The effect of glucose, starch, and pH on growth, enterotoxin and haemolysin production by strains of Bacillus cereus associated with food poisoning and non-gastrointestinal infection.

Brain-Heart Infusion medium, modified by (a) 1.0% w/v glucose supplement, (b) 1.0% w/v soluble starch supplement, (c) pH adjustment to 8.8 or (d) pH adjustment to 5.0, was used to investigate the influence of glucose, starch and pH on growth, enterotoxin and haemolysin production by Bacillus cereus. The four test strains selected for comparison originated from episodes of emetic-syndrome food poisoning, diarrhoeal-syndrome food poisoning, traumatic wound infection and bovine mastitis, respectively. In the presence of either glucose or starch, growth of all strains was found to be near-optimum and accompanied by enhanced enterotoxin production. However, under the moderately acid and alkaline test conditions B. cereus strains exhibited varying degrees of growth inhibition and partial repression of enterotoxin and haemolysin production. In this respect the food-poisoning isolates proved to have greater resistance to adverse pH environments than did the non-gastrointestinal infection isolates.