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Glossary

What is a probiotic strain?

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

A probiotic strain is one specific line of a microbe, named by genus, species and a strain code, as in Lacticaseibacillus rhamnosus GG. The strain matters because results found for one strain do not automatically apply to another strain of the same species. Look for all three parts of the name on the label.1,2,3

Key facts

  • Probiotics are identified by genus, species, subspecies where there is one, and an alphanumeric strain designation.1
  • In 2020, the genus Lactobacillus, then 261 species, was split into 25 genera, so many familiar names changed.4
  • NCCIH notes that what one kind of Lactobacillus does, another Lactobacillus or a Bifidobacterium will not necessarily do.3
  • Some probiotic mechanisms are widely shared, while others, such as specific effects on the immune system, are strain specific.1

How a strain name is built

Examples of probiotic names, from NIH's fact sheet1
GenusSpeciesSubspeciesStrain
Lacticaseibacillus (formerly Lactobacillus)rhamnosusnoneGG
BifidobacteriumanimalislactisDN-173 010
Bifidobacteriumlongumlongum35624

The strain code is the part that pins down which culture you are getting. Two products that both say Bifidobacterium longum may contain different strains with different research behind them.1,3

Why the 2020 name changes matter

Genome studies showed that the old genus Lactobacillus held very different organisms, so in 2020 taxonomists split it into 25 genera. Lactobacillus rhamnosus became Lacticaseibacillus rhamnosus, for example, and NIH now lists Limosilactobacillus reuteri among common probiotics. Older studies and labels may use the former names for the same strains.1,2,4

Single strain and multi strain products

Supplements can contain one strain or many. More strains is not, by itself, a sign of a better product: NIH notes that many commercial products have never been studied, and that a product's effects depend on its specific strains and its number of CFU.1,2

Before you take one

NCCIH notes that some probiotic products have been found to contain microbes other than those on the label, and that the risk of harm is greater in people with severe illness or weakened immune systems. Ask a doctor first if either applies to you.3

Questions people ask

What does a 10 strain probiotic mean?

It contains ten different strains, each of which should be named on the label. The number of strains says nothing on its own about effects; look for named strains that have been studied in people, at the amounts studied.1

Why do some labels still say Lactobacillus?

Many species moved to new genera in 2020, and older labels and studies keep the names in use at the time. NIH's fact sheet keeps original names when reporting older studies.1,4

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Sources

  1. Office of Dietary Supplements, National Institutes of Health. Probiotics: Fact Sheet for Health Professionals. Updated March 25, 2025. Opened 2026-10-07.
  2. Office of Dietary Supplements, National Institutes of Health. Probiotics: Fact Sheet for Consumers. Updated November 17, 2025. Opened 2026-10-07.
  3. National Center for Complementary and Integrative Health. Probiotics: What You Need To Know. Opened 2026-10-07.
  4. Zheng J, Wittouck S, Salvetti E, et al. A taxonomic note on the genus Lactobacillus: Description of 23 novel genera, emended description of the genus Lactobacillus Beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae. Int J Syst Evol Microbiol. 2020;70(4):2782-2858. Opened 2026-10-07.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.