Lactobacillus parakefiri

Lactobacillus parakefiri (Lentilactobacillus parakefiri)

1. Identity, Nomenclature, and Taxonomy

Current and Historical Names

Current valid name: Lentilactobacillus parakefiri (Takizawa et al. 1994) Zheng et al. 2020.
Former name (basonym): Lactobacillus parakefiri Takizawa et al. 1994 (also originally proposed as Lactobacillus parakefir sp. nov.).
Type strain designations: GCL 1731^T = JCM 8573^T = DSM 10551^T = ATCC 51648^T.

L. parakefiri is a heterofermentative lactic acid bacterium described by Takizawa et al. in 1994, with strain GCL 1731^T (= JCM 8573^T = DSM 10551^T = ATCC 51648^T) designated as its type strain. It was originally isolated from kefir grains and, together with another kefir-isolated species, L. kefiri, belongs to the L. buchneri group.

The species was originally described alongside Lactobacillus kefirgranum sp. nov. in the same 1994 publication. Both species were isolated in Japan from kefir grains obtained from Chr. Hansen's Laboratory in Copenhagen, Denmark. Both were characterized as facultatively anaerobic, Gram-positive, non-motile, non-spore-forming rods occurring as single cells, in pairs, or occasionally in short chains. L. kefirgranum produced DL-lactic acid homofermentatively, while L. parakefir produced L-lactic acid and CO₂ via heterofermentation, while hydrogen sulfide, catalase, and oxidase were not produced by either species.

Reclassification into the Genus Lentilactobacillus

In 2020, a landmark taxonomic revision reorganized the entire genus Lactobacillus. Based on a polyphasic approach, Zheng et al. (2020) proposed reclassification of the genus Lactobacillus into 25 genera, including the emended genus Lactobacillus and 23 novel genera, among them Lentilactobacillus. The name Lentilactobacillus was derived from Latin lentus (slow, sluggish), referring to the slow growth of species in the genus with lactate or propanediol as the carbon source. Accordingly, Lactobacillus parakefiri was reclassified as Lentilactobacillus parakefiri. In the current scientific literature both names remain in use, frequently together with cross-references.

The taxonomic position of the species had previously attracted controversy. Conflicting views were reported by two research groups on the basis of genomic analyses, resulting in controversies about the taxonomic status of L. parakefiri: Zheng et al. suggested that L. parakefiri is a later heterotypic synonym of L. kefiri, whereas Sun et al. acknowledged it as the species with the largest genome in the genus Lactobacillus. These controversies were resolved by a whole-genome sequencing study published in 2017. Genome-wide metrics, including average nucleotide identity and digital DNA-DNA hybridization, and phylogenomic analysis based on multiple genes confirmed its taxonomic status as a distinct species in the genus Lactobacillus.

Taxonomic Classification

• Domain: Bacteria
• Phylum: Bacillota (formerly Firmicutes)
• Class: Bacilli
• Order: Lactobacillales
• Family: Lactobacillaceae
• Genus: Lentilactobacillus Zheng et al. 2020
• Species: Lentilactobacillus parakefiri (Takizawa et al. 1994) Zheng et al. 2020

The genus Lentilactobacillus comprises Gram-stain-positive, catalase- and oxidase-negative, nonmotile, non-spore-forming, rod-shaped, heterofermentative and facultatively anaerobic bacteria. Member species are isolated from a variety of sources, including fermented vegetables, kefir grains, cereal mashes, silage, and (spoiled) beer and wine.

Morphology and Physiology

Lentilactobacillus parakefiri is a Gram-positive, mesophilic, non-motile, non-spore-forming rod. The type strain is an anaerobe, mesophilic, Gram-positive bacterium isolated from kefir grain. As a heterofermentative organism, it produces l-lactic acid and CO₂ from glucose, but not from gluconate (Takizawa et al., 1994). The genomically characterized type strain contains 2,444 protein-coding sequences (CDSs). It has been reported that L. parakefiri produces gas from glucose but not from gluconate. This unusual trait is likely due to a frameshift mutation that resulted in a premature stop codon in the coding region of gluconate permease, located adjacent to the gluconate kinase gene. In other heterofermentative species, including L. buchneri and L. kefiri, these two genes are thought to take roles in uptake and phosphorylation of gluconate, constituting an initial stage of its metabolic pathway.

2. Natural Sources and Occurrence

Primary Habitat: Kefir Grains and Kefir Beverage

Lentilactobacillus parakefiri is intrinsically associated with kefir, one of the oldest fermented dairy beverages known. Kefir is a viscous, slightly carbonated dairy beverage that has its origins in the Caucasian, Tibetan, and Mongolian mountains. It comprises a complex microbial consortium of mainly lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeasts, and is considered a functional dairy product associated with a wide range of health benefits.

Three Lactobacillus species have been identified in the microbiota of the traditional dairy product kefir: Lentilactobacillus kefiri (basonym: Lactobacillus kefir), Lactobacillus kefiranofaciens, and Lentilactobacillus parakefiri (basonym: Lactobacillus parakefir). Multiple culture-based and culture-independent studies have confirmed L. parakefiri as a consistent resident of kefir grains across geographically diverse grain origins. The most common species of Lactobacillus detected in kefir grains have been L. kefiranofaciens, L. kefiri, and L. parakefiri.

Due to their complex microbiota, kefir grains or water kefir grains can be considered as natural reservoirs of safe and potentially probiotic strains. Studies on kefir grain microbiota revealed that Lactobacillus kefiranofaciens, Lentilactobacillus kefiri, and Lentilactobacillus parakefiri are the most representative species; however, other species are also described, including Lacticaseibacillus paracasei, Lactobacillus acidophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactiplantibacillus plantarum, and Lactococcus lactis.

Other Dairy and Food Sources

Beyond kefir, the organism has been detected in other fermented dairy matrices. It was originally isolated from kefir grains but has been recently identified as a predominant LAB in butter (Syromyatnikov et al., 2020). Earlier culture-based surveys also showed that Lactobacillus kefiri is mainly associated with fermented milk products in the Northern Caucasus along with Lactobacillus parakefiri and Lactobacillus kefirigranum. Additionally, L. parakefiri has been detected as a minor but consistent component in kefirs prepared from cow, goat, and sheep milk across different countries. OTUs belonging to L. parakefiri, along with L. pseudomesenteroides and L. plantarum, have been observed in these varied kefir milk samples.

Role in the Kefir Grain Matrix

L. parakefiri is one of two major exopolysaccharide-producing bacteria in kefir grains and plays a structural role in the grain architecture itself. Kefir grains are held together by a complex mixture of protein and a polysaccharide (kefirin) that is a component of the capsular material of Lentilactobacillus parakefiri and Lb. kefiranofaciens, which are the major exopolysaccharide (EPS)-producing bacteria present in kefir grains (Kök-Taş et al., 2012).

3. Traditional and Historical Use

Kefir's Origins and Ethnographic History

L. parakefiri is not a botanical extract or isolate with a separately recorded ethnomedicinal history; rather, its traditional use is inseparable from the centuries-old human practice of preparing and consuming kefir. The origins of kefir predate written records and it has been consumed for centuries as part of the daily diet, valued for its perceived health-promoting properties. Owing to its long history of consumption, kefir has attracted increasing scientific interest as a functional food, prompting clinical investigations into its potential health effects.

The word kefir is derived from the Turkish word keyif, which means "feeling good" after its ingestion. The kefir beverage is originally from the Caucasus Mountains, a traditional product highly consumed in Eastern Europe, Russia, and Southwest Asia. In the early twentieth century, Irina Sakharova introduced kefir production in Moscow, after which it became a staple food in Russian cuisine. Today, kefir is recognized as a traditional Middle Eastern and Central Asian drink that is typically thick, self-carbonating, whitish, slightly alcoholic, and smooth in texture.

Traditional Preparation Method

Traditionally, kefir was prepared by hanging goatskin bags containing kefir grains and milk near doors. Every time someone passed through, they would shake the bags to ensure that the milk and kefir grains were thoroughly mixed. Since the first established use, hundreds of years ago, the propagation of kefir has been performed by transferring kefir grains from one batch to fresh milk and incubating at ambient temperature. Today, the gelatinous kefir grains are typically placed in a sterile jar or other nonmetallic container, and milk is poured on top; single-use powdered kefir cultures are also available for use at home. The mixture ferments at room temperature for one or two days, resulting in the tangy flavour that has become synonymous with the drink. Upon completion of fermentation, the kefir is separated from the grains by passing it through a sieve.

Perceived Traditional Health Uses

Kefir has traditionally been associated with longevity, digestive health, and resistance to disease in the populations of the Caucasus region. Kefir is a traditional example of the co-existence of bacteria and yeasts, and the importance of this symbiotic relationship seems clear, since it is necessary to produce compounds beneficial to health. Although the evidence is not conclusive and further studies should be conducted, the existing scientific studies demonstrate the health benefits reported empirically by historical kefir consumption. It must be emphasized that these traditional attributions were made to kefir as a whole beverage; specific attributions to L. parakefiri as an isolated organism were not made historically.

4. Scientific Discovery and Taxonomic Milestones

The formal scientific discovery of L. parakefiri as a distinct species was made by Japanese researchers in the early 1990s. A new medium, Rogosa-CW, which supports good growth of Lb. kefiranofaciens, was developed (Kojima et al., 1993), and by using this medium, Lactobacillus kefirgranum, which did not form ropy colonies, and Lactobacillus parakefir (now named Lentilactobacillus parakefiri) were also proposed as new species (Takizawa et al., 1994). The original 1994 study by Takizawa, Kojima, Tamura, Fujinaga, Benno, and Nakase was conducted at the Central Research Laboratory of Glico Dairy Co., Ltd. and the Japan Collection of Microorganisms (RIKEN). Twelve strains of homofermentative lactobacilli and two strains of heterofermentative lactobacilli were isolated from kefir grains by using R-CW agar medium. The physiological and biochemical characteristics, DNA guanine-plus-cytosine contents, and levels of DNA–DNA relatedness of these isolates and previously described lactobacilli were compared.

A key whole-genome-based study in 2017 definitively resolved controversies about the species' identity. Whole-genome sequencing was performed for Lactobacillus parakefiri JCM 8573^T to confirm its hitherto controversial taxonomic position, reporting its first reliable reference genome. Genome-wide metrics, including average nucleotide identity and digital DNA-DNA hybridization, and phylogenomic analysis based on multiple genes supported its taxonomic status as a distinct species in the genus Lactobacillus. The availability of a reliable genome sequence was noted as an aid to future investigations on the industrial applications of L. parakefiri in functional foods such as kefir grains.

5. Key Constituents, Active Compounds, and Mechanisms of Action

Exopolysaccharide Production (Kefiran / Capsular EPS)

The most extensively characterized bioactive product associated with L. parakefiri is the capsular exopolysaccharide (EPS) it produces, which contributes to the structural integrity of kefir grains and may confer direct biological activities. Kefir grains are held together by a complex mixture of protein and a polysaccharide (kefirin) that is a component of the capsular material of Lentilactobacillus parakefiri and Lb. kefiranofaciens, which are the major EPS-producing bacteria present in kefir grains.

Kefiran, the polysaccharide associated with kefir grain LAB including L. parakefiri, consists primarily of glucose and galactose residues. The exopolysaccharide kefiran has been characterised and quantified from kefir grains originating from the Caucasian Mountains, with capillary electrophoresis used for the characterisation and quantification of d-glucose and d-galactose at a mass ratio of 1:0.7.

Heterofermentative Metabolic Products

As an obligately heterofermentative lactic acid bacterium, L. parakefiri produces a characteristic suite of metabolites during fermentation. Lentilactobacillus parakefiri produces l-lactic acid and CO₂ from glucose, but not from gluconate. In fermentation studies using single strains in milk medium, LAB including Lentilactobacillus parakefiri synthesise compounds such as CO₂, acetic acid, and formic acid. Lactic acid contributes to the acidification and preservation of the kefir matrix, and in traditional kefir, although lactic acid is the main fermentative metabolite, small amounts of alcohol and carbon dioxide are also produced by the yeast present in the kefir grain giving a pronounced effervescence typical of kefir.

Contribution to Volatile Aroma Profile

Research has investigated the specific contribution of L. parakefiri to the volatile compound profile of kefir. Fermented milk samples were produced using single strains of Lactobacillus kefiranofaciens (LKF), Lentilactobacillus parakefiri (LP), and Lentilactobacillus kefiri (LK), as well as two control samples using kefir grain and commercial kefir culture. The change in LAB amounts, physicochemical properties (pH, titration acidity), rheological and chemical properties (organic acid, sugar, and volatile flavour compound content) were investigated. The results showed no significant difference between LAB numbers and physicochemical properties of the samples. The LK, LP, and LKF strains respectively were observed to show more activity in acetic acid production, citrate and lactose consumption.

Genomic Characteristics Relevant to Metabolic Potential

The reference genome of L. parakefiri JCM 8573^T contains 2,444 protein-coding sequences (CDSs). The species produces gas from glucose but not from gluconate. This unusual trait is likely due to a frameshift mutation that resulted in a premature stop codon in the coding region of gluconate permease, located adjacent to the gluconate kinase gene. In other heterofermentative species, including L. buchneri and L. kefiri, these two genes are thought to take roles in uptake and phosphorylation of gluconate. Members of the genus Lentilactobacillus broadly have the capacity to convert agmatine, a metabolic byproduct of bacterial decarboxylation of arginine via the agmatine deiminase pathway.

Gut Colonization and Probiotic Mechanisms

An animal study examined the fate of kefir-specific lactobacilli, including L. parakefiri, after ingestion of natural kefir by mice. The transfer of the L. kefiranofaciens, L. kefiri, and especially the L. parakefiri strains, which are specific to natural-kefir produced using kefir grain, into mice feces microbiota was determined for the first time. The L. parakefiri strain with the highest amount of increase supported the mice-feces-microbiota. This finding provides preliminary (animal-model) evidence that the organism can survive transit through the gastrointestinal tract and become temporarily established in the gut microbiota, a prerequisite for probiotic activity.

6. Scientific Evidence by Area of Application

Important caveat: L. parakefiri has not been the subject of dedicated human clinical trials as an isolated probiotic organism. The scientific evidence relating specifically to this species derives overwhelmingly from (a) in vitro or ex vivo characterization studies, (b) animal studies, and (c) its role as a component within the complex kefir microbiome — in which it cannot be studied in isolation from the dozens of other organisms present in kefir. Where relevant kefir clinical evidence is cited below, it must be understood that attributing outcomes specifically to L. parakefiri is not scientifically justified based on current data.

6.1 Structural Role in Kefir Grain Formation and Fermentation

Evidence level: Well-established (in vitro / microbiological). The structural and fermentative roles of L. parakefiri within kefir grains are among the most firmly established facts about this organism. Kefir grains are held together by a complex mixture of protein and a polysaccharide (kefirin) that is a component of the capsular material of Lentilactobacillus parakefiri and Lb. kefiranofaciens, which are the major exopolysaccharide (EPS)-producing bacteria present in kefir grains. The contribution of L. parakefiri to grain architecture, acidification, and volatile compound production has been characterized using culture-based and analytical chemistry approaches, as described in the preceding section.

6.2 Gut Microbiota Interaction and Colonization

Evidence level: Preliminary (animal study only). The translocation and survival of L. parakefiri following kefir consumption has been demonstrated only in a Balb/c mouse model. The transfer of kefir-specific strains, including especially L. parakefiri, into mice feces microbiota was confirmed. The L. kefiranofaciens strain had higher colonization efficiencies than the others; however, the L. parakefiri strain with the highest amount of increase supported the mice-feces microbiota. Thus, the efficacy of natural kefir in transferring these probiotic strains to mice feces was established. No equivalent human data confirming gut colonization by L. parakefiri specifically has been published in the sources examined.

6.3 Kefir Clinical Evidence (Contextual)

Evidence level: Moderate for kefir as a product; species-specific attribution not possible. A 2026 systematic review of human clinical trials of kefir found substantial clinical study activity across diverse health areas. This review aimed to evaluate the available clinical evidence on kefir consumption and its impact on human health. A literature search of PubMed, Web of Science, and Scopus was conducted up to 30 August 2025. Eligible studies were human clinical trials investigating kefir as a fermented milk beverage without the addition of defined probiotic strains, prebiotics, or synbiotics. A total of 28 clinical studies were identified and included diverse study designs, such as crossover trials, parallel-group randomized controlled trials, multi-arm trials, early-phase exploratory studies, and pilot studies. Kefir is traditionally produced by fermenting milk with kefir grains, which consist of a complex microbial community of lactic acid bacteria — including Lentilactobacillus parakefiri — acetic acid bacteria, and yeasts.

Because kefir is a multi-organism product, none of the clinical evidence obtained in these 28 studies can be specifically attributed to L. parakefiri. The organisms present in the kefir preparations used in each study were highly variable: across the 28 included clinical studies, kefir was produced using traditional grains in 8 studies and commercial starter cultures in 12 studies. The microbial composition — including the relative abundance of L. parakefiri — was generally not reported at the species level in most of these trials.

6.4 Immunomodulatory Properties

Evidence level: Preliminary (animal and in vitro only for L. parakefiri specifically). The exopolysaccharide kefiran, co-produced by L. parakefiri and L. kefiranofaciens, has been studied for immunomodulatory effects in animal models. Kefiran was investigated for its immunomodulatory effects in bone marrow-derived mast cells (BMMCs). Pre-treatment with kefiran reduced levels of degranulation by mast cells, and also significantly reduced TNF-α secretion. These findings are in vitro and cannot be attributed exclusively to the EPS fraction produced by L. parakefiri as opposed to that produced by L. kefiranofaciens.

6.5 Cholesterol and Cardiovascular Parameters

Evidence level: Preliminary (animal model for kefiran; no species-specific human data). Animal model research on kefiran (the EPS co-produced by L. parakefiri and L. kefiranofaciens) has examined effects on lipid metabolism. Rabbits were fed a high-cholesterol diet with or without kefiran every day for eight weeks. The total area of atherosclerotic lesions was reduced compared to controls, with the biggest improvements seen at points in the aorta furthest from the heart. The liver also exhibited significantly lower levels of total cholesterol (TC). Again, these findings relate to the EPS as a compound, not to L. parakefiri specifically, and involve an animal model only.

6.6 Contribution to Fermented Food Flavor and Safety

Evidence level: Well-established (in vitro / food science). Single-strain fermentation studies have defined the specific contribution of L. parakefiri to the physicochemical and sensory properties of fermented milk. In a study comparing strains of L. parakefiri, L. kefiri, and L. kefiranofaciens in UHT milk as single-strain fermentations, the results showed no significant difference between LAB numbers and physicochemical properties of the samples. The LK, LP, and LKF strains respectively were observed to show more activity in acetic acid production, citrate and lactose consumption. In the volatile aroma compound (VAC) profiles, the LKF strain was associated with hexanol, 2-octanol, and octanal, and the LK strain with ethyl octanoate, ethyl hexanoate, acetaldehyde, and geraniol.

7. Dosage Forms and Preparations

Lentilactobacillus parakefiri is not currently commercially available as an isolated probiotic supplement with standardized dosage data comparable to strains such as Lactobacillus rhamnosus GG or Bifidobacterium longum. It is encountered primarily in the following forms:

• Traditional kefir (grain-fermented): Kefir is traditionally produced by fermenting milk with kefir grains, which contain Lentilactobacillus parakefiri among a complex microbial community. Traditional grain-fermented kefir is the vehicle in which L. parakefiri is naturally consumed. The quantities of viable L. parakefiri cells per milliliter of kefir vary widely by grain origin, fermentation time, and temperature, and specific counts for this species have not been standardized in published clinical studies.
• Commercial kefir products: Commercial kefir starter cultures used in some clinical studies frequently use defined mixes of LAB strains. Across 28 clinical studies of kefir, kefir was produced using traditional grains in 8 studies and commercial starter cultures in 12 studies. Whether commercial starter cultures include L. parakefiri at defined concentrations is not consistently reported in the clinical literature reviewed.
• Freeze-dried starter cultures: Research has explored the use of freeze-dried kefir cultures for reproducible production. Five bacterial species including Lentilactobacillus kefiri, Lactobacillus kefiranofaciens, Lactococcus cremoris, Leuconostoc mesenteroides, and Acetobacter pasteurianus, and four yeast species underwent freeze-drying prior to viability testing and use as starter cultures in kefir fermentations. The specific inclusion of L. parakefiri in such standardized preparations, and at what CFU, has not been specifically reported in the reviewed literature.
• Deposited reference strains: The type strain Lentilactobacillus parakefiri (Takizawa et al. 1994) Zheng et al. 2020 is maintained in culture collections, including DSMZ (DSM 10551), JCM (JCM 8573), and ATCC (ATCC 51648), where it is available for research purposes. The culture conditions for the DSMZ strain are Medium 11, 28°C, microaerobic.

No dosage ranges specific to L. parakefiri as an isolated supplement have been reported in human clinical studies. Dosage information from kefir studies is reported in terms of volume of kefir consumed (e.g., milliliters per day), not in terms of colony-forming units (CFU) of specific constituent species.

8. Body Systems Associated with Research Interest

The following body systems have been highlighted in the kefir and kefir-LAB research literature as areas of scientific interest, within the important caveat that species-specific clinical evidence for L. parakefiri is absent:

• Gastrointestinal system: Gut colonization (mouse model), contribution to kefir acidification, and fermentation of lactose to lactic acid.
• Immune system: EPS (kefiran) immunomodulation in mast cell models (in vitro / ex vivo); TNF-α and degranulation modulation.
• Cardiovascular system: Kefiran effects on atherosclerotic lesion area and hepatic cholesterol in a rabbit model of high-fat diet.
• Structural / food science: EPS-mediated grain matrix integrity; contribution to acidification and volatile aroma compounds in fermented dairy.

9. Safety Considerations

General Safety Status of Kefir-Derived Lactobacilli

Lentilactobacillus parakefiri has a long history of safe human consumption as part of kefir. Lactobacilli are generally regarded as safe; however, certain strains have been associated with cases of infection. No specific safety concerns uniquely attributable to L. parakefiri have been identified in the peer-reviewed literature examined. Formal GRAS (Generally Recognized As Safe) designation or EFSA Qualified Presumption of Safety (QPS) status specific to L. parakefiri as an isolated species has not been documented in the sources reviewed.

Antibiotic Susceptibility

Antibiotic susceptibility is a key safety parameter assessed for candidate probiotic strains. The closest published safety characterization data in the literature relates to the closely related sister species L. kefiri. In a study of kefir-isolated L. kefiri strains, all tested bacteria exhibited MIC values lower than the breakpoints recommended for heterofermentative lactobacilli for tetracycline, clindamycin, streptomycin, ampicillin, erythromycin, kanamycin, and gentamicin. However, strains CIDCA 8321 and 8345 were resistant to chloramphenicol, although amplification of the CAT-encoding gene was negative for all L. kefiri strains. Further research, including study of the distribution of chloramphenicol MICs, could contribute to determining whether resistance is acquired (not acceptable) or intrinsic (acceptable) according to EFSA criteria. These findings are for L. kefiri, not L. parakefiri directly; however, they illustrate the type of antibiotic susceptibility testing considered relevant by EFSA for this group of heterofermentative kefir lactobacilli.

Hemolytic Activity

For the closely related L. kefiri, none of the L. kefiri strains tested caused α- or β-hemolysis. Absence of hemolytic activity is a standard safety requirement for candidate probiotics and has been documented for multiple kefir-derived Lactobacillus species, though published data specifically for L. parakefiri were not located in the sources reviewed.

In Vivo Safety Data (Animal Model)

In vivo safety data exist for L. kefiri but not specifically for L. parakefiri as an isolated organism. For L. kefiri, mice treated daily with an oral dose of 10⁸ CFU during 21 days showed no signs of pain, lethargy, dehydration, or diarrhea, and histological studies were consistent with those findings. Moreover, no differences in proinflammatory cytokine secretion were observed between treated and control mice. No translocation of microorganisms to blood, spleen, or liver was observed.

Taxonomic Reclassification and Nomenclature Ambiguity

A practical safety-related consideration is that the 2020 reclassification of the genus Lactobacillus means that older regulatory approvals, safety dossiers, and product labels may still refer to this organism as Lactobacillus parakefiri. Many scientific genetic analyses ran in the past few years have shown that the huge heterogeneity within the genus made it no longer reasonable to group all 261 species under Lactobacillus. The International Journal of Systematic and Evolutionary Microbiology released in April 2020 a new classification scattering the species of the Lactobacillaceae family under Lactobacillus, Paralactobacillus, Pediococcus, and 23 novel genera based on several genetic approaches and markers. Both names — Lactobacillus parakefiri and Lentilactobacillus parakefiri — may therefore appear in regulatory and commercial contexts, referring to the same organism.

Immunocompromised Populations

While no specific contraindication data exist for L. parakefiri in immunocompromised patients, the general principle applicable to all live microbial preparations is that the rare but documented risk of bacteremia or sepsis is higher in severely immunocompromised individuals. This consideration, which applies broadly to the genus Lentilactobacillus and related genera, has been noted in the general probiotic safety literature.

10. Research Limitations and Evidence Gaps

The current state of the literature on Lentilactobacillus parakefiri as a dietary supplement or standalone functional ingredient is characterized by the following significant limitations:

• No dedicated human clinical trials: There are no published randomized controlled trials, or any other category of human interventional study, in which L. parakefiri has been administered as an isolated preparation to human subjects. All human evidence relates to kefir as a complex multi-organism product.
• Limited strain-specific mechanistic data: Most mechanistic data in the literature — including immunomodulation by kefiran and cholesterol-lowering effects — cannot be attributed specifically to L. parakefiri because the EPS kefiran is co-produced by multiple organisms in kefir.
• Taxonomic reclassification in 2020: The reclassification of the genus means that a significant portion of the older literature does not clearly distinguish L. parakefiri from the broader kefir microbiome, and many publications lump it with L. kefiri.
• Absence of standardized supplement formats: Unlike well-characterized probiotic species, no standardized, single-strain commercial supplement formulation based on L. parakefiri with published clinical dose–response data has been identified in the sources reviewed.
• Animal and in vitro data predominance: The available species-specific research is confined to microbiological characterization, genomics, fermentation technology, and one mouse colonization study. The translational significance of these findings for human health remains unknown.

References

• Tanizawa Y et al. (2017). Genomic characterization reconfirms the taxonomic status of Lactobacillus parakefiri. Bioscience of Microbiota, Food and Health 36(3):129–134. PMC5510158
• Tanizawa Y et al. (2017). Genomic characterization reconfirms the taxonomic status of Lactobacillus parakefiri. PubMed 28748134
• Nikoloudaki O et al. (2022). Invited review: Review of taxonomic changes in dairy-related lactobacilli. Journal of Dairy Science. ScienceDirect
• Nikoloudaki O et al. (2022). Invited review: Review of taxonomic changes in dairy-related lactobacilli. Journal of Dairy Science. Full text
• Georgalaki M et al. (2021). Lactobacillus kefiranofaciens: From Isolation and Taxonomy to Probiotic Properties and Applications. Microorganisms 9(10):2158. MDPI
• Cuffia F et al. (2021). Health-Promoting Properties of Lacticaseibacillus paracasei: A Focus on Kefir Isolates and Exopolysaccharide-Producing Strains. Foods 10(10):2239. MDPI
• Bourrie BCT et al. (2016). The Microbiota and Health Promoting Characteristics of the Fermented Beverage Kefir. Frontiers in Microbiology 7:647
• Leite AMO et al. (2013). Microbiological, technological and therapeutic properties of kefir: a natural probiotic beverage. Brazilian Journal of Microbiology. PMC3833126
• Brouwer RJ et al. (2026). Kefir Consumption and Health Effects Based on Human Clinical Trials: An Overview of Literature. Healthcare 14(5):652. MDPI
• Brouwer RJ et al. (2026). Kefir Consumption and Health Effects Based on Human Clinical Trials: An Overview of Literature. PMC12984562
• Takizawa S, Kojima S, Tamura S, Fujinaga S, Benno Y, Nakase T (1994). Lactobacillus kefirgranum sp. nov. and Lactobacillus parakefir sp. nov., two new species from kefir grains. International Journal of Systematic Bacteriology 44(3):435–439
• Zheng J et al. (2020). A taxonomic note on the genus Lactobacillus: Description of 23 novel genera. International Journal of Systematic and Evolutionary Microbiology 70(4):2782–2858
• Zheng J et al. (2020). A taxonomic note on the genus Lactobacillus. PubMed 32293557
• LPSN (List of Prokaryotic names with Standing in Nomenclature). Genus: Lentilactobacillus. DSMZ
• DSMZ Culture Collection Catalogue: Lentilactobacillus parakefiri DSM 111871
• BacDive (DSMZ). Lactobacillus parakefiri type strain GCL 1731 / BacDiveID:6567
• Wang H et al. (2023). Microbiological profiles, physiochemical properties and volatile compounds of goat milk kefir fermented by reconstituted kefir grains. LWT - Food Science and Technology. ScienceDirect
• Kök-Taş T et al. Presence of Lactobacillus kefiranofaciens subsp. kefiranofaciens, Lentilactobacillus kefiri and Lentilactobacillus parakefiri in the stools of Balb/c consuming natural kefir. ResearchGate
• Duran FE et al. (2022). Prominent strains of kefir grains in the formation of volatile compound profile in milk medium: the role of Lactobacillus kefiranofaciens subsp. kefiranofaciens, Lentilactobacillus kefiri and Lentilactobacillus parakefiri. European Food Research and Technology 248:975–989. ResearchGate
• Carasi P et al. (2014). Safety Characterization and Antimicrobial Properties of Kefir-Isolated Lactobacillus kefiri. BioMed Research International. PMC4052788
• Bourrie BCT et al. (2019). Analysis of Health Benefits Conferred by Lactobacillus Species from Kefir. Nutrients 11(6):1252. MDPI
• Wang H et al. (2023). Microbiological profiles, physicochemical properties and volatile compounds of kefir. LWT. ScienceDirect
• Holm JB et al. (2025). Fermentation of kefir with traditional freeze-dried starter cultures successfully recreates fresh culture fermented kefir. PMC12549565
• Nagaoka S et al. (2025). Identification of dominant species common to kefir grains from 7 origins for kefir grain reconstruction. Journal of Dairy Science. ScienceDirect
• Watanabe K (2025). Lentilactobacillus. In: Bergey's Manual of Systematics of Archaea and Bacteria. Wiley Online Library
• Wikipedia. Lentilactobacillus parakefiri
• Islam MZ et al. (2026). A comprehensive review on kefir: composition, microbial diversities, meta-analysis and biological significances on human health. Food Production, Processing and Nutrition. Springer