Isolation and Characterization of Bacillus cereus Group Species in Powdered Infant Formula and Infant Cereal Using a Newly Developed Detection System

Bacillus cereus group species are frequently detected at low levels in infant foods, including powdered infant formula and infant cereals. Although the infectious dose in neonates and infants has not been established, evidence suggests it may be approximately 1,000 CFU/g. When infant foods are exposed to temperature abuse, B. cereus group species could grow beyond acceptable limits, resulting in microbiologically unsafe products. Therefore, a detection scheme using an enrichment broth may be necessary to assess their potential risk in these critical foods. In this study, the R & F® Bacillus cereus Group Enrichment Broth was developed, and a detection scheme was evaluated for its efficacy in recovering low-level B. cereus group species from powdered infant formula and infant cereals. Additionally, we used whole genome sequencing to gain deeper insights into the genomic characteristics of the recovered isolates and performed in vitro cytotoxicity assays to assess their virulence potential. The detection scheme recovered B. cereus group species in 52% (26/50) of samples that had initially screened below 100 CFU/g, resulting in a predictive positive value (PPV) of 97.6% as confirmed by whole-genome sequencing of the recovered isolates. Cytotoxicity testing of selected isolates revealed varying levels of toxicity toward Caco-2 cells. The results demonstrate that the enrichment method effectively recovered potentially virulent B. cereus group strains, highlighting the need for regular monitoring of these species in infant foods, especially for vulnerable populations such as premature neonates and infants.