT have been described. Bisphosphonates and structurally related compounds (BSRCs) were previously reported to disrupt conjugative transfer of the F (fertility) plasmid in Escherichia coli. We have further investigated the effect of these compounds on the transfer of two additional conjugative plasmids, pCU1 and R100, between E. coli cells. The impact of BSRCs on E. coli survival and plasmid transfer was found to be dependent on the plasmid type, the length of time the E. coli were exposed to the compounds, and the ratio of plasmid donor to plasmid recipient cells. Therefore, these data indicate that BSRCs produce a range of effects on the conjugative transfer of bacterial plasmids in E. coli. Since their impact appears to be plasmid type-dependent, BSRCs are unlikely to be applicable as broad inhibitors of antibiotic resistance propagation.