Bacteroides Caccae

Bacteroides caccae is one of the most common bacteria in the human colon. Finding it in your stool is normal. What a stool panel tells you is not whether it is there but how much of it is there compared with everything else, and that number moves with the state of your gut rather than pointing at any one disease.

The direction matters more than the value. Stool panels that count several gut species at once have, in early head-to-head work, separated inflammatory bowel disease from irritable bowel syndrome at least as well as the standard stool inflammation test. No single species does that work alone, including this one.

What This Test Actually Measures

The assay amplifies bacterial DNA from your stool sample and counts copies of a genetic sequence unique to this species. PCR stands for polymerase chain reaction. It copies a target stretch of DNA millions of times, so a tiny amount becomes measurable.

Labs report the answer in different ways. Some give an amount per gram of stool, others a share of the total bacterial DNA in the sample. Either way, you are reading how much of your gut community this one species makes up.

Unlike most things on a lab report, this is a living organism, so the number reflects who is living in your colon rather than how one of your organs is working. It arrives early. In a Scandinavian cohort of 608 mother-child pairs, a single globally distributed strain of this species was the most commonly shared Bacteroidaceae strain between mothers and their children, and vaginal delivery led to earlier colonization than cesarean section. Early feeding leaves a mark too: in a study of 75 infants, formula-fed babies carried this species more often than breastfed babies at both one week and four months.

It earns its keep by fermenting complex carbohydrates your own enzymes cannot touch, including the sugars in your colon's mucus layer. Most of what lives down there survives without oxygen, and this is one of the abundant ones. Its outer membrane carries a molecule called lipopolysaccharide. Your immune system watches that molecule closely, which is part of why these species turn up in so many inflammation studies.

Telling Inflammatory Bowel Disease From IBS

The strongest evidence here belongs to panels, not to single species. A droplet digital PCR test that counts several bacterial targets at once distinguished inflammatory bowel disease from irritable bowel syndrome with 79% sensitivity and 92% specificity, and fecal calprotectin managed 68% sensitivity and 89% specificity on the same samples. That head-to-head result came from a small in-house comparison of 108 stool samples, evenly split between ulcerative colitis, Crohn's disease, and irritable bowel syndrome.

The same research group also tested the panel across international cohorts totaling nearly 6,000 samples, but that was a different and harder comparison: inflammatory bowel disease against a mix of other conditions, where accuracy was more modest. And calprotectin does better in larger pooled analyses than it did in that 108-sample pilot, with a meta-analysis putting it around 85% sensitivity and 91% specificity for the same question. So the microbial panel is promising for this specific distinction, not settled.

That gap matters in one specific situation. If you have persistent diarrhea, cramping, and urgency, the hard question is whether the bowel wall is structurally inflamed or whether the gut is misbehaving without visible damage. Calprotectin answers that imperfectly. A microbial pattern may add something, though the direct comparison rests on small numbers so far.

Your number on this one species does not deliver that performance, and it is not established as one of the markers carrying those panels. Read it as one line in a profile.

Kidney Disease

Bacteroides species in the gut produce compounds that healthy kidneys clear from the blood. When filtration drops, those compounds build up. A Taiwanese study comparing 119 healthy volunteers with 22 people on peritoneal dialysis and 16 on hemodialysis found these toxin-producing Bacteroides species more abundant in chronic kidney disease. The published report does not make clear which individual species drove the hemodialysis finding, so treat this as a genus-level signal rather than one specific to this species. Larger sequencing studies independently find Bacteroides raised in advanced kidney disease.

That is not the same as the bacteria causing the kidney disease. A failing kidney changes the chemistry of the gut, which changes which bacteria do well there. The arrow probably runs both ways. If your filtration is reduced and you are tracking your gut, this is a plausible reason your Bacteroides numbers look different from someone with normal kidneys.

What the Cancer Studies Show

Shotgun sequencing of stool from 65 people, 33 with chronic gastritis and 32 with gastric cancer, found this species enriched in the cancer group. Small study, and it does not turn the test into a cancer screen.

For the colon, the useful work again comes from multi-species panels. In a screening study of 676 adults, 435 of them without symptoms, a panel of fecal microbial DNA markers detected colorectal cancer in that asymptomatic group with 84.9% sensitivity and advanced precancerous polyps with 38.6% sensitivity, beating the standard fecal immunochemical test. Those panels ran on species such as Fusobacterium nucleatum and Bacteroides clarus, not on this one. Stool DNA screening for colon neoplasia is promising, and this particular species is not the marker doing the work.

Dyslipidemia and Metabolic Patterns

A study of 1,384 adults compared 895 people with abnormal cholesterol or triglycerides against 489 controls. Stool abundance of this species ran higher in the dyslipidemia group, and the difference held after adjusting for age, sex, body mass index, blood glucose, and systolic blood pressure.

Carry one caveat forward. The signal survived one statistical model and not a second one the same researchers ran, and the study was a snapshot rather than a follow-up over years. It points somewhere interesting without settling anything, and it cannot tell you whether a higher number today means a heart attack later.

Why the Number Alone Does Not Mean Much Yet

You may have noticed the pattern. Elevated in kidney disease, elevated in gastric cancer, elevated in abnormal cholesterol, and depleted in severe gut inflammation when the whole oxygen-free community collapses. That looks contradictory until you stop treating it as a good-number-bad-number marker.

It is an abundant resident that responds to its surroundings. When the colon's chemistry shifts, from kidney failure, from inflammation, from diet, or from a drug, the species suited to the old conditions grow or shrink. The abundance is a readout of the ecosystem, not a verdict on you. Pooling gut microbiome studies across ten diseases showed that many microbial shifts are shared across unrelated conditions rather than specific to any one of them.

Correlation, Not Causation

Genetic studies have tested whether Bacteroides actually causes disease. The method is called Mendelian randomization, and it uses inherited gene variants as a natural experiment to separate cause from consequence. The results are mixed rather than clean. One analysis found no causal link between gut bacteria, including Bacteroides, and ankylosing spondylitis. Others point the opposite way, with genetically predicted higher Bacteroides abundance linked to lower odds of ankylosing spondylitis (odds ratio about 0.66), and a 2025 review of eight such studies concluded that lower Bacteroides abundance is genetically tied to spondyloarthritis. In periodontitis, other bacterial groups emerged as causal drivers and this genus did not. A longevity analysis found the arrow ran backward: living longer changed Bacteroides abundance, not the other way around.

All of that is genus-level work, not about this one species. So a high or low result here is not something to attack with antibiotics or a targeted supplement. Nothing shows that changing this one species changes any clinical outcome.

Why a Single Reading Can Fool You

Day-to-day variation is the biggest obstacle to reading one result. Your own baseline usually outweighs the effect of short-term diet changes, and a single stool sample captures one moment in a community that drifts.

• Gut transit time: how fast stool moves through you changes measured Bacteroides abundance a lot. Quantitative profiling work found transit time and stool moisture to be major drivers, and most studies do not adjust for either.
• Recent diet: fiber intake in the days before collection shifts which fiber-fermenting species dominate the sample.
• Medications: antibiotics, daily aspirin, and several psychiatric drugs measurably move Bacteroides levels.
• Lab method: a quantitative PCR result and a sequencing-based result are not interchangeable, so compare like with like across time.

Tracking Your Trend

One sample carries a real risk of misclassifying where you actually sit. Sampling more than once, across set time windows, gives a much better picture of your baseline than any single specimen.

If you are making a deliberate change, sample before and after rather than once in the middle. Be careful what you conclude from a flat retest, though. The evidence that fiber or prebiotics move Bacteroides comes mostly from genus-level or other-species measurements. Fiber responses inside this genus are species-specific: in controlled feeding work, a prebiotic that enriched two Bacteroides species left close relatives unchanged. If this number does not budge after a dietary change, that does not mean the change failed.

What to Do With an Unexpected Result

Start with the rest of the panel. This species is interpretable only in context, so look at overall diversity, the balance of other oxygen-free residents such as Faecalibacterium prausnitzii and Akkermansia muciniphila, and whether anything else on the report moved in the same direction.

Then pair it with host markers. Fecal calprotectin measures actual inflammation of the gut lining and is the right companion when you have diarrhea, blood, or persistent pain. A stool pathogen panel rules out an acute infection mimicking a flare. If your result is unusual and your kidney function is reduced, cystatin C and creatinine-based filtration estimates tell you whether the kidney picture explains the gut picture.

Two combinations warrant a gastroenterologist rather than watchful waiting: a disrupted microbial pattern plus elevated calprotectin plus ongoing symptoms, and any result accompanied by visible blood, unintended weight loss, or nighttime symptoms. Those call for endoscopy, not another stool test. An isolated shift in this species with a clean calprotectin and no symptoms is not a reason to intervene.