Your Probiotic Is a Strain, Not a Species: Reading the Code After the Name

Why so many people search for strain codes

Every month, people type strings such as “bifidobacterium lactis HN019”, “b lactis HN019”, “lactobacillus acidophilus NCFM”, “B420 probiotic” or “DSM 17938” into search engines. They have usually seen these letters and numbers on a label and want to know what they mean. Most pages answer with a list of claimed benefits. This article does something more useful: it explains how to read the code, because the code after the name is the most important part of a probiotic label. Without it, you cannot tell which microbe you are buying, or whether anyone has ever studied it.

What is a probiotic strain? Genus, species and strain explained

Scientists name every microbe in layers. Think of a person’s family name, first name and identity number. The genus is the family name (Lactobacillus, Bifidobacterium). The species is the first name (acidophilus, rhamnosus). The strain is the identity number: one particular, traceable line of that species, grown from one original microbe. A 2020 expert paper by scientists linked to the International Scientific Association for Probiotics and Prebiotics (ISAPP), a non-profit scientific body, explains that a proper strain name has two parts: the official genus and species (and subspecies, where one exists), followed by a strain designation. That designation can be a catalogue number from a recognised culture collection or a company’s own code [2].

Some species are split once more into subspecies. The best-known case is Bifidobacterium animalis subsp. lactis (“subsp.” means subspecies), which almost everyone shortens to B. lactis. So “Bifidobacterium animalis subsp. lactis B420” and “Bifidobacterium lactis B420” are the same strain written two ways [12]. The same logic applies to a supplement: a Bifidobacterium lactis HN019 probiotic cannot borrow evidence from a different B. lactis strain, and a label that reads only “B. lactis” tells you far less than one that reads Bifidobacterium lactis HN019. The table shows how a few published strain names break down. These are examples of what codes look like, not recommendations.

Why benefits are strain-specific, and when they are not

Here is the core argument. Two strains of the same species can behave very differently, so a result found with one strain does not automatically carry over to another. A systematic review (a study that gathers and weighs all the trials on a question) looked at 228 randomised trials and found strong evidence that probiotic effects are both strain-specific and condition-specific: among strains of the same or closely related species, some showed a benefit for a given problem while others did not [3]. The authors warned that reviews which pool different strains together can reach misleading conclusions [3].

Animal work shows the same pattern. In one mouse study described in a 2018 review, three strains of L. reuteri were given to mice on a high-fat diet: only one reduced weight gain, while mice given another strain gained some weight [10]. Mouse results prove nothing in people, but they show how far strains of one species can differ [10].

How a strain gets its code: culture collections and genome sequencing

Experts recommend that every probiotic strain be deposited (placed for safe-keeping) in a recognised culture collection, a kind of library that stores living microbes so that other scientists can obtain and check them [2]. Under the Budapest Treaty of 1977, the World Intellectual Property Organization (WIPO), the United Nations agency for patents and inventions, recognises 53 international depositary authorities as of March 2026 [6]. They include the American Type Culture Collection (ATCC) in the United States, the German Collection of Microorganisms and Cell Cultures (DSMZ), and three in India: the Microbial Type Culture Collection (MTCC), the Microbial Culture Collection (MCC) and the National Agriculturally Important Microbial Culture Collection (NAIMCC) [6]. That is why a code beginning “DSM” points to the German collection, and “ATCC PTA 6475” points to the American one. Other codes, such as HN019, NCFM or La-14, are a company’s or laboratory’s own designation for a strain [2]. Experts recommend that each strain keep a single designation, because several names for one strain cause confusion [2].

How do scientists prove a strain is what the label says? The “gold standard” for probiotic strain identity testing is whole-genome sequencing (WGS): reading the strain’s complete DNA, its full instruction book, letter by letter [2]. This genomic sequencing for strain validation can tell apart strains that older laboratory tests could not. Two examples show why it is needed:

• The genomes of L. acidophilus La-14 and L. acidophilus NCFM are 99.98% the same, differing at about 111 single spots, plus one larger deletion, in roughly two million DNA letters [8]. Two separate strains, almost twins.
• Two B. lactis strains, Bl-04 and DSM 10140, differ by only 47 single DNA letters and four small insertions or deletions. Older typing methods had failed to tell B. lactis strains apart; a test built on these tiny differences sorted 24 strains into 14 groups [9].
• A strain can even be changed on purpose. Scientists removed two plasmids (small extra rings of DNA that carried antibiotic-resistance genes) from L. reuteri ATCC 55730, using methods that do not genetically modify the microbe. The result was a new “daughter” strain, which received its own code: DSM 17938 [7].

The Lactobacillus reclassification of 2020: why the names changed

For decades, Lactobacillus was a giant catch-all genus. By March 2020 it held 261 species that were extremely different from one another in their genes, habits and homes [4]. In April 2020, an international team of 15 scientists published a study in the International Journal of Systematic and Evolutionary Microbiology that compared the whole genomes of all these species [4]. They split the old genus into 25 genera: a smaller, amended Lactobacillus, the existing genus Paralactobacillus, and 23 new genera [4]. The new groups bring together species that are truly related and share similar ecology and metabolism (how they live and feed) [4].

The informal word “lactobacilli” is still useful for all the species that were classed as Lactobacillaceae until 2020 [4]. Helpfully, every new genus name begins with “L”, so the short form L. rhamnosus still works [5]. The research team also built a free online tool for looking up the new names for any former Lactobacillus species [5]. Here are the new names for Lactobacillus species most often seen on probiotic labels:

What did not change? The species part of each name stayed the same [5]. The strain code is a catalogue or company number, not part of the scientific name [2], so it stays too: Lactobacillus rhamnosus HN001 is simply written Lacticaseibacillus rhamnosus HN001 today. The microbe in the capsule is exactly the same. Labels that still use the old name are not wrong about what is inside; they simply use the older spelling.

What our research shows about strain names in clinical trials

Aesclebio’s own analysis of 3,070 probiotic-type clinical trials (research studies in people) registered on ClinicalTrials.gov, the public trial registry run by the US National Library of Medicine, shows how much the 2020 change touches everyday science. Of the eight leading species in that analysis, five now carry a new genus name [14].

The same analysis found a bigger problem. Only 57.6% of these trials name a strain designation anywhere in the registry record, so more than two in five trials cannot be tied to a specific strain [14]. By contrast, a single neutral deposit code, L. reuteri DSM 17938, appears in 106 registered trials [14]. For anyone looking for probiotic strains with clinical data, or planning a study, the lesson is simple: good clinical trial design for probiotics starts with naming the exact strain in the record.

Myth or fact?

How to read a probiotic label: a strain checklist

Probiotic strain names explained in one line: genus + species (+ subspecies) + strain code. Use the code to check the evidence.

• Look for the full name of every strain in the probiotic supplement, including the code after the species. A label that lists only “Lactobacillus acidophilus” tells you the species, not the strain.
• Check the evidence for that exact code. Search the code on PubMed (a free database of medical research) or ClinicalTrials.gov and see whether it was tested in people for the benefit you want.
• Do not mind old or new genus names. L. plantarum and Lactiplantibacillus plantarum are the same species [5].
• Check the live count until the end of shelf life, stated in colony-forming units (CFU), the standard count of live microbes [2].
• Ask suppliers for proof of identity. Buyers and brands can request genome sequencing results and the culture-collection deposit number for each strain [2].
• If you are pregnant, breastfeeding, buying for a baby or child, or living with a health condition, speak to your doctor before choosing a probiotic.

The bottom line

Your probiotic is a strain, not a species. The letters and numbers after the name are not decoration; they are the identity number that links a product to the studies done with it. Benefits found with one strain do not automatically transfer to its cousins, even cousins with 99.98% of the same DNA. The 2020 renaming of Lactobacillus changed the family names on many labels, but not the microbes inside. When you read a label, look past the genus and species to the code, and then look for the human evidence behind that code.

Frequently asked questions

What is a probiotic strain?

A probiotic strain is one specific, traceable line of microbes within a species, grown from one original microbe and named by a code after the species name, such as the “NCFM” in Lactobacillus acidophilus NCFM. Experts recommend that each strain be identified by whole-genome sequencing and deposited in a recognised culture collection, so that its identity can always be checked [2].

What is Bifidobacterium lactis HN019, and what are its benefits?

HN019 is a strain code of Bifidobacterium animalis subsp. lactis, usually shortened to B. lactis [11]. This article does not assess the benefits of any named strain. Any benefit belongs to the exact strain, amount and group of people tested, so look up the published human trials for that code [3], and ask a doctor whether it suits you.

Is Lactobacillus acidophilus NCFM the same as La-14?

No. They are two separate strains of the same species, each with its own code. Their genomes are 99.98% the same, with about 111 small differences [8]. Because benefits are often strain-specific [3], evidence for one cannot simply be borrowed for the other; each strain needs its own studies in people.

What does a code like DSM 17938 or ATCC PTA 6475 mean?

These are deposit codes. “DSM” points to the German culture collection DSMZ (German Collection of Microorganisms and Cell Cultures) and “ATCC” to the American Type Culture Collection, both recognised international depositary authorities [6]. The number is the strain’s catalogue entry, so scientists can obtain the same strain and check it. Both of these codes are strains of L. reuteri [7, 10].

Why was Lactobacillus renamed, and what are the new names?

By 2020 the genus held 261 very different species. A whole-genome study split it into 25 genera so that names reflect true relationships [4]. Common changes: L. casei, L. paracasei and L. rhamnosus became Lacticaseibacillus; L. plantarum became Lactiplantibacillus; L. reuteri and L. fermentum became Limosilactobacillus; L. salivarius became Ligilactobacillus. L. acidophilus and L. gasseri kept the name Lactobacillus [5].

Did the 2020 name change alter my probiotic?

No. Only the genus part of the name changed; the species name stayed the same [5], and so did the strain code, which is a catalogue number rather than part of the scientific name [2]. A product labelled Lactobacillus rhamnosus and one labelled Lacticaseibacillus rhamnosus with the same strain code contain the same microbe.

Are strain-specific probiotics always better than species-level products?

Not always better, but always easier to check. Some core benefits, such as support for a healthy digestive tract, are seen across many strains of commonly studied species [1]. Still, experts say every probiotic should be identified to the strain level [2], because many other effects are strain-specific [1, 3].

How do companies prove probiotic strain identity?

The gold standard is whole-genome sequencing, which reads a strain’s full DNA and can tell even near-identical strains apart [2, 9]. Good suppliers also deposit each strain in a recognised culture collection and keep their production cultures genetically pure, so that every batch contains the same strain over time [2].

Related reading

• What Probiotics Are, and the Five Myths That Survive Every Explainer
• Billions of CFU, Little Meaning: Why the Biggest Number on the Label Rarely Wins
• Probiotic Foods vs Probiotic Supplements: Why a Probiotic Foods List Is Not a Dose
• L. reuteri: The Most Searched Probiotic Species (Aesclebio blog)
• Choosing a Probiotic Contract Manufacturer (Aesclebio blog)