Biofilm Production and Persistence on Table Eggshells by the Bacillus pacificus B630 Strain—A Pilot Study

In this study, we evaluated the biofilm-forming capacity of the B. pacificus B630 strain on table eggshells and its behavior in the presence of egg components, in comparison with B. cereus ATCC 14579. Strain B630, previously characterized as nhe+ and cytK+ and as a strong biofilm producer on glass, was confirmed as motile and positive for protease and phospholipase production. In static assays on disinfected eggshell pieces, B630 formed significantly more biofilm than ATCC 14579, while both strains exhibited comparable numbers of vegetative cells and spores embedded in the biofilm. Scanning electron microscopy and Fourier transform infrared (FT-IR) analysis revealed a dense extracellular matrix, altered eggshell crystal morphology, and a reduction in calcite-associated bands in biofilm-positive shells. In brain–heart infusion (BHI) broth supplemented with egg white, growth and spore germination of ATCC 14579 were strongly inhibited, whereas B630 displayed markedly higher tolerance. In an eggshell contamination model with an initial inoculum of 1 × 105 colony-forming units, B630 persisted on the shell for at least 15 days at room temperature, while neither strain was recovered from egg white or yolk. These findings indicate that B. pacificus B630 combines robust biofilm formation with enhanced tolerance to egg white, favoring prolonged persistence on eggshells and underscoring the potential role of highly biofilm-forming B. cereus s.l. strains in table egg contamination. The persistence of strains of the B. cereus s.l. group in the eggshell may compromise the safety of the product.