Bisphosphonium Amphiphiles Yield Insights into Gram-Negative Bacterial Disinfectant Resistance and Cell Membrane Interactions

As microbial resistance to commercially available disinfectants has increased over recent decades, the development of new biocides with distinct mechanisms of action has become a priority. Accordingly, our groups have developed and investigated quaternary phosphonium compounds (QPCs) that have displayed novel mechanisms of bactericidal activity against Gram-negative bacterial species. We aimed to characterize the structure–activity relationship of the cation-separating linker length of diphenylphosphonium scaffolds on membrane interactions and resistance mechanisms using Gram-negative model bacterium Pseudomonas aeruginosa (PAO1 and PA14). Antibacterial activity against lab strain PAO1 and a panel of P. aeruginosa clinical isolates from facilities in Ukraine exhibited potent activity with minimum inhibitory concentrations of 2–4 μM. Surprisingly, the linker length minimally affected the inner-membrane specificity of the QPCs. In comparing the known resistance mechanism for these QPCs, we found that the shorter linker lengths were much more susceptible to efflux by the SmvRA system than the longer linker chain bolaamphiphilic compounds. Additionally, we determined the critical micelle concentration of the QPCs and found that supramolecular aggregation properties do not correlate with the distinct inner-membrane-targeting mechanism of the QPCs. These results represent important advances in the structure-guided investigation of inner-membrane-selective disinfectants.