To select Lactobacillus acidophilus group bacteria as a probiotic yogurt starter, we designed a new screening method that measures the binding activity of surface layer protein to rat colonic mucin, which contains sugar chains similar to those in human colonic mucin. The B1 subgroup (Lactobacillus gasseri), which is the dominant strain in the human intestinal tract, showed the highest binding activity to rat colonic mucin among all the subgroups of L. acidophilus. The binding activity of the surface layer protein was also shown to be significantly reduced after periodate oxidation of the rat colonic mucin. This new screening method is useful for rapid selection of L. acidophilus strains that have high adhesion to the human intestinal tract. Lectin-like proteins that were bound to rat colonic mucin were isolated from the surface layer proteins with a rat colonic mucin-coated membrane and were analyzed by SDS-PAGE. A few main bands together with several minor bands were observed on the electrophoretograms obtained from the strains tested. It is possible that those lectin-like proteins contribute to adhesion of the bacterial cell to human colonic mucosa by binding specifically to carbohydrate portions.
In the mouse, L-amino acid oxidase (LAO) produces hydrogen peroxide by utilizing free amino acids and is a proven antibacterial factor in mammary glands. Mastitis, a bacterial infection of the mammary gland, is the most frequent disease in dairy cattle. Here, we investigate whether LAO is expressed in the mammary gland of dairy cattle and is antibacterial. In dairy cattle, the expression level of LAO mRNA in the mammary gland was considerably lower than that in mice, and LAO activity was not observed in cattle milk that produced hydrogen peroxide. The expression of LAO mRNA was also low in Japanese Black cattle, the same as in Holstein cattle. A higher LAO mRNA expression was observed in the mastitis glands than in the lactating glands. Furthermore, spleen and lymph nodes expressed high levels of LAO mRNA in dairy cattle. We conclude that mammary glands in dairy cattle have lower ability to express the LAO gene compared to that in mice, which may result in a high incidence of mastitis.
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