Survival and Germination of Bacillus cereus Spores without Outgrowth or Enterotoxin Production duringIn VitroSimulation of Gastrointestinal Transit

Abstract

ABSTRACTTo study the gastrointestinal survival and enterotoxin production of the food-borne pathogenBacillus cereus, anin vitrosimulation experiment was developed to mimic gastrointestinal passage in 5 phases: (i) the mouth, (ii) the stomach, with gradual pH decrease and fractional emptying, (iii) the duodenum, with high concentrations of bile and digestive enzymes, (iv) dialysis to ensure bile reabsorption, and (v) the ileum, with competing human intestinal bacteria. Four differentB. cereusstrains were cultivated and sporulated in mashed potato medium to obtain an inoculum of 7.0 log spores/ml. The spores showed survival and germination during thein vitrosimulation of gastrointestinal passage, but vegetative outgrowth of the spores was suppressed by the intestinal bacteria during the final ileum phase. No bacterial proliferation or enterotoxin production was observed, despite the high inoculum levels. Little strain variability was observed: except for the psychrotrophic food isolate, the spores of all strains survived well throughout the gastrointestinal passage. Thein vitrosimulation experiments investigated the survival and enterotoxin production ofB. cereusin the gastrointestinal lumen. The results obtained support the hypothesis that localized interaction ofB. cereuswith the host's epithelium is required for diarrheal food poisoning.