Missing gut bacterium linked to chronic IBS after food poisoning, study finds

If a bout of food poisoning left you with abdominal pain, bloating, or unpredictable bowel habits that never fully went away, you are not imagining a link between that infection and your current gut trouble. A new mechanistic study from a Mayo Clinic-led team, published in Nature Microbiology, traces a specific case of post-infection irritable bowel syndrome (IBS that persists after a gut infection has cleared) back to a single missing gut bacterium and a chemical trick it normally performs on a bile pigment called bilirubin. The finding does not just describe another correlation between gut bacteria and IBS, it identifies a mechanism the researchers could reproduce, and then reverse, in mice.

Alistipes Putredinis Loss Drives Excess Gut Protease Activity

The study found that people with excess gut protease activity (protease: a digestive enzyme that breaks down proteins and, left unchecked, can damage the gut lining) after a Campylobacter jejuni infection are commonly missing a specific gut bacterium, Alistipes putredinis, that otherwise keeps that enzyme activity under control. The bacterium and its relatives carry an enzyme called beta-glucuronidase, or GUS, that converts a bound form of bilirubin (a yellow-brown pigment made when the body breaks down old red blood cells) into unconjugated bilirubin, a form the researchers showed directly blocks the digestive enzyme trypsin in lab tests. When A. putredinis disappears from the gut, that brake on protease activity disappears with it.

Post-Infection IBS Patients Show the Clearest Signal

The people most affected are those who develop IBS after a case of food poisoning, a condition doctors call post-infection IBS, or PI-IBS. In the study's human cohort, 37% of the participants with PI-IBS had elevated gut protease activity, and this subgroup reported more frequent, looser bowel movements and showed signs of a leakier gut lining than PI-IBS patients with normal enzyme activity. A prior Minnesota cohort study of Campylobacter infections found that roughly one in five previously healthy people who caught the infection went on to develop IBS within six to nine months. For that group, and for anyone whose IBS symptoms trace back to a specific food poisoning episode, this study offers the first concrete biological reason those symptoms might persist for years after the infection itself is gone.

Human Cohort Plus Germ-Free Mouse Experiments Confirmed Causality

To establish this was cause and not just correlation, the team combined a human observational cohort with mechanistic mouse experiments. On the human side, they enrolled 52 patients with post-infection IBS (confirmed using the Rome III diagnostic criteria after a documented Campylobacter jejuni infection) and 38 healthy volunteers through Mayo Clinic, then used metagenomic sequencing (a technique that reads all the microbial DNA in a stool sample) and fecal enzyme assays to compare gut bacteria and protease activity between groups. On the mouse side, germ-free mice, animals raised with no gut bacteria at all, had tenfold higher protease activity than normal mice, direct evidence that gut bacteria normally suppress the enzyme. Colonizing germ-free mice with stool from healthy or low-protease human donors lowered protease activity; colonizing with stool from high-protease PI-IBS patients did not. A fecal transplant from a healthy donor only lowered protease activity in high-protease mice when the donor microbiome contained A. putredinis, and adding A. putredinis alone to a high-protease stool sample reproduced the same calming effect.

What This Could Mean If Your IBS Followed a Stomach Bug

For someone whose IBS symptoms began after food poisoning, this research offers a possible explanation for why the problem outlasted the original infection: a resident gut bacterium that normally regulates digestive enzyme activity may never have recovered. That said, nothing here has been established as a treatment. The researchers did not test an Alistipes putredinis probiotic, a bilirubin supplement, or any other intervention in humans, and past attempts to treat IBS by restoring gut bacteria through fecal transplants or probiotics have had inconsistent results in clinical trials. Anyone with persistent digestive symptoms following a gut infection should still raise it with a doctor and be evaluated for IBS and other explanations, rather than self-treating based on a single mechanistic study. What is worth mentioning to a doctor is the timeline: if symptoms began soon after a documented case of food poisoning and have persisted, that history is now backed by a specific biological mechanism, not just anecdote.

Modest Human Sample Size Is the Study's Key Limitation

The clearest caveat is scale: the human side of the study included only 52 people with post-infection IBS and 38 healthy comparison volunteers, a modest sample for drawing firm conclusions about who does and doesn't carry this specific bacterial deficiency. All of the causal experiments, the colonizations, the fecal transplants, the bilirubin dosing, the enzyme-blocking drugs, were performed in mice, and mouse models of the human gut microbiome have known limits, including differences in immune development and incomplete transfer of a donor's full microbial community. The researchers themselves note that further work is needed to determine whether A. putredinis is essential for suppressing protease activity or simply one of several bacteria capable of doing so.

Next Steps Point Toward GUS-Targeted Therapies

The research team frames the beta-glucuronidase enzyme, and the bilirubin pathway it controls, as a potential therapeutic target rather than a finished treatment. A separate peer-reviewed review of gut microbial beta-glucuronidase has already highlighted the enzyme as a broader regulator of chemical balance in the body beyond digestive enzymes, suggesting this mechanism could matter for more than IBS alone. Before any of this reaches patients, researchers would need to test whether restoring A. putredinis, supplementing unconjugated bilirubin, or otherwise boosting GUS activity actually reduces IBS symptoms in a controlled human trial, something that has not yet been scheduled or reported.

Common Questions

What is post-infection IBS? Post-infection IBS (PI-IBS) is irritable bowel syndrome that develops after a gut infection, such as food poisoning from Campylobacter jejuni, and persists even after the infection itself has cleared.

What does Alistipes putredinis do in the gut? Alistipes putredinis is a gut bacterium that produces the enzyme beta-glucuronidase, which converts bilirubin into a form that suppresses excess digestive protease activity and helps protect the intestinal lining.

Can a probiotic with this bacterium treat IBS right now? No. This study did not test an Alistipes putredinis probiotic or a bilirubin supplement in humans, and prior attempts to treat IBS by restoring gut bacteria have had mixed results in clinical trials.

How common is IBS after food poisoning? A separate Minnesota cohort study found that roughly one in five previously healthy people who contracted Campylobacter jejuni went on to develop IBS within six to nine months of the infection.

References

1. Adam L. Edwinson, Lu Yang, Stephanie Peters, et al. (2022). Gut microbial β-glucuronidases regulate host luminal proteases and are depleted in irritable bowel syndrome. Nature Microbiology. https://doi.org/10.1038/s41564-022-01103-1
2. Symptoms & Causes of Irritable Bowel Syndrome. NIH. https://www.niddk.nih.gov/health-information/digestive-diseases/irritable-bowel-syndrome/symptoms-causes