What’s the difference between probiotic species, subspecies, and strains?

Probiotic Species, Subspecies, and Strains: What’s the Difference?

Species

A species is the broad category that groups microorganisms with shared defining traits.

• Example: Bacillus subtilis or Bacillus coagulans.
• Members of a species share a genetic blueprint and core features, such as being spore-forming bacteria.

But species are not identical across the board. Just as all dogs are the same species yet differ in size, temperament, and abilities, bacteria within one species can behave differently. Some may have potential health benefits, while others may not.

Subspecies

A subspecies is a subdivision within a species that has consistent genetic or functional differences.

• Example: Lactobacillus delbrueckii subspecies bulgaricus, widely used in yogurt fermentation.
• Not every probiotic species has subspecies, but when they do, the label usually reflects an ecological or functional distinction.

You can think of subspecies like breeds of dogs within the same species: all are dogs, but they may have different traits or strengths.

Strains

A strain is the most specific level. It refers to a single, genetically unique version within a species.

• Example: Bacillus subtilis DE111, Bacillus coagulans GBI-30, 6086, or Saccharomyces boulardii CNCM I-745.
• Strains are the level most often highlighted in research studies and on supplement labels.

Different strains of the same species may not act the same way. One might improve stool quality in dogs, while another shows no effect. This is why clinical studies focus on strain-specific results rather than assuming all members of a species behave alike.

Where do strain names come from?

When scientists want to work with a probiotic, they begin by isolating a single colony of bacteria or yeast from a mixed culture. That colony is then grown on its own, creating a stable “line” of microorganisms that all descend from one original cell. This ensures consistency — every sample of that strain is genetically identical.

Once isolated, the strain goes through a process of characterization, where researchers study its traits:

• Can it survive heat, oxygen, or stomach acid?
• Does it produce beneficial compounds like enzymes or acids?
• Is it safe for the target host (humans, dogs, etc.)?

If the strain is deemed valuable, it is deposited into an official culture collection — essentially a microbial library. Well-known collections include ATCC (American Type Culture Collection) in the U.S. and CNCM (Collection Nationale de Cultures de Microorganismes) in France.

At this point, the strain is given a unique identifier:

• Bacillus subtilis DE111 (a number assigned by Deerland/Deerland Enzymes, catalogued in ATCC).
• Saccharomyces boulardii CNCM I-745 (registered in the CNCM collection in Paris).

These codes act like a passport or fingerprint. They ensure that when scientists across the world talk about a specific strain, or when a company uses it in a supplement, everyone is working with the exact same organism, not just “something similar” from the same species.

Examples in Common Dog Probiotics

This system applies across probiotics, whether bacterial or yeast:

• Lactobacillus: Lactobacillus acidophilus is the species, but NCFM is a specific strain that has been studied for immune effects.
• Bifidobacterium: A genus commonly used in canine nutrition, with different strains studied for digestion and immunity.
• Saccharomyces: A yeast species. Saccharomyces cerevisiae is broad, while Saccharomyces boulardii is often treated as a subspecies or unique strain. S. boulardii CNCM I-745 is one of the most studied yeast probiotics in humans and dogs.

Why Strain Identification Matters

Knowing the species tells you the general type of probiotic, but strain-level detail shows what has been studied. In dogs, research at the strain level helps confirm whether a probiotic can:

• Survive stomach acid and reach the intestines alive
• Be safely tolerated in dogs
• Deliver measurable benefits such as improved stool quality, reduced diarrhea, or immune support

Not every product lists the strain, and that doesn’t automatically mean it’s ineffective. Species-level information still gives a broad idea of what a probiotic might do. But when a strain is named, it connects directly to published research and ensures consistency between what has been studied and what appears in the product.