Occurrence and characterization of toxigenic Bacillus cereus in dairy products with an inactivation trial using D-Tryptophan and ascorbic acid in the rice pudding

Abstract

Bacillus cereus is one of the foodborne pathogens that is incriminated in several outbreaks worldwide. The objectives of the current study were first to determine the prevalence of B. cereus-contaminated milk and dairy products retailed in Egypt. Secondly, the antimicrobial resistance profiling and virulence-associated genes of the recovered B. cereus isolates were assessed. Finally, natural and eco-friendly natural additives such as d-tryptophan and l-ascorbic acid were used for controlling the viability of Bacillus cereus spores. A total of 200 samples including market raw milk, Ultra-Heat Treated (UHT) milk, Kariesh cheese, soft white cheese (Damietta), and rice pudding, 50 of each were examined. The results of our study indicated that 31% of the examined dairy samples were contaminated with B. cereus. Surprisingly, 90% of the isolates showed multidrug-resistance against ampicillin, amoxicillin, oxacillin, and streptomycin. The molecular characterization revealed that 15 isolates harbored both hemolytic and non-hemolytic enterotoxin genes. Co-treatment of B. cereus spores-contaminated rice pudding with d-tryptophan at a concentration of 40 mM and l-ascorbic acid at a concentration of 3% revealed a significant reduction (P < 0.05) in the spore growth. Therefore, d-tryptophan and l-ascorbic acid are considered promising eco-friendly food preservatives with anti-B. cereus effects in the dairy industry.