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| Lactobacillus | |
|---|---|
 | |
| Lactobacillus sp. near asquamousepithelial cell | |
Scientific classification | |
| Domain: | Bacteria |
| Kingdom: | Bacillati |
| Phylum: | Bacillota |
| Class: | Bacilli |
| Order: | Lactobacillales |
| Family: | Lactobacillaceae |
| Genus: | Lactobacillus Beijerinck 1901 (Approved Lists 1980)[1] |
| Type species | |
| Lactobacillus delbrueckii (Leichmann 1896) Beijerinck 1927 (Approved Lists 1980)[1] | |
| Species | |
See text | |
Lactobacillus is agenus ofgram-positive within theLactobacillaceae family,aerotolerant anaerobes ormicroaerophilic, rod-shaped, non-spore-formingbacteria.[2][3] Until 2020, the genusLactobacillus comprised over 260 phylogenetically, ecologically, and metabolically diverse species; a taxonomic revision of the genus assignedlactobacilli to 25 genera (see§ Taxonomy below).[3]
Lactobacillusspecies constitute a significant component of the human and animalmicrobiota at a number of body sites, such as thedigestive system and the femalegenital system.[4] In women of European ancestry,Lactobacillus species are normally a major part of thevaginal microbiota.[5][6]Lactobacillus formsbiofilms in thevaginal andgut microbiota,[7] allowing them to persist in harsh environmental conditions and maintain ample populations.[8]Lactobacillus exhibits amutualistic relationship with the human body, as it protects the host against potentialinvasions bypathogens, and in turn, the host provides a source of nutrients.[9] Lactobacilli are among the most commonprobiotic found in food such as yogurt, and the bacteria are diverse in their application in maintaining human well-being, by helping to treat diarrhea, vaginal infections, and skin disorders such aseczema.[10]
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Lactobacilli arehomofermentative, i.e., hexoses are metabolized byglycolysis to lactate as the major end product, or heterofermentative, i.e., hexoses are metabolized by thephosphoketolase pathway to lactate, CO2, and acetate or ethanol as major end products.[11] Most lactobacilli areaerotolerant and some species respire if heme and menaquinone are present in the growth medium.[11] Aerotolerance of lactobacilli ismanganese-dependent and has been explored (and explained) inLactiplantibacillus plantarum (previouslyLactobacillus plantarum).[12] Lactobacilli generally do not requireiron for growth.[13]
TheLactobacillaceae are the only family of thelactic acid bacteria (LAB) that includes homofermentative and heterofermentative organisms; in theLactobacillaceae, homofermentative or heterofermentative metabolism is shared by all strains of a genus.[3][11]Lactobacillus species are all homofermentative, do not expresspyruvate formate lyase, and most species do not fermentpentoses.[3][11] InL. crispatus, pentose metabolism is strain specific and acquired by lateral gene transfer.[14]
The genomes of lactobacilli are highly variable, ranging in size from 1.2 to 4.9 Mb (megabases).[3] Accordingly, the number of protein-coding genes ranges from 1,267 to about 4,758 genes (inFructilactobacillus sanfranciscensis andLentilactobacillus parakefiri, respectively).[15][16] Even within a single species, there can be substantial variation. For instance, strains ofL. crispatus have genome sizes ranging from 1.83 to 2.7 Mb, or 1,839 to 2,688open reading frames.[17]Lactobacillus contains a wealth of compoundmicrosatellites in the coding region of the genome, which are imperfect and have variant motifs.[18] Many lactobacilli also contain multipleplasmids. A recent study has revealed that plasmids encode the genes which are required for adaptation of lactobacilli to the given environment.[19]
The genusLactobacillus comprises the following species:[20][21]
The genusLactobacillus currently contains 44 species which are adapted to vertebrate hosts or to insects.[3] In recent years, other members of the genusLactobacillus (formerly known as theLeuconostoc branch ofLactobacillus) have been reclassified into the generaAtopobium,Carnobacterium,Weissella,Oenococcus, andLeuconostoc. ThePediococcus speciesP. dextrinicus has been reclassified as aLapidilactobacillus dextrinicus[3][22] and most lactobacilli were assigned toParalactobacillus or one of the 23 novel genera of theLactobacillaceae.[3] Two websites inform on the assignment of species to the novel genera or species (http://www.lactobacillus.uantwerpen.be/;http://www.lactobacillus.ualberta.ca/).
| 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 | (Food) 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 (host adapted) lactobacilli | Type species:L. salivarius. Homofermentative, vancomycin resistant, most ligilactobacilli are host adapted and many strains are motile. Several strains ofLigilactobacillus 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 (biofilm-forming) 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 | (Dough)-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 (growing) 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 andL. kribbianus form an outgroup to the genus; both species were isolated from vertrebrates and may transition to a host-adapted lifestyle. |
The currently accepted taxonomy is based on theList of Prokaryotic names with Standing in Nomenclature[20] and the phylogeny is based on whole-genome sequences.[3]
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Lactobacilluss.s. species are considered "keystone species" in thevaginal flora of reproductive-age women.[23] Most, but not all, healthy women have vaginal floras dominated by one of four species ofLactobacillus:L. iners,L. crispatus,L. gasseri, andL. jensenii. Other women have a more diverse mix of anaerobic microorganisms and are still considered to have a healthy microbiome.[5]
Lactobacilli producelactic 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 microflora.[24]
Lactobacilli are also proposed to producehydrogen peroxide, which inhibits the growth andvirulence of the fungal pathogenCandida albicansin vitro,[25][26] though this is arguably not the main mechanismin vivo.[27]
In vitro studies have also shown that lactobacilli reduce the pathogenicity ofC. albicans through the production of organic acids and certain metabolites.[28] Both the presence of metabolites, such assodium butyrate, and decrease in environmental pH caused by the organic acids reduce the growth ofhyphae inC. albicans, which reduces its pathogenicity.[28] Lactobacilli also reduce the pathogenicity ofC. albicans by reducingC. albicans biofilm formation.[28] On the other hand, followingantibiotic therapy, certainCandida species can suppress the regrowth of lactobacilli at body sites where they cohabitate, such as in the gastrointestinal tract.[25][26]
In addition to its effects onC. albicans,Lactobacillus sp. also interact with other pathogens. For example,Limosilactobacillus reuteri (formerlyLactobacillus reuteri) can inhibit the growth of many different bacterial species by using glycerol to produce the antimicrobial substance calledreuterin.[29] Another example isLigilactobacillus salivarius (formerlyLactobacillus salivarius), which interacts with many pathogens through the production of salivaricin B, a bacteriocin.[30]
Because of the interactions with other microbes, fermenting bacteria likelactic acid bacteria (LAB) are now in use asprobiotics with many applications.
Lactobacilli administered in combination with otherprobiotics provides benefits in cases ofirritable bowel syndrome (IBS), although the extent of efficacy is still uncertain.[31] The probiotics help treat IBS by re-establishing homeostasis when the gut microbiota experiences unusually high levels of opportunistic bacteria.[9] In addition, lactobacilli can be administered as probiotics during cases of infection by the ulcer-causing bacteriumHelicobacter pylori.[32]Helicobacter pylori is linked to cancer, and antibiotic resistance impedes the success of current antibiotic-based eradication treatments.[32] When probiotic lactobacilli are administered along with the treatment as anadjuvant, its efficacy is substantially increased and side effects may be lessened.[32] In addition, lactobacilli with other probiotic[33] organisms in ripened milk and yogurt aid development of immunity in the intestine mucus in humans by raising the number of immunoglobulin A (IgA (+)) antibodies.
Gastroesophageal reflux disease (GERD) is a common condition associated withbile acid-inducedoxidative stress and accumulation ofreactive oxygen species (ROS) inesophageal tissues that cause inflammation andDNA damage.[34] In an experimental model of GERD,Lactobacillus species(L. acidophilus,L. plantarum, andL. fermentum) facilitated the repair of DNA damage caused by bile-induced ROS.[34] For patients with GERD, there is significant interest in the anti-inflammatory effect of lactobacilli that may help prevent progression toBarrett's esophagus andesophageal adenocarcinoma.[34]
Given the known microbial associations, lactobacilli are currently available asprobiotics to help control urogenital and vaginal infections, such asbacterial vaginosis (BV). Lactobacilli producebacteriocins to suppress the pathogenic growth of certain bacteria,[35] 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 asLacticaseibacillus rhamnosus (previouslyL. rhamnosus) are associated with a reduction of atopic eczema, also known asdermatitis, due to anti-inflammatorycytokines secreted by this probiotic bacteria.[9]
Some lactobacilli have been associated with cases ofdental caries (cavities).Lactic acid can corrode teeth, and theLactobacillus 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 inducingdental decay. The scientific research of lactobacilli in relation tooral health is a new field and only a few studies and results have been published.[36][37] Some studies have provided evidence of certain lactobacilli which can be a probiotic for oral health.[38] Some species, but not all, show evidence in defense to dental caries.[38] Due to these studies, there have been applications of incorporating such probiotics in chewing gum and lozenges.[38] There is also evidence of certain lactobacilli that are beneficial in the defense of periodontal disease such as gingivitis and periodontitis.[38]
Species ofLactobacillus (and related genera) comprise many food fermenting lactic acid bacteria[39][40] and are used as starter cultures in industry for controlled fermentation in the production ofwine,yogurt,cheese,sauerkraut,pickles,beer,cider,kimchi,cocoa,kefir, and otherfermented foods, as well asanimal feeds and thebokashi soil amendment.Lactobacillus species are dominant in yogurt, cheese, and sourdough fermentations.[39][40]
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 ofbacteriocins and low molecular weight compounds that inhibit these microorganisms.[41][42]
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 ofyeast andlactic acid bacteria growing in awater andflourmedium.[43] 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 traditionalpickling processes, vegetables are submerged inbrine, 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 asfungi, and the vegetables are thus preserved, remaining edible for long periods.[44]
Lactobacilli, especiallyPediococcus andL. brevis, are some of the most common beer spoilage organisms. They are, however, essential to the production of sour beers such as Belgianlambics and American wild ales, giving the beer a distinct tart flavor.[45]
ScientistElie Metchnikoff won a Nobel prize in 1908 for his work on LAB, the connection to food, and possible usage as a probiotic.[46]
In addition, GI fungal infection is reported even among those patients with normal immune status. Digestive system-related fungal infections may be induced by both commensal opportunistic fungi and exogenous pathogenic fungi. ...
In vitro, bacterial hydrogen peroxide or organic acids can inhibitC. albicans growth and virulence61
In vivo,Lactobacillus sp. can inhibit the GI colonisation and infection ofC. albicans62
In vivo,C. albicans can suppressLactobacillus sp. regeneration in the GI tract after antibiotic therapy63, 64
Small intestinal fungal overgrowth (SIFO) is characterized by the presence of excessive number of fungal organisms in the small intestine associated with gastrointestinal (GI) symptoms. Candidiasis is known to cause GI symptoms particularly in immunocompromised patients or those receiving steroids or antibiotics. However, only recently, there is emerging literature that an overgrowth of fungus in the small intestine of non-immunocompromised subjects may cause unexplained GI symptoms. ... Fungal-bacterial interaction may act in different ways and may either be synergistic or antagonistic or symbiotic [29]. Some bacteria such asLactobacillus species can interact and inhibit both the virulence and growth ofCandida species in the gut by producing hydrogen peroxide [30]. Any damage to the mucosal barrier or disruption of GI microbiota with chemotherapy or antibiotic use, inflammatory processes, activation of immune molecules and disruption of epithelial repair may all cause fungal overgrowth [27].
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