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 <10⁴ cfu/g (mean 3.8 × 10² cfu/g) and a Bacillus cereus count of <10³ cfu/g powder (mean 1.9 × 10² 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 10³ 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.