Purpose: The purpose of this study was to evaluate the genetic and phenotypic diversity of B. cereus Group strains isolated from all stages of the dairy value chain, including the dairy farm environment, and raw and pasteurized dairy commodities.
Methods: We selected a total of 48 B. cereus Group isolates from a frozen stock collection representing 41 unique rpoB allelic types and evaluated their ability to grow at 6°C. We performed MLST according to the B. cereus PubMLST scheme, and constructed a neighbor-joining tree based on (i) the rpoB gene sequences and (ii) the concatenated sequences of seven MLST housekeeping genes.
Results: The 48 strains represented 46 unique MLST sequence types. Of the 48 selected strains, 13 grew at 6°C. The isolates clustered into the same five clades based on both rpoB and MLST sequences. Of the 13 that grew at 6°C, 10 clustered within the same clade.
Significance: As some strains of the B. cereus Group produce toxins, the ability of some strains to grow at 6°C presents a potential food safety concern to the dairy industry, as they may cause milk spoilage and present risk for foodborne disease. This work suggests that B. cereus Group isolates that can grow at refrigeration temperatures largely represent a phylogenetically homogeneous sub-group.