Simulating Intestinal Growth Conditions Enhances Toxin Production of Enteropathogenic Bacillus cereus

Abstract

Bacillus cereus is a ubiquitous bacterial pathogen increasingly reported to be the causative agent of foodborne infections and intoxications. Since the enterotoxins linked to the diarrheal form of food poising are foremost produced in the human intestine, the toxic potential of enteropathogenic B. cereus strains is difficult to predict from studies carried out under routine cultivation procedures. In this study, toxigenic properties of a panel of strains (n = 19) of diverse origin were compared using cell culture medium pre-incubated with CaCo-2 cells to mimic intestinal growth conditions. Shortly after contact of the bacteria with the simulated host environment, enterotoxin gene expression was activated and total protein secretion of all strains was accelerated. Although the signal stimulating enterotoxin production still needs to be elucidated, it could be shown that it originated from the CaCo-2 cells. Overall, our study demonstrates that the currently used methods in B. cereus diagnostics, based on standard culture medium, are not allowing a conclusive prediction of the potential health risk related to a certain strain. Thus, these methods should be complemented by cultivation procedures that are simulating intestinal host conditions.

Porcine Gastric Mucin Triggers Toxin Production of Enteropathogenic Bacillus cereus

“…In this study, the B. cereus strains F837/76 (DSM 4222), F528/95, SDA KA 96, INRA A3, INRA C3, WSBC 10035, 6/27/S, NVH 0075-95, MHI 226, and emetic F4810/72 (AH187) were used. Enterotoxin production of most strains under standard laboratory and simulated intestinal conditions has been characterized in detail in earlier studies (25,26). Overnight cultures were grown in CGY (casein-glucose-yeast) medium with 1% glucose at 32°C under continuous agitation (24).…”

“…So far, adhesion (23) as well as toxicity studies (24,25) have been performed only with cell lines, neglecting the possible role of mucus in the gut. Recently, we showed that incubation of enteropathogenic B. cereus under simulated intestinal conditions results in increased enterotoxin gene expression and enhanced toxin production (26). The mucus layer was not considered.…”

“…Enterotoxin components NheB and Hbl L2 were detected in culture supernatants after 6 h of incubation in minimal medium with 0.25% PGM. Toxin production of these strains under standard and simulated intestinal conditions has already been well investigated(25,26).…”

Evidence for Complex Formation of the Bacillus cereus Haemolysin BL Components in Solution

“…They were pre-mixed in appropriate ratios and added in 1:40 dilutions to the cells. Propidium iodide (PI) influx tests were performed as described before [ 33 , 49 ]. WST-1 bioassays were carried out as previously described [ 20 , 32 , 49 ].…”

Potential Enterotoxicity of Phylogenetically Diverse Bacillus cereus Sensu Lato Soil Isolates from Different Geographical Locations

“…Lack of a statistically significant relationship between gene expression and cell viability suggests that many genetic determinants can play important role in B. cereus diarrhoea. Naturally, the diarrhoeal syndrome can be caused simultaneously by a number of different toxins, such as non-haemolytic enterotoxin NHE, haemolysin II, haemolysin III, phospholipases, and various proteases [3,49].…”