Bacillus subtilis

Other Names

B. subtilisBacillus globigiiBacillus mesentericusBacillus nattoBacillus subtilis (Ehrenberg 1835) Cohn 1872Bacillus subtilis subsp. amylosacchariticusBacillus subtilis subsp. chungkookjangBacillus subtilis subsp. endophyticusBacillus subtilis subsp. globigiiBacillus subtilis subsp. inaquosorumBacillus subtilis subsp. nattoBacillus subtilis subsp. nigerBacillus subtilis subsp. spizizeniiBacillus subtilis subsp. stercorisBacillus subtilis subsp. subtilisBacillus subtilis var. nigerBacillus uniflagellatusgrass bacillushay bacillusnatto bacillusVibrio subtilis

Synopsis

Bacillus subtilis: A Comprehensive Reference

1. Identity

Taxonomic and Chemical Names

Bacillus subtilis is a Gram-positive bacterium that is rod-shaped and catalase-positive. It can form a tough, protective endospore, allowing it to tolerate extreme environmental conditions, and has historically been classified as an obligate aerobe, though evidence exists that it is a facultative anaerobe. It is considered the best-studied Gram-positive bacterium and a model organism to study bacterial chromosome replication and cell differentiation.

The species belongs to the family Bacillaceae, order Bacillales, class Bacilli, phylum Firmicutes. A well-characterized Gram-positive bacillus, it comprises multiple subspecies, including B. subtilis variant natto (B. subtilis var. natto), which is essential for fermenting soybeans to produce natto. Bacillus subtilis natto is closely related to the laboratory standard strain B. subtilis Marburg 168, and functions as a starter for the production of the traditional Japanese food "natto" made from soybeans.

Natural Sources and Ecology

B. subtilis is the most ubiquitous species of the genus and can be isolated from a broad variety of environments including animal and human gastrointestinal (GI) tracts. Bacillus subtilis BS50 is a Gram-positive, spore-forming bacterium that has been isolated from soil. The organism is also intimately associated with fermented foods: consumption of Japanese fermented soybean in the form of natto, which is commonly consumed in Japan, contains as many as 10⁸ viable cells per gram.

Common Commercial Strains and Preparations

Multiple distinct strains are used in commercial dietary supplement preparations. Prominent examples documented in the peer-reviewed and regulatory literature include:

B. subtilis DE111® — The Bacillus subtilis DE111 strain has certain properties which have been found to make the strain well-suited for use as a probiotic.
B. subtilis BS50 (also known as BS8-74) — isolated from soil collected from Gallatin County, Montana, USA on 4 July 2015, and deposited in the American Type Culture Collection with Accession No. PTA-127287.
B. subtilis DSM32315 — used in a 4-week human metabolic intervention study.
B. subtilis var. natto — the subspecies responsible for producing natto food and the source of nattokinase.

It is particularly attractive as a probiotic because of its ability to form shelf-stable, acid-resistant spores that lend to diverse applications in the food system. Durable spore-forming probiotics are increasingly formulated into foods, beverages, and dietary supplements. Common dosage forms include hard capsules, powders for reconstitution, liquid suspensions, and food-integrated formulations (e.g., fermented soybean products). It is one of the bacterial champions in secreted enzyme production and is used on an industrial scale by biotechnology companies.

2. Traditional and Historical Use

Japan — Natto and B. subtilis natto

Among traditional fermented foods, natto, produced by fermentation of soybeans by Bacillus subtilis natto (a subspecies of Bacillus subtilis), has been consumed in Japan as a traditional fermented food for at least a thousand years. It represents a typical food and staple in Japanese cooking and diet, frequently served as a breakfast with rice, and has been introduced to human consumption since the period of northwest Japan cities.

The preparation method has been described in detail: to make natto, soybeans are soaked, steamed, inoculated with B. subtilis var. natto, and fermented at 40 °C for 24 hours, then cooled and aged in a refrigerator for up to one week, allowing the development of stringiness.

The fermented beans are recognized for their contribution to a healthy gut flora and vitamin K2 intake, during this long history of widespread consumption. Natto, containing an abundant amount of soybean protein, has a high nutritive value and unique flavor and viscous texture; in recent years, it has been reported to have probiotic action, antibacterial action, and various types of health promotion actions provided by functional ingredients (e.g., antithrombotic action, hypotensive action, hypocholesterolemic action, bone formation promoting action).

Broader Asian Context

Related fermented soybean products made with Bacillus species exist across East Asia. Other fermented soybean foods from various Asian traditions, such as cheonggukjang from Korea and thua nao from Thailand, may contain related fibrinolytic enzymes produced by Bacillus species, though nattokinase specifically is associated with B. subtilis var. natto and natto production.

Industrial and Pharmaceutical History

Bacillus subtilis has been used for more than 50 years in many different industrial applications, including farming, precision fermentation, and probiotic supplements. In the United States, an opinion letter issued in the early 1960s by the Food and Drug Administration (FDA) designated some substances derived from microorganisms as generally recognized as safe, including carbohydrase and protease enzymes from B. subtilis; these opinions were predicated on the use of nonpathogenic and nontoxicogenic strains, and on the use of current good manufacturing practices. The FDA stated that the enzymes derived from the B. subtilis strain were in common use in food prior to January 1, 1958, and that nontoxigenic and nonpathogenic strains of B. subtilis are widely available and have been safely used in a variety of food applications.

3. Key Constituents and Active Compounds

The Spore Itself

Bacterial endospores exhibit extreme resistance to most conditions that rapidly kill other life forms, remaining viable in this dormant state for centuries or longer. When B. subtilis is administered orally, the spore form confers substantial physiological advantages: as spore-forming bacteria, they are able to survive the harsh gastric environment and reach the small intestine alive. B. subtilis spores survived gastric transit at a rate of nearly 100%, germinated in the intestine, and consumed oxygen to create an anaerobic niche favorable for Lactobacillus and Bifidobacterium — a distinct "oxygen bio-capture" strategy against dysbiosis of the intestinal flora.

Nattokinase (Subtilisin NAT)

Nattokinase (NK) is a serine protease derived from natto and secreted by the bacterium Bacillus subtilis var. natto, discovered in 1980 by Japanese scholar Yoko Sumi. NK consists of a single polypeptide chain composed of 275 amino acids (molecular weight 27,724), containing no disulfide bonds, and displays strong fibrinolytic activity. NK not only has fibrinolysis activity itself but also activates other fibrinolytic enzymes such as pro-urokinase and tissue plasminogen activator.

More specifically, NK breaks down blood clots by directly hydrolyzing fibrin and plasmin substrate, converts endogenous prourokinase to urokinase, degrades plasminogen activator inhibitor-1, and increases tissue plasminogen activator, all of which support its fibrinolytic activity.

Vitamin K2 (Menaquinone-7 / MK-7)

The health benefits of eating natto are attributed in part to chemical constituents such as nattokinase and vitamin K2 (menaquinone-7; MK-7). Bacillus subtilis is one of the few strains that can secrete synthetic menaquinone-7 (MK-7) to the outside of the cell, and its purpose and mechanism have not been clearly studied. Vitamin K2 produced by B. subtilis natto is important for bone metabolism and cardiovascular health through its role in activating vitamin K-dependent proteins.

Lipopeptides: Iturin, Surfactin, and Fengycin

The three families of Bacillus lipopeptides — namely surfactin, iturin, and fengycin — demonstrate significant antagonistic effects against a wide range of phytopathogens. Iturin is a cyclic lipopeptide originating from Bacillus subtilis and related bacteria; these compounds are structurally diverse and possess potent inhibitory effects against plant disease-causing bacteria and fungi; notably, Iturin A exhibits strong antifungal properties and low toxicity. All strains of B. subtilis are capable of synthesizing the iturin family of lipopeptides.

In Bacillus subtilis spore metabolites, the lipopeptides consist of a lipophilic fatty acid chain and a hydrophilic peptide ring; the most common are surfactin, iturin, and fengycin, which possess antibacterial and biosurfactant properties with potential utility in medicine, agriculture, food, cosmetics, and environmental applications.

Antimicrobial Compounds and Bacteriocins

Bacillus subtilis produces a remarkably diverse array of antimicrobial compounds — bacteriocins, lipopeptides (iturin, fengycin, surfactin), and polyketides — that have inhibitory activity against a wide spectrum of pathogenic organisms including Staphylococcus aureus, Escherichia coli, Salmonella, Clostridium difficile, and Helicobacter pylori.

Digestive Enzymes

By secreting various digestive enzymes, B. subtilis directly enhances small intestine digestive and absorptive efficiency. Vegetative B. subtilis has been shown to secrete digestive enzymes in vitro; taken together, the organism may germinate in the intestine and secrete enzymes that help digest food and improve nutrient absorption, theoretically leading to less fermentation and gas production in the lower intestine.

Poly-γ-glutamic Acid (γ-PGA) and Other Compounds

The fermentation process supports secretion of proteases by bacilli to degrade soy proteins, the production and racemization of L- and D-glutamic acids, and the synthesis and secretion of poly-γ-glutamic acid. Under the action of B. subtilis natto, new active substances such as nattokinase, antioxidant peptides, and antibacterial peptides are produced; a variety of cationic peptides and nattokinase in natto peptide have good biological activities, including lipopolysaccharide neutralization activity, thrombolytic effect, and angiogenic activity. In addition, natto is rich in superoxide dismutase (SOD), which can inhibit cardiovascular and cerebrovascular diseases and has anti-aging potential.

Dipicolinic Acid

Dipicolinic acid (also called 2,6-pyridinedicarboxylic acid) is an antibiotic produced by B. subtilis and is known as a compound with antiblood coagulation properties; this compound has been found in 100 g of commercial natto in an amount of 20.55 ± 13.67 mg.

4. Mechanisms of Action

Spore Germination and Colonization

The exact mechanism by which B. subtilis improves GI symptoms remains unknown, but it is likely dependent on the transition of spores to vegetative cells in the stomach and small intestine; Bacillaceae spores, including B. subtilis, have previously been detected in human fecal and ileal biopsy samples in numerous studies, suggesting that spores naturally occur and germinate in the human intestine.

The number of both spores and vegetative cells increases over the course of 6 hours in ileum effluxes and remains constant through to the end of the time course (8 hours); Bacillus species are known to adhere to intestinal mucus. While spores of B. subtilis have been shown to enhance host immunity in the small intestine, additional host benefits are only possible if the vegetative form of the bacteria is also present; detecting vegetative cells of B. subtilis DE111® in the small intestinal tract suggests metabolically active bacteria are present, producing key beneficial molecules and supporting a healthy microbiome.

Antimicrobial and Competitive Exclusion

In recent times, there has been significant progress in scientific evaluation and studies on probiotic Bacillus subtilis, revealing possible mechanisms of action like antimicrobial effect by synthesis of antimicrobial substances, antidiarrheal effect, immunostimulatory effect, competitive exclusion of pathogens, prevention of intestinal inflammation, and normalization of intestinal flora. The production of these antimicrobial compounds appears to occur in the gastrointestinal environment and may explain B. subtilis's documented ability to reduce pathogen colonization in clinical settings.

Fibrinolytic and Cardiovascular Mechanisms (Nattokinase)

NK stimulates endothelial cells to produce t-PA and inhibits PAI-1; t-PA activates fibrinogen to form plasmin, which dissolves thrombus skeleton structure fibrin net, releasing platelets so blood flow gradually returns to normal. Additionally, as a serine protease produced by Bacillus subtilis, nattokinase has potential anti-coagulatory, thrombolytic, anti-atherosclerotic, lipid-lowering, and anti-hypertensive effects.

Metabolic and Immunomodulatory Mechanisms

B. subtilis is part of the normal gut microbiota of humans and can play a critical role in immune development and supporting gastrointestinal system health; the exopolysaccharide produced by B. subtilis creates an aerobic microenvironment in the gut.

5. Scientific Evidence by Area of Use

5.1 Gastrointestinal Health — Gas, Bloating, and Bowel Regularity

Human clinical evidence (B. subtilis BS50): The safety and efficacy of daily supplementation of Bacillus subtilis BS50 for 6 weeks was investigated in a randomized, double-blind, placebo-controlled, parallel clinical trial of 76 healthy adults; before and during supplementation, gastrointestinal symptoms were recorded daily using a multi-symptom questionnaire, and clinical chemistry, hematology, plasma lipids, and intestinal permeability and inflammation markers were measured at baseline and end of study. Compared to placebo, 2 × 10⁹ CFU BS50 per day increased the proportion of participants showing improvement from baseline to week 6 in the composite score for bloating, burping, and flatulence (47.4% vs. 22.2%), whereby the odds of detecting an improvement were higher with BS50 (OR [95% CI]: 3.2 [1.1, 8.7], p = .024). The results suggest that dietary supplementation of 2 × 10⁹ CFU Bacillus subtilis BS50 per day is a well-tolerated and safe strategy to alleviate gas-related gastrointestinal symptoms in healthy adults.

Human clinical evidence (B. subtilis DE111®, bowel regularity): The efficacy of Bacillus subtilis DE111® in capsule form for regulation of bowel movements was tested in a double-blind, randomized study; 50 adults (18–65 years of age) suffering from occasional constipation and/or diarrhea were assigned to consume either 1 × 10⁹ CFU of Bacillus subtilis DE111® or placebo; each group consumed one capsule per day, with a meal, for 90 days; efficacy was assessed through participant-reported bowel movement records as well as dietary intake logs.

Evidence strength: For gas and bloating outcomes, a single industry-associated randomized controlled trial in healthy adults supports benefit; evidence is promising but preliminary, requiring replication in larger, independent cohorts.

5.2 Gastrointestinal Health — Diarrhea Treatment and Prevention

Numerous preclinical and clinical studies on B. subtilis have shown its promising efficacy in the treatment and prevention of diarrhea of various etiologies. A randomized, double-blind, controlled clinical study assessed the efficacy of a liquid-form Bacillus spore probiotic containing B. subtilis, B. clausii, and B. coagulans at 5 billion CFU/5 mL ampoule in the supportive treatment of persistent diarrhea in children; the findings revealed a significant 3-day shorter recovery period, 1.60-fold enhanced efficacy, and a 9.47-fold increase in odds (all p-values < 0.0001) for effectively resolving diarrhea by day 5 with the Bacillus spores.

Evidence strength: For diarrhea, published trials are often multi-strain (not B. subtilis alone), making strain-specific attribution difficult. Evidence is moderate in strength but not definitive for B. subtilis as a single agent.

5.3 Gastrointestinal Health — Irritable Bowel Syndrome (IBS)

Irritable bowel syndrome is a common functional gastrointestinal disorder that affects quality of life and the ability to work; it is known to occur as a result of a multifactorial change in microbiota and immunology; a study evaluated the effects of Bacillus subtilis on inflammatory parameters and quality of life in IBS. Irritable bowel syndrome volunteers diagnosed according to Rome IV criteria were recruited in the single-center prospective study; recent evidence indicates that B. subtilis is part of the normal gut microbiota of humans and may play a critical role in immune development and supporting digestive health.

Evidence strength: Pilot-level only; IBS evidence for B. subtilis as a single strain is limited to single-center, small studies. Larger, adequately powered RCTs are needed.

5.4 Immune Modulation

In a pilot randomized, double-blind, placebo-controlled four-week intervention, the immunomodulatory properties of Bacillus subtilis strain DE111 were examined in a healthy human population; peripheral blood mononuclear cells (PBMCs) were measured at basal levels pre- and post-intervention, as well as in response to stimulation with bacterial lipopolysaccharide (LPS); an increase in anti-inflammatory immune cell populations in response to ex vivo LPS stimulation of PBMCs was observed in the DE111 intervention group.

Overall perceived gastrointestinal health, microbiota, and circulating and fecal markers of inflammation (IL-6, sIgA) and gut barrier function (plasma zonulin) were largely unaffected by DE111 intervention, although the study may have been underpowered to detect these differences; the pilot data provide information and justification to conduct an appropriately powered clinical study to further examine the immunomodulatory potential of B. subtilis DE111 in human populations.

Evidence strength: Preliminary; a pilot trial showed potential signals for immune modulation but was underpowered. No definitive conclusions can be drawn from available human data alone.

5.5 Cardiovascular Health — Nattokinase and Blood Pressure

Six studies were eligible for quantitative analysis in a systematic review and meta-analysis with 546 participants. Nattokinase supplementation significantly reduced systolic blood pressure (MD = −3.45, 95% CI: −4.37 to −2.18, p < 0.00001) and diastolic blood pressure (MD = −2.32, 95% CI: −2.72 to −1.92, p < 0.00001), and led a slight increase in blood glucose (MD = 0.40, 95% CI: 0.20 to 0.60, p < 0.0001) as compared to placebo.

This study further supports that nattokinase can be used as an effective adjunctive therapy for hypertension, but relatively low-dose supplementation of nattokinase may have no significant lipid-lowering effect.

Lipid effects (mixed/complex): Relatively low total dosage of nattokinase had a negative effect on blood total cholesterol (MD = 5.27, 95% CI: 3.74 to 6.81, p < 0.00001), high-density lipoprotein cholesterol (MD = −2.76, 95% CI: −3.88 to −1.64, p < 0.00001), and low-density lipoprotein cholesterol (MD = 6.49, 95% CI: 0.83 to 12.15, p = 0.02). More work will need to be done to determine whether the positive efficacy of nattokinase on cardiovascular risk factors is dose-dependent.

RCT data on combined intervention: A 90-day randomized, double-blind trial investigated the effect of nattokinase (NK) and red yeast rice (RYR) supplementations on cardiometabolic parameters in patients with stable coronary artery disease (CAD), with 178 CAD patients randomized to four groups: NK + RYR, NK, RYR, and placebo. In comparisons across groups, NK + RYR showed the maximum effect in reducing triglyceride (−0.39 mmol), total cholesterol (−0.66 mmol/L), diastolic blood pressure (−7.39 mmHg), and increase in high-density lipoprotein cholesterol (0.195 mmol/L); both NK + RYR and NK groups had significantly better-improved lactate dehydrogenase than the others. No adverse effects due to the interventions were reported.

Evidence strength: Antihypertensive effects of nattokinase are supported by a meta-analysis of six RCTs with 546 participants, representing moderate-to-good quality evidence for blood pressure. Lipid effects are dose-dependent and inconsistent — evidence is mixed. Notably, these findings pertain specifically to isolated nattokinase supplements, not to whole B. subtilis probiotics.

5.6 Metabolic Health — Lipids and Blood Glucose

In a 4-week intervention involving 18 healthy adults, dietary supplementation with Bacillus subtilis DSM32315 significantly improved fasting blood glucose, circulating lipid profiles, and the satiety hormones glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and fecal butyrate levels, suggesting that B. subtilis might regulate human lipid metabolism by enhancing intestinal butyrate levels. Another separate human study indicated that the serum total cholesterol and LDL levels in subjects were significantly reduced after a continuous natto diet for 2 weeks, and the mechanism needs to be further explored.

Evidence strength: Very preliminary; the human metabolic study had only 18 participants and 4-week duration. Results are hypothesis-generating only.

5.7 Gut Microbiota Modulation

Levels of B. subtilis DNA detected in fecal samples collected pre- and post-intervention indicate that DE111 consumption increases B. subtilis in the GI tract; however, four weeks of DE111 consumption did not significantly alter the composition and structure of the gut microbiota.

Evidence strength: Colonization of the GI tract has been confirmed in a clinical study, but measurable effects on overall microbiota composition over four weeks were not detected. Longer duration studies are needed.

6. Body Systems and Health Areas Associated with Bacillus subtilis

Gastrointestinal system: Management of bloating, flatulence, burping, bowel regularity, diarrhea, and IBS.
Immune system: Immunomodulation via interaction with gut-associated lymphoid tissue (GALT) and peripheral blood immune cells.
Cardiovascular system: Blood pressure, fibrinolysis, lipid metabolism (primarily via nattokinase from B. subtilis var. natto).
Metabolic system: Satiety hormone regulation (GLP-1, PYY), blood glucose, and lipid metabolism.
Musculoskeletal/Bone system: Via production of vitamin K2 (MK-7), which supports carboxylation of osteocalcin and other vitamin K-dependent proteins.
Antimicrobial defense: Bacillus bacteria are increasingly attracting the attention of researchers as promising probiotics due to their strong antimicrobial, antidiarrheal, and immunostimulatory effects, ability to stimulate growth of natural flora and prevent intestinal inflammation, besides having an excellent stability profile in otherwise unfavorable conditions.

7. Dosage Forms and Dosages Reported in Studies

Probiotic (Live Spore) Preparations

Bacillus subtilis DE111® may be used in an effective total daily dose from about 1 × 10⁸ CFU to about 1 × 10¹¹ CFU; one preferred daily dose range is from about 1 × 10⁹ CFU to about 1 × 10¹⁰ CFU.

Each probiotic capsule in the BS50 trial contained 2 × 10⁹ CFU of B. subtilis BS50 with identity-preserved maltodextrin extracted from waxy maize as the excipient; this dose was selected based on published clinical trials demonstrating that doses as little as 1 × 10⁹ CFU/day and up to 5 × 10⁹ CFU/day of Bacillaceae strain probiotics yielded clinically meaningful results.

In the bowel regularity trial, 50 adults consumed either 1 × 10⁹ CFU of Bacillus subtilis DE111® or placebo; each group was instructed to consume one capsule per day, with a meal, for 90 days.

Multi-strain Liquid Preparations

The food supplement LiveSpo DIA30 is a liquid water suspension containing B. subtilis ANA48, B. clausii ANA39, and B. coagulans ANA40 spores at a concentration ≥ 5 × 10⁹ colony-forming units (CFU) per 5 mL ampoule. The first study on the safety and efficacy of multi-strain Bacillus spore probiotics (20–30 billion CFU daily) was reported for managing persistent diarrhea in children aged 3 to 24 months.

Nattokinase Supplementation

Nattokinase (NK) is used as a dietary supplement, mainly in Japan, as both a prophylactic and a curative medicine. In non-traditional natto diet areas such as Europe and the United States, nattokinase is mainly obtained in the form of supplements, but there are problems such as insufficient dose standardization, large differences in the activity (FU) of commercially available supplements, and some products not labeled with a clear titer.

A 6-month study in Taiwan among 46 adults (average age 54) with untreated high cholesterol showed that taking 7,000 FU of nattokinase in two divided doses daily did not significantly reduce levels of cholesterol or triglycerides compared to placebo.

8. Safety Considerations and Interactions

Regulatory Status

At least five B. subtilis strains are the subject of "generally regarded as safe" (GRAS) dossiers, for which the Food and Drug Administration (FDA) has issued "no objection letters" for safe use in food. Furthermore, the European Food Safety Authority (EFSA) maintains a qualified presumption of safety (QPS) list of biological agents that includes B. subtilis, which allows their use in food with no restrictions on age or exposure limit.

In 2007, EFSA granted Bacillus subtilis species Qualified Presumption of Safety (QPS) status, provided that no toxigenic activity was proven for the specific species; this opinion was upheld in 2008 in a safety review of probiotic strains.

Strain-Level Safety Assessment Requirements

It is essential to assess the safety of each individual strain before clinical testing and safe use in dietary supplements, food, and beverages; importantly, several Bacillus spp., including B. cereus, are capable of producing emetic toxins (e.g., cereulide), hemolytic and non-hemolytic enterotoxins, as well as cytotoxins, all of which can cause serious illness in humans and animals. The QPS qualification for Bacillus spp. specifically requires the absence of toxigenic potential for all Bacillus spp., as well as absence of acquired genes conferring resistance to clinically relevant antimicrobials.

The BS50 genome does not encode any known Bacillus toxins; the BS50 genome contains several gene clusters involved in the biosynthesis of secondary metabolites, but many of these antimicrobial metabolites (e.g., fengycin) are common to Bacillus spp. and may even confer health benefits related to gut microbiota health.

Risk in Immunocompromised Patients

Although B. subtilis is of low pathogenicity, case reports document rare infectious events in vulnerable individuals. B. subtilis var. natto, a low-pathogenic bacterium used in the traditional Japanese food "natto," has rarely been reported as a pathogen of infectious diseases in humans; a case of persistent bacteremia caused by B. subtilis var. natto was reported in an immunocompetent patient without any gastrointestinal involvement; a 53-year-old Japanese woman who had been consuming natto every day was admitted with complaints of fever and chills, and B. subtilis was isolated from blood cultures, with abdominal contrast-enhanced CT showing multiple low-absorption areas in the liver and spleen.

Older or immunocompromised patients could be at risk for bacteremia from ingesting natto; B. subtilis is a Gram-positive, rod-shaped, spore-forming bacterium with low pathogenicity.

Bacteremia was diagnosed in a highly immunocompromised patient suffering from gut dysbiosis with a B. subtilis strain also present in fermented soya (natto), which was consumed daily by the patient.

Potential as a Respiratory Sensitizer

The FEEDAP Panel concluded that Bacillus subtilis DSM 28343 is not an eye/skin irritant but should be considered as a potential respiratory sensitizer and that no conclusion could be drawn on its skin sensitisation potential; these conclusions apply also to subsequent applications. This finding, from occupational/inhalation exposure assessments, is relevant to manufacturing workers and may not directly apply to oral supplementation at consumer doses.

Nattokinase and Anticoagulant Drugs

No notable adverse events were reported in all studies due to intake of nattokinase in the meta-analysis. However, because nattokinase degrades plasminogen activator inhibitor-1 and promotes fibrinolysis, it has a theoretical potential to amplify the effects of anticoagulant or antiplatelet medications. No high-quality human interaction data are currently available specifically quantifying this risk.

Vitamin K2 (MK-7) and Warfarin

Because B. subtilis natto produces substantial amounts of vitamin K2 (MK-7), regular natto consumption may interact with warfarin anticoagulant therapy. Vitamin K is a cofactor for clotting factor synthesis and is antagonized by warfarin; fluctuating intake of vitamin K-containing foods is a well-documented cause of warfarin instability. Individuals on warfarin who also consume natto or MK-7 supplements should have their anticoagulant status carefully monitored.

Antibiotic Co-administration

Because antibiotics can kill or suppress live probiotic bacteria, concurrent administration of broad-spectrum antibiotics with B. subtilis spore preparations may reduce their efficacy. However, the exceptional spore stability of B. subtilis provides some protection relative to non-spore-forming probiotics. The body of evidence on optimal timing and spacing of B. subtilis probiotics relative to antibiotic doses in human clinical settings remains limited.

Adverse Events in Clinical Trials

Dietary supplementation of 2 × 10⁹ CFU Bacillus subtilis BS50 per day was described as a well-tolerated and safe strategy in the 6-week RCT in healthy adults. No notable adverse events were reported in all nattokinase studies included in the meta-analysis.

9. Summary of Evidence Quality

The evidence base for Bacillus subtilis as a dietary supplement spans multiple domains, with varying degrees of rigor. For gastrointestinal symptom relief (especially bloating and gas), there is at least one rigorous RCT; for diarrhea management, data frequently come from multi-strain studies. The cardiovascular effects of nattokinase — a specific product of B. subtilis natto fermentation — are supported by a meta-analysis of six RCTs showing consistent blood pressure reduction, though lipid effects are mixed. Immunomodulatory evidence in humans is pilot-level only. Most mechanistic data in areas beyond GI symptoms and nattokinase cardiovascular effects remain in vitro or animal-based.

A comprehensive review of human intervention studies utilizing B. subtilis as a probiotic for supporting gastrointestinal health, as well as the reported impacts of B. subtilis use on the human gut microbiota and other biomarkers of health, has been published. Current research suggests that the immunomodulatory effects of probiotics are strain-specific and vary in mode of action. The strain-specificity principle is critical: effects demonstrated for one B. subtilis strain cannot automatically be extrapolated to all strains or formulations.

References

Health Conditions

Health conditions that Bacillus subtilis may help support.

Gut Microbiome HealthScientific
Bacillus subtilis is a spore-forming bacterium used as a probiotic that positively modulates gut microbiota composition. It inhibits colonization of pathogenic bacteria, restores intestinal epithelial barrier function, and modulates gut immune responses. Both preclinical and clinical data support its beneficial effects on the gut microbiome.
IBSScientific
Bacillus subtilis is a spore-forming probiotic included in evidence-based IBS probiotic literature. It is cited in clinical probiotic guidance as a soil-based organism with benefits for gut barrier function relevant to IBS. It is included in multi-strain probiotic preparations studied for IBS, with spore-forming properties ensuring GI delivery.

Body Systems

Body systems that Bacillus subtilis may help support.

No body systems available.