Probiotic Definitions:

(Adapted from Sanders, M. E. 2003. Probiotics: considerations for human health. Nutr. Rev. 61:91-99)

Although the concept of probiotics was introduced in the early 20th century, the term was not coined until the 1960’s.  The definition of the term has evolved through the years (see following table).  Perhaps the most appropriate definition, published by an Expert Consultation at a meeting convened by the FAO/WHO in October, 2001, is “probiotics are live microorganisms which when administered in adequate amounts confer a health benefit on the host”. This definition has the following characteristics:

bulletProbiotics must be alive.  Although it is recognized that dead cells may mediate physiological benefits, it was suggested that a different term refer to these agents, as consumer and scientific understanding is that probiotics are alive.
bulletProbiotics must deliver a measured physiological benefit, substantiated by studies conducted in the target host. 
bulletProbiotics needn’t be restricted to food applications or oral delivery.  Probiotics used as pharmaceuticals or as topical agents are not excluded from this definition.
bulletA definition of probiotics shouldn’t limit the mechanism of action.  Therefore, survival of gastrointestinal tract transit or impact on normal flora shouldn’t be required.  For example, the delivery of lactase by, for example, Streptococcus thermophilus, to the small intestine was recognized as a probiotic activity.

Implied by this definition is that probiotics are defined strains. It is scientifically untenable to validate probiotic function and monitor probiotic impact on a preparation of microbes of unknown composition.  Probiotic activities have been deemed to be largely strain-specific, so definition to the strain level is important.  Deposit of a probiotic strain into an internationally recognized culture collection is recommended.

An agreed upon definition by the scientific community, even in the absence of regulatory definitions, is important.  In the absence of a definition, consumers cannot know what to expect from a product carrying this designation nor is there a common understanding among scientists about appropriate usage of the term.     

Published definitions of probiotics  

Published Definition


Substances produced by microorganisms which promote the growth of other microorganisms

Lilly and Stillwell 1965

Organisms and substances which contribute to intestinal microbial balance

Parker 1974

A live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance

Fuller 1989

A viable mono- or mixed-culture of microorganisms which applied to animal or man, beneficially affects the host by improving the properties of the indigenous microcflora

Havenaar and Huis In’t Veld 1992

Living microorganisms, which upon ingestion in certain numbers, exert health benefits beyond inherent basic nutrition

Schaafsma 1996

A microbial dietary adjuvant that beneficially affects the host physiology by modulating mucosal and systemic immunity, as well as improving nutritional and microbial balance in the intestinal tract

Naidu et al. 1999

A preparation of or a product containing viable, defined microorganisms in sufficient numbers, which alter the microflora (by implantation or colonization) in a compartment of the host and by that exert beneficial health effects in this host

Schrezenmeir and de Vrese 2001

Live microorganisms which when administered in adequate amounts confer a health benefit on the host.

FAO/WHO report, October 2001



Naidu, A. S., Bidlack, W. R. and Clemens, R. A. 1999. Probiotic spectra of lactic acid bacteria (LAB). Crit. Rev. Food Sci. Nutr. 38:13-126.

Lilly, D. M. and R. H. Stillwell. 1965. Probiotics:  growth promoting factors produced by microorganisms. Science 147:747-748.

Parker, R. B. 1974. Probiotics, the other half of the antibiotic story. Anim. Nutr. Health. 29:4-8.

Fuller, R. 1989. Probiotics in man and animals. J. Appl. Bacteriol. 66:365-378.

Havenaar, R. and Huis In’t Veld, J. M. J.  1992.  Probiotics:  a general view.  In: Lactic acid bacteria in health and disease, Vol. 1.  Elsevier Applied Science Publishers, 1992.

Schaafsma, G. 1996. State of art concerning probiotic strains in milk products. 5:23-4.

Schrezenmeir, J. and de Vrese, M.  2001. Probiotics, prebiotics, and synbiotics – approaching a definition. Am .J. Clin. Nutr. 73 (suppl):  361S-4S.


        [Home] [Consultant Profile] [Services]  [Publications] [Presentations] [Affiliations] [CV]

Send mail to with questions or comments about this web site.
Last modified: January 31, 2007