Endospore Appendages Enhance Bacillus cereus Spore Adhesion to Industrial Surfaces, Modulated by Physicochemical Factors

Spores of species belonging to the Bacillus cereus group ( B. cereus spp.) are common contaminants in food processing environments due to their ability to adhere to surfaces and resist cleaning procedures. These spores are equipped with pilus-like endospore appendages (ENAs), which are believed to promote surface adhesion. We have investigated the role of ENAs in spore adhesion to abiotic surfaces using wild-type (WT) B. cereus spp. strains and isogenic mutants lacking ENAs or an intact exosporium. WT spores expressing both short and long ENAs (S+L+) adhered significantly more to stainless steel (SS) and polypropylene (PP) compared to bald spores (S–L–) and spores of an exosporium-deficient mutant (Δ exsY ), while adhesion to polystyrene (PS) and glass was not significantly affected by the presence of ENAs. The Δ exsY mutant showed the lowest adhesion across all tested surfaces, a pattern also observed for vegetative cells. The individual roles of S-ENA and L-ENA were also assessed, where the strongest adhesion occurred when both fibers were present on PP. A trend also emerged on PP; WT remained adhered for an hour, while bald spores tended to detach within that time. For saline conditions and pH, bald spores adhered strongly to SS, while for non-ionic surfactant and concentrated protein solutions, WT spores exhibited the strongest adhesion. These results highlight the crucial role of ENAs in B. cereus spp. spore adhesion to industrial relevant surfaces, providing mechanistic insight into spore persistence. This understanding supports the design of surface treatments to prevent contamination, spoilage, and foodborne illness.