Mechanisms of Listeria monocytogenes disinfection with Benzalkonium chloride: from molecular dynamics to kinetics of time-kill curves

Unravelling the mechanisms of action of disinfectants is essential to optimise dosing regimes and minimise the emergence of antimicrobial resistance. In this work, we examine the mechanisms of action of a commonly used disinfectant - benzalkonium chloride (BAC)-over a significant pathogen -L. monocytogenes- in the food industry. For that purpose, we use modelling at multiple scales, from the cell membrane to the cell population inactivation. Molecular modelling reveals that the integration of the BAC into the membrane requires three phases: (1) the BAC approaches the cellular membrane, (2) the BAC is adsorbed on its surface, and (3) it is rapidly integrated into the lipid bilayer, where it remains at least for several nanoseconds, probably destabilising the membrane. We hypothesise that the equilibrium of adsorption, although fast, is limiting for sufficiently large BAC concentrations, and a kinetic model is derived to describe time-kill curves of a large population of cells. The model is tested and validated with time series data of free BAC decay and time-kill curves of L. monocytogenes at different inocula and BAC dose concentrations. The knowledge gained from the molecular simulation plus the proposed kinetic model offers the means to design novel disinfection processes rationally.