Lactobacilli

Lactobacilli are a group of bacteria within the lactic acid bacteria, comprising species primarily in the genus Lactobacillus. They are Gram-positive, non-spore-forming rods that are typically facultative anaerobes or microaerophiles. Most are fermentative, converting carbohydrates to lactic acid, which lowers pH and inhibits many spoilage organisms.

They are common members of the human microbiota, found in the oral cavity, gastrointestinal tract, and vagina, and they occur on plant surfaces and in a wide range of fermented foods. Many species tolerate acidic and bile-rich conditions, helping them persist in the gut. Lactobacilli can be homofermentative, producing lactic acid as the main product, or heterofermentative, producing lactic acid along with ethanol or acetic acid and carbon dioxide.

Lactobacilli play important roles in food production and health. They are widely used as starter cultures in dairy and vegetable fermentation and as probiotics in dietary supplements. Some strains are associated with digestive health, immune modulation, and competition with pathogens through acidification and the production of bacteriocins. They are generally regarded as safe for food use, though rare cases of infection have been reported in severely immunocompromised individuals.

Taxonomic changes have affected the conventional grouping of Lactobacillus species. The genus has been revised, with many species reassigned to several new genera. The term lactobacilli is often used to refer collectively to these bacteria, though strict classification may place different species in related genera such as Lactiplantibacillus, Lacticaseibacillus, Levilactobacillus, or Limosilactobacillus. Notable species include L. acidophilus, L. plantarum, L. casei, L. rhamnosus, and L. delbrueckii subsp. bulgaricus.