The researchers say there is cause for concern for consumers and those involved in clinical trials.
“These results suggest that quality control of probiotics is lacking,” they wrote.
The study published in Pediatric Research was conducted by scientists at the University of California and University of Massachusetts in the US and University of Modena and Reggio Emilia in Italy.
Species confusion
Bifidobacterium longum (B. longum) has two subspecies found in humans - B. longum subsp. longum and B. longum subsp. infantis - that are challenging to distinguish using common methods.
The authors said one commonly used probiotic product recently re-classified its strains, causing confusion as the published research listed the previous strains.
Motivated by the potential consequences of species and sub-species confusion in clinical trials, the authors set out to evaluate products’ label claims using new techniques.
Only one product matched
They used a reliable and inexpensive DNA-based method to accurately identify B. longum subsp. Infantis and verified their methods against artificial mock communities.
After testing 16 probiotic products available in local Californian stores and also online, they found only one of the products exactly matched the bifidobacterial species claims on the label. Some products had pill-to-pill and lot-to-lot variation.
One of the products tested did not appear to contain any of the label species but contained a footnote from the manufacturers re-classifying the strains, which could be confusing to clinicians and consumers, they said. Some products also contained non-label species.
The authors wrote: “Despite the GRAS (generally recognized as safe) status of probiotic supplements, the strain identity issues discussed here must be taken into account when planning and conducting clinical trials to ensure the proper interpretation the data generated.
"Misidentified probiotics are not likely to pose a danger to patients, however they certainly cloud clinic trial interpretations and are particularly problematic when the properties possessed by one strain are confused with another.”
The authors note some limits to the methods used, but recommend the use of similar appropriate tools to distinguish between closely related strains that impact differently on health outcomes and clinical trial data.
'Probiotic treatment will likely be ineffective'
David A. Mills the corresponding author at the University of California (UC Davis) told NutraIngredients:“Our original intent on this paper was to determine if those folks out there selling B. longum subsp. infantis were actually getting it right (the subspecies has a long and confusing taxonomic history). Unfortunately many commercial probiotics get this wrong.
“This is a concern in that true B. longum subsp. infantis is increasingly considered for use in premature babies (mostly from years of research here at UC Davis). However if clinicians read our research and choose a commercial probiotic that says it is B. longum subsp. infantis and it is not, the probiotic treatment will likely be ineffective.”
Infant administration
Probiotics, particularly Bifidobacterium products are increasingly being administered to infants due to studies showing reduced risk for necrotising enterocolitis, allergies, higher resistance to pathogens and improved response to vaccines.
Bifidobacterium-containing products have a status of generally recognised as safe (GRAS) by the American Food and Drug Administration (FDA).
They are also used widely in commercial products in Europe.
Source: Pediatric Research
Published online ahead of print, doi:10.1038/pr.2015.244
“Validating bifidobacterial species and subspecies identity in commercial probiotic products”
Authors: Z.T. Lewis et al.