Effect of dry sanitizing methods on Bacillus cereus biofilm

Abstract

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.

Keywords: Bacillus cereus; Biofilm; Dry sanitation; Food contact surfaces; Food hygiene.

Fig. 1

Biofilm formation and sanitizing protocol scheme

Fig. 2

Effect of sanitizing protocols against Bacillus cereus biofilm formed on stainless steel ( ) and polypropylene ( ) coupons. a 70% ethanol, b commercial product, c dry heat, d UV-C light, e gaseous ozone, f sodium hypochlorite (200 mg/l) pH 7, and g sodium hypochlorite (200 mg/l) pH 11; (---) count below the limit of detection (< 1.69 log CFU/cm²). N₀, initial population; N, population after treatment. Bars represent standard deviation. All the experiments were performed three times