The role of S-layer in adhesive and immunomodulating properties of probiotic starter culture Lactobacillus brevis D6 isolated from artisanal smoked fresh cheese

An autochthonous strain isolated from traditionally produced smoked fresh cheese, Lactobacillus brevis D6, carries a 45-kDa S-layer protein. In this study, the functional role of S-layer proteins of L. brevis D6 was investigated to define this strain as probiotic starter culture. Presence of S-layer proteins and microencapsulation of L. brevis D6 cells in casein increased survival during freeze-drying, which is important prerequisite for exertion of probiotic properties. This strain displayed the highest autoaggregation ability among all the Lactobacillus strains tested, which was decreased by the removal of S-layer proteins using 5 M guanidine hydrochloride. The capacity of the L. brevis D6 to adhere to extracellular matrix proteins and Caco-2 intestinal epithelial cell line in vitro was assayed, where the removal of S-layer proteins negatively affected adhesion properties. Exclusion of Salmonella Typhimurium FP1 by L. brevis D6 and the survival of D6 in simulated conditions of the gastrointestinal tract, were better before removal of S-layer from the cell surface. Additionally, cytokine production in monocyte-derived dendritic cells (moDC) and moDC maturation in response to purified S-layer proteins of L. brevis D6 were determined by ELISA and FACS, respectively. Interleukin production remained unaltered, while a slight induction of TNF-α production in moDC was observed.