Lactobacillus's a genus of Gram-positive facultative anaerobic or microaerophilic bacteria. They're a major part of the lactic acid bacteria group, named as such because most of its members convert lactose and other sugars to lactic acid. They're common and usually benign. In humans they're present in the vagina and the gastrointestinal tract, where they're symbiotic and make up a small portion of the gut flora. Many species are prominent in decaying plant material. The production of lactic aci… (More on Lactobacillus)