Kefiran antagonizes cytopathic effects of Bacillus cereus extracellular factors.

Kefiran, the polysaccharide produced by microorganisms present in kefir grains, is a water-soluble branched glucogalactan containing equal amounts of D-glucose and D-galactose. In this study, the effect of kefiran on the biological activity of Bacillus cereus strain B10502 extracellular factors was assessed by using cultured human enterocytes (Caco-2 cells) and human erythrocytes. In the presence of kefiran concentrations ranging from 300 to 1000 mg/L, the ability of B. cereus B10502 spent culture supernatants to detach and damage cultured human enterocytes was significantly abrogated. In addition, mitochondrial dehydrogenase activity was higher when kefiran was present during the cell toxicity assays. Protection was also demonstrated in hemolysis and apoptosis/necrosis assays. Scanning electron microscopy showed the protective effect of kefiran against structural cell damages produced by factors synthesized by B. cereus strain B10502. Protective effect of kefiran depended on strain of B. cereus. Our findings demonstrate the ability of kefiran to antagonize key events of B. cereus B10502 virulence. This property, although strain-specific, gives new perspectives for the role of bacterial exopolysaccharides in functional foods.