Abstract

Enterotoxinproduction of Bacillus cereus under simulated intestinal conditions Bacillus cereus is an important food-borne pathogen. Enteropathogenic B. cereus produce enterotoxins in the humane intestine after ingestion of contaminated food and cause diarrhea. The most important enterotoxins are the nonhemolytic enterotoxin (Nhe) and the hemolysin BL (HBL) each consisting of three components. The toxic potential of B. cereus depends on the amount of produced enterotoxins and cannot be determined by simple detection of the toxin genes. We analyzed enterotoxin production and the cytotoxic potential of 19 B. cereus strains associated with food and food-borne diseases with different toxin gene profiles and different toxin expression levels both under simulated intestinal and laboratory conditions. The growth rates of all analyzed strains were reduced under simulated intestinal conditions. The highest enterotoxin titers, determined by EIA with specific monoclonal antibodies, were detected after 6 h under laboratory conditions and were strain-dependent. In contrast, the Toxin production efficiency (enterotoxintiter in relation to growth) was highest after 4 h under simulated intestinal conditions. Enhanced toxin production of all strains was observed after 2 h under simulated intestinal conditions in comparison to laboratory conditions and was caused by so far unknown factors secreted by the Caco-2-cells. The cytotoxic activity after 6 h was determined in WST-1-bioassays using Vero- and Caco-2-cells. The cytotoxicity titers were strain-dependent, dependent on enterotoxin titers and reduced under simulated intestinal conditions. In the latter, discrimination between high and low toxic strains was less distinct. PI influx in Caco-2-cells was mainly dependent on HBL, not Nhe. It was also shown that the enterotoxins were secreted completely by all B. cereus strains and that a possible defect in the secretion mechanism is not the reason for the highly variable amounts of enterotoxins. The results of this work show that cultivation under laboratory and simulated intestinal conditions cause differences in growth rate, enterotoxin production and cytotoxicity. So far unknown factors secreted by Caco-2-cells enhance enterotoxin production of B. cereus.