Probiotic nomenclature matters redux: confusion on Bifidobacterium longum subsp. infantis taxonomy persists

Dear Editor,

A recent meta-analysis by Yuan et al.¹ examined probiotic products purportedly containing Bifidobacterium longum subsp. infantis for application in treatment of irritable bowel syndrome. Three subspecies of B. longum (subsp. suis, longum, infantis) were designated in 2008 by Mattarelli et al.² and pan-genome sequence of B. longum subsp. infantis that same year clarified the unique position of the subspecies infantis³. Today it is common to use the name “B. infantis” only after prior elaboration of the full species and subspecies name; however, despite this taxonomic acceptance and resolution nearly a decade ago, the inaccurate use of the subspecies designation infantis remains problematic⁴.

This subject is made more confusing by the frequent mislabeling of probiotics – as evidenced by the recent call for improved quality control in a position paper by the ESPGHAN Working Group on Probiotics and Prebiotics⁵. Many probiotic products that claim to contain B. longum subsp. infantis do not actually possess the subspecies⁴. Such is the case in the meta-analysis recently performed by Yuan et al.¹. These authors examined “Bifidobacterium infantis” 35624 in three clinical trials and examined two other trials that used probiotic cocktails (VSL#3 and Probinul) that supposedly contain B. infantis as well. As pointed out in their accompanying commentary, Allen et al.⁶ note that the strain 35624 is actually B. longum subsp. longum (and therefore not “B. infantis”). To make matters worse, the product VSL#3 does not contain any B. longum subsp. infantis and the label indicates these “B. longum” and “B. infantis” strains have been reclassified to “B. lactis” (see Probiotic #6 in Lewis et al.⁴). So it appears that four of the five studies examined in the meta-analysis by Yuan et al.¹ do not contain any actual B. longum subsp. infantis.

I strongly agree with Allen et al.⁶ that it is critically important to use strain designations in comparisons of probiotic trials. Comparing different probiotic strains, species and genera across different clinical trials is indeed problematic; however, it is also critical to use the proper nomenclature for the genus, species and subspecies of the probiotic strains involved in scientific publications as recently advocated in a commentary from the Board of Directors of the International Scientific Association of Probiotics and Prebiotics⁷. By continuing to use the designation “B. infantis” 35624 in their title and throughout the body of their commentary, while acknowledging that strain 35624 is actually B. longum subsp. longum, Allen et al.⁶ perpetuate incorrect nomenclature and, unfortunately, confound this issue.

Transparency

Declaration of funding

This letter received no funding.

Declaration of financial/other relationships

D.A.M. has disclosed that he has received grant/research funding from Mars, Mengiu Dairy, Yili Dairy, Clorox and Nu Skin; he is a co-founder of, and scientific consultant of, Evolve Biosystems Inc.

Acknowledgments

D.A.M. acknowledges funding from National Institutes of Health Awards AT007079 and AT008759, and the Peter J. Shields Endowed Chair in Dairy Food Science. These funding bodies did not play any role in the writing of this letter to the editor.