Abstract EN:

Bacillus cereus is an opportunistic pathogen frequently associated with food poisoning and involved in rare but severe local or systemic infections. Contamination of food industry products by B. Cereus can result in economical injuries and might raise safety concerns. The capacity of B. Cereus to form biofilm on different surfaces increases its persistence in the food industry equipments. Here, we have determined the dynamics of biofilm formation by B. Cereus and the roles played by flagella and flagellar motility in B. Ce reus biofilm formation in different growth conditions. We have shown that, in static cultures runned in glass tubes or in microtiter plates, flagellar motility is required for biofilm formation. Motility was necessary for the bacteria to have access to the air-liquid interface where the biofilm develops. Flagellar motility was also involved in the recruitment of planktonic bacteria by the biofilm and promoted biofilm expansion on the colonized surface. We found that B. Cereus is able to form immersed biofilms in continuous flow conditions in flow­cells. However, in these growth conditions, flagellar motility was not required for biofilm formation. Observation of biofilms by confocal microscopy have shown the presence of a subpopulation of bacteria able to move through the different biofilm. The speed of these mobile bacteria could reach values up to approximately 16 μm/s. This speed decreased when the biofilm became older and mature, probably as a consequence of an increase in the exopolysaccharide matrix density. Finally, we demonstrated that flagellar mobility was involved in the bacterium pathogenicity in an isect model. In this model, larvae of the wax moth Galleria mellonela was infected by the oral route. Motility, but not the simple presence of flagella, promoted adhesion of bacteria on epithelial HeLa cells.