Study of Bacillus cereus adhesion on mucin surfaces as influenced by environmental factors

Introduction: Adhesion is an essential bacterial mechanism associated with the ability of microorganisms to persist in the gastrointestinal tract. The potency of B. cereus, an important foodborne pathogen, to adhere to the gut mucosa is a determinant of virulence. Although adhesion of B. cereus on the intestinal epithelium has been documented, the attachment to the mucus layer that overlies the epithelial cells of a healthy host can be considered an important prerequisite to the virulence process. Purpose: Here, we evaluated the capability of B. cereus to adhere to mucus covered surfaces that are encountered in the human gut. Methods: Using plates coated with mucin, we monitored the initial colonization of pathogenic B. cereus on mucin agar in vitro. The role of several environmental factors such as pH, oxygen and nutrient conditions in modulating the mucus adhesion of B. cereus was evaluated. Results: Our tests showed that not all pathogenic B. cereus strains tested could adhere well on mucin surfaces, thus adhesion is strain specific and may not be directly linked to virulence. Adhesion was not affected by the reduced oxygen availability (1.7%) prevailing in the small intestine (air with ~ 21% oxygen was used as control). Additionally, the neutral pH of the small intestine slightly improves bacterial attachment compared to that of slightly acidic conditions (pH 5.9). In terms of the nutrient conditions affecting the adhesion of B. cereus on mucin, no differences were observed between a 10% solution of peas, a carbohydrate and protein rich feed and the supernatant of a simulated small intestinal suspension. Bacterial concentration in the liquid phase above the mucin layer did not vary among the media, but in the absence of a mucin layer, Bacillus growth was differentially supported by these media. We observed that B. cereus could grow on an unidentified component present in the mucin agar, which explains why adhesion was not reduced when low nutrient media, such as diluted intestinal suspension, were used. Significance: It appears that B. cereus can adhere well on mucin surface because under all conditions tested, components present in the mucin agar resulted in growth in the liquid phase in contact with the mucus (lumen). As long as the experimental parameters do not influence the growth in the lumen, the adhesion potential of a given B. cereus strain remains unaffected