A new probiotic strain called Bacillus subtilis THC1I significantly reduced antibiotic-associated diarrhea and restored healthy gut bacteria in mice, according to a 2026 research study. The treatment improved stool consistency, repaired intestinal lining damage, reduced inflammation, and rebalanced gut bacteria composition compared to untreated mice. While these results are promising, human clinical trials are needed before this probiotic could be used to treat diarrhea in people taking antibiotics.
When antibiotics kill harmful bacteria, they also destroy helpful gut bacteria, causing diarrhea. Researchers tested a new probiotic strain called Bacillus subtilis THC1I on mice with antibiotic-associated diarrhea. According to Gram Research analysis, the treatment restored the mice’s healthy gut bacteria, reduced inflammation, and improved digestive symptoms. The probiotic helped repair the intestinal lining and brought back beneficial bacteria that antibiotics had wiped out. While this is promising early research in mice, scientists hope it could eventually help people who experience diarrhea after taking antibiotics.
Key Statistics
A 2026 mouse study of 50 animals found that Bacillus subtilis THC1I probiotic treatment significantly improved fecal scores and reduced water content in stool, indicating substantial improvement in antibiotic-associated diarrhea symptoms.
Research published in Current Microbiology showed that the new probiotic strain reduced pro-inflammatory markers TNF-α and IL-1β in mice with antibiotic-induced diarrhea, demonstrating decreased intestinal inflammation.
In a 50-mouse study, Bacillus subtilis THC1I treatment restored beneficial bacteria including Bacteroides and Lactobacillus while reducing harmful bacteria like Escherichia-Shigella and Clostridioides that had overgrown from antibiotic use.
Histopathological analysis in the 2026 study revealed that probiotic-treated mice showed restored epithelial architecture and increased goblet cell density, indicating repair of intestinal barrier damage caused by antibiotics.
The Quick Take
- What they studied: Whether a new probiotic bacteria called Bacillus subtilis THC1I could fix diarrhea and restore healthy gut bacteria in mice that had been given antibiotics
- Who participated: Fifty laboratory mice divided into five groups: a healthy control group, mice with antibiotic-induced diarrhea, and three treatment groups receiving either a standard probiotic or different doses of the new Bacillus subtilis THC1I strain
- Key finding: Mice treated with Bacillus subtilis THC1I showed significant improvements in diarrhea symptoms, restored healthy gut bacteria, reduced inflammation markers, and repaired intestinal lining damage compared to untreated mice with antibiotic-associated diarrhea
- What it means for you: This research suggests a potential new probiotic treatment for antibiotic-related diarrhea, though human studies are needed before it could be used in people. If proven safe and effective in humans, it could help prevent or treat diarrhea caused by antibiotics
The Research Details
Researchers used fifty laboratory mice and divided them into five equal groups of ten mice each. One group served as the healthy control. The other four groups were given antibiotics (gentamycin and cefradine) for five days to create antibiotic-associated diarrhea. Three of these sick groups then received different treatments: one got a standard probiotic called Enterogermina, and two got different doses of the new Bacillus subtilis THC1I probiotic. The researchers measured multiple outcomes including body weight, water intake, stool consistency, blood work, inflammation levels, intestinal tissue damage, and the composition of gut bacteria using genetic sequencing.
This research approach is important because it tests whether a new probiotic can actually repair the damage antibiotics cause to the gut. By measuring so many different outcomes—from visible symptoms to microscopic intestinal changes to genetic analysis of bacteria—the researchers could see exactly how the probiotic works. This comprehensive approach helps determine if the treatment is truly effective and safe before considering human trials.
This is a controlled laboratory study with clear comparison groups, which is a solid foundation for early research. However, it was conducted only in mice, so results may not directly apply to humans. The study used objective measurements like genetic sequencing and tissue analysis, which strengthens reliability. The relatively small sample size (ten mice per group) is typical for early-stage research but means results should be confirmed in larger studies before human use
What the Results Show
Mice treated with Bacillus subtilis THC1I showed dramatic improvements across multiple measures. Body weight recovered better in treated mice compared to untreated sick mice. Water intake normalized, and most importantly, stool consistency improved significantly—diarrhea symptoms decreased. The probiotic treatment restored the balance of electrolytes (sodium and potassium) in the blood that antibiotics had disrupted. White blood cell counts, which had been elevated due to inflammation, returned to healthier levels. The colon, which had become swollen and inflamed from antibiotic damage, returned closer to normal size and appearance.
Microscopic examination of intestinal tissue revealed that the probiotic helped repair the intestinal lining. Goblet cells, which produce protective mucus in the intestines, increased in number. Inflammatory markers in the blood (TNF-α and IL-1β proteins that signal inflammation) were significantly reduced. Genetic analysis of gut bacteria showed the probiotic helped restore beneficial bacteria like Bacteroides and Lactobacillus while reducing harmful bacteria like Escherichia-Shigella and Clostridioides that had overgrown during antibiotic treatment. The diversity of gut bacteria, measured by the Shannon index, partially improved with treatment.
This research builds on existing knowledge that probiotics can help restore gut health after antibiotics. The new Bacillus subtilis THC1I strain performed similarly to or better than Enterogermina (a standard probiotic used as a positive control), suggesting it may be a viable alternative. The comprehensive measurement of both intestinal barrier repair and microbiota restoration adds new understanding about how this specific strain works, going beyond previous studies that may have focused on only one aspect
This study was conducted only in mice, so results may not directly translate to humans. The study period was relatively short, so long-term effects are unknown. Only one dose of antibiotics was tested, so results may differ with different antibiotic types or doses. The study didn’t test whether the probiotic would work if given at different times relative to antibiotic treatment. Finally, while the probiotic improved microbial diversity, it didn’t completely restore it to normal levels, suggesting it may work best as part of a broader treatment approach
The Bottom Line
Based on this mouse research, Bacillus subtilis THC1I shows promise as a potential probiotic treatment for antibiotic-associated diarrhea. However, human clinical trials are necessary before any recommendations can be made for people. Current evidence is moderate-to-strong in mice but preliminary for humans. Anyone experiencing antibiotic-related diarrhea should consult their healthcare provider about proven probiotic options while this research continues
This research is most relevant to people who experience diarrhea after taking antibiotics, healthcare providers treating antibiotic-associated diarrhea, and probiotic manufacturers developing new treatments. It’s less immediately relevant to people without antibiotic-related digestive issues. Patients with weakened immune systems should consult doctors before using any new probiotic
In this mouse study, improvements appeared within the treatment period (during and shortly after antibiotic use). If human trials proceed, benefits might appear similarly quickly, but this would need to be confirmed. Long-term benefits and whether the restored bacteria remain stable after treatment stops would require longer-term human studies
Frequently Asked Questions
Can this new probiotic help me if I get diarrhea from antibiotics?
This research is promising but only tested in mice so far. Human studies are needed before doctors can recommend it. Talk to your healthcare provider about proven probiotic options available now if you experience antibiotic-related diarrhea
How does Bacillus subtilis THC1I compare to other probiotics for antibiotic diarrhea?
In this mouse study, Bacillus subtilis THC1I performed similarly to or better than Enterogermina, a standard probiotic. However, direct human comparisons haven’t been done yet, so more research is needed to determine which works best
When should I take this probiotic if I’m on antibiotics?
This study doesn’t specify optimal timing in mice. Generally, probiotics work best when separated from antibiotics by 2-3 hours. Consult your pharmacist or doctor about the best timing for any probiotic you use alongside antibiotics
Will this probiotic completely restore my gut bacteria after antibiotics?
In mice, Bacillus subtilis THC1I partially restored bacterial diversity and composition but didn’t completely return it to normal levels. Full recovery may require time and possibly additional interventions beyond probiotics alone
Is this probiotic safe for people with weak immune systems?
This study only tested healthy mice. People with compromised immunity should consult their doctor before using any new probiotic, as safety in immunocompromised individuals hasn’t been established in this research
Want to Apply This Research?
- Track daily stool consistency (using a simple 1-5 scale), water intake in ounces, and any digestive symptoms when taking antibiotics. Record probiotic doses taken and timing relative to antibiotic doses to identify patterns
- If prescribed antibiotics, users could set reminders to take a probiotic supplement at a consistent time daily, ideally separated from antibiotic doses by 2-3 hours. Log any changes in digestive symptoms to share with healthcare providers
- Create a simple daily log during and for two weeks after antibiotic treatment tracking: stool frequency and consistency, abdominal discomfort level, energy levels, and appetite. This data helps identify whether a probiotic is working and provides useful information for healthcare discussions
This research was conducted in mice and has not been tested in humans. Bacillus subtilis THC1I is not currently approved for human use. Anyone experiencing diarrhea or other side effects from antibiotics should consult their healthcare provider before starting any new supplement or probiotic. This article is for educational purposes only and should not be considered medical advice. Do not self-treat antibiotic-associated diarrhea without professional medical guidance, especially if symptoms are severe or persistent.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.