Lactococcus

Most of what this test finds got there from your fridge. Lactococcus, the genus of lactic acid bacteria that turns milk into cheese, buttermilk, and sour cream, is a passenger in the human gut rather than a settled resident. It arrives with food, passes through, and mostly disappears within a couple of weeks once you stop eating it.

That makes the reading closer to a transit receipt than a health score, which is exactly why it's useful if you take a probiotic or eat a lot of cultured dairy. There is a second, much weaker signal underneath it: in stool studies, people with colorectal cancer carry less of this genus than healthy people do.

What the Test Actually Counts

These stool counts come from PCR, a lab method that copies and counts specific stretches of DNA. What it counts is bacterial DNA in your stool. The organisms come from outside you: no part of your body makes them.

PCR doesn't care whether the cell it finds was alive. It copies the DNA either way. In one study of a related organism, Lactobacillus casei Shirota, the PCR count ran about ten times higher than the count from culturing live cells out of the same stool, because the assay was picking up dead and broken-open cells that had simply ridden through the gut. That finding comes from a different species, but the same physics applies here: a positive result proves DNA passed through, not that anything moved in.

This is also a genus-level result, not a species one. Lactococcus lactis and Lactococcus cremoris, the two species most people have heard of, both roll up into the same number.

Where It Comes From

Diet sets this number more than anything else. In a randomized crossover trial, healthy adults on a high-dairy diet had higher stool levels of this genus than the same people on a low-dairy diet. Cheese and cultured milk are literally made with these bacteria as starter cultures, so you are eating them by the billion.

Genetics tilts the same number a second way. If you make little lactase, the enzyme that digests milk sugar, undigested lactose reaches your colon and feeds lactic acid bacteria already there. In a study of 330 healthy multi-ethnic US adults, those with the lactase non-persistent genotype who ate a lot of lactose carried more of this genus than those who didn't. Two people eating identical cheese can land at different readings.

How long it lasts is the more useful fact. When seven adults drank fermented milk containing a Lactococcus lactis subsp. cremoris strain, all seven shed it in stool, anywhere from a hundred thousand to a billion cells per gram, for as long as they kept drinking. Two weeks after they stopped, only one of the seven still had detectable levels.

Colorectal Cancer

The clearest human association points one way in stool: people with colorectal cancer carry less of this genus than healthy people do. A case-control comparison of 489 people with colorectal cancer and 536 healthy people found Lactococcus lactis depleted in the cancer group. That is one comparison, not a signal shown to hold up across many separate cohorts, and some studies that sampled tumor tissue rather than stool have reported the opposite direction.

The mechanism work behind that finding is animal work. In mice, feeding a Lactococcus lactis strain suppressed tumor formation, and the effect traced to an enzyme the bacterium secretes called alpha-mannosidase. That hasn't been tested in people, so treat it as a reason the association is plausible, not as evidence that eating these bacteria prevents cancer.

A low reading is not a cancer signal you should act on. Microbiome researchers analyzing colorectal cancer cohorts have shown that diet, medication, and stool consistency confound most single-genus associations, and that rigorous adjustment shrinks many of them. If colorectal cancer is what's on your mind, a stool blood test or a colonoscopy answers that question and this does not.

Stomach Cancer

A Korean case-control study of 556 people found that carrying Lactococcus lactis in the stomach lining went with roughly one-fifth the odds of having gastric cancer. Helicobacter pylori pushed risk hard in the opposite direction in the same analysis.

Most of the rest of the stomach literature runs the other way. A 2024 systematic review of case-control studies found lactic acid bacteria, this genus among them, increased in the stomach lining of people with gastric cancer, and sequencing of tumor tissue has found it enriched inside the cancer. Researchers have a mechanism for that direction too: the lactate these bacteria produce can feed tumor cells. So the stomach association is genuinely conflicting, not protective.

There is a second catch. All of this work sampled the stomach lining, not stool. Stomach and colon carry different communities, and nobody has shown that a stool reading predicts what's growing on your stomach lining. Read it as a reason the genus is biologically interesting, not as something your stool result tells you about your stomach.

Depression

In a study comparing 106 people with mood disorders who had never taken an antidepressant against 151 healthy controls, stool levels of this genus were lower in the patients, and the drop tracked with a broader score of how disrupted the whole community was. Studying people before any medication matters, because antidepressants themselves shift gut bacteria and muddy most comparisons.

This is a snapshot comparison, not a follow-forward study, so it can't tell you which came first. Low mood changes what people eat, and what people eat changes this number. Across psychiatric conditions generally, the gut findings that replicate best involve butyrate-producing residents like Faecalibacterium, not this genus.

Crohn's Disease in Remission

In 171 people with inflammatory bowel disease in remission, higher levels of this genus in the intestinal lining went with better psychological quality of life among those with Crohn's. The samples came from mucosal tissue rather than stool, which again is a different measurement from the one you're ordering.

Why a Low Result Usually Means Something Boring

You now have two facts pulling against each other. Sick cohorts carry less of this genus, and yet almost anyone who doesn't eat cultured dairy carries very little of it either. Both are true, and the way to hold them together is to stop reading this as a good-number, bad-number marker. Very few gut genera are universal: a genetic study of more than 18,000 people found only a handful present in nearly everyone, and this one isn't among them.

Low is the default state, not a finding. The result only carries information once you know the diet and medication history sitting behind it. Someone who eats yogurt daily and still reads near zero is telling you something different from someone who has been dairy-free for a year and reads the same.

When a Reading Can Fool You

• Recent dairy or probiotic intake: this is the single biggest driver of the number. A cheese-heavy week before collection can move you from near zero to the top of the distribution with nothing having changed about your gut.
• Dead cells count too: the assay copies DNA from cells that died in your stomach as readily as from cells that thrived in your colon, so a high number never proves colonization.
• A recent antibiotic course: gut lactic acid bacteria are flattened for months afterward. A sample drawn in that window describes the drug, not your usual gut.
• Lab and naming differences: these bacteria were historically classed with Streptococcus and are still sometimes misidentified as Enterococcus by older lab methods, and DNA extraction protocols vary enough between labs that counts don't transfer cleanly. Compare your results within one lab, not across two.

Tracking Your Trend

A single reading of a low-abundance, food-driven genus is close to noise. Six years of repeat sampling in 86 adults showed that stool communities are more stable over time than skin or nasal ones, but that the rare genera inside them swing hard with diet, illness, and antibiotics. What's stable is the core. This isn't the core.

Get a baseline, then retest four to eight weeks after any deliberate change: starting or stopping a probiotic, adding or cutting fermented dairy, finishing a course of antibiotics. After that, retest annually alongside the rest of a stool panel. Write down what you ate for the week before each collection, because without that the number can't be interpreted at all.

One thing this test can honestly do is verify a supplement. The evidence that swallowing these bacteria raises this specific reading is direct: the seven-person feeding study measured the strain in feces by PCR, the same analyte in the same matrix you're ordering. If you take a Lactococcus-containing product and your level doesn't move, that's real information about the product.

What an Odd Result Should Make You Do

Never act on this genus alone. It earns its keep as one line inside a fuller stool panel, and the useful signal lives in combinations.

• Low, with no dairy in your diet: nothing to do. This is the expected reading and it says more about your groceries than your health.
• Low, alongside gut symptoms and a raised fecal calprotectin: the calprotectin is what drives the workup. Order it if you haven't, and bring a raised result to a gastroenterologist rather than chasing the microbiome line.
• Low across the whole panel, with core residents like Faecalibacterium prausnitzii and Akkermansia also down, after antibiotics: read that as broad depletion rather than a specific finding, and repeat the panel around three months out, which is roughly when diversity comes back toward baseline.
• High right after starting a probiotic: your capsule is surviving the trip. That's the whole message, and it doesn't imply the strain has colonized or that anything downstream has changed.

If the colorectal cancer association is what pulled you here, the move is not to retest this. It's to be current on age-appropriate screening, because that is the test that answers the question.