Potential probiotic lactic acid bacteria Lactobacillus rhamnosus (HN001), Lactobacillus acidophilus (HN017) and Bifidobacterium lactis (HN019) do not degrade gastric mucin in vitro

The mucus layer (mucin) coating the surface of the gastrointestinal tract (GIT) plays an important role in the mucosal barrier system. Any damage or disturbance of this mucin layer will compromise the host's mucosal defence function. In the present study, the ability of three potential probiotic lactic acid bacteria (LAB) strains (Lactobacillus rhamnosus HN001, Lactobacillus acidophilus HN017, Bifidobacterium lactis HN019) to degrade mucin in vitro was evaluated, in order to assess their potential pathogenicity and local toxicity. The LAB strains were incubated in medium containing hog gastric mucin (HGM, 0.3%) at 37 degrees C for 48 h, following which any decrease in carbohydrate and protein concentration in the ethanol-precipitated portion of the culture medium was determined, using phenol-sulphuric acid and bicinchonic acid (BCA) protein assays, respectively. The change in molecular weight of mucin glycoproteins, following incubation with the test strains, was monitored by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). In order to expose any ability of the test strains to degrade mucin visually and more directly, the test strains were also cultured on agarose containing 0.3% HGM and incubated anaerobically for 72 h at 37 degrees C. No significant change in the carbohydrate or protein concentration in mucin substrates was found following incubation with the test strains. No mucin fragments were derived from the mucin suspension incubated with test strains, and no mucinolysis zone was identified on agarose. These results demonstrate that the potential probiotic LAB strains tested here were unable to degrade gastrointestinal mucin in vitro, which suggests that these novel probiotic candidates are likely to be non-invasive and non-toxic at the mucosal interface.