Variability among Bacillus cereus strains in spore surface properties and influence on their ability to contaminate food surface equipment

Seven strains of Bacillus cereus isolated from the environment and from patients with diarrheic symptoms were examined from two angles: their spore surface properties, and their ability to adhere to stainless steel and to resist a cleaning in place (CIP) procedure. Our results revealed significant differences in their morphology (size of exosporium, length and number of appendages), hydrophobic character and surface protein composition. Most of these proteins originated in the vegetative cell and were tightly bound to the external surface of the exosporium such as EA1 or alanine racemase. Spore adhesion properties also varied from strain to strain. The ability to adhere was higher when spores were surrounded by long appendages, while the largest spores displayed the least resistance to cleaning. These observations suggest that food processing line contamination might be due to a given type of strain with specific surface properties (long appendages and small exosporium), which would represent an increased threat under the milder processing conditions required by consumers (minimally heat-treated foods for example) and by legal requirements (to limit effluents caused by hygiene procedures). Elsewhere, no clear relationship of the strain characteristics to the clinical vs. foodborne strains could be established.