Characterization of Bacillus cereus sensu lato isolates from milk for consumption; phylogenetic identity, potential for spoilage and disease. (February 2021) - Porcellato, Davide
Abstract: This study addresses the biodiversity of Bacillus cereus group population present along the value chain of milk for consumption. The B. cereus population did not grow and remained mainly unaltered during storage of milk at 4 °C while storage at a suboptimal temperature at 8 °C (representative of a broken cold chain) caused a major shift in its composition. Mesophilic strains dominated the B. cereus population in raw milk and after storage at 4 °C, while psycrotrophic strains dominated after storage at 8 °C. All psycrotrophic and mesophilic isolates (n = 368) demonstrated high spoilage potentials of the milk components. Fifteen out of 20 mesophilic isolates but only two out of 40 psychrotrophic isolates, exhibited vero cell toxicity. No genes encoding the emetic toxin cereulide were detected in the genomes of 100 milk isolates while 14 of them harbored the enterotoxin genes cytK1 / cytK2 . Both psycrotrophic and mesophilic isolates carried the enterotoxin genes nheA and hblA. Together, the results provide insight into the composition and properties, of the B. cereus population present in milk along the value chain and during storage at optimal refrigerated temperature and at suboptimal temperature. This knowledge is useful in the dairy industry's work to assure high quality products and for risk assessment. Highlights: B. cereus spp. milk isolates were analyzed genetically and for virulence and spoilage potentials. At optimal storage of milk (4 °C), the B. cereus population remained mainly unaltered. Suboptimal storage of milk (8 °C), changed the initial B. cereus population. Mesophilic and psychrotrophic isolates carried the enterotoxin genes nheA and hblA. 14% of genomes contained the cytK2 gene but emetic toxin genes were not present.