Lactobacillus

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.
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. ILactobacillus species are normally a major part of the microbiota species of the lower reproductive tract of women|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 in Lactiplantibacillus plantarum ''. Lactobacilli generally do not require iron for growth.
The Lactobacillaceae are the only family of the lactic acid bacteria 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. Accordingly, the number of protein-coding genes ranges from 1,267 to about 4,758 genes. 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. 1986Lactobacillus acidophilus Hansen and Mocquot 1970 Lactobacillus agrestimuris Afrizal et al. 2023Lactobacillus amylolyticus Bohak et al. 1999Lactobacillus amylovorus Nakamura 1981Lactobacillus apis Killer et al. 2014Lactobacillus bombicola Praet et al. 2015Lactobacillus colini Zhang et al. 2017Lactobacillus corticus Tohno et al. 2021Lactobacillus crispatus Moore and Holdeman 1970 Lactobacillus delbrueckii Beijerinck 1901 Lactobacillus equicursoris Morita et al. 2010Lactobacillus fornicalis Dicks et al. 2000Lactobacillus gallinarum Fujisawa et al. 1992Lactobacillus gasseri Lauer and Kandler 1980Lactobacillus gigeriorum Cousin et al. 2012Lactobacillus hamsteri Mitsuoka and Fujisawa 1988Lactobacillus helsingborgensis Olofsson et al. 2014Lactobacillus helveticus Bergey et al. 1925 Lactobacillus hominis Cousin et al. 2013Lactobacillus huangpiensis Li and Gu 2022Lactobacillus iners Falsen et al. 1999Lactobacillus intestinalis Fujisawa et al. 1990Lactobacillus isalae Eilers et al. 2023Lactobacillus jensenii Gasser et al. 1970 Lactobacillus juensis Jiang and Gu 2024Lactobacillus johnsonii Fujisawa et al. 1992Lactobacillus kalixensis Roos et al. 2005Lactobacillus kefiranofaciens Fujisawa et al. 1988Lactobacillus kimbladii Olofsson et al. 2014Lactobacillus kitasatonis Mukai et al. 2003Lactobacillus kullabergensis Olofsson et al. 2014Lactobacillus laiwuensis Li and Gu 2022Lactobacillus leichmannii Bergey et al. 1923 Lactobacillus melliventris Olofsson et al. 2014Lactobacillus mulieris Rocha et al. 2020Lactobacillus nasalidis Suzuki-Hashido et al. 2021Lactobacillus panisapium Wang et al. 2018Lactobacillus paragasseri Tanizawa et al. 2018Lactobacillus pasteurii Cousin et al. 2013Lactobacillus porci Kim et al. 2018Lactobacillus psittaci Lawson et al. 2001Lactobacillus rhamnosus Collins et al. 1989Lactobacillus rizhaonensis Jiang and Gu 2024Lactobacillus rodentium Killer et al. 2014Lactobacillus rogosae Holdeman and Moore 1974 Lactobacillus taiwanensis Wang et al. 2009Lactobacillus timonensis Afouda et al. 2017Lactobacillus ultunensis Roos et al. 2005Lactobacillus xujianguonis Meng et al. 2020Lactobacillus 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 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.

Genus	Meaning of the genus name	Properties of the genus
Lactobacillus	Rod-shaped bacillus from milk	Type species: L. delbrueckii. Homofermentative with strain-specific ability to ferment pentoses, thermophilic, vancomycin-sensitive, adapted to vertebrate or insect hosts.
Holzapfelia	Wilhelm Holzapfel's lactobacilli	Type species: H. floricola. Homofermentative, vancomycin sensitive, unknown ecology but likely host-adapted.
Amylolactobacillus	Starch-degrading lactobacilli	Type species: A. amylophilus. Homofermentative, vancomycin sensitive, extracellular amylases are frequent, unknown ecology but likely host-adapted.
Bombilactobacillus	Lactobacilli from bees and bumblebees	Type species: B. mellifer. Homofermentative, thermophilic, vancomycin resistant, small genome size, adapted to bees and bumblebees
Companilactobacillus	Companion-lactobacillus, referring to them growing in association with other lactobacilli in cereal, meat and vegetable fermentations	Type species: C. alimentarius. Homofermentative with strain- or species-specific ability to ferment pentoses, vancomycin resistant, unknown ecology, likely nomadic
Lapidilactobacillus	Lactobacilli from stones	Type species: L. concavus. Homofermentative with strain- or species-specific ability to ferment pentoses, vancomycin resistant, unknown ecology.
Agrilactobacillus	Lactobacilli from fields	Type 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.
Schleiferilactobacillus	Karl Heinz Schleifer's lactobacilli	Type 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	spoiling lactobacilli	Type species: L. coryniformis. Homofermentative, vancomycin resistant, mesophilic or psychrotrophic organisms.
Lacticaseibacillus	Lactobacilli related to cheese	Type 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.
Latilactobacillus	Widespread lactobacilli	Type species: L. sakei. Homofermentative, mesophilic free living and environmental lactobacilli. Many strains are psychrotrophic and grow below 8 °C.
Dellaglioa	Franco Dellaglio's lactobacilli	Type species: D. algida. Homofermentative, vancomycin resistant, aerotolerant and psychrophilic.
Liquorilactobacillus	Lactobacilli from liquor or liquids	Type 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.
Ligilactobacillus	Uniting lactobacilli	Type 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.
Lactiplantibacillus	Lactobacilli related to plants	Type 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 bran	Type species: F. rossiae. Heterofermentative, vancomycin resistant, with large genome size, broad metabolic potential and unknown ecology.
Paucilactobacillus	Lactobacilli fermenting few carbohydrates	Type species: P. vaccinostercus. Heterofermentative, vancomycin resistant, mesophilic or psychrotrophic, aerotolerant, most strains ferment pentoses but not disaccharides.
Limosilactobacillus	Slimy lactobacilli	Type 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.
Fructilactobacillus	Fructose-loving lactobacilli	Type 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.
Acetilactobacillus	Lactobacilli from vinegar	Type 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.
Apilactobacillus	Lactobacilli from bees	Type species: A. kunkeei. Heterofermentative, vancomycin resistant, small genome size, fermenting only few carbohydrates, adapted to bees and/or flowers.
Levilactobacillus	-leavening lactobacilli	Type species: L. brevis. Heterofermentative, vancomycin resistant, mesophilic or psychrotrophic, metabolise agmatine, environmental or plant-associated lifestyle.
Secundilactobacillus	Second lactobacilli, growing after other organisms depleted hexoses	Type species: S. collinoides. Heterofermentative, vancomycin resistant, mesophilic or psychrotrophic, environmental or plant-associated lifestyle. Adapted to hexose-depleted habitats, most strains do not reduce fructose to mannitol but metabolize agmatine and diols.
Lentilactobacillus	Slow lactobacilli	Type species: L. buchneri. Heterofermentative, vancomycin resistant, mesophilic, fermenting a broad spectrum of carbohydrates. Most lentilactobacilli are environmental or plant-associated, metabolise agmatine and convert lactate and/or diols. L. senioris and L. kribbianus form an outgroup to the genus; both species were isolated from vertrebrates and may transition to a host-adapted lifestyle.

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature and the phylogeny is based on whole-genome sequences.

Human health

Vaginal tract

Lactobacillus s.s. species are considered "keystone species" in the vaginal microbiota of reproductive-age women. Most, but not all, healthy women have a vaginal mcirobiota dominated by one of four species of Lactobacillus: L. iners, L. crispatus, L. gasseri, and L. jensenii. Other women have a more diverse mix of anaerobic microorganisms and are still considered to have a healthy microbiome.

Interactions with pathogens

Lactobacilli produce lactic acid, which contributes to the vaginal acidity, and this lowered pH is generally accepted to be the main mechanism controlling the composition of the vaginal microbiota.
Lactobacilli are also proposed to produce hydrogen peroxide, which inhibits the growth and virulence of the fungal pathogen Candida albicans ''in vitro, though this is arguably not the main mechanism in vivo.
In vitro studies have also shown that lactobacilli reduce the pathogenicity of C. albicans through the production of organic acids and certain metabolites. Both the presence of metabolites, such as sodium butyrate, and decrease in environmental pH caused by the organic acids reduce the growth of hyphae in C. albicans, which reduces its pathogenicity. Lactobacilli also reduce the pathogenicity of C. albicans by reducing C. albicans biofilm formation. On the other hand, following antibiotic therapy, certain Candida species can suppress the regrowth of lactobacilli at body sites where they cohabitate, such as in the gastrointestinal tract.
In addition to its effects on C. albicans, Lactobacillus sp. also interact with other pathogens. For example, Limosilactobacillus reuteri can inhibit the growth of many different bacterial species by using glycerol to produce the antimicrobial substance called reuterin. Another example is Ligilactobacillus salivarius, which interacts with many pathogens through the production of salivaricin B, a bacteriocin.

Probiotics

Because of the interactions with other microbes, fermenting bacteria like lactic acid bacteria are now in use as probiotics with many applications.
Lactobacilli administered in combination with other probiotics provides benefits in cases of irritable bowel syndrome, although the extent of efficacy is still uncertain. The probiotics help treat IBS by re-establishing homeostasis when the gut microbiota experiences unusually high levels of opportunistic bacteria. In addition, lactobacilli can be administered as probiotics during cases of infection by the ulcer-causing bacterium Helicobacter pylori. Helicobacter pylori is linked to cancer, and antibiotic resistance impedes the success of current antibiotic-based eradication treatments. When probiotic lactobacilli are administered along with the treatment as an adjuvant, its efficacy is substantially increased and side effects may be lessened. In addition, lactobacilli with other probiotic organisms in ripened milk and yogurt aid development of immunity in the intestine mucus in humans by raising the number of immunoglobulin A antibodies.
Gastroesophageal reflux disease is a common condition associated with bile acid-induced oxidative stress and accumulation of reactive oxygen species in esophageal tissues that cause inflammation and DNA damage. In an experimental model of GERD, Lactobacillus species facilitated the repair of DNA damage caused by bile-induced ROS. For patients with GERD, there is significant interest in the anti-inflammatory effect of lactobacilli that may help prevent progression to Barrett's esophagus and esophageal adenocarcinoma.
Given the known microbial associations, lactobacilli are currently available as probiotics to help control urogenital and vaginal infections, such as bacterial vaginosis. Lactobacilli produce bacteriocins to suppress the pathogenic growth of certain bacteria, as well as lactic acid, which lowers the vaginal pH to around 4.5 or less, hampering the survival of other bacteria.
In children, lactobacilli such as Lacticaseibacillus rhamnosus'' are associated with a reduction of atopic eczema, also known as dermatitis, due to anti-inflammatory cytokines secreted by this probiotic bacteria.

Oral health

Some lactobacilli have been associated with cases of dental caries. Lactic acid can corrode teeth, and the Lactobacillus count in saliva has been used as a "caries test" for many years. Lactobacilli characteristically cause existing carious lesions to progress, especially those in coronal caries. The issue is, however, complex, as recent studies show probiotics can allow beneficial lactobacilli to populate sites on teeth, preventing streptococcal pathogens from taking hold and inducing dental decay. The scientific research of lactobacilli in relation to oral health is a new field and only a few studies and results have been published. Some studies have provided evidence of certain lactobacilli which can be a probiotic for oral health. Some species, but not all, show evidence in defense to dental caries. Due to these studies, there have been applications of incorporating such probiotics in chewing gum and lozenges. There is also evidence of certain lactobacilli that are beneficial in the defense of periodontal disease such as gingivitis and periodontitis.

Food production

Species of Lactobacillus comprise many food fermenting lactic acid bacteria and are used as starter cultures in industry for controlled fermentation in the production of wine, yogurt, cheese, sauerkraut, pickles, beer, cider, kimchi, cocoa, kefir, and other fermented foods, as well as animal feeds and the bokashi soil amendment. Lactobacillus species are dominant in yogurt, cheese, and sourdough fermentations.
Their importance in fermentation comes from both metabolism of the food itself, as well as the inhibition of growth of other potentially pathogenic microbes. The antibacterial and antifungal activity of lactobacilli relies on production of bacteriocins and low molecular weight compounds that inhibit these microorganisms.
Sourdough bread is made either spontaneously, by taking advantage of the bacteria naturally present in flour, or by using a "starter culture", which is a symbiotic culture of yeast and lactic acid bacteria growing in a water and flour medium. The bacteria metabolize sugars into lactic acid, which lowers the pH of their environment and creates the signature sourness associated with yogurt, sauerkraut, etc.
In many traditional pickling processes, vegetables are submerged in brine, and salt-tolerant lactobacilli feed on natural sugars found in the vegetables. The resulting mix of salt and lactic acid is a hostile environment for other microbes, such as fungi, and the vegetables are thus preserved, remaining edible for long periods.
Lactobacilli, especially Pediococcus and L. brevis, are some of the most common beer spoilage organisms. They are, however, essential to the production of sour beers such as Belgian lambics and American wild ales, giving the beer a distinct tart flavor.
Scientist Elie Metchnikoff won a Nobel prize in 1908 for his work on LAB, the connection to food, and possible usage as a probiotic.