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Probiotic Bacteria: Today and Tomorrow¹

Southeast Dairy Foods Research Center and Department of Food Science, College of Agriculture and Life Sciences, North Carolina State University, Raleigh, NC 27695-7624

	ABSTRACT

TOP ABSTRACT INTRODUCTION Probiotics: key issues Probiotics: tomorrow REFERENCES

 
This paper provides an overview of the key issues raised during this symposium. Probiotic cultures have been associated historically with cultured milks and dairy products, from which there is substantial evidence for positive effects on human health and general well-being.

KEY WORDS: • probiotics • lactic acid bacteria • lactobacillus • bifidobacterium • dairy

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Probiotics: key issues Probiotics: tomorrow REFERENCES

 
The food industry in the United States is the country’s largest manufacturing industry with revenues exceeding $500 billion/y. One key research priority of this industry is to increase the development of foods that promote health and well-being. Among these, the exploding area of functional foods and probiotics shows considerable promise to expand the industry into new arenas. The economic effect of the projected U.S. functional foods market is significant, recently estimated at $134 billion (Sanders 1998 ); it includes foods such as natural functional foods (cranberry juice, green tea), foods and ingredients for specified health use (FOSHU), formulas (infant and elderly), medical foods, nutraceuticals and drug foods. Within this continuum between food and drug, there are unlimited niches for the development of food systems that promote optimal health and general well-being. Tomorrow’s challenge is to strengthen the science supporting the probiotic concept and establish direct cause and effect mechanisms that are responsible for effects on human health and nutrition.

	Probiotics: key issues

TOP ABSTRACT INTRODUCTION Probiotics: key issues Probiotics: tomorrow REFERENCES

 
A probiotic is a "live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance" (Fuller 1989 ). This definition was broadened by Havenaar and Huis in’t Veld (1992) to a "mono- or mixed-culture of live microorganisms which benefits man or animals by improving the properties of the indigenous microflora." Most recently, this definition has been further refined to "living microorganisms, which upon ingestion in certain numbers, exert health benefits beyond inherent basic nutrition" (Guarner and Schaafsman 1998 ).

The gastrointestinal tract of vertebrate animals is the most densely colonized region of the human body (Tannock 1995 ). There are ~10¹² bacteria/g of contents in the large intestine, which is estimated to contain several hundred bacterial species (Savage 1977 ). It is widely accepted that this collection of microbes has a powerful influence on the host in which it resides. It is implicit in the definition of probiotics that their consumption positively affects the composition of this microflora and extends a range of host benefits (Sanders 1998 , Tannock 1999 ). In addition, it has now been established that "prebiotics" can contribute to the benefits derived from commensal lactic acid bacteria residing in the gastrointestinal tract. Prebiotics are defined as "nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon" (Gibson and Roberfroid 1995 ).

Over the course of the symposium, evidence was presented to illustrate the following benefits elicited by probiotics, prebiotics and synbiotics: 1) pathogen interference, exclusion and antagonism; 2) immunostimulation and immunomodulation; 3) anticarcinogenic and antimutagenic activities in animal models; 4) alleviation of symptoms of lactose intolerance; 5) vaginal/urinary tract health; 6) reduction in blood pressure in hypertensive subjects; 7) decreased incidence and duration of diarrhea (antibiotic-associated diarrhea, Clostridium difficile, travelers and rotaviral); and 8) maintenance of mucosal integrity.

Many of the specific effects attributed to the ingestion of probiotics, however, remain unsubstantiated scientifically (O’Sullivan et al. 1992 ), and it is rare that specific health claims can be made (Sanders 1993 ). Over decades of work, the science supporting the probiotic concept remains remarkably weak (Sanders 1993 , Tannock 1999 ) because of a number of issues, including the following: 1) numerous candidate probiotic strains and species; 2) confusion over results obtained with strains that are improperly identified and inadequately described; 3) variable storage quality in probiotic cultures resulting in losses of dose and activity delivered in clinical trials; 4) single probiotic strains are often proposed to contribute a multitude of benefits across many individuals in a test population; and 5) high costs of clinical trials that force consideration of "one strain versus one placebo" experiments in attempts to prove efficacy of the simplest probiotic concepts in limited subject populations.

Over the last decade, progress in the microbiology, genetics and molecular taxonomy of probiotic cultures has virtually eliminated issues concerning strain identification and tracking (Klaenhammer 1998 , O’Sullivan 1999 ). Significant progress has also been made in developing high quality probiotic cultures that exhibit levels of viability and activity that are more stable and better suited for use in clinical investigations. Therefore, the stage is set to carry out well-designed investigations on the clinical and in vivo effects of probiotics and synbiotics. Concurrently, interest in developing probiotics and probiotic-functional foods is thriving in the food and nutraceutical industries under the recognized marketing potential for products that target general health and well-being (Sanders 1998 ). In this regard, funds to establish clinical efficacy have increased dramatically in the past few years, fueled by the promise of concept substantiation and label claims. International efforts are now underway across a variety of fronts to conduct clinical trials to investigate the effect of probiotic cultures on a range of health and well-being issues. Most importantly, these studies are employing well-characterized probiotic formulations composed of high quality and stable cultures. Concurrently, efforts are underway to determine the DNA sequence of Lactobacillus acidophilus and use this information to understand the behavior and functional roles of the organism in the gastrointestinal tract, and then link this behavior to clinical performance and outcomes. This effort is being funded by Dairy Management, under the auspices of the National Dairy Foods Research Center Program.

	Probiotics: tomorrow

TOP ABSTRACT INTRODUCTION Probiotics: key issues Probiotics: tomorrow REFERENCES

 
Looking ahead, this field holds substantial promise to deliver effective probiotics to the food and pharmaceutical industries. The challenge, emphasized by speakers throughout this symposium, will be to conduct well-designed, multicenter, clinical investigations to determine the health effects of consuming well-characterized probiotics, prebiotics and synbiotics. Furthermore, it will be important to investigate optimum vehicles (powder, liquid, dairy foods) for delivery of probiotics and whether certain delivery formats promote probiotic survival and activity. Identification of direct cause and effect relationships, with the mechanistic rigor of the pharmaceutical industries, will be required to discover the active principles, define clinical efficacy and establish the ultimate market potential of probiotics and prebiotics.

	FOOTNOTES

 
¹ Presented at the symposium entitled "Probiotic Bacteria: Implications for Human Health" as part of the Experimental Biology 99 meeting held April 17–21 in Washington, DC. This symposium was sponsored by the American Society for Nutritional Sciences and was supported in part by an educational grant from the National Dairy Council. The proceedings of this symposium are published as a supplement to The Journal of Nutrition. Guest editor for this supplement was Douglas B. DiRenzo, National Dairy Council, Rosemont, IL.

	REFERENCES

TOP ABSTRACT INTRODUCTION Probiotics: key issues Probiotics: tomorrow REFERENCES

 

1. Fuller R. Probiotics in man and animals. J. Appl. Bacteriol. 1989;66:365-378[Medline]

2. Gibson G. R., Roberfroid M. B. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. J. Nutr. 1995;125:1401-1412

3. Guarner F., Schaafsma G. J. Probiotics. Int. J. Food Microbiol. 1998;39:237-238[Medline]

4. Havenaar R., Huis in’t Veld J.H.J. Probiotics: a general view. Wood B.J.B. eds. The Lactic Acid Bacteria, Vol. 1: The Lactic Acid Bacteria in Health and Disease 1992:209-224 Chapman & Hall New York, NY.

5. Klaenhammer T. R. Functional activities of Lactobacillus probiotics: genetic mandate. Int. Dairy J. 1998;8:497-506

6. O’Sullivan D. J. Methods for the analysis of the intestinal microflora. Tannock G. W. eds. Probiotics: A Critical Review 1999:23-44 Horizon Scientific Press Norfolk, England.

7. O’Sullivan M. G, Thorton G., O’Sullivan G. C., Collins J. K. Probiotic bacteria: myth or reality?. Trends Food Sci. Technol 1992;3:309-314

8. Sanders M. E. Summary of conclusions from a consensus panel of experts on health attributes of lactic cultures: significance of fluid milk products containing cultures. J. Dairy Sci. 1993;76:1819-1828[Abstract]

9. Sanders M. E. Overview of functional foods: emphasis on probiotic bacteria. Int. Dairy J. 1998;8:341-347

10. Savage D. C. Microbial ecology of the gastrointestinal tract. Annu. Rev. Microbiol. 1977;31:107-133[Medline]

11. Tannock G. W. Introduction. Tannock G. W. eds. Probiotics: A Critical Review 1999:1-4 Horizon Scientific Press Norfolk, England.

12. Tannock G. W. Normal Microflora 1995 Chapman and Hall London, UK.

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