Probiotic Strains and Labels: Genus, Species, Strain, CFU, Viability and Storage

Genus, species, strain

A full probiotic name has up to three parts, and ISAPP (a scientific association) says a label should give all three for each strain in the product. [4]

• Genus, the broad group (for example Lactobacillus).
• Species, a kind within the genus (for example rhamnosus).
• Strain, a specific lineage with a letter-and-number code (for example GG).

A label that stops at genus and species does not say which strain is inside. ISAPP notes that labels sometimes give no strain designation at all, or only a group word. [4] In a Washington, DC-area survey described by ISAPP, 45% of retail supplement products did not provide strain designations. [4] A 2026 storage study also found limited strain-level labeling across all the products it examined. [5]

Old and new names on the same strain

In 2020 researchers proposed splitting the genus Lactobacillus, which had 261 species, into 25 genera. [6] ISAPP says the species part of each name did not change. [7] Papers and labels mix the two systems, so the strain code is the part to match. The full table is on Probiotic strain names and the 2020 renaming.

CFU: what the number is

CFU means colony-forming units, the unit probiotic counts are usually given in. [4] The FAO/WHO guidelines, as ISAPP summarizes them, call for the minimum viable number of each strain at the end of the shelf life. [4] A count "at time of manufacture" is a different thing. ISAPP says most strains lose cell count over shelf life, some more than others. [4] More is not automatically better: the amounts used in trials belong to the strain and the study. NCCIH says we do not know how much of the probiotic people would have to take. [1] Details are on CFU: what the number means and does not.

Storage and viability

In a 12-month test of commercial multi-strain supplements, storage temperature was the main factor in viability, and cold storage preserved counts best. [5] The same study found one bifidobacteria group held up much better than others, and some products missed their declared counts whatever the storage. [5] Whether a given product needs refrigeration is a question for its label. See Probiotic storage.

Single-strain, multi-strain and heat-killed products

Multi-strain does not automatically mean better. ISAPP points out that with a total count alone you do not know whether equal amounts of all strains are included. [4] In irritable bowel syndrome, the AGA described one review of 53 trials that found no significant benefit when single-strain trials were grouped by genus, but a possible benefit when 19 multistrain trials were analyzed together. [8] Evidence belongs to the exact combination tested; see multi-strain versus single-strain products. Some trials also tested heat-killed preparations, which do not meet the strict definition of a probiotic. [8]

Can the label be trusted?

Studies that tested products against their labels have found gaps. One laboratory study of products from the local market (the authors are based in Pakistan) reported that almost none met the label claim and 11% had no viable cells. [9] A review of authenticity concluded that products are frequently not compliant with their labels for strain and viable cell number. [10] These are not a ranking of any market. NCCIH notes that many probiotics are sold as dietary supplements, which do not require FDA approval before they are marketed. [1] The AGA also noted there are no guidelines for reporting product testing in trials, so results for the same strain from different manufacturers are hard to compare. [8] See label accuracy, contamination and third-party testing and quality testing and certifications.

What to check on a label

1. The full strain name and code, not only the species.
2. The count, and whether it applies at the end of shelf life or at manufacture.
3. The storage line and the expiry date.
4. Other ingredients you need to avoid.
5. Whether a study exists for that exact strain (see strain specificity).

The step-by-step version is How to read a probiotic label, and the general guide is Reading supplement labels.