IngredientsLactococcus lactis is a Gram-positive, non-sporulating, non-motile, aerotolerant, homofermentative bacterium belonging to the family Streptococcaceae, order Lactobacillales, class Bacilli, and phylum Firmicutes. It is a Gram-positive, non-sporulating, aerotolerant bacterium belonging to the Streptococcaceae family. Formally classified as a lactic acid bacterium (LAB), it was originally described under the name Streptococcus lactis before being reclassified into the genus Lactococcus in 1986. The subspecies L. lactis subsp. lactis was formally attributed to (Lister 1873) Schleifer et al. 1986, with the type strain ATCC 19435, and was previously classified as Streptococcus lactis subsp. lactis.
Lactococcus lactis currently contains four subspecies: L. lactis subsp. lactis, L. lactis subsp. hordniae, L. lactis subsp. cremoris, and L. lactis subsp. tructae. Of these, only subsp. lactis and subsp. cremoris are of industrial interest. Additionally, a biovar known as Lactococcus lactis subsp. lactis biovar diacetylactis is recognized. On the basis of their 16S rRNA gene sequence, the two primary subspecies are estimated to have diverged some 17 million years ago.
Phenotypically, the subspecies are distinguishable. The ability to grow in 4% NaCl at 40°C and pH 9.2, and to degrade arginine, are the main characteristics of L. lactis subsp. lactis, whereas L. lactis subsp. cremoris does not share these features. However, genotype–phenotype mismatches are well documented: several molecular taxonomic studies have revealed that many natural (wild) Lactococcus lactis strains of dairy origin that are phenotypically representative of subsp. lactis cluster genotypically within subsp. cremoris and vice versa.
Lactococcus species are widely distributed in dairy products, plants, insects, fish, and animals. Lactococcus lactis is an organism of substantial economic importance, used extensively in the production of fermented foods, and widely held to have evolved from plant strains. The domestication of this organism to the milk environment is associated with genome reduction and gene decay, and the acquisition of specific genes involved in protein and lactose utilization by horizontal gene transfer. Lactococcus lactis, a lactic acid-producing bacterium, is commonly found in buttermilk and cheese products. It has also been isolated from traditional fermented foods across Asia and from raw, spontaneously fermented milk products worldwide. Strains have been isolated from spontaneously fermented buffalo milk called Dadih.
Lactococcus lactis is encountered in several forms, both in food and in supplement and research contexts:
Although Lactococcus lactis was not formally described or named as a distinct species until modern bacteriology, the microorganism has been integral to human food preparation for millennia through the spontaneous fermentation of milk and other foodstuffs.
The use of lactic acid bacteria in the fermentation process to produce fermented foods has a long history. Lactococcus lactis has been used for centuries in the fermentation of food, especially cheese, yoghurt, sauerkraut, and the like. For a very long time, L. lactis has been used in milk fermentation, both in well-monitored industrial settings and on a small scale in traditional operations.
The practical applications of L. lactis in food preservation and fermentation span virtually all dairying civilizations. Through the consumption of fermented dairy products, it is estimated that humans ingest up to 1018 lactococcal cells per annum. Across Asia and Europe, traditional fermented dairy preparations — including artisanal cheeses, buttermilk, sour cream, and kefir — have historically relied on naturally occurring lactococcal strains. In Asia, a wide variety of traditional fermented foods are consumed, and these traditional fermented foods can be explored for the isolation of probiotics with preservation potential. Strains indigenous to specific regions, such as Dadih (a fermented buffalo milk from Indonesia), continue to be characterized as authentic traditional vehicles for L. lactis.
The purposeful use of these preparations historically included the preservation of milk from spoilage, the development of flavor and texture in cultured dairy products, and the acidification of food to inhibit putrefactive microorganisms — all effects now understood to result from the metabolic activities of the bacterium itself. The organism was not recognized or consciously selected as a health ingredient in the modern supplement sense until the late twentieth century, when understanding of the gut microbiome and probiotics began to accelerate.
Lactococcus lactis exerts its biological effects through a range of metabolites and structural components produced during fermentation and cellular activity:
Lactococci are homofermentative and are used for the production of L(+) lactic acid from glucose. Lactic acid reduces environmental pH, creating conditions hostile to many pathogenic and spoilage organisms, and is a key preservative metabolite of the species.
Certain strains of L. lactis produce ribosomally synthesized antimicrobial peptides called bacteriocins. Nisin is a ribosomally synthesized bacteriocin containing lanthionine residues, classified as a lantibiotic. It is produced only by certain strains of Lactococcus lactis. It has a relatively wide antimicrobial spectrum and can inhibit the proliferation of most Gram-positive bacteria. Nisin is heat stable and active at low pH, making it a good candidate for a natural food preservative. Nisin has been granted "Generally Recognized as Safe" (GRAS) status for certain applications by the U.S. Food and Drug Administration (FDA).
The mechanism of nisin involves interaction with the bacterial cell wall precursor Lipid II. Bacteriocins such as the lactococcal lantibiotics nisin and lacticin 3147, as well as the non-lantibiotic lactococcin 972, have been reported to inhibit cell wall biosynthesis by binding to cell wall precursors. Beyond nisin, L. lactis strains can produce other bacteriocins such as lacticin Q. The lactococcal strain QU 5 produces a bacteriocin termed lacticin Q (LnqQ), and both LnqQ and nisin A have been reported to have widespread antimicrobial activity against Gram-positive bacteria at concentrations in the nanomolar range.
During fermentation, LAB have the capacity to produce significant amounts of bioactive substances, such as peptides, bacteriocins, lactic acid, exopolysaccharides (EPSs), enzymes, and others. Lactic acid bacteria with immunomodulatory capabilities exert their beneficial effects through several molecules, including cell wall components, peptidoglycan, and exopolysaccharides (EPS), that are able to interact with specific host cell receptors. The postbiotic effects attributed to EPS include: antioxidant effects, immunomodulatory activities, anti-tumour effects, gut microbiota stimulation, and cholesterol-lowering activities. A strain of Lactococcus lactis F-mou was found to produce a type of EPS showing good water and oil holding capacities, high antioxidant efficiency and excellent anti-clotting activity, and strong inhibitory activity against a variety of pathogenic bacteria.
The dairy starter bacterium Lactococcus lactis has the potential to synthesize both folate (vitamin B11/B9) and riboflavin (vitamin B2). These vitamins play essential roles in cellular metabolism and red blood cell formation. Research has demonstrated that engineered riboflavin-producing strains of L. lactis are biologically active: Lactococcus lactis is a commonly used starter strain that can be converted from a riboflavin consumer into a riboflavin-producing factory by overexpressing its riboflavin biosynthesis genes. These riboflavin-producing strains were able to eliminate most physiological manifestations of ariboflavinosis, such as stunted growth, elevated erythrocyte glutathione reductase activation coefficient values, and hepatomegaly, in a riboflavin depletion–repletion model. With respect to folate, hematologic studies showed that administration of L. lactis strains was able to revert partial megaloblastic anemia caused by folate deficiency. No significant differences were observed in the bioavailability of folates containing different glutamyl tail lengths. This was the first study to demonstrate that folates produced by engineered lactic acid bacteria represent a bioavailable source of this essential vitamin.
The structural components of the L. lactis cell wall, including peptidoglycan and surface-associated proteins, are recognized by pattern-recognition receptors of the host immune system. L. lactis strain Plasma directly activates plasmacytoid dendritic cells (pDCs) and induces type I and III interferons (IFNs) through toll-like receptor 9 (TLR9) stimulation. This TLR9-mediated pathway is now considered a primary mechanism by which heat-killed preparations of the JCM 5805 strain activate innate immunity.
Some strains of L. lactis have been reported to produce gamma-aminobutyric acid (GABA), a neurotransmitter with potential neurological and anxiolytic relevance, though research in this area specific to L. lactis remains limited compared to studies in other LAB species. GC-MS analysis of L. lactis MKL-8 revealed bioactive metabolites reported in the literature to have immunomodulatory effects, antioxidant, collagen synthesis, and wound healing properties.
The health-relevant mechanisms ascribed to Lactococcus lactis encompass both direct microbial activities and host-mediated responses:
The most clinically studied immune application of L. lactis involves a specific heat-killed strain, L. lactis JCM 5805 (LC-Plasma / IMMUSE™). Multiple randomized controlled trials (RCTs) have reported that oral intake of Lactococcus lactis strain Plasma (LC-Plasma) activates pDCs and reduces cold-like symptoms. A meta-analysis was conducted to comprehensively evaluate the effects of oral LC-Plasma intake on pDC activation and cold-like symptoms by comparing healthy adults.
LC-Plasma has been shown to be a unique LAB that activates pDCs in vitro and in vivo. There are several reports regarding the efficacy of LC-Plasma supplementation in healthy subjects. LC-Plasma yogurt intake for 4 weeks activated maturation markers of pDC, and intake for 12 weeks reduced the cumulative number of incidence days of influenza-like symptoms.
A double-blinded, randomized, placebo-controlled trial in male athletes examined the effect of heat-killed L. lactis JCM 5805 on immunity and fatigue during consecutive high-intensity exercise. The primary efficacy outcomes were maturation markers (CD86, HLA-DR) on dendritic cells and subjective indices (evaluation of influenza and upper respiratory tract infection, and symptom severity including fatigue). Secondary outcomes were markers of muscle damage (creatine phosphokinase and lactate dehydrogenase) and stress markers (adrenaline and salivary cortisol).
Mechanistic in vitro data corroborate the clinical findings. Probiotics including Lactococcus lactis strain Plasma (LC-Plasma) have recently shown antiviral effects by activating plasmacytoid dendritic cells (pDCs). In a study stimulating peripheral blood mononuclear cells (PBMCs) collected from healthy participants with LC-Plasma, the supernatant derived from LC-Plasma-stimulated PBMCs exhibited dose-dependent inhibition of replication in Influenza A virus subtype H1N1 and SARS-CoV-2.
Evidence strength: Multiple RCTs and a published meta-analysis support the pDC-activating effect of the JCM 5805 strain (LC-Plasma). Evidence for reduction in cold and influenza-like symptoms in healthy adults is promising. The evidence is strain-specific and cannot be generalized to other L. lactis strains. The majority of trials are relatively small and conducted primarily in Japan; independent large-scale replication in diverse populations is limited.
The most notable human clinical investigation used a genetically modified strain of L. lactis (LL-Thy12) engineered to deliver human IL-10 in situ to the colonic mucosa. Ten Crohn's disease patients were treated with genetically modified Lactococcus lactis (LL-Thy12) in which the thymidylate synthase gene was replaced with a synthetic sequence encoding mature human interleukin-10. Ten patients were included in a placebo-uncontrolled trial. Treatment with LL-Thy12 was safe because only minor adverse events were present, and a decrease in disease activity was observed. Fecally recovered LL-Thy12 bacteria were dependent on thymidine for growth and interleukin-10 production, indicating that the containment strategy was effective. Treatment with the bacterium was safe because only minor adverse events were being reported, with flatulence being the most prominent temporary side effect.
The clinical parameters, including the assessment of adverse events and scoring for disease activity, showed that the topical application of recombinant proteins by L. lactis-mediated delivery is indeed safe for the patient, and that systemic side effects can be circumvented by such an approach. This absence of major side effects allows long-term treatment, as is necessary for the management of chronic disease.
Evidence strength: The IBD application is based on a single, small (n=10), placebo-uncontrolled Phase I trial in Crohn's disease patients using a genetically modified strain. While the safety findings are clinically meaningful, the trial was not powered to detect efficacy. This remains an investigational application for a GMO strain, not a commercially available probiotic supplement. Preclinical (animal model) evidence is more extensive and consistently positive, but translation to human clinical benefit has not been established in controlled trials.
Lactococcus lactis is a globally recognized safe microorganism for the regulation of the intestinal micro-ecological balance of animals and improving the immune performance of the host. Some studies indicate that EPS demonstrates the potential to stimulate and enhance the populations of beneficial bacteria in the gut. To act as a stimulant in the gut, it is of great importance that the EPS can survive the harsh gastrointestinal environment. Some literature reports that EPS produced by Lactococcus strains maintains integrity through digestive stress, making the potential of the polysaccharide as a prebiotic-like substrate viable.
The LAB are evidenced to be good probiotics as they accelerate the growth of beneficial microbial gut flora and have been proven effective against diarrhoea, irritable bowel disorder, allergies, stimulation of immunity, and lactose intolerance. However, it should be noted that much of this evidence comes from LAB as a broad category and is not always L. lactis-specific.
Evidence strength: Largely preclinical (animal and in vitro) for gut barrier and microbiota effects specific to L. lactis. Human trial evidence in this area is limited and primarily derives from trials conducted with the LC-Plasma postbiotic strain or from broader LAB research not isolating L. lactis effects.
A double-blind, randomized, placebo-controlled Phase I–II trial enrolled 81 healthy subjects (median age 28, range 18–59 years) to investigate the immunomodulatory effects of L. lactis spp. cremoris (EDP1066). The aim was to investigate the pharmacodynamic effects of three monoclonal microbial formulations of L. lactis spp. cremoris (EDP1066) on the immune response to keyhole limpet hemocyanin (KLH). Potential effects on the gut microbiota were also investigated. Subjects were randomized to 28 days of enteric-coated capsules at five doses (n=13) (1.5 × 1012 total cells daily), freeze-dried powder at one dose (n=12) (3.0 × 1011 total cells daily) or five doses (n=12), minitablets at one or five doses (n=12 each), or placebo (n=20) prior to KLH immunization.
Evidence strength: This is a Phase I/II randomized controlled trial in healthy adults, providing the most rigorous human evidence for immunomodulatory effects of a live L. lactis probiotic formulation. Results are strain-specific and the trial was primarily a dose-finding, safety, and pharmacodynamic study. Confirmation in larger efficacy-powered trials in clinically relevant populations is needed.
Data concerning the anti-proliferative effect of L. lactis strains are limited. Soluble cell extract of a L. lactis ssp. lactis strain (L.lac CF) was shown to have an antiproliferative effect on the human stomach cancer cell line SNU-1.
More experiments should be done in vivo and clinical studies conducted to confirm these positive effects. These additional studies in the future seem essential as a means to ensure product reliability and effectiveness for health promotion in humans.
Evidence strength: Currently limited to cell-line (in vitro) and animal studies. No human clinical evidence supports an anti-cancer use. This area is at an early, preclinical stage of investigation.
The dairy starter bacterium Lactococcus lactis has the potential to synthesize both folate (vitamin B9) and riboflavin (vitamin B2). Novel foods enriched through fermentation using multivitamin-producing starters could compensate for B-vitamin deficiencies that are common even in highly developed countries. Research has demonstrated bioavailability of folate produced in vivo by L. lactis: hematologic studies showed that administration of the L. lactis strains was able to revert a partial megaloblastic anemia caused by folate deficiency.
Evidence strength: The folate- and riboflavin-producing capacity of engineered L. lactis strains has been demonstrated in animal models, with some bioavailability data. This application is primarily of interest for functional food fortification rather than dietary supplementation in the traditional sense, and most evidence is from metabolic engineering research rather than clinical human trials.
Cell-free supernatant from Lactococcus lactis A5 showed inhibitory activities against both Gram-positive pathogens (Bacillus cereus and Staphylococcus aureus) and the Gram-negative pathogen Salmonella typhimurium. These effects are primarily mediated through bacteriocin production and lactic acid-mediated acidification.
Evidence strength: Largely in vitro. While the antimicrobial mechanisms are well characterized at the biochemical level, human clinical evidence for specific infectious disease prevention attributable to L. lactis supplementation is absent.
Dosages in clinical and research settings vary substantially by strain, form (live vs. heat-killed), and indication. The following are stated in the cited sources:
No consensus or officially recommended human dietary supplement dose has been established. Doses studied are formulation- and strain-specific.
Based on its history of use in food fermentations, L. lactis has GRAS (Generally Recognized as Safe) status (FDA, 2010). The Qualified Presumption of Safety (QPS) status was also granted by the European Food Safety Authority (EFSA) to the majority of LAB genera at the species level, including Lactococcus.
L. lactis bacteria are harmless in nature and have been ingested even at high doses by healthy children, adults, elderly, as well as immune-compromised individuals without health-compromising issues. Several clinical trials using live genetically modified L. lactis have been completed, showing clearly that treating patients with mucosal pathologies was safe and well tolerated.
Despite its general safety profile, the literature documents rare cases where L. lactis has acted as an opportunistic pathogen in clinically vulnerable individuals. L. lactis is known to play a commercially important role in feed fortification, milk fermentation, and vaccine production, but pathogenic L. lactis has been isolated from many clinical cases in recent years, including the brain of silver carp with lactococcosis, the liver and spleen of diseased waterfowl, milk samples with cow mastitis, and blood and urine from human patients with endocarditis. Based on its history in food fermentation, L. lactis has GRAS status, with few case reports of it being an opportunistic pathogen.
The investigational use of recombinant L. lactis strains raises distinct regulatory and safety considerations separate from conventional probiotic use. Only a few recombinant L. lactis strains have been approved for human clinical trials. Genetically modified bacteria are considered under the safety regulations for genetically modified organisms (GMOs) by regulatory agencies to prevent adverse effects on human health and the environment. Biological containment strategies — including the use of thyA-deficient strains that cannot replicate without exogenous thymidine — have been employed in clinical trials to limit environmental dissemination of the transgene. The parent organism, L. lactis subspecies MG1363, is a non-pathogenic, food-derived bacterium that was cured of all resident plasmids, shown to be deficient of conjugative transposition, and the organism is thyA-deficient and unable to replicate in an environment lacking thymine or thymidine.
With growing evidence of clinical efficacy of probiotics in various diseases, safety concerns have arisen regarding the therapeutic use of live probiotic bacteria, especially in critically ill, immunocompromised, and pediatric populations. Serious probiotic-related adverse effects have been reported in these patients, including bloodstream infection and sepsis. These concerns, while documented for probiotics broadly, inform the cautious use of live L. lactis preparations in vulnerable individuals. No specific drug–L. lactis interaction data have been formally characterized; antibiotic co-administration would be expected to reduce viable bacterial counts and efficacy, as is true for all live bacterial preparations.
Wild-type L. lactis strains can carry or acquire antibiotic resistance genes. Many expression systems developed for L. lactis have antibiotic resistance genes (ARGs) as selective markers, which are among the major concerns because of the possibility of transfer of ARGs to microbial communities of the host microbiota or the environment. Genomic screening for antibiotic resistance is a standard criterion in the safety assessment of strains intended for probiotic use. For example, L. lactis subsp. lactis Lac3 was shown to be non-pathogenic and neither harbored virulence factors nor acquired antibiotic resistance phenotypes.
Health conditions that Lactococcus lactis may help support.
L. lactis has been studied in the context of low-grade colon inflammation associated with IBS-like abdominal discomfort, where IL-10-secreting recombinant strains reduced gut permeability and serotonin dysregulation — both implicated in abdominal pain. The GABA-producing L. lactis data additionally shows reduction in visceral hypersensitivity, the primary driver of abdominal pain in IBS.
Specific L. lactis strains (NRRL B-50571 and NRRL B-50572) produce bioactive milk peptides with documented antioxidant properties during fermentation. These peptides have been characterized in multiple patent filings and peer-reviewed animal studies alongside their ACE-inhibitory and antihypertensive activities.
GM L. lactis has been engineered to deliver autoantigens (e.g., human insulin) and anti-inflammatory cytokines mucosally to induce tolerance in autoimmune conditions, including autoimmune type 1 diabetes. A Frontiers in Immunology review documents L. lactis as a versatile vehicle for tolerogenic immunotherapy with completed human clinical trials in mucosal pathologies, and preclinical data supporting autoimmune diabetes reversal.
A randomized, double-blind, placebo-controlled pilot clinical trial demonstrated that fermented milk with L. lactis NRRL B-50571 reduced systolic and diastolic blood pressure in prehypertensive subjects, attributed to ACE-inhibitory peptides. In spontaneously hypertensive rats, the same fermented milk reduced SBP, DBP, heart rate, and had a hypolipidemic effect. The hypotensive effect was observed only in subjects with elevated baseline blood pressure.
L. lactis strains — particularly genetically modified (GM) variants secreting IL-10 — have demonstrated anti-inflammatory activity in multiple pre-clinical models. Several completed clinical trials with GM L. lactis confirmed safety and tolerability in patients with mucosal inflammatory pathologies. Wild-type strains modulate cytokine profiles (reducing IFN-γ, IL-6, TNF-α) and expand regulatory T-cell populations in colitis models. Evidence is strongest in the context of intestinal inflammation.
Multiple preclinical studies demonstrate that L. lactis — both wild-type and GM strains — attenuates experimental colitis by reducing inflammatory cytokines, preserving tight junction integrity, and modulating the colonic immune environment. Heat-killed L. lactis L8 reduced TNF-α and clinical colitis scores in DSS-induced murine colitis. GM L. lactis secreting IL-10 and IL-1Ra have also shown efficacy in rodent colitis models and have proceeded to human clinical safety trials.
Preclinical studies demonstrate that L. lactis supplementation modulates intestinal immunity, reduces pathogen colonization, and normalizes gut microbiota composition in diarrhea models. In weaning piglet studies, L. lactis improved growth, regulated the GABAergic system, and modulated intestinal immune gene expression. Human evidence is indirect but supported by its role in restoring barrier integrity in inflammatory diarrhea contexts.
A human clinical study found that children with atopic dermatitis (AD) who consumed yogurt containing L. lactis 11/19-B1 daily for 8 weeks showed a significant reduction in SCORAD scores. Parallel mouse model work identified L. lactis 11/19-B1 as the most active strain among five tested LAB species for suppressing AD-like inflammatory findings. A recent topical pilot RCT in adults using L. lactis lysate cream found no significant efficacy on EASI scores.
Lactococcus lactis is a lactic acid bacterium used in fermented dairy production that demonstrates gut microbiota-modulating effects and is being studied as a vehicle for delivery of therapeutic proteins to the gut. Clinical evidence supports its role in gut microbiome modulation and mucosal immune stimulation.
GABA-producing L. lactis strains have been shown to modulate the gut-brain axis by upregulating GABA receptor expression in both the gut and brain in IBS mouse models, reducing visceral hypersensitivity and neurobehavioral abnormalities. Separately, engineered L. lactis has been used in optogenetic micro-nano systems to precisely regulate brain functions via vagal afferent signaling from the small intestine.
GABA-producing L. lactis strains significantly ameliorated IBS-related outcomes in a validated mouse model, including visceral hypersensitivity, intestinal barrier dysfunction, and neurobehavioral abnormalities in a dose-dependent manner. Recombinant IL-10-secreting L. lactis also reduced gut hyperpermeability and serotonin dysregulation in a chronic IBS-like rodent model. Clinical evidence is preclinical-dominant, but mechanistically well-grounded.
Lactococcus lactis has been studied in IBD, particularly as part of probiotic combinations for UC. Engineering strains to deliver anti-inflammatory molecules such as IL-10 directly to the gut mucosa represents one of the most novel therapeutic applications for IBD studied in clinical trials.
Recombinant IL-10-secreting L. lactis significantly reduced intestinal hyperpermeability (P < 0.05) in a chronic murine colitis/IBS model, with upregulation of tight junction proteins. L. lactis engineered to express SlpA showed elevated occludin and ZO-2/3 tight junction proteins in murine colitis. Even wild-type L. lactis produced a non-significant trend toward decreased permeability, suggesting an intrinsic barrier-supportive property.
Lactococcus lactis is a lactic acid bacterium that produces nisin and other bacteriocins documented for activity against oral pathogens including S. mutans and periodontal bacteria. It has been identified in research on oral microbiome modulation and is referenced in scientific literature on oral microbial ecology.
Body systems that Lactococcus lactis may help support.
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