Lactobacilli are a family of immobile, gram-positive, sporeless rod-shaped bacteria that can ferment glucose to lactic acid. They belong to the order of lactic acid bacteria (Lactobacillales), which includes other families.
Lactobacilli are catalase- and oxidase-negative. Most representatives of the family Lactobacillaceae tolerate only a low oxygen content in their environment and are therefore also called microaerophilic. Some species are obligate anaerobes. A special feature of lactobacilli is the formation of bacteriocins. These are proteins or peptides that have a toxic effect on competing bacterial species or hinder their growth. Bacteriocins produced by lactobacilli include lactacin-F and bavaricin-A.
Lactobacilli are commensal inhabitants of the animal and human gastrointestinal tracts as well as the human mouth and vagina. Commercial preparations of lactobacilli are used as probiotics, e.g. to restore normal flora after an imbalance caused by antibiotic therapy.