Lactobacillus acidophilus

Figure 1. An electron micrograph of Lactobacillus acidophilus.

Lactobacillus acidophilus is a species of gram-positive bacteria in the genus Lactobacillus. Lactobacillus acidophilus ferments sugars into lactic acid and grows readily at low/acidic pH values (usually below pH 5.0). Lactobacillus acidophilus is found in the human gastrointestinal tract, mouth, and vagina. It is also one of the most common types of probiotics and can be found in fermented foods, yogurt and dietary supplements. Lactobacillus acidophilus is one of many species of bacteria in the family Lactobacillaceae (or "rod shaped" bacteria). 

Lactobacillus acidophilus produces the enzyme Lactase, which breaks down sugars into lactic acid. As such, probiotic supplements with Lactobacillus acidophilus are often taken to help with lactose intolerance in the human body.

Like other probiotics, Lactobacillus acidophilus is considered a "good" bacteria and important for a healthy gut flora. Lactobacillus acidophilus helps fight off "bad" bacteria that might cause diseases, such as irritable bowel syndrome, hence taken as a supplement to aid digestive health.

Outside of the gut, Lactobacillus acidophilus is also used to stave off an overgrowth of "bad" bacteria in the vagina such as Helicobacter pylori which may cause infections.

For nutritional values, refer to the Codex entry for Probiotic.