Characterization of Enterotoxigenic Bacillus cereus sensu lato and Staphylococcus aureus Isolates and Associated Enterotoxin Production Dynamics in Milk or Meat-Based Broth.

species, as well as , are important pathogenic bacteria which can cause foodborne illness through the production of enterotoxins. This study characterised enterotoxin genes of these species and examined growth and enterotoxin production dynamics of isolates when grown in milk or meat-based broth. All isolates harboured , and toxin genes, with lower prevalence of and . When grown at 16 °C, toxin production by individual isolates varied depending on the food matrix; toxin was detected at cell densities below 5 log(CFU/mL). At 16 °C no staphylococcal enterotoxin C (SEC) production was detected by isolates, although low levels of SED production was noted. At 30 °C all isolates produced detectable enterotoxin in the simulated meat matrix, whereas SEC production was significantly reduced in milk. Relative to toxin production, typically required reaching higher cell numbers to produce detectable levels of enterotoxin. Phylogenetic analysis of the and genes suggested population evolution which correlated with animal host adaptation, with subgroups of bovine isolates or caprine/ovine isolates noted, which were distinct from human isolates. Taken together, this study highlights the marked differences in the production of enterotoxins both associated with different growth matrices themselves, but also in the behaviour of individual strains when exposed to different food matrices.