Bacteriological Quality of Infant Milk Formulae Examined under a Variety of Preparation and Storage Conditions

One hundred infant milk formulae (IMFs), representative of the 10 leading brands available in the UK, were subjected to a variety of preparation and storage conditions. Each IMF was the subject of triplicate trials in which duplicate samples were analyzed. All IMFs analyzed immediately after reconstitution were of satisfactory bacteriological quality, exhibiting a total aerobic count of < 10⁴ CFU g^-1 (mean 2.3 × 10² CFU g^-1) and a Bacillus cereus count of <10³ CFU g^-1 of powder (mean 1.3 × 10² CFU g^-1 for formulae containing this bacterium). Seventeen percent of all dried IMF examined contained B. cereus ; subsequent reconstitution and storage over a 24-h period at ≥30°C resulted in this organism being detected in a further 46% (63 of 100), so that the majority of these foods exceeded the International Dietetics Association of the European Community (IDAEC) proposed reconstitution safety limit of 10³ CFU g^-1. Variations in preparation conditions did not significantly influence the numbers of Bacillus CFU present (P < 0.05). The bacteriological quality of an IMF depended on the type and number of organisms initially present and on product temperature and duration of product storage. Microbial numbers in IMFs were influenced by storage temperatures of ≥ 20°C for 14 h, while incubation at ≤ 10°C for 24 h had no effect (P < 0.05). Although the microflora of dried IMFs predominantly consisted of B. licheniformis (46%) and B. subtilis (30%), subsequent reconstitution and incubation resulted in the shift to B. cereus I (31 %) and II (38%) as dominant organisms. The latter often grew to the exclusion of the former two Bacillus spp. Diarrheagenic enterotoxin was detected in 4% of IMFs analyzed after 14 h of storage at ≥ 25°C.