Probiotics are good bacteria that are found in food or supplements. The definition is ”Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” (WHO/FAO, 2002)

Important criteria for qualifying as a true probiotic is that health benefits should be proven in clinical trials. Furthermore, a probiotic product must contain the same bacterial strain(s) and the same dose that was used in the clinical trials.

What is a probiotic strain?

Bacteria are classified into genus, species and strains. Different strains of bacteria have different genetic composition resulting in different characteristics. A bacteria strain is a population of bacteria that descends from a single individual or pure culture. Bacteria of the same strain have certain characteristics that differentiate them from bacteria of other strains.

Different probiotic strains have different effects

Different probiotic products contain different probiotic strains. This means that one probiotic product with Limosilactobacillus reuteri (for example L. reuteri NCIMB 30242) is not equal to another probiotic product that contains another strain of Limosilactobacillus reuteri (for example L. reuteri DSM 17938). This is why bacteria must be defined and tested in clinical trials at strain level. A metaphor could be used to clarify. Different strains of the same bacteria may have different characteristics, just like a Chihuahua from a Great Dane, even though both are dogs.

When talking about lactic acid bacteria we need to clarify which strain we refer to, because the fact that a product contains “lactic acid bacteria” or “Lactobacillus reuteri” is not enough. We need to specify both species and strain name, for example Limosilactobacillus reuteri DSM 17938, to know what probiotic we are referring to and what benefits to expect. A probiotic bacteria must be defined and tested in clinical trials on strain level.