Microbiome Fundamentals

intestinal villi with bacteria

The mechanisms of action of probiotics are complex, diverse, and strain-specific.1,2 The same probiotic strain may inhibit different pathogens using different mechanisms.3

In addition, different strains within the same species can have very different effects.2 Combination probiotics (consisting of more than one strain) are not necessarily more effective than single strain probiotics.3,4 Probiotics are also dose-dependent, therefore clinical research is needed to establish the appropriate amount of a particular strain of bacteria required for efficacy.

assuring the efficacy icon

A number of probiotics are available for pets, but few have proven efficacy.

In addition, numerous studies have raised questions about the quality and purity of commercially available probiotics for humans and pets.1,5-9 Only two of 136 and four of 258 human and veterinary probiotics evaluated were accurately represented on the product label. Additional findings included low concentrations of viable organisms; failure to contain one or more of the organisms claimed on the label; contaminating organisms; and inaccurate and nonrepresentative labeling of contents.6-9


In addition to meeting all of the criteria for an effective probiotic, stability studies must be conducted to establish that the probiotic (living organisms) survives typical manufacturing, shipping, and storage conditions. Purina’s extensive research into this area has led to the development of probiotics that are effective, stable and safe.

finding a safe and effective probiotic
choosing a probiotic

As investigation and knowledge of probiotics expands, certain probiotics may not meet all of the above-listed criteria but still provide specific health non-gastrointestinal health benefits (such as reducing anxious behaviors or improving metabolic response in obese individuals).

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  1. Cunningham, M., Azcarate-Peril, M. A., Barnard, A., Benoit, V., Grimaldi, R., Guyonnet, D.,…Gibson, G. R. (2021). Shaping the future of probiotics and prebiotics. Trends in Microbiology, 29(8), 667—685. doi:10.1016/j.tim.2021.01.003
  2. Barros, C. P., Guimarães, J. T., Esmerino, E. A., Duarte, M. C. K. H., Silva, M. C., Silva, R.,…Cruz, A. G. (2020). Paraprobiotics and postbiotics: concepts and potential applications in dairy products. Current Opinion in Food Science, 32, 1–8. doi:10.1016/j.cofs.2019.12.003
  3. Kekkonen R. A.,Kajasto, E., Miettinen, M., Veckman, V., Korpela, R., & Julkunen, I. (2008). Probiotic Leuconostoc mesenteroides ssp. cremoris and Streptococcus thermophilus induce IL12 and IFN-γ production. World Journal of Gastroenterology, 14, 1192–1203.
  4. Viljanen, M., Kuitunen, M., Haahtela, T., Juntunen-Backman, K., Korpela, R., & Savilhati, E. (2005). Probiotic effects on faecal inflammatory markers and on faecal IgA in food allergic atopic eczema/dermatitis syndrome infants. Pediatric Allergy and Immunology, 16, 65–71.
  5. Rolfe, R.D. (2000). The role of probiotic cultures in the control of gastrointestinal health. Proceedings of the Probiotic Bacteria: Implications of Human Health Symposium. Journal of Nutrition, 130, 396S–402S.
  6. Weese, J. S. (2002). Microbiologic evaluation of commercial probiotics. Journal of the American Veterinary Medical Association, 220, 794–797.
  7. Weese, J. S., & Arroyo, L. (2003). Bacteriological evaluation of dog and cat diets that claim to contain probiotics. Canadian Veterinary Journal, 44, 212–215.
  8. Weese, J. S. (2003). Evaluation of deficiencies in labeling of commercial probiotics. Canadian Veterinary Journal, 44, 982–983.
  9. Weese, J. S., & Martin, H. (2011). Assessment of commercial probiotic bacterial contents and label accuracy. Canadian Veterinary Journal, 52,43–46.