Inactivation of Bacterial Spores on Polystyrene Substrates Pre-exposed to Dry Gaseous Ozone: Mechanisms and Limitations of the Process

Abstract

Some polymers can both absorb dry gaseous ozone and release it efficiently. This occurs, for example, with polystyrene (PS) surfaces, which acquire biocidal properties: bacterial spores are indeed inactivated when deposited wet on polystyrene exposed to ozone. Two main features need to be examined in relation with these assertions: PS surfaces pre-exposed to dry ozone can release O3 molecules, possibly solubilized in water, and thus bacterial spores can be inactivated when present in a suspension. We used Bacillus atrophaeus spores, which are the recommended bio-indicators in sterilization processes. Efficiency of the inactivation mechanism requires an optimized water volume to provide maximal concentration of active molecules. We find that the sporicidal effect increases: i) with the dimensions of the O3 pre-exposed PS surfaces and ii) with the contact time of the spore suspension with the released ozone, while it decreases iii) with time elapsed after ozone pre-exposure of PS. A numerical model, accounting for decomposition of ozone in water, predicts the existence of many different molecules, the main concentrations of which being (besides ozone) those of hydrogen peroxide and hydroxyl radical. Experimentally, under our conditions, the concomitant presence of ozone and hydrogen peroxide in water is observed; the participation of these chemical species to the inactivation process is investigated.