In vitro interaction between Bacillus megaterium strains and Caco-2 cells

Abstract

To further our understanding of the virulence potential of Bacillus megaterium strains, cell association and invasion assays were conducted in vitro by infecting human enterocytes (Caco-2 cells) with 53 strains of this bacterium isolated from honey. Two series of experiments were performed: (i) necrosis and cell detachment assays with the supernatants of bacterial culture fi ltrates from 16-h cultures and (ii) adhesion/invasion assays in which cultured enterocytes incubated with bacteria from 3-h cultures were resuspended in Dulbecco’s modifi ed Eagle’s medium and chloramphenicol. The detachment of Caco-2 cells was evaluated by staining the cells with crystal violet. Necrosis was assessed by fl uorescence microscopy of cells labeled with propidium iodide. Association (adhesion plus invasion) was determined by plate counts and invasion in an aminoglycoside protection assay. The results showed that spent culture supernatants detached and necrotized Caco-2 cells in a strain-dependent manner. Seven out of 53 B. megaterium fi ltered culture supernatants caused complete cell detachment. Suspensions of these same bacterial strains adhered and invaded enterocytes in 2-h infection experiments. To our knowledge, this is the fi rst report on the interaction between B. megaterium and intestinal epithelial Caco-2 cells.