Enhanced plasmid loss in bacterial populations exposed to the antimicrobial compound irgasan delivered from interpenetrating polymer network silicone hydrogels

Abstract

The spread of antimicrobial resistance, usually mediated by horizontal transfer of plasmids, limits the options of treating bacterial infections and thereby poses a crucial human health problem. The disturbance of plasmid stability within bacterial species in clinical environments serves as a novel strategy to reduce the development and dissemination of antibiotic resistance.We tested the ability of irgasan to destabilize plasmids from Escherichia coli K-12 cells when added directly into liquid growth medium at concentrations below levels of marked bacterial growth inhibition, or when released into liquid growth medium from irgasan-impregnated Interpenetrating Polymer Network (IPN) silicone hydrogel objects, a novel technology developed as drug-delivery platform. IPN-mediated irgasan-release was indirectly monitored as the extent of plasmid loss from bacterial cells during a 24-hour period or during repeated exposure to new irgasan-loaded IPN devices every 24h for a total of 10days. The cells were genetically modified so that plasmid loss could be quantified by applying a combination of fluorescence-based reporter gene technology and flow cytometry.When exposing bacterial cells to the irgasan-impregnated IPNs for 24h, we observed a modest (2.8–4.7%), but significant (P<0.05), plasmid loss as well as an inhibition of bacterial growth, both gradually increasing with increasing impregnation concentration. Repeated exposure to irgasan-impregnated IPNs drastically increased the plasmid loss of up to 83%, but cells adapted over time, which indicated the limitations of this specific drug for future medical applications. This study, however, illustrates the ability of IPNs to release an impregnated compound into a liquid suspension to induce a significant biological impact on growing bacterial cells.