Acidity levels of below pH 4.0 inhibit lactobacilli and favour acid-tolerant yeasts. Healthy, normal vaginal microbiota that is dominated by lactobacilli may differ among some ethnic groups. Historically, the difference between "Lactobacillus paracasei" and other "lactobacilli" has been based on biochemical characteristics. Galacto-oligosaccharides are a substrate for bacteria, such as bifidobacteria and lactobacilli. It also occurs in some kinds of bacteria (such as lactobacilli) and some fungi. Sourdough bread is made by the fermentation of dough using naturally occurring lactobacilli and yeast. Estrogen, glycogen and lactobacilli impact these levels. In addition, other lactobacilli and bifidobacteria are sometimes added during or after culturing yogurt. Therefore, the predominance of lactobacilli in the vaginal canal creates a more acidic environment. Drying the vagina also removes the natural antiseptic lactobacilli which combat sexually transmitted diseases. Other lactobacilli found in the vagina are "L. jensenii, L. delbruekii" and "L. gasseri". Claims that some lactobacilli may contribute to weight gain in some humans remain controversial. Typically, bacteria other than "Lactobacilli" become more common. As "B. bifidum" decreases, other gut bacteria such as "Lactobacilli", "Enterococci", "Enterobacteria" and "Clostridia" increase. It is a potential basis for Low-Copy-Number vectors in Lactobacilli.