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Gut Bacteria, a Toxin, and Colon Cancer: What a New Mechanism Study Found
A Nature study identified claudin-4 as a receptor that helps a Bacteroides fragilis toxin damage colon cells. It is mechanistic research, not a new screening test or treatment.
A plain-language summary based on public reporting and trusted sources, linked below.
Please note: this page is educational only — it is not medical advice, and it does not speculate about anyone’s health beyond reliable public reporting. For questions about your own health, talk with your healthcare team.
What the study actually reported
The human colon holds trillions of bacteria. Most are harmless or helpful. A few appear to push cancer along.
One of them is enterotoxigenic Bacteroides fragilis. It drives colon tumor formation in laboratory work through a single toxin, called B. fragilis toxin, or BFT.
Researchers already knew what BFT does. It is a metalloprotease, an enzyme that cuts other proteins. It attaches to a receptor on a colon lining cell and cuts off part of E-cadherin, the protein that holds neighboring cells together. That breaks the barrier, brings inflammation, and makes cells divide more.
What nobody knew was which receptor it grabs. A team led by Maxwell White reported the answer in Nature in 2026. Using a genome-wide CRISPR screen, which switches off each gene in turn to see which one matters, they identified claudin-4. Claudin-4 sits in the tight junctions that seal cells to one another. Binding it lets BFT cut E-cadherin at the cell surface.
The authors state the point of finding it plainly: knowing the receptor opens a route to anti-BFT drugs, which might one day help with colorectal cancer prevention and with acute B. fragilis infection.
Why a receptor matters
Naming a receptor is not a small thing in drug development. It converts a vague idea — some bacteria seem to matter in colon cancer — into a specific molecular handhold.
But it does not shorten the road. What exists here is a mechanism in cells, not a treatment, a test, or a prevention strategy. Nothing about clinical care changes because of it.
The other bacterial toxin story
BFT is not the only case, and the parallel one is further along.
Some strains of Escherichia coli carry a stretch of DNA called the pks island, which lets them make a compound called colibactin. Colibactin damages DNA directly.
In 2020, researchers grew human intestinal organoids — small clumps of gut tissue in a dish — and injected them with pks-positive E. coli repeatedly over five months. Sequencing the organoids afterwards showed a distinct pattern of mutations that did not appear when the same bacteria had the pks genes disabled. The team then found that same pattern in human tumors, in a set of 5,876 cancer genomes, mostly colorectal.
A 2025 study in Nature took it further. Researchers analyzed 981 colorectal cancer genomes from 11 countries. The colibactin fingerprints, labeled SBS88 and ID18, were 3.3 times more common in people diagnosed before 40 than in those diagnosed after 70, and they appeared early in the tumor's development. Colibactin damage was also tied to mutations in APC, a gene that acts as a brake on colon cell growth, accounting for roughly 25% of APC driver insertions and deletions in colibactin-positive cases.
That study was looking for reasons behind a real change: colorectal cancer diagnosed under 50 has roughly doubled in many countries over two decades. The authors suggest exposure to colibactin-producing bacteria early in life may contribute. They do not claim to have proved it.
How to read microbiome cancer news
Microbiome research connects diet, infection, immunity, and cancer biology, which makes it easy to overstate. Four questions sort most of it out.
Was the work done in cells, in animals, in human tissue samples, or in a clinical trial? Did it show an association, a mechanism, or a benefit to patients? Did it identify a possible target, or did it test an actual intervention? And does it change any current screening or treatment advice?
For the claudin-4 study the answers are: human cells and a genetic screen; a mechanism; a possible target; and no. Our page on reading cancer statistics and headlines covers the same habit of mind.
When to get checked
None of this changes what actually lowers colorectal cancer risk today, which is screening and acting on symptoms. See a clinician for any of these:
- Blood in the stool, or stools that look black or tarry
- A change in bowel habit lasting more than three weeks, including looser stools or new constipation
- A feeling that the bowel does not empty fully
- Abdominal pain or cramping that keeps returning
- Losing weight without trying
- Unexplained tiredness, or an iron-deficiency anemia found on a blood test
Age matters less than it used to. Early-onset disease is rising, and symptoms in someone in their thirties deserve the same workup as symptoms in someone in their sixties. Our page on early-onset cancer in young adults covers that shift, and our page on colorectal cancer screening sets out the test options.
What this does not mean
- It does not mean most colorectal cancers are caused by one bacterium. Diet, inherited risk, inflammation, and other factors all feed in.
- It does not support taking probiotics, supplements, or antibiotics to alter the microbiome for cancer prevention. Nothing in this work tested that.
- There is no routine clinical test for BFT or for colibactin that should guide screening.
- The colibactin findings are associations across large groups of tumor genomes. They point at a plausible cause; they do not establish one for any individual.
- A receptor identified in a laboratory screen is the start of drug development, not the end. Most such targets never yield a drug.
Sources
- White MT, Wang K, Zhang H, et al. A pro-carcinogenic bacterial toxin binds claudin-4 to cleave E-cadherin. Nature. 2026;654 (PMID 42020735) — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=42020735&retmode=xml
- Pleguezuelos-Manzano C, Puschhof J, Rosendahl Huber A, et al. Mutational signature in colorectal cancer caused by genotoxic pks+ E. coli. Nature. 2020 (PMID 32106218) — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=32106218&retmode=xml
- Diaz-Gay M, Dos Santos W, Moody S, et al. Geographic and age variations in mutational processes in colorectal cancer. Nature. 2025 (PMID 40267983) — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&id=40267983&retmode=xml
- NCI, Screening Tests to Detect Colorectal Cancer and Polyps — https://www.cancer.gov/types/colorectal/screening-fact-sheet
- NCI, Risk Factors: Infectious Agents — https://www.cancer.gov/about-cancer/causes-prevention/risk/infectious-agents
How this article was prepared
An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.
The National Cancer Information Foundation publishes Cancer Explained. This page is for learning. It is not medical advice and does not suggest a test or treatment.
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Put the story in context
Prevention, possible warning signs, screening, and diagnosis
This story relates to Colorectal cancer and the microbiome. The information below is general: it does not reveal anything else about a public person’s health, and not every point applies to every cancer. Personal advice depends on age, symptoms, family history, exposures, and medical history.
Prevention and risk reduction
Not every cancer can be prevented. Avoiding tobacco, protecting skin from ultraviolet radiation, limiting alcohol, staying active, and receiving recommended HPV or hepatitis B vaccination can lower the risk of certain cancers. A risk factor is not a prediction or a cause in one individual.
Symptoms and possible early signs
Possible signs vary and are often caused by conditions other than cancer. Changes worth discussing include a new lump, unexplained bleeding or weight loss, a persistent cough, lasting bowel or bladder changes, a changing skin spot, or symptoms that persist or worsen. Some early cancers cause no symptoms.
Screening and early detection
Screening looks for certain cancers before symptoms begin. Recommended tests exist only for some cancers and depend on age and risk. Screening can have benefits and harms; it is not the same as evaluating a new symptom, and there is no single routine scan or blood test that reliably screens for every cancer.
How cancer is diagnosed
Diagnosis may involve a history and exam, imaging, laboratory tests, and often a biopsy. Pathology can identify the cancer type and may test biomarkers that guide treatment. Symptoms, screening results, tumor markers, or online stories alone cannot confirm cancer.
Learn about this story’s cancer topic
A public story may encourage questions, but it should not be used to estimate your risk or choose testing. Contact a healthcare professional about a persistent or concerning change. Seek urgent care for severe or rapidly worsening symptoms.