No abstract

Enteropathogenic Bacillus cereus causes foodborne infections due to the production of pore-forming enterotoxins in the intestine. Before that, spores have to be ingested, survive the stomach passage, and germinate. Thus, before reaching epithelial cells, B. cereus comes in contact with the intestinal mucus layer. In the present study, different aspects of this interaction were analyzed. Total RNA sequencing revealed major transcriptional changes of B. cereus strain F837/76 upon incubation with porcine gastric mucin (PGM), comprising genes encoding enterotoxins and further putative virulence factors, as well as proteins involved in adhesion to and degradation of mucin. Indeed, PGM was partially degraded by B. cereus via secreted, EDTA-sensitive proteases. The amount of enterotoxins detectable in culture media supplemented with PGM was also clearly increased. Tests of further strains revealed that enhancement of enterotoxin production upon contact with PGM is broadly distributed among B. cereus strains. Interestingly, evidence was found that PGM can also strain-specifically trigger germination of B. cereus spores and that vegetative cells actively move toward mucin. Overall, our data suggest that B. cereus is well adapted to the host environment due to massive transcriptome changes upon contact with PGM, attributing mucin an important and, thus far, neglected role in pathogenesis.M ucus is a highly complex viscous substance that covers gastrointestinal cells.Besides salts, lipids, and several proteins involved in defense mechanisms, it consists mainly of water (approximately 95%) and the glycoprotein mucin (1, 2). A large number of different mucins has been discovered. These can be divided into membranebound and secretory mucins, which form the mucus layers (3, 4). Mucins have a molecular weight of 0.5 to 20 MDa and consist of ϳ20% proteins and ϳ80% carbohydrates (1). The protein core is organized in tandem repeats of serine-, threonine-, and proline-rich regions, which are mostly O-glycosylated. At the C and N termini, large amounts of cysteine are found. The carbohydrates include N-acetylgalactosamine, N-acetylglucosamine, N-acetylneuraminic acid, fucose, galactose, and mannose. Mucin monomers dimerize and multimerize via disulfide bonds (1).Mucus functions as a lubricant in the gastrointestinal tract, facilitating the passage of food. It is also important for growth, adhesion, and protection of the intestinal microbiota (2). Furthermore, it represents a biophysical barrier between epithelial cells and the environment, including chemical and mechanical insults as well as the commensal microbiota and pathogens (2,5,6). The mucus layer is a reservoir for many antimicrobial molecules, and various mucin oligosaccharides themselves show antimicrobial activity (5). By adhesion to mucin oligosaccharides, pathogens are trapped and removed due to the constant renewal of the mucus layer (5, 6). Cell surface-bound mucins can even initiate intracellular signaling in response to bacteria (5).On the other hand, pathogens, espe...

Enteropathogenic Bacillus cereus cause diarrhea due to the production of enterotoxins in the intestine. To start this process, spores have to be ingested together with contaminated food and survive the stomach passage. In this study, the influence of consumed foodstuffs on spore survival as well as on cytotoxicity toward colon epithelial cells was investigated. Spore survival of 20 enteropathogenic and apathogenic B. cereus strains during simulated stomach passage was highly strain-specific and did not correlate with the toxic potential. Survival of three tested strains was strain-specifically altered by milk products. Whereas milk, a follow-on formula and rice pudding had only little influence, spores seemed to be protected by milk products with high fat content such as whipped cream and mascarpone. Furthermore, tested milk products decreased the toxic activity of three B. cereus strains toward CaCo-2 cells. Investigating the individual components, lactoferrin, a skim milk powder and vitamins C, B5 and A showed the most inhibiting effects. On the other hand, biotin, vitamin B3 and another skim milk powder even enhanced cytotoxicity. Further studies suggested that these inhibiting effects result only partially from inhibiting cell binding, but rather from blocking the interaction between the single enterotoxin components.