P-065. Spore Appendages of the Toxigenic B. cereus Group

R. Labbe, A. Sayedahmed;
Univ. of Massachusetts, Amherst, MA.

Members of the Bacillus cereus group have been implicated in foodborne disease outbreaks especially in Europe and Japan. Spores of B. cereus isolates from spoiled food products, environmental samples, and food processing surfaces possess appendage-like structures of uncertain function. We wished to determine whether toxigenic species of the B. cereus group also possessed these structures. Spores of sixty foodborne B. cereus isolates, 13 food-poisoning B. cereus isolates and 11 foodborne Bacillus thuringiensis isolates were examined. PCR was used to determine the emetic and enterotoxigenic potential of isolates. Enterotoxin-producing ability of the B. cereus and B. thuringiensis isolates was confirmed by commercial assay kits. The presence of spore appendages was determined by examination of spores on carbon-coated collodion-filmed grids by negative staining with uranyl acetate or shadowed with carbon-palladium. Thread-like appendages on the spore surface were visible on all B. cereus spores examined and on 8 of 11 foodborne isolates of B. thuringiensis. The lengths of appendages varied 0.45 µm to 3.8 µm. Appendages arose randomly from the spore surface but were mostly associated with polar ends where multiple appendages passed through the exosporium. The length and appearance of appendages of both species appeared similar. The results confirm the enterotoxigenic potential of B. thuringiensis. The role of spore appendages of the B. cereus group is unclear. Together with hydrophobicity of the spore surface they may be involved with binding to inanimate surfaces. In view of the current concepts regarding B. cereus mode of action during foodborne illness they are unlikely to be associated with in vivo binding of intestinal mucosa as in the case of pili of certain gram-negative pathogens.