Adhesion of Bacillus Cereus Spores to Surface

Abstract

This thesis deals with the adhesion and removal of the spore forming pathogenic bacterium Bacillus cereus. The spores of Bacillus cereus are known for being hydrophobic and adhere well to other hydrophobic surfaces. The spores also possess appendages which have been suggested to promote adhesion of the spores.

To assess any relation between the appendages and hydrophobicity, spores with and without appendages were subjected to a well known hydrophobicity test. Both native and mutant spores show ed high relative hydrophobicity measured against two apolar solvents: hexadecane and hexane. The results suggest that no apparent relation exists betw een the high level of hydrophobicity and the presence of appendages and that the constituents responsible for the hydrophobicity must be located on the exosporium and/or the spore coat. Further, the results indicate that the spores possess important Lewis acid-base components where the electron donating (γθ) component is the most important.

Adhesion experiments suggest that appendages promote adhesion of Bacillus cereus spore strains NVH 74, IAM 1110 and NVH 1230-88 to stainless steel and polypropylene surfaces immersed in w aterunder static conditions. Moreover, when subjected to a cleaning procedure by a controlled variable shear force, spores of strain NVH 1230-88 without appendages were more easily removed from the stainless steel surfaces.

The relativ effect of flowrate, temperature and appendages on spore removal from stainless steel surfaces were compared. When subjecting adhering spores of Bacillus cereus strain NVH 1230-88 to cleaning flows at two temperature levels and two mean channel velocity levels, removal of the appendages gave the most significant effect on the cleaning effciency. Raising the temperature from 30 to 50 ◦C also gave a significant effect. How ever, the flow rate was not statistically significant when raising the mean channel velocit y from 1.70 to 2.84m/s.