Probiotic Strain Designations Explained

Species of bacteria from two genera, Lactobacillus and Bifidobacterium, comprise the vast majority of probiotic microorganisms. Most species are further divided into strains that have very similar but not exactly equal genetics compared to the type strain (identity standard) for a particular species. For example Lactobacillus acidophilus NCFM is very similar but not genetically equal to Lactobacillus acidophilus 4356 (the designated type strain for L. acidophilus). Yet both are recognized as L. acidophilus. Since there is no universal standard in microbiology for how much genetic difference is permitted for a new bacterial isolate to qualify as a strain of an existing species versus becoming a new species itself, confusion often exists. This, in part, explains why taxonomists are regularly changing species names. For example, what used to be called Bifidobacterium lactis is now officially called Bifidobacterium animalis subspecies lactis but this longer designation is rarely used on product labels. Other reclassification examples exist where once designated Lactobacillus acidophilus cultures (with various strain designations) were changed to Lactobacillus gasseri and Lactobacillus curvatus species because the genetic differences were too great to justify retaining them as an acidophilus species.

There can be numerous strain designations for a particular probiotic species, and to further complicate things, some may be identical genetically while others are not. Generally, when a new bacterial culture is isolated by a university research group for example, and the full DNA genome is determined to be very close to that of an existing species, that species name is used and a new strain designation is given. However, it’s not uncommon for strain designations to be changed once the culture is commercialized or utilized in a different country. For example, L. acidophilus NCFM has also been designated LA-1, LA-5, and DDS-1 in various probiotic formulas. One way around this confusion is for customers to ask probiotic companies for more information on strains in a particular product; for example, if a commercial strain designation is different from one sited in a clinical trial, and that trial is used as evidence of efficacy, it becomes necessary for the probiotic company to prove the strains are identical.

Theralac probioticHere is a specific example of how to prove strain equivalence in a commercial product: The probiotic product Theralac® designates the L. acidophilus it contains as the LA-1 strain but it sites research and clinical trials that have been run on the L. acidophilus NCFM strain. Master Supplements, Inc. (The makers of Theralac®) purchases the NCFM strain in concentrated form from Dupont/Danisco and it is so designated on their invoice to Master Supplements. Due to a contractual relationship with another company, Dupont/Danisco cannot allow Master Supplements to use the NCFM designation on the Theralac® label. However, Master Supplements can verify that the NCFM strain is used in the production of Theralac® batches as the only L. acidophilus ingredient.

The bottom line on judging probiotic strains revolves around whether they have been verified in clinical and laboratory studies. When strain designations differ, probiotic companies must prove equivalency to any other strain they may site for clinical efficacy or not make such a connection.

Randolph S. Porubcan MSc
Consulting Microbiologist