Resistances to UV-C irradiation of Salmonella Typhimurium and Staphylococcus aureus in wet and dried suspensions on surface with egg residues

Effect of dry sanitizing methods on Bacillus cereus biofilm

Bacillus cereus is a relevant foodborne pathogen and biofilm producer which can contaminate and persist in the processing environment of both high and low water activity foods. Because of this, it is crucial to understand better the resistance of this pathogen biofilm to different sanitation methods. The aim of this study was to evaluate the efficacy of dry sanitizing treatments against B. cereus biofilm formed on stainless steel (SS) and polypropylene (PP). Biofilm formation was held through the static method at 25 °C. After 4 days of incubation, coupons were exposed for up to 30 min to UV-C light, dry heat, gaseous ozone, 70% ethanol, and a commercial sanitizer. Sodium hypochlorite (200 mg/l) was also tested in two different pH values (7 and 11) for comparison purposes. In general, the surface material did not influence (p > 0.05) the performance of the treatments. From 10 min of exposure, 70% ethanol and the commercial product caused the lowest reductions on both surfaces. In addition, dry heat exhibited a poor performance on PP, with reductions < 1 log CFU/cm². UV-C light on SS and PP and ozone on PP achieved reductions around 2 log CFU/cm² after 30 min. The same level of reduction was obtained after 5 or 10 min using sodium hypochlorite (200 mg/l). Therefore, the results showed that dry sanitizing methods are not as effective as sodium hypochlorite against B. cereus biofilms. Further studies to evaluate the efficacy of the combination of dry methods are necessary.

Survival of foodborne pathogens on stainless steel soiled with different food residues

Insufficient and ineffective cleaning practices can cause food residues to remain in kitchen and can facilitate bacterial attachment and persistence by protective films. The present study investigated the survival of five major foodborne pathogens on stainless steel coupons, in the presence of cooked rice, whole eggs, and soymilk. Foodborne pathogens showed different survival rates by desiccation and disinfection depending on food residues. Overall, the pathogens showed stronger survival than the control at 0.13-3.97 log CFU/coupon with 5% residues, and at 0.75-5.29 log CFU/coupon with 50% residues. Staphylococcus aureus was not affected by the food residue with showing the least difference in concentration, while Escherichia coli O157:H7 showed the most significant increase by food residue. The cells with cooked rice were observed using FE-SEM, and demonstrated bacterial binding or embedment. All results suggest that food safety can be practically ensured by food residue types and appropriate cleaning and disinfectants.