QUANTIFICATION AND BEHAVIORAL CHARACTERIZATION OF BACILLUS-CEREUS IN FORMULATED INFANT FOODS .1. GENERATION TIME

The ability of Bacillus cereus to grow in three different types of rec onstituted formulated food, and the growth rates of the bacterium in e ach food, were investigated. The foods tested were: caramel-flavored p orridge, chocolate-flavored porridge and bean soup with noodles, all o f which are commonly served in public institutions. Generation times ( gt) were measured at 25-degrees-C, and 45-degrees-C, both for B. cereu s that were naturally present in the products and for B. cereus that h ad been inoculated in the form of B. cereus NCTC2599 spores into steri lized and unsterilized food. The gt values were calculated from growth curves obtained by counting colony formation units (CFU) on selective indicator-agar medium (MYP). Intrinsic microflora were not observed t o have an deleterious effect on the growth of B. cereus NCTC 2599 in a ny of the experiments at the indicated temperatures. In experiments us ing both caramel and chocolate-flavored porridge, naturally occurring B. cereus displayed similar characteristic to B. cereus that were inoc ulated, and where incubation temperatures were found to have a signifi cant effect on growth rates: mean generation times of 54.20,31.30 and 56.00 minutes were recorded at temperatures of 25-degrees-C, 35-degree s-C and 45-degrees-C, respectively. Our results demonstrate that B. ce reus is able to multiply rapidly in all three foods, especially in bea n soup with noodles, at temperatures around 35-degrees-C, in the prese nce or absence of indigenous microorganisms. We conclude that care sho uld be taken to observe basic hygiene practices during the preparation (rehydration) and consumption of these products, especially with rega rd to storage times and temperatures.