Thermosonication pretreatment enhances the killing of germinated Bacillus spores adhered to stainless steel surface

The retention of bacterial spores on food processing stainless steel (SS) surfaces can be a source of cross-contamination from food contact surfaces to food products. This study aimed to develop an effective strategy to inactivate spores of Bacillus subtilis and Bacillus cereus on SS by stimulating spore germination and killing germinated spores with a combination of thermosonication (TS) pretreatment and other subsequent treatments (nisin/thyme essential oil (TEO)/UV). A mixture of l-asparagine, fructose, glucose, and potassium chloride (AGFK) initiated the maximum germination of spores at 37 °C. Notably, the implementation of a germination-inducing step did increase the susceptibility of spores to environmental stress. Moreover, TS pretreatment enhanced the efficacy of subsequent inactivation treatments (UV irradiation), resulting in an additional 2.74 to 3.78 log reductions in germinated spores of both Bacillus suspension. Whereas the sporicidal activities of subsequent nisin/TEO incubation were not greatly increased by TS pretreatments. TS pretreatment still increased sporicidal activity of UV irradiation against both Bacillus spores attached to SS coupons, even though adhered spores germinated not fast as those in suspension. Collectively, the findings from this study could be beneficial for reducing contamination of Bacillus spores on food contact surface and the potential risks of food poisoning outbreaks.