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Bacillus cereus group species isolated from dairy products and dairy environments are not appropriate for use in inoculated-milk human sensory studies.

S. Reichler

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06-23-2020

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Abstract:

T41
Bacillus cereus group species isolated from dairy products and dairy environments are not appropriate for use in inoculated-milk human sensory studies.
S. Reichler*, N. Martin, M. Wiedmann. Cornell University Ithaca, NY.

Bacterial spoilage limits the refrigerated shelf-life of conventionally pasteurized fluid milk, but the specific metabolic processes that result in many types of milk spoilage are not well-understood. To address this deficiency, bacterial strains that reliably and reproducibly generate specific sensory defects in fluid milk must first be identified. Human sensory panels are the current standard for sensory defect identification, but the safety of panelists must be ensured if they are to taste intentionally inoculated milk. This raises a particular concern for the Bacillus cereus group, members of which are associated with both milk spoilage and foodborne illness. We used BTyper, a computational tool for virulence-based classification of B. cereus group isolates, to examine the whole genome assemblies of 37 dairy-associated Bacillus spp. for 4 common virulence factors associated with enteric illness: cereulide, hemolysin BL, non-hemolytic enterotoxin, and cytotoxin K. Genes encoding all 4 of these factors were detected among the 37 Bacillus spp. isolate assemblies. Specifically, a gene necessary for cereulide production (cesC) was detected in 4 isolates, the 4-gene operon necessary for hemolysin BL production (hblCDAB) was detected in 27 isolates, the 3-gene operon necessary for non-hemolytic enterotoxin production (nheABC) was detected in 36 isolates, and the gene necessary for cytotoxin K-2 production was detected in 16 isolates. In addition to these virulence factors, genes encoding resistance to β-lactams, fosfomycin, or vancomycin were detected in each of the 37 Bacillus spp. genomes. In contrast, none of these 4 virulence factors and very few antimicrobial resistance genes were detected in 61 whole genome assemblies of Paenibacillus spp. or in 5 whole genome assemblies of Viridibacillus spp. Based on these findings, we were unable to identify any B. cereus group isolates that we judged sufficiently lacking in potential hazards to justify their intentional exposure to a human sensory panel. Hence, other methods must be used to assess the spoilage potential of Bacillus spp.

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