The strain is the claim
An organism’s name has three levels and a supplement label usually prints two of them. The missing level is the one that connects a bottle to a piece of research, which makes a species-only label an unfinished sentence.
Bacteria are named at three levels: genus, species and strain. A label that prints Bifidobacterium infantis has given you the first two. The strain is the third — a designation such as ATCC BAA-835, tied to a deposit in a culture collection — and it is the only level at which a published trial can be matched to what is in the capsule.
The National Institutes of Health’s Office of Dietary Supplements is explicit that probiotic effects are strain-specific and warns that ignoring the strain produces misleading conclusions. Its own example: Lactobacillus rhamnosus reduced the risk of atopic dermatitis where L. reuteri did not.
Three levels of a name
Every organism on every probiotic label sits somewhere on this ladder, and the label decides how far down it takes you.
A bacterial name is built in levels, each narrower than the one above it. The genus is the broad group. The species sits inside the genus. The strain sits inside the species, and it is the level at which one particular isolate — one culture, from one place, kept and grown from one deposit — is distinguished from every other member of its species.
- Genus — Bifidobacterium
- The broad group. Useful for orienting yourself and almost useless for anything else. Hundreds of published findings sit under a genus and contradict one another.
- Species — Bifidobacterium infantis
- Narrower, and the level most labels stop at. It tells you what kind of organism the powder was made from. It does not tell you which one, and members of a species differ from each other in ways that matter.
- Strain — a designation such as ATCC BAA-835
- One specific isolate, identified by a code and usually deposited in a recognised culture collection. This is the level a published trial is conducted at, and therefore the only level at which a trial can be matched to a bottle.
- What a label usually prints
- Genus and species. Two of the three levels, stopping exactly one step above the level where the evidence lives.
The ladder is not a technicality. Two products can print identical species lists and contain different organisms, grown from different deposits, with different published records behind them. At the species level those two products look the same. At the strain level they may have nothing in common at all.
Why only the third level can be looked up
This is the sentence that makes the whole argument, and it is not this site’s sentence.
The Office of Dietary Supplements is explicit: the health effects of probiotics are strain-specific, and it warns that researchers who do not take strain into account can reach misleading conclusions. That is a statement about the structure of the evidence, not a preference about labelling.
ODS gives the example itself. Lactobacillus rhamnosus was found to reduce the risk of atopic dermatitis; L. reuteri did not. Two organisms in what was then the same genus, one finding, and it does not transfer between them. If a finding does not travel between species, there is no reason to assume it travels between strains of one species.
That is what makes a species name an unfinished sentence. “Contains Bifidobacterium infantis” is a true statement about the contents and an incomplete statement about the evidence. The completion — which B. infantis, from which deposit, studied by whom, at what dose, for what outcome — is exactly the part that got left off.
What a reader does with an unfinished sentence
Usually, finishes it. A buyer who reads a species name goes looking, finds a trial of that species, and imports the result into the bottle in their hand. It is a reasonable thing to do and it is not supported by the label.
The trial studied a strain. The bottle names a species. Nothing on the bottle says the two are the same organism, and nothing on the bottle says they are not, because the level at which that question is answered was not printed.
What a strain designation looks like
Once you have seen one you will spot its absence immediately.
A strain designation is a code, usually attached to a deposit in a culture collection so that anybody can obtain the same organism and work on it. The collection is named, and the code identifies the deposit within it. It reads like a catalogue reference, because that is what it is.
The European Union’s authorisation of pasteurised Akkermansia muciniphila as a novel food is a useful worked example, because a regulator writing an authorisation cannot be vague about what was authorised. The organism is identified by strain: ATCC BAA-835, also deposited as CIP 107961. Two collections, two codes, one organism.
| Level | How it reads | What you can do with it |
|---|---|---|
| Genus | Akkermansia | Orient yourself. Nothing more. |
| Species | Akkermansia muciniphila | Find the general literature on the species, and import none of it safely into a specific bottle. |
| Strain | A. muciniphila ATCC BAA-835 / CIP 107961 | Look up that deposit, find the work done on it, and know whether the bottle in your hand contains the organism the work was done on. |
| Form and condition | Pasteurised; adults, excluding pregnant and lactating women; up to 3.4 × 1010 cells a day | Know that the authorised form is the non-viable one, who it was authorised for, and the daily amount. This is what a complete specification looks like. |
Scroll this table sideways →
Note the last row, because it is the part that surprises people. What the EU authorised for this organism is the pasteurised form — that is, the non-viable one — for adults, excluding pregnant and lactating women, up to a stated daily cell count, under that named strain. Four constraints, all of them written down, none of which can be checked against a bottle that prints a species name alone.
European rules do not govern a product sold in the United States, and that authorisation is cited here as an example of what a complete organism specification reads like, not as a rule anything is being measured against.
How to read an organism list in thirty seconds
Works on any probiotic on any shelf, including the ones that do this well.
Count the levels in each name
Two words is genus and species. A code after the two words — letters, digits, often a collection prefix — is the strain. If there is no code, you are one level short.
Check whether the strain is attached to an amount
A strain designation with no quantity beside it is better than no strain at all and still not checkable. The pair you want is a named strain and a count.
Look for the timing on the count
End of shelf life is the figure ODS tells you to prefer. At manufacture describes the factory. No date at all should be read as the kinder of the two.
Search the strain, not the species
A search on the designation finds the work done on that isolate. A search on the species finds a literature that may have nothing to do with what you are holding.
Decide what the gap is worth to you
A species-only label is not proof of a bad product. It is a product you cannot check, which is a different complaint and a fair one to make before you spend anything.
The last step is the honest one. Plenty of good organisms are sold under species-only labels, and a missing designation is not evidence of anything except that the manufacturer did not print it. The point is that it removes your ability to verify, and the verification was the only thing that separated the claim from the marketing.
This bottle: three species, no strains
The same ladder, applied to the label the rest of this site is about.
The SlimTide panel names three organisms underneath its 36 mg Probiotic Blend: Bifidobacterium infantis, Clostridium butyricum and Akkermansia muciniphila. Genus and species for all three, which is more than a great many blends manage.
No strain designation appears for any of them. Not a collection code, not a deposit number, not a proprietary strain name. The names stop at level two of three, which means none of the three can be matched to any published trial, safety record or dose.
Two of the three make that gap unusually visible. C. butyricum has been used as a probiotic in Japan for decades under the MIYAIRI 588 strain — a named strain, which is how it is discussed in the literature — and the genus also contains species that are not benign. That is precisely the situation in which a strain designation stops being a nicety.
A. muciniphila is the other. The European authorisation described above names a strain, restricts the form to the pasteurised one, excludes pregnant and lactating women and states a daily cell count. This label gives none of those four things, and does not say whether the organism in the capsule is live or not.
The panel here is honest and complete by the standards of what labelling rules ask for. The strain is not among the things they ask for, which is why the gap exists on a good label — and why it is worth knowing that the level the evidence lives at is the level that was left off.
See the SlimTide packs
One, three or six bottles. The price is on the seller’s checkout page, because it is one of the few figures this site was never given — and a figure we were not given is not a figure we will print.
Shipping cost and delivery time were not supplied either, which matters more than usual on a product whose label asks for refrigeration. The guarantee is 60 days from purchase unless the sales page prints longer.
References
The sources behind the numbers on this page.
- Office of Dietary Supplements, National Institutes of HealthProbiotics — Health Professional Fact Sheet · sourceThe definition of a probiotic, what colony-forming units are, the fact that US regulations require total microorganism weight rather than viable CFU, the advice to prefer products stating CFU at end of shelf life, strain specificity, and the safety record in immunocompromised people.
- European UnionCommission Implementing Regulation (EU) 2022/168 of 8 February 2022 authorising pasteurised Akkermansia muciniphila as a novel food · sourceOnly the pasteurised form is authorised, for adults excluding pregnant and lactating women, at up to 3.4 × 10¹⁰ cells a day, under a named strain and a required designation.