lactobacillus
(LAK-toh-buh-SIH-lus)
A type of bacterium that makes lactic acid (a substance that is made from sugars found in milk and is also made in the body). Lactobacilli usually do not cause disease, but may cause tooth decay. They are normally found in the mouth, gastrointestinal tract, and vagina. They are being studied in the prevention of infections in patients having donor stem cell transplants and in other conditions.