Emergence of Bacillus Cereus as a Dominant Organism in Irish Retailed Powdered Infant Formulae (Pif) When Reconstituted and Stored Under Abuse Conditions

One hundred powdered infant formulae (PIF), representative of the 10 leading brands available in Ireland, were subjected to a variety of preparation and storage conditions. All PIF analyzed immediately after reconstitution were of satisfactory bacteriological quality, exhibiting a total aerobic mesophilic count of < 10 4 cfu/g (mean 3.8 × 10 2 cfu/g) and a Bacillus cereus count of < 10 3 cfu/g powder (mean 1.9 × 10 2 cfu/g). Enterobacter sakazakii was not detected in PIF. While 24 of all PIF examined contained B. cereus, subsequent reconstitution and storage over a 24‐h period at ≥ 20C resulted in this organism being detected in a further 35 PIF at levels in excess of 10 3 cfu/g. The bacteriological quality of PIF depended on the type and number of organisms initially present and on the product temperature and duration of storage. While PIF predominantly consisted of members of the Bacillus subtilis group, subsequent reconstitution and storage at ≥ 20C for 14 h resulted in the emergence of B. cereus as the dominant organism. Co‐culture studies revealed that B. cereus inhibited the growth of members of the B. subtilis group and Listeria monocytogenes. Not all diarrheagenic and emetic strains of B. cereus exhibited antagonistic activity, and there was also evidence of intraspecies antagonism among B. cereus isolated from PIF. PRACTICAL APPLICATION The high biocidal temperatures that occur during spray drying of powdered infant formulae (PIF) combined with good manufacturing practice compliance ensure that these high‐risk foods are of satisfactory bacteriological quality. However, acceptably low numbers of recalcitrant bacterial endospores with toxigenic potential do frequently survive this process. Thus, identifying interrelated preparation and storage conditions (including abuse scenarios) that foster growth of bacterial contaminants in reconstituted PIF to potentially hazardous levels is of paramount importance, as this will inform and safeguard consumer health. This study reports on the occurrence, interaction, emergence and predominance of Bacillus cereus in reconstituted PIF under various storage regimes. The tests described in this study are practical and will benefit food technologists in the profiling of spoilage and potentially pathogenic bacteria that may contaminate these high‐risk products. Guidance is also provided to consumers on conditions for safe storage of reconstituted PIF prior to consumption.