Whole room disinfection with hydrogen peroxide mist to control Listeria monocytogenes in food industry related environments.

Listeria monocytogenes surviving daily cleaning and disinfection is a challenge for many types of food industries. In this study, it was tested whether whole room disinfection (WRD) with HO mist could kill L. monocytogenes under conditions relevant for the food industry. Survival of a mixture of four L. monocytogenes strains exposed to HO mist was investigated in a 36 m room. A commercial machine produced HO mist by pumping a 5% HO solution containing 0.005% silver through a nozzle, and breaking the liquid up in droplets using pressurized air. When a suspension of bacteria in 0.9% NaCl applied on stainless steel coupons was exposed to WRD with HO mist, a >5 log reduction (LR) of L. monocytogenes was observed. Similar reductions were observed in all tests with conditions between 12 and 20 °C, HO concentrations of 35-80 ppm and 1-2 h exposure. It was shown that the HO in the mist dissolved and accumulated in the liquid on the steel, and acted against L. monocytogenes in the liquid phase. At high cell concentrations, the effect was reduced if cells were pregrown at highly aerated conditions. The anti-listerial effect was robust against protein and fat, but the effect was quenched by raw meat and raw salmon, probably due to high catalase activity. The effect of whole room disinfection with HO against dried L. monocytogenes cells was 1-2 LR, however the effect of air-drying by itself lead to 3-4 LR. When biofilms were exposed to WRD, no surviving L. monocytogenes were observed on stainless steel, however for L. monocytogenes on a PVC conveyor belt material, there were surviving bacteria, with about 2 LR. Screening of 54 L. monocytogenes strains for growth susceptibility to HO showed that their sensitivity to HO was very similar, thus WRD with HO are likely to be robust against strain variation in susceptibility to HO. Production of HO mist resulted in increased room humidity, and this may limit the maximum HO concentration achievable, especially at low temperatures. The results in this study show that whole room disinfection with HO may have potential to control L. monocytogenes in the food industry, however intervention studies in the food industry are needed to verify the effect in practical use.