Probiotic strains
live microorganisms identified to strain level: genus, species, subspecies where one applies, and strain designation
ProbioticsIngredient formSources last checked: October 15, 2026
Medical & Industry Advisor: Dr. James Pendleton, ND
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What it is
- A probiotic is identified by its strain: the genus, the species, the subspecies where one applies, and an alphanumeric strain designation. In 2020 the genus Lactobacillus was reclassified into 25 genera, so many strains now carry a new genus name, for example Lacticaseibacillus, Lactiplantibacillus or Limosilactobacillus, and older documents may show the former one. [NIH Office of Dietary Supplements, Probiotics fact sheet][Zheng et al., International Journal of Systematic and Evolutionary Microbiology 2020]
Forms compared
How probiotic strains compares with related forms on a spec sheet and a label.
| Form | Declared on the label as | Content | Identity check |
|---|---|---|---|
| Single-strain product | The strain by weight; CFU may follow the weight (FDA draft guidance). Industry guidelines: declare that strain's CFU | One strain, named to strain level[CRN and IPA, Best Practices Guidelines for Probiotics, 2026-10-15][FDA draft guidance, quantitative labeling of dietary supplements containing live microbials, 2026-10-15] | A strain-specific identity test at release when the label names the strain; a species-specific test confirms only the species |
| Multi-strain blend | Each strain with its weight, or, in a proprietary blend, the blend's total weight with the strains listed beneath it in descending order by weight. Industry guidelines: the blend's total CFU, plus each genus or species when technically feasible | Two or more strains, each named to strain level[21 CFR 101.36(c), 2026-10-15][CRN and IPA, Best Practices Guidelines for Probiotics, 2026-10-15] | A strain-specific identity result for every labeled strain at release, not one result for the blend as a whole |
| Refrigerated or room-temperature product | The storage instruction on the label | Stability conditions named in the CRN and IPA guidelines (from ICH Q1A(R2)): refrigerator 5°C ± 3°C; general case 25°C ± 2°C at 60% relative humidity, or 30°C ± 2°C at 65%[CRN and IPA, Best Practices Guidelines for Probiotics, 2026-10-15] | Real-time stability data at the labeled storage condition, in the final package |
On the Supplement Facts label
The Supplement Facts panel must declare the microorganisms by weight, and that weight counts live and dead cells together. CFU, the count of live cells, may be added: FDA's September 2018 draft guidance (still labeled a draft on FDA's page, read 2026-10-15) describes enforcement discretion when the CFU figure follows the weight, is clearly separate from it, counts only live organisms, and the label otherwise complies. Industry guidelines (CRN and IPA, 2017) recommend stating the CFU at the end of shelf life: for a single strain, that strain's CFU; for a blend, the total CFU, plus each genus or species when technically feasible.[NIH Office of Dietary Supplements, Probiotics fact sheet, 2026-10-15][FDA draft guidance, quantitative labeling of dietary supplements containing live microbials, 2026-10-15][CRN and IPA, Best Practices Guidelines for Probiotics, 2026-10-15]
Spec parameters buyers should demand
What to ask for on the certificate of analysis and spec sheet. Identity, quality, and regulatory parameters only. This is not advice about efficacy.
| Parameter | What to ask | Why it matters |
|---|---|---|
| Strain identity | Name each strain in full on the spec: genus, species, subspecies where one applies, and strain designation, written as in NIH's nomenclature table, for example Lacticaseibacillus rhamnosus GG (an example of the format, not a recommendation). Where the genus was renamed in 2020, give the current name with the former one.[NIH Office of Dietary Supplements, Probiotics fact sheet][Zheng et al., IJSEM 2020][CRN and IPA, Best Practices Guidelines for Probiotics] | The strain, not the species, identifies a probiotic, and the 2020 reclassification means old and new genus names both appear on documents. |
| Count at end of shelf life | Set the CFU you will declare as the count at the end of shelf life, not at manufacture, and ask what overage the manufacturer's stability data support.[CRN and IPA, Best Practices Guidelines for Probiotics][NIH Office of Dietary Supplements, Probiotics fact sheet] | The CRN and IPA guidelines say the labeled quantity should reflect live organisms at the end of the stated shelf life, with 100% of the declared quantity present then apart from method variability; NIH advises users to look for that basis. |
| Stability in the final package | Ask for real-time stability data in the final package at the storage condition the label will state, for example 25°C at 60% relative humidity for a room-temperature product or 5°C for a refrigerated one.[CRN and IPA, Best Practices Guidelines for Probiotics] | The guidelines tie survival to the strains, formulation, dosage form and packaging, and accelerated testing used for release needs a documented scientific justification. |
| Water activity and atmosphere | Ask for the water activity of the fill and whether the package is nitrogen-flushed or carries a desiccant, with the stability data behind the choice.[Celik and O'Sullivan, Journal of Dairy Science 2013] | In a 2013 study of freeze-dried bifidobacteria, one strain kept best at up to 21°C and water activity up to 0.44 in all atmospheres tested, while a sensitive strain needed frozen storage, nitrogen and water activity between 0.11 and 0.22. |
| Identity at release | Ask for a strain-specific identity test on each lot at release for every strain the label names; a species-specific test confirms only the species. Also confirm the manufacturer runs at least one appropriate identity test on each incoming lot of each strain, as 21 CFR 111.75(a)(1) requires for every dietary ingredient unless FDA has granted a petition exemption.[21 CFR 111.75(a)(1)][Shehata and Newmaster, Frontiers in Microbiology 2020] | A species-specific result cannot tell two strains of the same species apart. Market surveys using species-specific PCR have found labeled species missing from some products, and a 2020 survey's authors call for strain-specific assays to authenticate strains, including in multi-strain products. |
QC and testing considerations
- For a multi-strain blend, test identity for every labeled strain at release with a strain-specific method; a test that only confirms each species can miss a missing or substituted strain. [Shehata and Newmaster, Frontiers in Microbiology 2020]
- Plate counts carry about ±0.5 log of method variation, so agree the count method and the acceptance range with the lab before release. [Mohar Lorbeg et al., Frontiers in Microbiology 2021]
Further reading: How to read a certificate of analysis and third-party supplement testing.
Published market surveys
Totals as each study reports them: what was measured, how many products, and the result. Methods and sampling differ between studies.
| Measured | Study | Market, products tested | Result | Funding or affiliation |
|---|---|---|---|---|
| Identity | Shehata and Newmaster, Frontiers in Microbiology 2020 | United States and Canada (products collected from manufacturers), n=182 | Species-specific tests did not detect 11 declared species in 10 of 182 products, and viable counts were below the label in 5 of the 72 samples counted, 1 with no viable cells; 15 of 182 products (8%) were non-compliant overall. | Industry-affiliated |
| Viable count | Mohar Lorbeg et al., Frontiers in Microbiology 2021 | Slovenia (bought in pharmacies, 2019), n=26 | 3 of 26 products (12%) had viable counts 0.5 to 1 log unit below the labeled number; 5 more were within 0.5 log, which the authors treated as method variation. | Industry-affiliated |
Government statements, quoted
Probiotics are identified by their specific strain, which includes the genus, the species, the subspecies (if applicable), and an alphanumeric strain designation [4]. Microbial organisms from the genera Bifidobacterium, Saccharomyces, Streptococcus, Enterococcus, Escherichia, and Bacillus are commonly used in probiotic products. In addition, products commonly contain microbes from the family Lactobacillaceae, which includes several species that were formerly in the Lactobacillus genus before that genus was restructured in 2020 [5].
Current labeling regulations only require manufacturers to list the total weight of the microorganisms on probiotic products’ Supplement Facts labels; this cellular mass can consist of both live and dead microorganisms and, therefore, has no relationship with the number of viable microorganisms in the product [14]. Manufacturers may voluntarily list the CFU in a product in addition to the total microorganism weight on the Supplement Facts label.
The use of probiotics has been linked to bacteremia, fungemia (fungi in the blood), or infections that have resulted in severe illness in some cases, most of which involved individuals who were severely ill or immunocompromised [88,89].
Reference list
- NIH Office of Dietary Supplements, Probiotics Health Professional Fact Sheet (updated March 25, 2025) Government reference
- FDA, Policy Regarding Quantitative Labeling of Dietary Supplements Containing Live Microbials: Draft Guidance for Industry (September 2018) Government reference
- CRN and IPA, Best Practices Guidelines for Probiotics (effective January 9, 2017) Industry standard
- 21 CFR 111.75: identity testing of dietary ingredients Regulatory
- Shehata and Newmaster, PCR-based identity testing of probiotic products in the US and Canada, Front Microbiol 2020;11:1095 Market survey
- Mohar Lorbeg et al., dietary supplements containing viable bacteria in Slovenian pharmacies, Front Microbiol 2021;12:700138 Market survey
A reference list is not claim substantiation. Under the FTC's Health Products Compliance Guidance (December 2022), marketing claims about a finished product require competent and reliable scientific evidence, typically randomized, controlled human clinical testing. Responsibility for substantiating product claims rests with the brand.
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Further reading
The decision framework behind this reference: five checkable criteria for choosing between a branded ingredient and its generic form.
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