The Strain Myth

strain myth

The Myth:
"L. acidophilus is a strain of probiotic."

Research says:
L. acidophilus is a species encompassing many different strains.


Classification is very important in the determination of the characteristics of probiotics. The level of classification can get quite complicated, so let’s start at the top. ‘Bacteria’ or ‘Yeast’ is a kingdom of organisms, in the same way that humans belong to the ‘Animal’ kingdom. The bacteria can then be separated out into different groups based on similar characteristics, with increasing detail down through the phylum, class, order and family, until the genus level is reached e.g. lactobacillus. Within the genus level is the species level e.g. acidophilus (for humans the equivalent would be Homo sapiens).

For many people their knowledge of probiotics stops here, without realising that it gets more detailed, and this detail allows us to find out more about the bacteria. The next step down from the species is the strain level, and there are tens, if not hundreds, of strains within the species L. acidophilus (as there are within any bacterial species) e.g. NCFM®, Rosell-52 etc. The strain name usually consists of numbers and letters which indicate a microbiology institute e.g. NCFM = ‘North Carolina Food Microbiology’ research centre. It’s only at this level that a probiotic can really be judged on its worth, as the strain name points towards the research and the quality of the probiotic1.

Take the example of L. plantarum. In this species the strain CECT 7528 has been shown in scientific research to be especially good at binding onto dietary cholesterol so it cannot be absorbed by the body, whereas the strain CECT 7529 is particularly good at producing propionic acid (a type ofshort chain fatty acid which helps to decrease cholesterol levels)2. Both of these strains are in the species L. plantarum, but there are subtle, yet significant, differences between them.

Well researched products that list high quality strains on the packaging.

This myth has been busted by Megan Crowch, BSc (Hons) Physiology, Herbal Medicine Diploma (IRH practicing member).


  1. Joint FAO/WHO (2002) Working Group Report on Drafting Guidelines for the Evaluation of Probiotics in Food: Ontario, Canada.
  2. Bosch et al. (2014) Lactobacillus plantarum CECT 7527, 7528 and 7529: probiotic candidates to reduce cholesterol levels. J Sci Food Agric; 94, 4: 803-9.

You might also be interested in: 

The Research Myth 
The Antibiotic Myth 
The Food Myth 
The Survival Myth 
The Numbers Myth 
The Cure-All Myth 
The Billions Myth 
The Fridge Myth