Mild positive pressure improves the efficacy of benzalkonium chloride against Staphylococcus aureus biofilm

Current protocols using liquid disinfectants to disinfect heat-sensitive hospital items frequently fail, as evidenced by the continued isolation of bacteria following decontamination. The contamination is, in part, due to biofilm formation. We hypothesize that mild positive pressure (PP) will disrupt this biofilm structure and improve liquid disinfectant/detergent penetration to biofilm bacteria for improved killing. Staphylococcus aureus biofilm, grown on polycarbonate coupons in the biofilm reactor under shear at 35 °C for 3 days, was treated for 10 min and 60 min with various dilutions of benzalkonium chloride without PP at 1 atmosphere (atm), and with PP at 3, 5, 7, and 10 atm. The effect on biofilm and residual bacterial viability was determined by standard plate counts, confocal laser scanning microscopy, and scanning electron microscopy. Combined use of benzalkonium chloride and PP up to 10 atm significantly increased biofilm killing up to 4.27 logs, as compared to the treatment using disinfectant alone. Microscopy results were consistent with the viability plate count results. PP improved disinfectant efficacy against bacterial biofilm. The use of mild PP is possible in many flow situations or if equipment/contaminated surfaces can be placed in a pressure chamber.