The Science of Bacillus subtilis MB40

Bacillus subtilis MB40 is a clinically studied spore-forming probiotic strain chosen for one reason: resilience. For athletes who train hard, sweat on shared mats, and push their bodies through demanding camps, day-to-day skin, immune, and digestive resilience isn’t a luxury — it’s part of performance. This page explains what MB40 is, how it works, and what the research says, in plain language and with sources you can check yourself.

What is Bacillus subtilis MB40?

Bacillus subtilis is a beneficial bacterium that has been part of the human and environmental microbiome for as long as we have records of it. MB40 is a specific, trademarked strain of Bacillus subtilis (used in Spöretz as WelBac™ 40) selected and characterized for use as a dietary supplement. Because it is a defined strain — not just “a probiotic” — its behavior and safety have been studied in controlled research rather than assumed from the species in general.

Why “spore-forming” matters

Most common probiotics (like many Lactobacillus strains) are fragile. Heat, stomach acid, and time on a shelf can destroy a large share of them before they ever reach your gut. Bacillus subtilis MB40 is different: it forms a protective endospore, a natural dormant shell that helps it survive manufacturing, storage at room temperature, and the acidic journey through the stomach. Human research on Bacillus subtilis spores has directly observed them surviving gastric transit and germinating in the small intestine within hours of ingestion.^[4] In practical terms, a spore probiotic is built to actually arrive — which is why it doesn’t require refrigeration.

MB40 and the skin microbiome

Your skin and your gut are connected through what researchers call the gut–skin axis. The community of microbes in your gut influences inflammation and immune signaling throughout the body, including at the skin barrier. In a widely cited review, gut microbes and their metabolites (such as short-chain fatty acids) were shown to promote regulatory T-cells and anti-inflammatory signaling that help maintain skin-barrier integrity.^[2] By helping support a balanced gut microbiome, strains like MB40 are relevant to supporting skin health from the inside out.

It’s worth being precise: most of the evidence linking MB40 to skin is indirect — it works through the gut microbiome and the gut–skin axis rather than a direct skin trial. Direct clinical studies of MB40 on skin are still emerging, and we’ll update this page as they publish.

Emerging research: MB40 and skin-relevant bacteria

One of the most compelling areas of research on this strain involves Staphylococcus aureus — a bacterium that lives on the skin and is all too familiar to grapplers. This work comes from independent, peer-reviewed science, including research supported by the U.S. National Institutes of Health (NIH).

Researchers found that Bacillus subtilis produces a natural compound called fengycin, which interferes with the chemical signalling (“quorum sensing”) that S. aureus relies on to establish itself. In a 2018 study published in Nature, this mechanism eliminated S. aureus colonization in an animal model.^[5] A later phase 2, double-blind, randomized, placebo-controlled human trial published in The Lancet Microbe studied the MB40 strain specifically (as Sporevia) and reported that it reduced S. aureus colonization by more than 95% compared with placebo.^[6]

MB40 and immune support

A large share of the body’s immune activity is concentrated in the gut, where resident microbes help train and regulate it. In a preclinical (animal) model, MB40 supplementation was studied for its effect on immune responses, offering early mechanistic support for its role in immune health.^[3] Animal-model findings are a starting point rather than proof of the same effect in people — but they point in a consistent direction, relevant for athletes whose training loads and travel challenge day-to-day resilience.

MB40 and digestive health

Because it survives the trip to the intestine, Bacillus subtilis MB40 is well positioned to support a balanced gut environment where it becomes active.^[4] In a human tolerability trial, 10 billion CFU per day for 21 days was well tolerated by healthy adults, with gastrointestinal symptoms comparable to placebo and no serious adverse events.^[1] For athletes managing high food volume, travel, or weight management, a well-tolerated daily probiotic is a sensible foundation.

Why combat-sports athletes care

If you train BJJ, wrestling, MMA, or any grappling sport, you already know your skin and your immune system take a beating — shared mats, close contact, repeated camps, and travel. Supporting your body’s natural resilience from the inside is a smart, foundational habit. Bacillus subtilis MB40 fits that goal: a shelf-stable, clinically studied spore probiotic that supports a balanced microbiome, healthy immune function, and skin health — without refrigeration, so it survives your gym bag.

An honest note: a probiotic is a support tool, not a substitute for the basics. Shower right after training, wash your gear every session, and see a medical professional for any skin lesion or infection. MB40 supports your baseline resilience; hygiene protects you on the mat.

Is it safe? How much do you take?

Bacillus subtilis has a long history of safe use in foods and supplements, and MB40 specifically has undergone a dedicated safety assessment across in silico, in vitro, and in vivo studies, including a human trial.^[1] It is taken as a daily dietary supplement at the dose shown on the product label. As with any supplement, if you are pregnant, nursing, immunocompromised, or taking medication, talk to your healthcare provider before starting.

Our product: Spöretz MB40 delivers Bacillus subtilis MB40 (WelBac™ 40) in convenient vegetable capsules — shelf-stable, no refrigeration required. See the Spöretz MB40 Probiotic product page for the full label, dose, and current offer.

The research

We believe health claims should be checkable. Below are the studies referenced on this page. We update this list as new peer-reviewed research is published.

1. Spears JL, Kramer R, Nikiforov AI, Rihner MO, Lambert EA. Safety Assessment of Bacillus subtilis MB40 for Use in Foods and Dietary Supplements. Nutrients. 2021;13(3):733.
2. Salem I, Ramser A, Isham N, Ghannoum MA. The Gut Microbiome as a Major Regulator of the Gut–Skin Axis. Front Microbiol. 2018;9:1459.
3. The Probiotic Bacillus subtilis MB40 Improves Immunity in a Porcine Model. Microorganisms. 2023;11(8):2110.
4. Colom J, et al. Presence and Germination of the Probiotic Bacillus subtilis in the Human Small Intestinal Tract. Front Microbiol. 2021;12:715863.
5. Piewngam P, et al. Pathogen elimination by probiotic Bacillus via signalling interference. Nature. 2018;562:532–537. (NIH-supported.)
6. Piewngam P, et al. Probiotic for pathogen-specific Staphylococcus aureus decolonisation in Thailand: a phase 2, double-blind, randomised, placebo-controlled trial. Lancet Microbe. 2023.

Frequently asked questions

What is Bacillus subtilis MB40?

It is a specific, clinically studied, spore-forming strain of the beneficial bacterium Bacillus subtilis, used as a daily dietary supplement to support a balanced gut microbiome, healthy immune function, and skin health.

How is MB40 different from regular probiotics?

MB40 forms a protective natural spore that helps it survive heat, shelf storage, and stomach acid, so it doesn’t need refrigeration and is built to reach the intestine intact — unlike many fragile, refrigerated probiotic strains.

Does Bacillus subtilis MB40 help with skin?

Through the gut–skin axis, a balanced gut microbiome is associated with a healthier skin barrier. MB40 is studied for its role in supporting a balanced microbiome and overall skin health from the inside out. It is a wellness supplement and is not a treatment for any skin condition.

Does it need to be refrigerated?

No. Its spore form makes it shelf-stable at room temperature, which is why it travels well in a gym bag.

Is MB40 safe for athletes?

In a published human trial, 10 billion CFU/day for 21 days was well tolerated by healthy adults with no serious adverse events.^[1] If you are pregnant, nursing, immunocompromised, or on medication, check with your healthcare provider first.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.