Survival of Bacillus cereus in the upper part of the gastrointestinal tract

摘要

The Bacillus cereus species of bacteria is commonly found in the environment, as well as in raw materials and foodstuffs. It may cause outbreaks of food-borne infections in humans. The course of the infection can be twofold: it can either take the form of intoxication caused by ingestion of food containing B. cereus emetic toxin (cereulide) - or toxicoinfection, resulting from the presence of enterotoxic B. cereus strains in food which produce diarrheal type of toxins in the small intestine.The ability of B. cereus to adapt to certain stress conditions, such as low pH, can influence their survival in the gastrointestinal tract, mainly the stomach. These bacteria can initially adapt to low pH in the course of food production or in the original environment of their occurrence, i.e. in the soil. This behavior leads to a higher acid resistance of the cells and, consequently, in the case of contaminated food ingestion, it may facilitate the transit of the pathogen to the upper gastrointestinal tract.The article discusses various aspects of B. cereus survival inside the human gastrointestinal tract, paying special attention to its upper part. The issues of B. cereus capacity to counter adverse environmental conditions inside the human stomach, as well as the so called cross-resistance of the bacteria have been elucidated. The following factors have been taken into consideration: the biological state of bacteria (vegetative or spore form), growth temperature profile, phases of vegetative cell growth, as well as the possible prior exposure of the bacteria to low pH. The influence of these factors on the resistance of B. cereus spores and vegetative forms to high acidity has been examined. Finally, the effect of digestive enzymes (pepsin) on the survival of B. cereus spores and vegetative forms in the medium simulating the human stomach environment have been analyzed.