Lactobacillus kefiri

Lactobacillus kefiri (Lentilactobacillus kefiri)

1. Identity, Nomenclature, and Taxonomy

Lactobacillus kefiri is a gram-positive, heterofermentative lactic acid bacterium (LAB) first formally described and named by Kandler and Kunath in 1983. Its current valid name is Lentilactobacillus kefiri (Kandler and Kunath 1983) Zheng et al. 2020, with the basonym Lactobacillus kefiri corrig. Kandler and Kunath 1983; the species epithet kefiri is a New Latin genitive noun meaning "of kefir," referring directly to its source of isolation. The older name Lactobacillus kefiri — and even earlier, Lactobacillus kefir (an orthographic variant) — remains widely used in the scientific literature and in product labeling, and both designations are retained for continuity purposes by regulatory bodies.

The reclassification into the genus Lentilactobacillus occurred as part of a landmark 2020 taxonomic revision. It was formally published by Zheng, Wittouck, Salvetti, Franz, Harris, Mattarelli, O'Toole, and colleagues in the International Journal of Systematic and Evolutionary Microbiology (2020; 70:2782–2858). This work proposed reclassification of the genus Lactobacillus into 25 genera — including the emended genus Lactobacillus itself and 23 novel genera — based on core genome phylogeny, pairwise average amino acid identity, clade-specific signature genes, physiological criteria, and ecology.

Genomically, growth of L. kefiri is observed at 15 °C but not at 45 °C; the genome size of the type strain is 2.23 Mbp; and the mol% G+C content of the DNA is 41.7. The species was isolated from kefir as part of its core microbiota. It is defined as a heterofermentative lactic acid bacterium primarily associated with fermented milk products, particularly in the Northern Caucasus, characterized by its growth at 15 °C, forming chains of rods or long filaments; it has approximately 40% DNA homology with Lactobacillus buchneri and is found in beer and kefir products.

The type strain is deposited under multiple culture collection numbers. These include ATCC 35411, CCUG 30673, CIP 103006, DSM 20587, IFO 15888, JCM 5818, LMG 9480, and NBRC 15888. Phylogenetically, the species belongs to the order Lactobacillales, family Lactobacillaceae, genus Lentilactobacillus.

Three Lactobacillus-group species are specifically and consistently identified in the core microbiota of kefir grains: Lentilactobacillus kefiri (basonym: Lactobacillus kefir), Lactobacillus kefiranofaciens, and Lentilactobacillus parakefiri (basonym: Lactobacillus parakefir). Of these, L. kefiri and L. kefiranofaciens are consistently reported as the dominant bacterial species in kefir grain ecosystems worldwide. Formerly known as Lactobacillus kefir or Lactobacillus kefiri, the organism is mainly found as part of the microbiota of kefir grains and kefir drinks (Kandler et al., 1983) but has also been isolated from Camembert cheese, ricotta forte (Baruzzi et al., 2000), and raw camel milk (Akhmetsadykova et al., 2015). It was isolated from more limited sources than other main dairy heterofermentative lactobacilli; it was mainly found in beer, kefir drink, and kefir grains.

2. Natural Sources and Ecological Habitat

Lentilactobacillus kefiri inhabits kefir grains — complex, cauliflower-shaped, gelatinous masses comprising a polysaccharide matrix (primarily kefiran) within which bacteria, acetic acid bacteria, and yeasts exist in a highly organized symbiotic consortium. Kefir is a traditionally fermented dairy beverage containing a complex microbial community of yeast and bacteria. Typically kefir is made by inoculating milk with kefir grains, an exopolysaccharide matrix containing said microbial community. While the microbial composition varies slightly among traditional kefirs from different sources, the key bacterial players include lactic acid bacteria such as Lactobacillus kefiranofaciens and Lentilactobacillus kefiri, acetic acid bacteria such as Acetobacter pasteurianus, and yeasts such as Saccharomyces cerevisiae, Pichia fermentans, Monosporozyma unispora, Kluyveromyces marxianus, and Kluyveromyces lactis.

Metagenomic and culture-dependent analyses of artisanal kefirs from diverse geographic origins confirm L. kefiri as a consistently abundant species. 16S rRNA gene sequencing was used to reveal bacterial populations and elucidate the diversity and abundance of LAB species in international artisanal kefirs from Fusion Tea (Britain), the Caucasus region, Ireland, Lithuania, and South Korea; bacterial species found in high abundance in most artisanal kefirs included Lactobacillus kefiranofaciens and Lentilactobacillus kefiri.

Despite desirable probiotic traits, research on L. kefiri remains relatively limited compared to other well-characterized probiotics. A bibliometric analysis using the Web of Science Core Collection database (2005 to 2025) identified only 173 relevant studies, underscoring the nascent stage of research on this species. The current body of work predominantly focuses on strain isolation and preliminary screening, reflecting foundational knowledge gaps that stem from its relatively recent taxonomic reclassification and limited early-stage research.

3. Traditional and Historical Use

The history of L. kefiri is inseparable from the history of kefir itself. Kefir has a rich history dating back thousands of years and is thought to have originated in the northern Caucasus, the region between the Black Sea and the Caspian Sea. For many centuries, milk kefir was a closely guarded secret of the Northern Caucasus region in Russia. The people of the Northern Caucasus region are renowned for their longevity, with one of the highest proportions of centenarians in the world; milk kefir is a dietary staple in this region.

Traditional kefir was made in goatskin bags that were hung near a doorway; the bags would be knocked by anyone passing through to keep the milk and kefir grains well mixed. Traditionally, milk kefir was made by combining fresh milk and kefir grains inside goatskin bags. During the daytime, the bags were hung in the sunshine of doorways and prodded or pushed by each person who went through. As the kefir was consumed, more fresh milk was added to the bag, forming a continuous fermentation cycle. Traditional kefir is fermented at ambient temperatures, generally overnight; fermentation of the lactose yields a sour, carbonated, slightly alcoholic beverage, with a consistency and taste similar to drinkable yogurt.

In this region, kefir grains are known by the name "Grains of the Prophet." The traditional legend holds that the prophet Mohammed gifted kefir grains to the Orthodox Christians in the area; Mohammed is said to have taught the people how to make kefir, and the people revered kefir as a health-promoting food. The kefir grains and methods for making kefir were kept secret for many generations.

Kefir spread from the former Soviet Union to the rest of Europe, Canada, Japan, and the United States by the early 21st century. Scientific interest in the fermented product gained momentum in the late 19th century. Elie Metchnikoff, who was awarded the 1908 Nobel Prize in Physiology or Medicine for the discovery of phagocytosis, had theories about fermented milk; he wondered about the beneficial effects of lactic acid bacteria and attempted to alter his own intestinal microbiota by drinking fermented milk he prepared himself from lactobacilli isolates. Metchnikoff noticed health benefits from drinking kefir and documented his work in The prolongation of life; optimistic studies.

The preparation in traditional cultures was therefore an empirical fermented dairy food used for general health maintenance, particularly digestive and longevity-associated purposes, well before the microbial species within it were characterised. L. kefiri itself was not isolated and formally described until 1983, so all traditional use attributable to this organism is necessarily indirect — it was consumed as part of the complex kefir microbial consortium, not as a purified isolate.

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

4.1 Surface Layer (S-layer) Proteins

One of the most studied and distinctive biological features of L. kefiri is the presence of a proteinaceous surface layer known as an S-layer. The S-layer is a proteinaceous envelope constituted by subunits that self-assemble to form a two-dimensional lattice that covers the surface of different species of Bacteria and Archaea, and it can be involved in cell recognition of microbes, among other distinct functions. Both proteomic and genomic approaches have been used to characterize the sequences of S-layer protein (SLP) encoding genes expressed by aggregative and non-aggregative strains of potentially probiotic L. kefiri. The O-glycosylation site SASSAS was found in all L. kefiri SLPs.

The S-layer proteins play a pivotal role in gut adhesion. Investigation of the mucus-binding properties of aggregating and non-aggregating kefir-isolated strains of L. kefiri demonstrated that all strains tested were able to adhere to commercial gastric mucin, and extracted mucus from small intestine and colon. Extraction of surface proteins significantly reduced the adhesion of three selected strains (CIDCA 8348, CIDCA 83115, and JCM 5818); the S-layer protein extracts from all strains of L. kefiri were capable of binding to gastric mucin and intestinal mucus. These findings establish S-layer proteins as the principal molecular mediators of gut adhesion in this species.

S-layer proteins of L. kefiri have also been demonstrated to have biological activity against bacterial toxins. The glycosylation of the S-layer from L. kefiri has been shown to play a role in receptor binding and thus in inhibition of infection. In published in vitro work, surface proteins from L. kefiri strains have been shown to antagonize the cytopathic effects of Clostridium difficile toxins — an activity that is reviewed in more detail under the gastrointestinal section below.

4.2 Heterofermentative Metabolism and Organic Acid Production

L. kefiri is an obligate heterofermentative organism. It produces l-lactic acid and CO₂ from glucose, but not from gluconate. This metabolic pathway generates lactic acid as the primary antimicrobial metabolite; lactic acid acts by lowering the local pH, inhibiting the growth of many enteric pathogens. The antimicrobial capacity of kefir-associated organisms may be ascribed to the presence of hydrogen peroxide, peptides (bacteriocins), ethanol, carbon dioxide, diacetyl, and organic acids (lactic and acetic acids), which inhibit pathogens, particularly in the intestinal mucosa.

4.3 Bacteriocins and Other Antimicrobial Peptides

Multiple strains of L. kefiri produce proteinaceous antimicrobial compounds. All tested L. kefiri strains were able to inhibit both Gram-positive and Gram-negative pathogens. The bacteriocins are a group of antimicrobial peptides that have been considered as novel bio-preservatives to combat foodborne pathogens. In a metagenomic study, L. kefiri strains showed tolerance to acidic pH and the presence of bile salts, adhesion capability to Caco-2 cells, in vitro antibacterial activity, and production of antibacterial proteins; metagenomic analysis of contigs associated with these species showed the presence of genes involved in exporting polyketide antibiotics and bacteriocin production.

4.4 Immunomodulatory Molecules

Lactobacillus kefiri, isolated from kefir, has shown potential for immunomodulatory response activity in several studies. The specific molecular mediators are not yet fully characterized, but the immunomodulatory effects observed in experimental models appear to be mediated in part by the S-layer glycoproteins and by the bacterium's direct interaction with immune cells. The S-layer glycoprotein from L. kefiri CIDCA 8348 has been reported in separate published work (Malamud et al., 2018) to enhance macrophage responses to LPS in a calcium-dependent manner, suggesting a pattern recognition receptor-mediated pathway.

4.5 Bile Salt Tolerance and Gastric Acid Resistance

Probiotic utility requires survival through the gastrointestinal tract. Certain isolates of L. kefiri exhibit strong tolerance to gastrointestinal conditions, enabling survival through the digestive tract. Experimental evidence confirms this: L. kefiri strains showed tolerance to acidic pH and the presence of bile salts, and adhesion capability to Caco-2 cells. Furthermore, L. kefiri strains preserve a high percentage of viability after both spray-drying and freeze-drying procedures, which is of direct relevance to their formulation as dietary supplements.

5. Scientific Evidence by Area of Use

5.1 Gastrointestinal Health and Gut Microbiota Modulation

Evidence level: Preclinical (animal and in vitro); limited ex vivo human tissue data.

The most substantial body of mechanistic research on L. kefiri concerns the gastrointestinal system. In a well-cited animal study, the strain L. kefiri CIDCA 8348 was selected based on in vitro assays on PBMC and Caco-2 cells and administered to healthy Swiss mice daily for 21 days. The probiotic treatment increased IgA in feces and reduced expression of proinflammatory mediators in Peyer's patches and mesenteric lymph nodes, where it also increased IL-10. In the ileum, IL-10, CXCL-1, and mucin 6 genes were upregulated; meanwhile, in the colon, mucin 4 was induced whereas IFN-γ, GM-CSF, and IL-1β genes were downregulated. These results collectively suggest that L. kefiri CIDCA 8348 can modulate mucosal immune responses and intestinal barrier gene expression in healthy mice, though the significance for humans requires further investigation.

The same strain, CIDCA 8348, has also been studied using ex vivo human tissue from IBD patients. Although L. kefiri has shown anti-inflammatory effects in animal models, few studies have been done using human mucosal T cells; this particular study investigated the immunomodulatory effects of this bacterium on intestinal T cells from patients with active IBD. Mucosal biopsies and surgical samples from IBD adult patients (n = 19) or healthy donors (n = 5) were used. It was found that L. kefiri reduced spontaneous release of IL-6 and IL-8 from inflamed biopsies ex vivo. Activated lamina propria T cells from IBD patients showed low proliferative rates and reduced secretion of TNF-α, IL-6, IFN-γ, and IL-13 in the presence of L. kefiri. In addition, L. kefiri induced an increased frequency of CD4+FOXP3+ T cells along with high levels of IL-10. This was reported as the first report showing an immunomodulatory effect of L. kefiri CIDCA 8348 on human intestinal cells from IBD patients. This work is important but uses ex vivo tissue, not a clinical intervention trial. No randomized controlled trials (RCTs) in IBD patients exist for L. kefiri at this time.

Regarding gut microbiota composition, L. kefiri supplementation in a mouse model generated an impact on gut microbiota composition, changing Bacteroidetes and Firmicutes profiles. The direction and clinical relevance of such shifts in humans have not been established in controlled human trials specifically for L. kefiri as an isolated strain.

In the area of colitis, the effects of oral administration of Lentilactobacillus kefiri SGL 13, combined with Andrographis paniculata (as "Paniculin 13™"), were evaluated in DSS-treated C57BL/6J mice. Colitis was induced by administering 1.5% DSS in drinking water for 9 days; forty male mice were divided into four groups. The results showed that body weight loss and Disease Activity Index (DAI) score were improved by Paniculin 13™. These are animal-model findings only.

5.2 Inhibition of Clostridium difficile Toxins

Evidence level: In vitro only.

A distinct and notable line of research concerns the capacity of L. kefiri S-layer proteins to antagonize the cytotoxic effects of Clostridium difficile toxins in vitro. Published research (Carasi et al., 2012) demonstrated that surface proteins from kefir-isolated L. kefiri strains could antagonize the cytopathic effects of C. difficile toxins in cell culture models. This finding is mechanistically plausible given the established role of S-layer proteins in receptor binding and pathogen exclusion, but no human clinical trials have evaluated whether L. kefiri supplementation reduces C. difficile-associated diarrhea in patients.

5.3 Chemotherapy-Induced Diarrhea

Evidence level: Single prospective observational study (human), no RCT.

One prospective observational study assessed L. kefiri as a specific isolate in a clinical setting. The aim of the study was to evaluate the clinical effectiveness of Lactobacillus kefiri LKF01 (Kefibios®) in the prevention or treatment of chemotherapy-related diarrhea in cancer patients. A prospective observational study design was used; patients enrolled were adults treated for at least four months with 5-FU-based chemotherapy, and Kefibios® was administered daily. The primary outcome was the evaluation of the incidence of grade 3–4 chemotherapy-induced diarrhea. Seventy-six patients were included in the final analysis. A 6.6% incidence of high-grade diarrhea was found in the evaluated population. The product was formulated as a powder in capsules dispersed in vegetable oil. Kefibios® was consumed every day — 5 drops per day with an empty or full stomach, before or after a meal with some liquid; five drops of Kefibios® include at least 1 billion vital microorganisms. As an uncontrolled observational study, these results are hypothesis-generating rather than conclusive.

5.4 Metabolic Health, Obesity, and Lipid Profile

Evidence level: Animal models; one small non-randomized human study.

Several preclinical studies have assessed L. kefiri in the context of metabolic disorders. In a mouse model using a fructose-rich diet to induce obesity and metabolic syndrome features, L. kefiri treatment completely inhibited local inflammation (TNF-α, IL-1β, IL-6, and IFN-γ) in epididymal adipose tissue; L. kefiri supplementation generated an impact on gut microbiota composition, changing Bacteroidetes and Firmicutes profiles. Overall, the results indicated that administration of the probiotic prevented the deleterious effects of high-fructose diet intake and should therefore be promoted to improve metabolic disorders. These results are in a rodent model and do not translate directly to human application.

Certain isolates of L. kefiri have also been shown to modulate immune responses, regulate lipid metabolism, support gut microbiota homeostasis, and reduce cholesterol levels. These attributes have been demonstrated largely in preclinical models.

In one small, non-randomized prospective human study, the effect of Lactobacillus kefiri, together with PENS T6 (percutaneous electrical nerve stimulation at acupoint T6) and a hypocaloric diet, on weight loss, hypertension, and laboratory glycemic and lipid profile was investigated. A prospective non-randomized study was conducted in adult patients with a body mass index (BMI) greater than 30 kg/m². Patients were divided into two groups: those undergoing PENS-T6 and hypocaloric diet, and those additionally receiving probiotics including Lactobacillus kefiri. The addition of Lactobacillus kefiri to PENS T6 and a low-calorie diet was reported to increase weight loss and further improve glycemic and lipid profiles. The non-randomized design and multicomponent intervention make it impossible to attribute observed effects to L. kefiri alone.

5.5 Antimicrobial Activity against Foodborne Pathogens

Evidence level: In vitro and food-science studies only.

All L. kefiri strains tested were able to inhibit both Gram-positive and Gram-negative pathogens in agar spot assays. Kefir, a fermented dairy beverage, exhibits antimicrobial activity due to many metabolic products, including bacteriocins generated by lactic acid bacteria; in studies of artisanal kefir products from Britain, Ireland, Lithuania, the Caucasus region, and South Korea, Listeria monocytogenes, Salmonella enterica serovar Enteritidis, Staphylococcus aureus, and Bacillus cereus were inhibited by artisanal kefirs made with kefir grains from diverse origins. Bacteriocins present in artisanal kefirs were determined to be the main antimicrobials in all kefirs examined. However, these studies examine kefir as a whole product rather than isolating the contribution of L. kefiri alone.

5.6 Mycotoxin Binding

Evidence level: In vitro only.

Lactobacillus kefiri, among other LAB species, has demonstrated the capacity to bind to prevalent mycotoxins like aflatoxin B1 (AFB1), ochratoxin A (OTA), patulin, zearalenone (ZEN), and deoxynivalenol (DON), thereby effectively diminishing their toxicity in in vitro settings. L. kefiri has also been found to bind toxic metals and mycotoxins, raising its potential for future use in emergency toxicology. These findings are entirely in vitro and their in vivo relevance in humans is unknown.

6. Body Systems and Health Areas Associated with L. kefiri

• Gastrointestinal system: Gut microbiota modulation, intestinal mucosal immunity (IgA secretion), mucosal barrier function (mucin gene expression), anti-inflammatory effects on intestinal T cells, and antagonism of pathogen-derived toxins.
• Immune system: Immunomodulation via cytokine regulation (upregulation of IL-10, downregulation of pro-inflammatory cytokines TNF-α, IL-6, IFN-γ, IL-1β, GM-CSF); induction of regulatory T cell (CD4+FOXP3+) populations in ex vivo IBD tissue.
• Metabolic system: Preclinical data on cholesterol, lipid metabolism, insulin sensitivity, and adipose tissue inflammation; limited clinical data.
• Antimicrobial/food safety: Inhibition of foodborne pathogens (in vitro); mycotoxin adsorption (in vitro).
• Oncology supportive care: One observational study in chemotherapy patients for reduction of treatment-associated diarrhea.

7. Dosage Forms and Doses Reported in Studies

As a dietary supplement or probiotic product, L. kefiri is administered in several forms, reflecting the practical need to maintain viability. L. kefiri strains preserve a high percentage of viability after both spray-drying and freeze-drying procedures, making lyophilized (freeze-dried) powder the most common formulation format. Other preparations include:

• As part of kefir fermented beverage: Traditional preparation via fermentation of cow, sheep, or goat's milk with kefir grains. Kefir is made by fermenting cow, sheep, or goat's milk using special microbial cultures called kefir grains, composed of symbiotic colonies of yeasts and bacteria. In this form, L. kefiri is not dosed in isolation.
• Lyophilized powder in oil suspension (Kefibios® LKF01, DSM 32079): Lactobacillus kefiri (Kefibios®) LKF01 (DSM 32079) powder was contained in capsules, and the content was then mixed in a vegetable oil solution. The solution had to be shaken well before use. Kefibios® was consumed every day (5 drops per day) with an empty or full stomach, before or after a meal with some liquid; five drops include at least 1 billion vital microorganisms.
• Animal study dosing: 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 normal findings. In the mouse colitis study, Paniculin 13™ was composed of lyophilized L. kefiri SGL 13 (DSM 27331), dry extract of A. paniculata, and inulin; each daily dose per mouse consisted of SGL 13 at 5 × 10⁸ CFU/kg body weight.
• Freeze-dried starter cultures for kefir production: Five bacterial species (Lentilactobacillus kefiri, Lactobacillus kefiranofaciens, Lactococcus cremoris, Leuconostoc mesenteroides, and Acetobacter pasteurianus) and 4 yeast species underwent freeze-drying prior to viability testing and use as starter cultures in kefir fermentations.

No established human clinical dosage guidelines for L. kefiri as a standalone supplement have been published by a pharmacopeial body or regulatory agency. The doses used in the only identified human observational study were those of the commercial product Kefibios® as described above. Research on L. kefiri remains relatively limited compared to other well-characterized probiotics, and dose-response relationships in humans have not been established.

8. Regulatory Status and Safety

8.1 Qualified Presumption of Safety (QPS) and GRAS Status

Lactobacilli are generally regarded as safe (GRAS) and most of them (as Lactobacillus kefiri) are included in the QPS list of the European Union due to their long history of use in fermented dairy products and their presence in the human intestinal tract. Lactobacillus species are generally recognized as safe (GRAS) by the US Food and Drug Authority (FDA) and belong to the qualified presumption of safety (QPS) list of the European Food Safety Authority (EFSA). EFSA further specifies that "to maintain continuity within the QPS list, all the strains belonging to a previously designated Lactobacillus species will be transferred to the new species" and that "both the previous and new names will be retained." This means the QPS status of Lactobacillus kefiri carries over to Lentilactobacillus kefiri under the 2020 reclassification.

8.2 Hemolytic Activity

Hemolytic activity is an important safety parameter for any organism intended for human consumption. None of the L. kefiri strains tested in published safety characterization work caused α- or β-hemolysis. This is consistent with the broader genus-level data: in the genus, hemolytic activity has a very low frequency and only α-hemolysis has been reported for lactobacilli isolated from foods and dairy products.

8.3 Antibiotic Susceptibility and Resistance

The absence of acquired antimicrobial resistance is a key safety criterion for probiotic organisms, since resistant genes could theoretically be transferred to pathogenic bacteria in the gut. All L. kefiri strains tested were susceptible to tetracycline, clindamycin, streptomycin, ampicillin, erythromycin, kanamycin, and gentamicin; meanwhile, two strains were resistant to chloramphenicol. All tested bacteria exhibited MIC values lower than the breakpoints recommended for heterofermentative lactobacilli by EFSA for tetracycline, clindamycin, streptomycin, ampicillin, erythromycin, kanamycin, and gentamicin. Further research, such as the study of the distribution of chloramphenicol MICs, could contribute to determining whether resistance is acquired (an unacceptable strain characteristic) or intrinsic (an acceptable strain characteristic) according to EFSA.

8.4 Potential for Infection in Vulnerable Populations

Certain Lactobacillus strains have been associated with cases of sepsis, endocarditis, or bacteremia, mostly in association with a severe underlying disease. This is a class-level consideration for the genus and not specific to L. kefiri. To fully exploit the potential probiotic properties of these microorganisms and help human health, further investigation is necessary to elucidate the mechanisms behind the biological activity and the genotypic characteristics of the isolated strains.

8.5 Animal Safety Data

Regarding in vitro results, L. kefiri CIDCA 8348 was selected to perform in vivo studies. 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 normal findings. While reassuring, these are mouse data and cannot be used to establish human safety with certainty.

8.6 Viability and Formulation Considerations

The viability of the probiotic upon consumption is a practical safety and efficacy consideration. The conditions of kefir production can alter the community composition of microorganisms of the kefir grains; chemical and probiotic composition of the final product may be affected by fermentation techniques, duration and temperature, milk variants, grain origin, grain-to-milk ratio, and post-fermentation cooling duration. For supplement formulations, freeze-dried starter culture fermentations were compared to kefir made with fresh starter cultures; all starter cultures were able to ferment milk to a similar pH, however freeze-dried cultures prepared with milk took a longer time to complete fermentation.

9. Current Research Gaps and Outlook

Many isolated strains of L. kefiri have shown antimicrobial activity against pathogens and their toxins, exhibited immunomodulatory activity, and induced some beneficial effects at the metabolic level. Certain L. kefiri strains therefore emerge as excellent candidates for the development of both food supplements and new fermented foods with health-promoting properties. However, the availability of genomic information is still very limited, and much more work must be done in order to explore the potentiality of L. kefiri as a probiotic and a source of bioactive metabolites.

There is currently very limited scientific evidence supporting the effects of kefir consumption on the human oral and gut microbiome. High-quality human clinical trials are essential to establish the safety and effectiveness of kefir before it can be advised for use in treating conditions linked to the oral and gut microbiota or metabolic health.

In summary, Lentilactobacillus kefiri (formerly Lactobacillus kefiri) is a distinctive, well-characterized kefir-associated lactic acid bacterium with an established taxonomic identity, a long history of empirical use as part of the kefir fermentation tradition, and a growing body of mechanistic and preclinical evidence supporting its potential as a probiotic. Its S-layer proteins represent a unique structural feature with demonstrated functional roles in gut adhesion and pathogen antagonism. However, robust human clinical trial data for L. kefiri as an isolated, defined-strain supplement remain sparse, and evidence-based conclusions about specific health indications, optimal doses, and comparative efficacy cannot yet be drawn. The species is considered safe under EFSA's QPS framework and FDA's GRAS designation, though vigilance is warranted in severely immunocompromised populations, consistent with class-level guidance for all lactobacilli.

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