Lactobacillus is a genus of gram-positive bacteria within the Lactobacillaceae family. Members of the genus are aerotolerant anaerobes or microaerophilic, rod-shaped, and do not form endospores. Until 2020, the genus Lactobacillus comprised 261 phylogenetically, ecologically, and metabolically diverse species; a taxonomic revision of the genus reassigned many former Lactobacillus species to 25 genera (see below).
Lactobacillus species constitute a significant component of the human and animal microbiota at a number of body sites, such as the digestive system and female genital system. Lactobacillus species are normally a major part of the vaginal microbiota. Lactobacillus forms biofilms in the vaginal and gut microbiota, allowing them to persist in harsh environmental conditions and maintain ample populations. Lactobacillus exhibits a mutualistic relationship with the human body, as it protects the host against potential invasions by pathogens, and in turn, the host provides a source of nutrients. Lactobacilli are among the most common probiotics found in food such as yogurt, and the bacteria are diverse in their application in maintaining well-being, by helping to treat diarrhea, vaginal infections, and skin disorders such as eczema.
Metabolism Lactobacilli are homofermentative, i.e., hexoses are metabolized by glycolysis to lactate as the major end product, or heterofermentative, i.e., hexoses are metabolized by the phosphoketolase pathway to lactate, CO2, and acetate or ethanol as major end products. Most lactobacilli are aerotolerant and some species respire if heme and menaquinone are present in the growth medium. Aerotolerance of lactobacilli is manganese-dependent and has been explored (and explained) in Lactiplantibacillus plantarum (previously Lactobacillus plantarum). Lactobacilli generally do not require iron for growth.
The Lactobacillaceae are the only family of the lactic acid bacteria (LAB) that includes homofermentative and heterofermentative organisms; in the Lactobacillaceae, homofermentative or heterofermentative metabolism is shared by all strains of a genus. Lactobacillus species are all homofermentative, do not express pyruvate formate lyase, and most species do not ferment pentoses. In L. crispatus, pentose metabolism is strain specific and acquired by lateral gene transfer.
Genomes The genomes of lactobacilli are highly variable, ranging in size from 1.2 to 4.9 Mb (megabases). Accordingly, the number of protein-coding genes ranges from 1,267 to about 4,758 genes (in Fructilactobacillus sanfranciscensis and Lentilactobacillus parakefiri, respectively). Even within a single species, there can be substantial variation. For instance, strains of L. crispatus have genome sizes ranging from 1.83 to 2.7 Mb, or 1,839 to 2,688 open reading frames. Lactobacillus contains a wealth of compound microsatellites in the coding region of the genome, which are imperfect and have variant motifs. Many lactobacilli also contain multiple plasmids. A recent study has revealed that plasmids encode the genes which are required for adaptation of lactobacilli to the given environment.
Species The genus Lactobacillus comprises the following species:
Lactobacillus acetotolerans Entani et al. 1986
Lactobacillus acidophilus (Moro 1900) Hansen and Mocquot 1970 (Approved Lists 1980)
Lactobacillus agrestimuris Afrizal et al. 2023
Lactobacillus amylolyticus Bohak et al. 1999
Lactobacillus amylovorus Nakamura 1981
Lactobacillus apis Killer et al. 2014
Lactobacillus bombicola Praet et al. 2015
Lactobacillus colini Zhang et al. 2017
Lactobacillus corticus Tohno et al. 2021
Lactobacillus crispatus (Brygoo and Aladame 195555) Moore and Holdeman 1970 (Approved Lists 1980)
Lactobacillus delbrueckii (Leichmann 1896) Beijerinck 1901 (Approved Lists 1980)
Lactobacillus equicursoris Morita et al. 2010
Lactobacillus fornicalis Dicks et al. 2000
Lactobacillus gallinarum Fujisawa et al. 1992
Lactobacillus gasseri Lauer and Kandler 1980
Lactobacillus gigeriorum Cousin et al. 2012
Lactobacillus hamsteri Mitsuoka and Fujisawa 1988
Lactobacillus helsingborgensis Olofsson et al. 2014 Lactobacillus helveticus (Orla-Jensen 1919) Bergey et al. 1925 (Approved Lists 1980)
Lactobacillus hominis Cousin et al. 2013
Lactobacillus huangpiensis Li and Gu 2022
Lactobacillus iners Falsen et al. 1999
Lactobacillus intestinalis (ex Hemme 1974) Fujisawa et al. 1990
Lactobacillus isalae Eilers et al. 2023
Lactobacillus jensenii Gasser et al. 1970 (Approved Lists 1980) Lactobacillus juensis Jiang and Gu 2024
Lactobacillus johnsonii Fujisawa et al. 1992
Lactobacillus kalixensis Roos et al. 2005
Lactobacillus kefiranofaciens Fujisawa et al. 1988
Lactobacillus kimbladii Olofsson et al. 2014
Lactobacillus kitasatonis Mukai et al. 2003
Lactobacillus kullabergensis Olofsson et al. 2014
Lactobacillus laiwuensis Li and Gu 2022 Lactobacillus leichmannii (Henneberg 1903) Bergey et al. 1923 (Approved Lists 1980)
Lactobacillus melliventris Olofsson et al. 2014
Lactobacillus mulieris Rocha et al. 2020
Lactobacillus nasalidis Suzuki-Hashido et al. 2021
Lactobacillus panisapium Wang et al. 2018
Lactobacillus paragasseri Tanizawa et al. 2018
Lactobacillus pasteurii Cousin et al. 2013
Lactobacillus porci Kim et al. 2018
Lactobacillus psittaci Lawson et al. 2001
Lactobacillus rhamnosus (Hansen 1968) Collins et al. 1989
Lactobacillus rizhaonensis Jiang and Gu 2024 Lactobacillus rodentium Killer et al. 2014 Lactobacillus rogosae Holdeman and Moore 1974 (Approved Lists 1980)
Lactobacillus taiwanensis Wang et al. 2009
Lactobacillus timonensis Afouda et al. 2017
Lactobacillus ultunensis Roos et al. 2005
Lactobacillus xujianguonis Meng et al. 2020 Lactobacillus xylocopicola Kawasaki et al. 2024
Taxonomy As of 2025, the genus Lactobacillus contains 50 validly published species which are adapted to vertebrate hosts or to insects. In recent years, other members of the genus Lactobacillus (formerly known as the Leuconostoc branch of Lactobacillus) have been reclassified into the genera Atopobium, Carnobacterium, Weissella, Oenococcus, and Leuconostoc. The Pediococcus species P. dextrinicus has been reclassified as a Lapidilactobacillus dextrinicus and most lactobacilli were assigned to Paralactobacillus or one of the 23 novel genera of the Lactobacillaceae. Two websites inform on the assignment of species to the novel genera or species (http://www.lactobacillus.uantwerpen.be/; http://www.lactobacillus.ualberta.ca/).
+The 23 New Genera of 2020GenusMeaning of the genus nameProperties of the genusLactobacillusRod-shaped bacillus from milkType species: L. delbrueckii. Homofermentative with strain-specific ability to ferment pentoses, thermophilic, vancomycin-sensitive, adapted to vertebrate or insect hosts.HolzapfeliaWilhelm Holzapfel's lactobacilliType species: H. floricola. Homofermentative, vancomycin sensitive, unknown ecology but likely host-adapted.AmylolactobacillusStarch-degrading lactobacilliType species: A. amylophilus. Homofermentative, vancomycin sensitive, extracellular amylases are frequent, unknown ecology but likely host-adapted.BombilactobacillusLactobacilli from bees and bumblebeesType species: B. mellifer. Homofermentative, thermophilic, vancomycin resistant, small genome size, adapted to bees and bumblebeesCompanilactobacillusCompanion-lactobacillus, referring to them growing in association with other lactobacilli in cereal, meat and vegetable fermentationsType species: C. alimentarius. Homofermentative with strain- or species-specific ability to ferment pentoses, vancomycin resistant, unknown ecology, likely nomadicLapidilactobacillusLactobacilli from stonesType species: L. concavus. Homofermentative with strain- or species-specific ability to ferment pentoses, vancomycin resistant, unknown ecology.AgrilactobacillusLactobacilli from fieldsType species: A. composti. Homofermentative, aerotolerant and vancomycin resistant. Genome size, G+C content of the genome and the source of the two species suggest a free-living lifestyle of the genus.SchleiferilactobacillusKarl Heinz Schleifer's lactobacilliType species: S. perolens. Homofermentative, vancomycin resistant, aerotolerant. Schleiferilactobacillus spp. have a large genome size, ferment a wide range of carbohydrates, and spoil beer and dairy products by copious production of diacetyl.Loigolactobacillus(Food) spoiling lactobacilliType species: L. coryniformis. Homofermentative, vancomycin resistant, mesophilic or psychrotrophic organisms.LacticaseibacillusLactobacilli related to cheeseType species: L. casei. Homofermentative, vancomycin resistant; many species ferment pentoses, and are resistant to oxidative stress. L. casei and related species have a nomadic lifestyle.LatilactobacillusWidespread lactobacilliType species: L. sakei. Homofermentative, mesophilic free living and environmental lactobacilli. Many strains are psychrotrophic and grow below 8 °C.DellaglioaFranco Dellaglio's lactobacilliType species: D. algida. Homofermentative, vancomycin resistant, aerotolerant and psychrophilic.LiquorilactobacillusLactobacilli from liquor or liquidsType species: L. mali. Homofermentative, vancomycin resistant, motile organisms growing in liquid, plant-associated habitats. Many liquorilactobacilli produce EPS from sucrose and degrade fructans with extracellular fructanases.LigilactobacillusUniting (host adapted) lactobacilliType species: L. salivarius. Homofermentative, vancomycin resistant, most ligilactobacilli are host adapted and many strains are motile. Several strains of Ligilactobacillus express urease to withstand gastric acidity.LactiplantibacillusLactobacilli related to plantsType species: L. plantarum. Homofermentative, vancomycin resistant organisms with a nomadic lifestyle that ferment a wide range of carbohydrates; most species metabolise phenolic acids by esterase, decarboxylase and reductase activities. L. plantarum expresses pseudocatalase and nitrate reductase activities.Furfurilactobacillus Lactobacilli from branType species: F. rossiae. Heterofermentative, vancomycin resistant, with large genome size, broad metabolic potential and unknown ecology.PaucilactobacillusLactobacilli fermenting few carbohydratesType species: P. vaccinostercus. Heterofermentative, vancomycin resistant, mesophilic or psychrotrophic, aerotolerant, most strains ferment pentoses but not disaccharides.LimosilactobacillusSlimy (biofilm-forming) lactobacilliType species: L. fermentum. Heterofermentative, thermophilic, vancomycin resistant with two exceptions, Limosilactobacillus species are vertebrate host adapted and generally form exopolysaccharides from sucrose to support biofilm formation in the upper intestine of animals.FructilactobacillusFructose-loving lactobacilliType species: F. fructivorans. Heterofermentative, vancomycin resistant, mesophilic, aerotolerant, small genome size. Fructilactobacilli are adapted to narrow ecological niches that relate to insects, flowers, or both.AcetilactobacillusLactobacilli from vinegarType species: A. jinshani. Heterofermentative, vancomycin resistant, grow in the pH range of 3–5; fermenting disaccharides and sugar alcohols but few hexoses and no pentoses.ApilactobacillusLactobacilli from beesType species: A. kunkeei. Heterofermentative, vancomycin resistant, small genome size, fermenting only few carbohydrates, adapted to bees and/or flowers.Levilactobacillus(Dough)-leavening lactobacilliType species: L. brevis. Heterofermentative, vancomycin resistant, mesophilic or psychrotrophic, metabolise agmatine, environmental or plant-associated lifestyle.SecundilactobacillusSecond lactobacilli, growing after other organisms depleted hexosesType species: S. collinoides.