A genus of Gram-positive, rod-shaped bacteria that convert sugars to lactic acid. In humans, they are a significant component of the microbiome and can survive in the harsh pH conditions of the digestive and genital systems. Lactobacillus species are normally a major part of the vaginal microbiota. While receiving nutrients from their human host, Lactobacilli protect the host against certain pathogens, even helping to treat diarrhea, vaginal infections, and skin disorders such as eczema. Lactobacillus is the most common probiotic, perhaps most notable for its use in yogurt.