A genus of bacteria commonly found in the vagina, mouth, and gastrointestinal tract. There are over 180 distinct species of Lactobacillus, and all of the species can live with or without oxygen.

Lactobacillus plays an important role in vaginal health, as it converts sugars into lactic acid. This process can affect pH levels in the vagina, which can decrease the chances of an infection—a health pH limits the growth of Candida albicans, the fungi that causes yeast infections, along with other potentially harmful microorganisms.