Bacillus subtilis MB40 Explained: Why Grapplers Are Trying This Spore Probiotic

Have you had staph, impetigo or a boil more than once from training? Then this page is for you. You already shower after every roll. You already wash your gi. It still comes back. Each time, it costs you a week off the mat and a round of antibiotics.

In the next ten minutes you will learn four things. Most people who sell probiotics would rather you did not check them. One: which single strain has a real human trial aimed at the exact germ behind your infections. Two: the dose that trial used, and whether the bottle in your hand matches it. Three: what that trial did and did not measure. Four: why your shower only ever fixes half the problem. If you read only one part, read "What the trial did not show." I would rather lose a sale than have you buy this for the wrong reason.

The study that started this company

In January 2021, a research team in Songkhla, Thailand, started testing people. They swabbed noses. They collected stool samples. More than 600 healthy adults took part. The team was looking for people who always carry Staphylococcus aureus. That is the germ behind most of the boils, impetigo and cellulitis that take grapplers off the mat. They found 115 carriers. They split them into two groups. For 30 days, one group took a capsule every morning. It held 250 mg of bacterial spores. The other group took a fake capsule with only maltodextrin in it. No one knew which they had.

The day after the last dose, the team tested everyone again. In the group that took the spores, staph in the stool had dropped 96.8 percent. Staph in the nose had dropped 65.4 percent. The capsule never touched the nose. The fake-pill group had not changed. The rest of the gut germs in the spore group had not changed either. The paper ran in The Lancet Microbe in January 2023. The US National Institutes of Health and the National Research Council of Thailand paid for it.^[1]

The spores in that capsule were Bacillus subtilis MB40. They came from BIO-CAT Microbials in Shakopee, Minnesota. That is the strain in every Spöretz bottle. Same daily dose.

Honestly, the first time I read that paper I was annoyed. I have been rolling for years. I have been through the staph cycle more than once. Nobody at any gym I have trained at had heard of it. So here is the long version.

Why this strain and not the one at the pharmacy

Michael Otto runs a lab at the National Institute of Allergy and Infectious Diseases. It is part of the NIH. In 2018 his group published a paper in Nature. It showed that people in rural Thailand who had Bacillus germs in their gut, mostly from fermented food, did not carry staph.^[2] In the 600 people screened for the 2021 trial, the same thing showed up again. Staph only lived in people who had no Bacillus in their gut.^[1]

Why? Bacillus subtilis makes a family of molecules called fengycins. Staph germs talk to each other with a signal system. Scientists call it Agr. Staph needs that signal to settle into your gut. Fengycins jam the signal. In mice, feeding Bacillus spores cleared staph out of the gut.

Otto put it this way in the NIH news release: the probiotic "does not 'kill' S. aureus, but it specifically and strongly diminishes its capacity to colonize." Hold onto that. It matters later.

Here is the part that matters for your wallet. Before the human trial, the team compared several B. subtilis strains you can buy. One was a natto strain. One was R0179, which is in a lot of pharmacy probiotics. They picked MB40 because it made a lot more fengycin than the others.^[1] The authors say it plainly. You should only expect this effect from strains that make enough fengycin. In their lab tests, several popular B. subtilis products did not. So a label that just says "Bacillus subtilis" with no strain code tells you nothing. You cannot know if you are getting the one that was tested.

What MB40 is, in plain words

MB40 is one single strain of Bacillus subtilis. It is stored at the American Type Culture Collection under the code PTA-122264. BIO-CAT Microbials made it and sells it as OPTI-BIOME. In June 2021, an Irish food company called Kerry licensed it. Kerry sells it to supplement brands as Sporevia. On the Spöretz label it is called WelBac 40. That is the name our supplier uses. One strain, three names. That is why searching for it is so confusing.

MB40 is a spore-former. The germs are dried into a hard, sleeping form called a spore. A spore can sit at room temperature for years. It can pass through stomach acid. Then it wakes up in the small intestine. The best proof of that trip in people comes from a 2021 study in Cork, Ireland. People in that study had an opening in their gut wall from surgery, so scientists could sample what was inside. Spores of a different B. subtilis strain, DE111, were waking up in the small intestine within three hours of being swallowed.^[3] That is proof for the species, not for MB40. I am telling you that so you know the difference.

In 2021, the FDA looked at BIO-CAT's safety file for MB40. The file is called GRN 955. The FDA sent back its standard "no questions" letter. That is the normal US path for putting a germ in food.^[4]

Every study on it, and what each one really showed

There are four published studies on MB40. Three are in people. You should see all four. Most brands would show you two.

2015: the safety study

BIO-CAT paid for a study of 30 people at PRISM Clinical Research in St. Paul, Minnesota. First, one week of a fake pill. Then 21 days of MB40. The dose was 5 billion CFU twice a day. That is 10 billion a day. Twenty-seven people finished. Five side effects were reported. All were grade 1, the mildest level on a scale of 1 to 4. Two were judged as likely caused by the probiotic. One person had vomiting and chills on the same day. Both were gone within 31 hours. Bowel habits did not change. The study came out in Nutrients in 2021. The same paper mapped the strain's whole genome. It found no toxin genes. It found no antibiotic resistance genes that could spread to other germs. The strain does resist one antibiotic, streptomycin. That trait is fixed in its own DNA, and it is common in this species.^[5]

2016 to 2017: gas and bloating

One hundred healthy adults took part at three clinics: Foothill Ranch, California; Orlando, Florida; and London, Ontario. Half took 5 billion CFU a day. Half took a fake pill. It ran four weeks. The main question was bloating scores. Across the whole group, MB40 did not beat the fake pill. The men in the study did improve on bloating and days with gas. But a win in one subgroup, after the main test failed, is weak proof. The paper also ran in Alternative Therapies in Health and Medicine. That is not a top journal.^[6] I include it anyway. A company that only shows you its wins is not one you should buy germs from.

2021: staph carriage

This is the Thai trial from the top of this page. 115 carriers. 55 took MB40. 60 took a fake pill. The dose was 10 billion CFU once a day for 30 days. No one knew who had which. It ran at one site, Prince of Songkla University. Stool staph fell 96.8 percent. Nose staph fell 65.4 percent. Side effects were the same in both groups. The rest of the gut germs did not change.^[1]

2023: piglets and Listeria

Virginia Tech fed 32 baby pigs for 14 days. Half got a normal diet. Half got a diet with MB40 in it. Then they gave half of each group a germ called Listeria monocytogenes. The MB40 pigs had 67 percent less Listeria in the liver. They had 49 percent less in the spleen.^[7] People who work at BIO-CAT helped write the paper. What this means for a human gut, I will not guess.

Why your shower can't reach the problem

From 2009 to 2014, athletic trainers at 17 NCAA wrestling programs kept records. They logged 112 skin infections in 87 wrestlers. Three out of four of those infections cost at least a full day of training. Almost one in four was a repeat. The wrestler had already had one before.^[8] In 2025, a review in the International Journal of Sports Medicine looked at MRSA in wrestlers. It said mat cleaning and skin checks are "insufficient on their own." It said the sport needs the kind of decolonization plans that hospitals already use.^[9]

The Lancet paper is the best answer I have found to why hygiene keeps failing. About one in four people always carries staph. Some studies say one in three. For a long time, doctors thought the nose was the main home for it. So getting rid of staph meant an ointment up the nose and a special body wash. The Thai team measured the nose and the gut in the same people. They found about a thousand times more staph in the gut than in the nose. Their reading: the gut keeps sending staph back to the nose. That is why nose-only treatment gets undone so fast.^[1]

Now put that next to your own routine. You shower after every roll. You wash the gi. Someone mops the mats with something that smells like a pool. All of that works on the outside of your body. It works on the day you do it. If you are a carrier, the main supply of staph is inside you. It comes to class with you. That is the half no soap has ever touched. It is the half MB40 was tested against.

What the trial did not show, and what a supplement cannot claim

I want to be exact here. The law requires it. It is also just true.

The trial counted germs. It did not count infections. No one has run a study where grapplers took MB40 and someone counted who got staph. Carrying less staph is likely a good thing for a person who gets mat burn every week. But "likely" is the honest word. Spöretz is a food supplement. It is not a treatment for staph, MRSA, impetigo, or anything else. It does not prevent them either. No supplement is allowed to claim that. If you have a sore or a lesion, see a doctor today. Do not reach for a probiotic.

The people in the trial were rural Thai adults. They were all carriers. It was one site. The authors think the fengycin effect should work on staph from anywhere. So a blue belt in Canada should respond the same way. That is a fair argument. It is not data. The whole trial was 30 days, once a day. And Bacillus subtilis does not stay in your gut for good. The paper says the effect is not expected to last long after you stop taking it.^[1]

What you actually get in a bottle of Spöretz

You take two capsules a day. That is it. Here is what is inside them, and why. If I were you, I would want to know before I swallowed it.

The big one is MB40. Two capsules give you 10 billion CFU of it. On the bottle it is called WelBac 40. That is the same amount people took in the Thai trial and in the 2015 safety study. So you get the strain that was tested, in the amount that was tested. I did not want to sell a smaller dose and point at someone else's study.

Next to it is 5 billion CFU more of Bacillus subtilis. Think of that as extra spores. The proof is in the MB40. I told you earlier that a label with no strain code does not tell you much. That is true here too, and I will not pretend it is not.

Then there are four more things. None of them were in the MB40 trials. We put them in for our own reasons. You should judge each one on its own. Here is what we know about each.

Garlic extract, 200 mg, with 1 percent allicin. Allicin is what garlic makes when you crush it. In 2004, a lab at the University of East London tested it on 30 MRSA germs taken from hospital patients. In a dish, it stopped all 30. Some of those germs were already resistant to mupirocin, which is the cream doctors put up your nose to get rid of staph.^[10] But be careful. A dish is not a gut. Once allicin gets into your blood, your body breaks it down fast. The real proof for garlic in people is about the immune system. In a 90-day study at the University of Florida, 120 healthy adults took aged garlic extract or a fake pill. The garlic group's natural killer cells and gamma-delta T cells grew better. That group also had 21 percent fewer cold and flu symptoms, and missed 58 percent fewer days of work or school.^[11] That study used a different kind of garlic, and more of it. So take it as a sign that garlic helps normal immune function. It is not a promise about this capsule.

Berberine, 200 mg, from Berberis root. Most people know berberine as a blood sugar supplement. So why is it in a probiotic? Because your body barely absorbs it. Less than 1 percent gets into your blood. Almost all of it stays in your gut. There, it changes which germs grow well. A 2021 study in the Journal of Advanced Research showed this. In patients, berberine's effect on cholesterol worked through the gut germs. When mice had their gut germs wiped out with antibiotics, berberine stopped working.^[12] So berberine is here to change the ground the spores land on. We kept the dose small on purpose. Studies on blood sugar use a gram or more a day. At that much, a lot of people get an upset stomach. We wanted the gut effect without that.

Oregano oil powder, 100 mg, with 70 percent carvacrol. Carvacrol is what gives oregano oil its taste. In lab tests, it breaks the outer skin of germs and fungus. People have used oregano oil to clean out the gut for a long time. I will be plain with you. There is not much proof in people. We put it in to help keep gut germs in balance in your first weeks. I cannot show you a trial for that. If that bothers you, that is fair. It bothers me a little too. That is why the dose is small.

BioPerine, 5 mg. This is black pepper extract. Most of it is piperine. It has one job. It helps your body absorb the other plant stuff. Piperine slows down the parts of your liver and gut that clear plant compounds out. In a 1998 study, 20 mg of it made curcumin blood levels 20 times higher in people.^[13] Berberine and garlic get cleared the same way. So a little piperine helps them stay around long enough to do something.

Inulin. This is a fiber from chicory root. Your body cannot break it down. So it goes all the way to your colon. There it feeds the good germs that already live there. It is cheap and plain. It is also a better use of space than filler.

How to take it: start slow. Week one, take one capsule every other day. Week two, take one a day. Week three, take two a day. Some people feel changes in their gut in the first days on any new probiotic. Starting slow keeps that mild. Take it with food. Once you are at two, take one with each meal. It does not need a fridge. It can live in your gym bag.

Did you skip down here to find out if you should buy it? Here is my answer. Do you train a contact sport a few times a week? Have you had a skin infection more than once? Then MB40 is the one probiotic strain with a real human trial aimed at the exact germ that keeps sending you to urgent care. That is a much smaller claim than most probiotic ads make. It is the only one I am comfortable making.

The question nobody has answered

How fast does staph come back after you stop? The Thai team tested people the day after the last dose. Then never again. Their best guess comes from the 2018 data. People who keep Bacillus in their gut seem to keep staph out. If that is right, this is a daily habit, like brushing your teeth. It is not a course you finish. I think that is probably right. I do not know it. No one does yet. I would rather tell you that than pretend the paper says something it does not.

So here is the deal. Take it for 90 days. That is one full fight camp. If you do not think it was worth it, email us. We refund you. You keep the bottle. That is the whole risk.

Frequently asked questions

Is Bacillus subtilis MB40 the same thing as Sporevia, OPTI-BIOME and WelBac 40?

Yes. MB40 is the strain. Its code is ATCC PTA-122264. OPTI-BIOME is BIO-CAT's name for it. Sporevia is Kerry's name for it, under a 2021 license. WelBac 40 is the name on the Spöretz label. If a product says only "Bacillus subtilis" with no strain code, you cannot tell what it is.

Does MB40 kill staph?

No. The scientists are careful about this. B. subtilis makes fengycins. Fengycins block the signal staph uses to settle into the gut. So the staph count falls, and the other gut germs are left alone. In the 2023 Lancet Microbe trial, 30 days of MB40 cut stool staph by 96.8 percent and nose staph by 65.4 percent in carriers.^[1] That trial counted germs, not infections. MB40 is not a treatment for any infection.

What dose of MB40 was used in the studies?

10 billion CFU a day in the 2015 safety study. That was 5 billion twice a day for 21 days. Also 10 billion a day in the 2021 staph trial. That was one dose a day for 30 days. The gas-and-bloating trial used 5 billion a day for four weeks. Two capsules of Spöretz give you 10 billion CFU of MB40.

Does MB40 need refrigeration?

No. It comes as sleeping spores. They are stable at room temperature. Keep the bottle dry. Keep it out of a hot car. Then it is fine in a gym bag.

Is MB40 safe?

The strain's whole genome has been mapped. It has no toxin genes. It has no antibiotic resistance genes that can spread. In the human safety study, 10 billion CFU a day for 21 days caused no serious side effects. The FDA raised no questions about its safety file in 2021.^[4][5] If you are pregnant, breastfeeding, have a weak immune system, or take prescription drugs, ask your doctor before starting any probiotic.

How long does the effect last after you stop taking it?

No one has measured it. Bacillus subtilis does not stay in your gut for good. The authors of the 2023 trial say the drop in staph is not expected to last long after you stop. The 2018 Nature data suggest that people who keep Bacillus in their gut keep staph out. That points to daily use, not a short course.

References

1. Piewngam P, Khongthong S, Roekngam N, Theapparat Y, Sunpaweravong S, Faroongsarng D, Otto M. Probiotic for pathogen-specific Staphylococcus aureus decolonisation in Thailand: a phase 2, double-blind, randomised, placebo-controlled trial. Lancet Microbe. 2023;4(2):e75-e83. Thai Clinical Trials Registry TCTR20210128003.
2. Piewngam P, Zheng Y, Nguyen TH, et al. Pathogen elimination by probiotic Bacillus via signalling interference. Nature. 2018;562(7728):532-537.
3. Colom J, Freitas D, Simon A, et al. Presence and germination of the probiotic Bacillus subtilis DE111 in the human small intestinal tract: a randomized, crossover, double-blind, and placebo-controlled study. Front Microbiol. 2021;12:715863. (DE111, not MB40.)
4. US Food and Drug Administration. GRAS Notice GRN 000955: OPTI-BIOME Bacillus subtilis MB40, submitted by BIO-CAT Microbials, LLC; filed November 10, 2020; agency response 2021.
5. 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. ClinicalTrials.gov NCT04655352.
6. Penet C, Kramer R, Little R, et al. A randomized, double-blind, placebo-controlled, parallel study evaluating the efficacy of Bacillus subtilis MB40 to reduce abdominal discomfort, gas, and bloating. Altern Ther Health Med. 2021;27(S1):146-157. ClinicalTrials.gov NCT02950012.
7. Garvey SM, Emami NK, Guice JL, et al. The probiotic Bacillus subtilis MB40 improves immunity in a porcine model of listeriosis. Microorganisms. 2023;11(8):2110.
8. Herzog MM, Fraser MA, Register-Mihalik JK, Kerr ZY. Epidemiology of skin infections in men's wrestling: analysis of 2009-2010 through 2013-2014 NCAA surveillance data. J Athl Train. 2017;52(5):457-463.
9. Thomas T, Moore A, Nath S, Kearns G. A silent opponent: Staphylococcus aureus and its impact on wrestlers. Int J Sports Med. 2025;46(6):383-389.
10. Cutler RR, Wilson P. Antibacterial activity of a new, stable, aqueous extract of allicin against methicillin-resistant Staphylococcus aureus. Br J Biomed Sci. 2004;61(2):71-74. (In vitro.)
11. Nantz MP, Rowe CA, Muller CE, Creasy RA, Stanilka JM, Percival SS. Supplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms: a randomized, double-blind, placebo-controlled nutrition intervention. Clin Nutr. 2012;31(3):337-344.
12. Wu C, Zhao Y, Zhang Y, et al. Gut microbiota specifically mediates the anti-hypercholesterolemic effect of berberine (BBR) and facilitates to predict BBR's cholesterol-decreasing efficacy in patients. J Adv Res. 2022;37:197-208.
13. Shoba G, Joy D, Joseph T, Majeed M, Rajendran R, Srinivas PS. Influence of piperine on the pharmacokinetics of curcumin in animals and human volunteers. Planta Med. 1998;64(4):353-356.

Related: The Science of MB40 · Why grapplers keep getting staph · The gut–skin axis

Written by Yassir Laarais, founder of Spöretz. Updated September 11, 2026. This article describes published research on a bacterial strain for educational purposes. 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.