Bacillus Cereus. Adhesion Ability to Biological and Non-Biological Surfaces, Enterotoxins, Characterization
The organism investigated in this thesis was Bacillus cereus, which is important as a food spoilage organism and as a pathogen. The adhesion of endospores to and the removal of endospores from siliconized glass surfaces were investigated to increase the knowledge of adhesion mechanisms and to improve the removal of endospores from surfaces. The most adhesive spores were the most hydrophobic and had the longest appendages situated on the spore surface. Dormant and heat-activated spores had the same adhesion ability, whereas the adhesion ability of germinated spores were significantly less. By germinating the spores, the removal was increased significantly. Therefore this work suggests that cleaning processes should consider factors that boost spore germination in order to improve the cleaning.
The adhesion of endospores to Caco-2 cells in vitro was also investigated. There have been food poisoning outbreaks with much more severe symptoms than normal B. cereus food poisoning. These outbreaks have the late onset of the symptoms in common. An explanation for the more severe symptoms could be adhesion of spores to the epithelium, growth and enterotoxin production in situ. The endospores from food poisoning strains involved in more severe foodborne outbreaks did adhere more to the Caco-2 cells in vitro compared to endospores from strains involved in outbreaks with milder symptoms.
Further, B. cereus strains isolated from dairy products, foodborne outbreaks and other sources were examined for their production of different enterotoxins. Of all the examined strains, 74% were cytotoxic to Vero cells. However, only 53% of the cytotoxic strains were positive for the B-component gene of the haemolysin BL, the protein complex considered to cause the enterotoxicity. Closer examination of strains involved in food poisoning showed that some of these strains also lacked proteins in the haemolysin BL complex and haemolysin BL was therefore not the cause of the food poisoning. From these results it was concluded that there is at least one enterotoxin complex in addition to the haemolysin BL.
The ability to discriminate B. cereus strains was compared for RiboPrintero/oo Microbial Characterization System and Random Amplified Polymorphic DNA, RAPD. It was concluded that RAPD-typing was only slightly more discriminatory than Automatic Ribotyping. Therefore Automatic Ribotyping proved to be a useful, standardized and quick method to discriminate between B. cereus strains. Further, it is shown that it is possible to make fairly good predictions of the enterotoxicity by correlating the enterotoxin production with the ribotype patterns using Partial Least Square Analysis.