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Probiotics: Definition, Sources, Selection, and Uses
Mary Ellen Sanders
International Scientific Association for Probiotics and Prebiotics and Dairy and Food Culture Technologies, Centennial, Colorado
DEFINITION OF PROBIOTICS
The internationally endorsed definition of probiotics is
live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.
Other definitions advanced through the years have been
restrictive by specification of mechanisms, site of action,
delivery format, method, or host. Probiotics have been
shown to exert a wide range of effects. The mechanism
of action of probiotics (e.g., having an impact on the
intestinal microbiota or enhancing immune function)
was dropped from the definition to encompass health
effects due to novel mechanisms and to allow application of the term before the mechanism is confirmed.
Physiologic benefits have been attributed to dead microorganisms [1]. Furthermore, certain mechanisms of
action (such as delivery of certain enzymes to the intestine) may not require live cells. However, regardless
of functionality, dead microbes are not probiotics.
The term “probiotic” is sometimes erroneously used
Reprints or correspondence: Dr. Mary Ellen Sanders, Dairy and Food Culture
Technologies, 7119 S. Glencoe Ct., Centennial, CO 80122 ([email protected]).
Clinical Infectious Diseases 2008; 46:S58–61
2008 by the Infectious Diseases Society of America. All rights reserved.
1058-4838/2008/4603S2-0002$15.00
DOI: 10.1086/523341
S58 • CID 2008:46 (Suppl 2) • Sanders
as a synonym for putatively beneficial members of commensal microbiota. The context for this misuse is the
assertion that certain dietary or environmental factors
may “encourage your native probiotics.” Members of
human commensal microbiota are often sources from
which probiotics are isolated, but, until such strains are
isolated and then adequately characterized for content,
stability, and health effects, they are not probiotics.
The US Food and Drug Administration (FDA) uses
other terms for live microbes for regulatory purposes;
live microbes used in animal feeds are called “directfed microbials” [2], and, when intended for use as human drugs, they are classified as “live biotherapeutics”
[3]. However, no legal definition of probiotics exists in
the United States or in other countries, which allows
the marketing of products labeled as “probiotics” that
do not meet the fundamental criteria stipulated in the
scientific definition. As public awareness of probiotics
increases, the use of the term has implications both for
the violation of the standard of truthful and not misleading labeling and for consumer confidence in this
product category. In the absence of a legal definition
of the term “probiotic,” it is incumbent on industry
participants to adopt and adhere to the scientific definition of the term. If the products are not properly
characterized and validated, the category will suffer.
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Interest in probiotics is at an all-time high in the United States, driven in part by new products emerging in
the market, by US researchers eager to evaluate efficacy claims rigorously, and by consumers interested in
potential therapeutic and preventive health benefits. The US marketplace is a mixed bag of products, some
well-defined and properly evaluated in controlled clinical studies and others with unsubstantiated claims of
efficacy. Validation of probiotic contents in commercial products is needed to ensure consumer confidence.
The term “probiotic” should be used only for products that meet the scientific criteria for this term—namely,
products that contain an adequate dose of live microbes that have been documented in target-host studies to
confer a health benefit. Probiotics must be identified to the level of strain, must be characterized for the
specific health target, and must be formulated into products using strains and doses shown to be efficacious.
Several characteristics commonly presumed to be essential to probiotics, such as human origin and the ability
to improve the balance of the intestinal microbiota, are discussed.
VALIDITY OF COMMERCIAL PRODUCTS
REGULATION OF PROBIOTICS
It is often misstated that probiotic products are unregulated.
Clearly, the FDA has regulatory authority over probiotic products and regulates manufacturers’ responsibilities, including the
labeling and safety of these products, whether in food, supplement, or drug form. Of note, on 24 August 2007, the FDA
issued regulations that require current good manufacturing
practices for dietary supplements to be phased in over the next
few years. Although these regulations do not address verification of efficacy claims, hopefully they will improve the compositional quality (identity, purity, and strength) of probiotic
supplements in the US market. However, manufacturers of
foods and supplements are not required to obtain premarket
approval of claims of efficacy or safety. In practice, the FDA
has never challenged the labeling or safety of a probiotic product except in cases where the product is represented as a drug
(i.e., to treat, cure, prevent, mitigate, or diagnose disease) and
1. Proper identification to the level of strain of all probiotics
in the product, with deposit of all strains in an international
culture collection
2. Characterization of each strain for traits important to
its safety and function
3. Validation of health benefits in human studies, including
identification of the quantity of the microorganism required to
provide the benefit
4. Truthful and not misleading labeling of efficacy claims
and content through the end of shelf life
REQUIRED ATTRIBUTES OF PROBIOTICS
Often, assumptions are made about mechanisms of action and
the “essential” characteristics of probiotics on the basis of supposition more than rigorous science. For example, it is commonly stipulated that probiotics must adhere to intestinal cells.
However, data that support adherence of probiotics are mostly
derived from in vitro assays, which have limited predictability
for the in vivo situation [10], and must be reconciled with the
fact that, in general, probiotics persist only short term in the
host after feeding has stopped. The nature of the association
of probiotics with the epithelial cell surfaces or mucous layer
remains to be determined.
Although it often suggested that probiotics for human use
must be of “human origin,” some strains that are not normally
isolated from humans have been shown to be effective probiotics (e.g., strains of the species Bifidobacterium animalis),
which negates this requirement [11].
The statement that probiotics “improve the balance of microflora” is often made. However, it is not clear what this
assertion means or how is it measured. Probiotics have been
shown to alter populations or activities of colonizing microbes,
but does this correspond to an “improved balance”? Improved
balance is often equated with increased fecal levels of lactobacilli
or bifidobacteria. This is a measure not of balance but of fecal
microbiota alteration. Since no scientific consensus exists on
the composition of a “healthy microbiota,” the health implications of such microbiota alterations remain unclear. Fur-
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Reports that the labels on commercial probiotic products are
inaccurate with regard to the identity and potency of the contents are numerous [4, 5]. However, care must be exercised in
interpreting some of these published reports, since not all arrive
at accurate conclusions, because of inappropriate methods used
to address the research question being asked [6–8]. Studies are
further complicated by the need to obtain statistically representative samples, by the difficulty in differentiating multiple
species and strains that may be combined into one product,
by the presence of injured cells that may be viable but not
culturable under certain circumstances, and by the need to use
DNA-based approaches to properly identify species of some
probiotic genera, including Lactobacillus and Bifidobacterium.
Consumer Reports reported that yogurts are better sources of
probiotics than are supplements [6]. But this conclusion may
have been in error. Although methods were not disclosed, the
results suggested that no differentiation of the different types
of bacteria present in yogurt was conducted. Reporting the total
number of bacteria in products containing multiple strains can
be misleading. In the case of yogurt, both starter cultures (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus) and extra bacteria added for health effects (e.g.,
strains of other species of Lactobacillus or Bifidobacterium) can
be present. If the health effects are derived from these additional
bacteria, then these need to be specifically enumerated before
a judgment can be made on the potency of the product. A total
count does not indicate the levels of each of the added probiotic
strains. For any product containing multiple strains of probiotics, counts of each strain should be provided so that consumers are clear on the relative potency of each added strain.
lacks approval as a drug. Usually, these cases result from incorrect product labeling by manufacturers that were intending
to market a dietary supplement. Lack of meaningful FDA oversight of claims of efficacy makes it difficult for consumers to
distinguish probiotic products that are properly formulated and
labeled from those that are not.
A reasonable approach for manufacturers marketing a product that contains a probiotic is to use guidelines established by
a working group convened jointly by the Food and Agriculture
Organization of the United Nations and the World Health Organization [9], which include the following.
THE ROLE OF STRAIN, DOSE, AND PRODUCT
FORMAT IN PROBIOTIC FUNCTION
Strains of the same probiotic species can be different, which
has been demonstrated both in vitro and in animals, although
similar data in humans are rare. Thus, clinical results from one
study are applicable only to the strain or strains being evaluated
in that study. Given this, however, different strains may have
the same effects, and similar immune effects have been documented for different strains [14]. As research continues, certain species- or genus-specific attributes are likely to be found.
Identification of genes or gene systems may make it feasible to
predict in vivo function, and documentation of expression of
these genes may become adequate substantiation for in vivo
function. Functional genomics may greatly aid this research,
which is progressing at a rapid pace [15]. Currently, however,
research specific to the strain or strain combinations should be
used to substantiate claims of physiological benefits. FurtherS60 • CID 2008:46 (Suppl 2) • Sanders
more, the genus, species, and strain designations should be
specified for all probiotic strains in a product.
Dose levels of probiotics should be based on levels found to
be efficacious in human studies. One dose level cannot be assumed to be effective for all strains. For example, the efficacy
of Bifidobacterium infantis 35264 has been documented at 108
cfu/day [16], whereas the recommended dose of VSL#3 (VSL
Pharmaceuticals) is 1.8 ⫻ 1012 cfu/day, a 4-log cycle difference
[17].
The impact of product format on probiotic function has yet
to be explored in depth. The common quality-control parameter of colony-forming units per gram may not be the only
parameter indicative of the efficacy of the final product. Other
factors, such as probiotic growth during product manufacture,
enteric coating, preservation technology, metabolic state of the
probiotic, and the presence of other functional ingredients in
the final product, may play a role in the effectiveness of a
product. More research is needed to understand how much
influence such factors have on in vivo efficacy.
CONCLUSIONS
The field of probiotics is growing quickly in the United States,
as is evidenced by the increasing interest of industry, consumers,
and researchers. As professionals embrace this burgeoning area,
they need to approach it in a manner that will ensure that
product formulations and communications about these products are done responsibly and with the primary objective to
benefit consumers. Both the science and its limitations should
be communicated with precision. Improper use of the term
“probiotic” and failure to recognize the importance of the dose
specificity and strain specificity of effects is a concern. There
is a great need for controlled studies in humans to further
document the health benefits of probiotics as part of the human
diet. Important target groups for such studies include healthy
people, people at elevated risk for developing a disease, and
people searching for dietary-management techniques to control
symptoms. All these groups would benefit from publicly funded
research of probiotics as foods or supplements. Probiotics could
also be studied for use as drugs.
Acknowledgments
Supplement sponsorship. This article was published as part of a supplement entitled “Developing Probiotics as Foods and Drugs: Scientific and
Regulatory Challenges,” sponsored by the Drug Information Association,
the National Institutes of Health National Center for Complementary and
Alternative Medicine (1R13AT003805-01 to Patricia L. Hibberd), the California Dairy Research Foundation, Chr. Hansen, the Dannon Company,
General Mills, Institut Rosell, and Yakult International.
Potential conflicts of interest. M.E.S. currently is a consultant for many
companies that market probiotic-containing food or supplement products
in the United States and also is a consultant for nonprofit organizations
that promote research on probiotics in the United States.
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thermore, it is difficult to measure intestinal microbiota; fecal
microbiota is not equivalent to intestinal microbiota, and luminal microbiota is not equivalent to epithelial microbiota [12].
Probiotics may, in fact, facilitate a return to normal status after
a perturbation of the microbiota (e.g., because of the use of
antibiotics or illness) or may reduce the degree of change invoked by such challenges. This function more closely supports
the concept that probiotics can improve the balance of microbiota. A few studies have measured a probiotic-enhanced return
to baseline levels after antibiotic use in humans [13]. The concept of probiotic-induced improved balance of microbiota
would benefit from further study.
When probiotic strains are selected, attributes important for
efficacy and technological function must be assessed. Because
the range of targets for in vivo function is broad, spanning
oral, stomach, respiratory, intestinal, vaginal, and immune
functions, it would be a daunting task to develop a list of
characteristics required for all probiotic functions. Basic initial
characterization of strain identity and taxonomy should be conducted, followed by evaluation with validated assays both in
studies of animal models and in controlled studies in the target
host. In vitro assays are frequently conducted that have not
been proved to be predictive of in vivo function [14]. Technological robustness must also be determined, such as the
strain’s ability to be grown to high numbers, concentrated,
stabilized, and incorporated into a final product with good
sensory properties, if applicable, and to be stable, both physiologically and genetically, through the end of the shelf life of
the product and at the active site in the host. Assessment of
stability can also be a challenge, since factors such as chain
length and injury may challenge the typical assessment of colony-forming units, as well as in vivo function.
References
10.
11.
12.
13.
14.
15.
16.
17.
Introduction to Probiotics • CID 2008:46 (Suppl 2) • S61
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1. Rachmilewitz D, Katakura K, Karmeli F, et al. Toll-like receptor 9
signaling mediates the anti-inflammatory effects of probiotics in murine experimental colitis. Gastroenterology 2004; 126:520–8.
2. US Food and Drug Administration. Direct-fed microbial products.
Section 698.100. Revised March 1995. Available at: http://www.fda.gov/
ora/compliance_ref/cpg/cpgvet/cpg689-100.html. Accessed 18 December 2007.
3. Vaillancourt J. Regulating pre- and probiotics: a U.S. FDA perspective.
In: Institute of Medicine of the National Academies. Ending the war
metaphor: the changing agenda for unraveling the host-microbe relationship. Washington, DC: National Academies Press, 2006:229–37.
4. Weese JS. Evaluation of deficiencies in labeling of commercial probiotics. Can Vet J 2003; 44:982–3.
5. Yeung PS, Sanders ME, Kitts CL, et al. Species-specific identification
of commercial probiotic strains. J Dairy Sci 2002; 85:1039–51.
6. Probiotics: are enough in your diet? Consum Rep 2005; Jul:34–5.
7. Berman S, Spicer D. Safety and reliability of Lactobacillus supplements
in Seattle, Washington (a pilot study). Internet J Altern Med 2003; 1:
2.
8. Huff B. Caveat emptor: “probiotics” might not be what they seem.
Can Fam Physician 2004; 50:583–7.
9. Joint FAO/WHO Working Group on Drafting Guidelines for the Evaluation of Probiotics in Food. Guidelines for the evaluation of probiotics
in food: report of a Joint FAO/WHO Working Group on Drafting
Guidelines for the Evaluation of Probiotics in Food, London, Ontario,
Canada, April 30 and May 1, 2002. Available at: http://www.who.int/
foodsafety/publications/fs_management/probiotics2/en/index.html.
Accessed 27 November 2007.
Blum S, Reniero R, Schiffrin EJ, et al. Adhesion studies for probiotics:
need for validation and refinement. Trends Food Sci Technol 1999; 10:
405–10.
Sanders ME. Summary of probiotic activities of Bifidobacterium lactis
HN019. J Clin Gastroenterol 2006; 40:776–83.
Eckburg PB, Bik EM, Bernstein CN, et al. Diversity of the human
intestinal microbial flora. Science 2005; 308:1635–8.
Engelbrektson AL, Korzenik JR, Sanders ME, et al. Analysis of treatment effects on the microbial ecology of the human intestine. FEMS
Microbiol Ecol 2006; 57:239–50.
Ibnou-Zekri N, Blum S, Schiffrin EJ, von der Weid T. Divergent patterns of colonization and immune response elicited from two intestinal
Lactobacillus strains that display similar properties in vitro. Infect Immun 2003; 71:428–36.
Marco ML, Pavan S, Kleerebezem M. Towards understanding molecular modes of probiotic action. Curr Opin Biotechnol 2006; 17:204–10.
Whorwell PJ, Altringer L, Morel J, et al. Efficacy of an encapsulated
probiotic Bifidobacterium infantis 35624 in women with irritable bowel
syndrome. Am J Gastroenterol 2006; 101:1581–90.
Gionchetti P, Rizzello F, Helwig U, et al. Prophylaxis of pouchitis onset
with probiotic therapy: a double-blind, placebo-controlled trial. Gastroenterology 2003; 124:1202–9.