Abstract: A strain of lactic acid bacteria was isolated from fresh milk by plate streaking method. The isolated strain was named as M8, which was rich in S-layer protein according to sodium dodecyl sulfonate polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The strain was identified as the species of Lactobacillus brevis via morphological observation, physiological and biochemical characteristics, and phylogenetic analysis of 16S rRNA sequences. Its excellent tolerance was found during sequential suspension at 37 ℃ in a mimic gastric juice (pH 2.5) containing pepsin (3 g/L) and citric acid-phosphate buffer (100 mmol/L) and then in a mimic small intestinal juice (pH 8.0) containing trypsin (10 g/L) and Tris-HCl buffer (25 mmol/L). Therefore, S-layer protein may function as a protective barrier and resist the invasion of digestive enzymes.

Key words: lactic acid bacteria, S-layer protein, digestive enzyme, tolerance