Advertisement

Probiotics: facts and myths

  • A.C. Senok
    Correspondence
    Corresponding author and reprint requests: A. C. Senok, Department of Microbiology, Immunology and Infectious Diseases, College of Medicine and Medical Sciences, Arabian Gulf University, PO Box 22979, Manama, Kingdom of Bahrain
    Affiliations
    Department of Microbiology, Immunology and Infectious Diseases, College of Medicine and Medical Sciences, Arabian Gulf University, Manama, Kingdom of Bahrain
    Search for articles by this author
  • A.Y. Ismaeel
    Affiliations
    Department of Microbiology, Immunology and Infectious Diseases, College of Medicine and Medical Sciences, Arabian Gulf University, Manama, Kingdom of Bahrain
    Search for articles by this author
  • G.A. Botta
    Affiliations
    Department of Microbiology, Immunology and Infectious Diseases, College of Medicine and Medical Sciences, Arabian Gulf University, Manama, Kingdom of Bahrain

    Department of Medical Research, Medical School, Udine, Italy
    Search for articles by this author

      ABSTRACT

      In recent years there has been a significant upsurge in research on the characterisation and verification of the potential health benefits associated with the use of probiotics. In addition, the market for probiotics continues to expand exponentially as consumers (mostly healthy individuals) rely on health claims made by manufacturers to make their choices. This review appraises the available evidence for and against the health claims associated with probiotics. The use of probiotics in promoting gastrointestinal health and immunity, and their use in the prevention of urogenital infections, allergies and cancer are reviewed. Furthermore, issues surrounding the use of probiotics in healthy individuals, the safety of probiotics and regulatory concerns are addressed. There is scientific evidence that specific strains of probiotic microorganisms confer health benefits on the host and are safe for human use. However, this evidence cannot be extrapolated to other strains, as these effects are strain-specific. Probiotics have potential health benefits for conditions such as gastrointestinal infections, genitourinary infections, allergies and certain bowel disorders, all of which afflict a considerable proportion of the global population. However, considerable work is still needed to confirm these potential health benefits.

      Keywords

      INTRODUCTION

      Probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a beneficial effect on the health of the host [
      • FAO/WHO
      ]. The original observation of the positive role of some bacteria can be credited to the pioneering work of Metchnikoff in the early 1900s [
      • Metchnikoff E
      Lactic acid as inhibiting intestinal putrefaction.
      ], which suggested that these beneficial bacteria could be administered with a view to replacing harmful microbes with useful ones. The term probiotic, meaning ‘for life', was first coined in the 1960s by Lilly and Stillwell [
      • Lilly DM
      • Stillwell RH
      Probiotics: growth promoting substances produced by microorganisms.
      ].
      In recent years, there has been an upsurge in research into probiotics, as well as growing commercial interest in the probiotic food concept. This increased research has resulted in significant advances in our understanding and ability to characterise specific probiotic organisms, as well as attempts to verify their attributed health benefits. Probiotic food constitutes a sizeable part of the functional food market [
      • Stanton C
      • Gardiner G
      • Meehan H
      • et al.
      Market potential for probiotics.
      ], and continues to grow at an exponential rate, with the potential for market growth estimated at a staggering US$120 million per month [
      • Anonymous
      Pro‐ and prebiotics gain popularity in a large US market for gut health.
      ,
      • Anonymous
      LGG at Ten.
      ]. However, this commercial exploitation of the probiotic food concept is still associated with a large body of unsubstantiated claims. After many years of popularity in the Japanese and European markets, manufacturers of these products are venturing into new markets, including the Arabian Gulf region, as evidenced by the variety of probiotic food products now available in supermarkets and healthfood stores. The perception that fermented milk or yoghurt is beneficial is already widespread within this region because, traditionally, these products have been used by local healers for the treatment of diverse conditions such as skin allergies, stomach upsets, especially diarrhoea, and vaginal discharges.
      However, major concerns regarding the quality, labelling and verification of claims attributed to some of these products still remain [
      • Elliot E
      • Teversham K
      An evaluation of nine probiotics available in South Africa, August 2003.
      ,
      • Weese JS
      Evaluation of deficiencies in labeling of commercial probiotics.
      ,
      • Hamilton‐Miller JM
      • Shah S
      • Winkler JT
      Public health issues arising from microbiological and labelling quality of foods and supplements containing probiotic microorganisms.
      ]. In the UK, where 3.5 million individuals take probiotic supplements in some form daily, a panel of European experts found that a number of probiotics tested had incorrect labelling, markedly reduced numbers of strains, and the presence of strains not included on labels, including the potentially pathogenic Enterococcus faecium (found in nine products) [
      • Hamilton‐Miller JM
      • Shah S
      • Winkler JT
      Public health issues arising from microbiological and labelling quality of foods and supplements containing probiotic microorganisms.
      ]. This is a cause for concern, and calls for an international consensus on evaluating the efficacy and safety of these products.

      PROBIOTIC MICROORGANISMS AND FOOD PRODUCTS

      Two main genera of Gram-positive bacteria, Lactobacillus and Bifidobacterium, are used extensively as probiotics [
      • FAO/WHO
      ,
      • Holzapfel WH
      • Haberer P
      • Geisen R
      • Bjorkroth J
      • Schillinger U
      Taxonomy and important features of probiotic microorganisms in food and nutrition.
      ]. However, other genera, such as Escherichia, Enterococcus and Saccharomyces, have also been marketed as probiotics [
      • Holzapfel WH
      • Haberer P
      • Geisen R
      • Bjorkroth J
      • Schillinger U
      Taxonomy and important features of probiotic microorganisms in food and nutrition.
      ,
      • Rolfe RD
      The role of probiotic cultures in the control of gastrointestinal health.
      ], although concerns still remain regarding the safe use of these organisms for this purpose [
      • Ishibashi N
      • Yamazaki S
      Probiotics and safety.
      ,
      • Donohue C
      • Salminen S
      Safety of probiotic bacteria.
      ,
      • Eaton TJ
      • Gasson MJ
      Molecular screening of Enterococcus virulence determinants and potential for genetic exchange between food and medical isolates.
      ]. Current evidence indicates that probiotic effects are strain-specific; therefore, a beneficial effect attributed to one strain cannot be assumed to be provided by another strain, even when it belongs to the same species [
      • Ibnou‐Zekri N
      • Blum S
      • Schiffrin EJ
      • Von Der Weid WT
      Divergent patterns of colonization and immune response elicited from two intestinal Lactobacillus strains that display similar properties in vitro.
      ]. Table 1 shows some of the organisms used commonly as priobiotics.
      Table 1Examples of microorganisms that are considered to be probiotics
      Lactobacillus spp.Bifidobacterium spp.Others
      L acidophilusB. bifidumEscherichia coli Nissle
      L. caseiB. breveSaccharomyces boulardii
      L. crispatusB. infantisStreptococcus thermophilus
      There is still debate about the probiotic activity.
      L. delbrueckii subsp. bulgaricus
      There is still debate about the probiotic activity.
      B. longumEnterococcus faecium
      Safety concerns remain because of potential pathogenicity and vancomycin resistance.
      L. fermentumB. lactis
      L. gasseriB. adolescentis
      L. johnsonii
      L. paracasei
      L. plantarum
      L. reuteri
      L. rhamnosus
      a There is still debate about the probiotic activity.
      b Safety concerns remain because of potential pathogenicity and vancomycin resistance.
      According to recent Food and Agriculture Organization (FAO) and WHO guidelines [
      • FAO/WHO
      ,
      • FAO/WHO
      ], probiotic organisms used in food must be capable of surviving passage through the gut; i.e., they must have the ability to resist gastric juices and exposure to bile. Furthermore, they must be able to proliferate and colonise the digestive tract. In addition, they must be safe and effective, and maintain their effectiveness and potency for the duration of the shelf-life of the product.
      Dairy products, including yoghurt, fermented milk products and cheese, remain at the forefront of probiotic food development. There is a common perception among consumers that yoghurt per se is a probiotic food product. Is this a fact or a myth? Even among experts in this field there is still a debate about whether or not the yoghurt starter cultures Lactobacillus bulgaricus and Streptococcus thermophilus should be considered as probiotics [
      • Pestka JJ
      • Ha CL
      • Warner RW
      • Lee JH
      • Ustunol Z
      Effects of ingestion of yogurts containing Bifidobacterium and Lactobacillus acidophilus on spleen and Peyer's patch lymphocyte populations in the mouse.
      ,
      • Tejada‐Simon MV
      • Lee JH
      • Ustunol Z
      • Pestka JJ
      Ingestion of yogurt containing Lactobacillus acidophilus and Bifidobacterium to potentiate immunoglobulin A responses to cholera toxin in mice.
      ]. These organisms are sensitive to conditions in the digestive tract and do not achieve very high numbers in the gut, although some beneficial effects, such as improved lactose digestion and immune system enhancement, have been associated with their use [
      • De Vrese M
      • Stegelmann A
      • Richter B
      • Fenselau S
      • Laue C
      • Schrezenmeir J
      Probiotics—compensation for lactase insufficiency.
      ]. Yoghurt with added live probiotic strains is now available commercially, and a number of such products that have emerged as leaders in the European market are now also marketed internationally. In the USA, the National Yoghurt Association has introduced a ‘Live Active Culture Seal’ to identify refrigerated or frozen yoghurt products that contain at least 108 or 107 viable lactic acid bacteria/g at the time of manufacture (http://www.aboutyogurt.com/lacYogurt/). However, these counts do not differentiate between true probiotic strains and starter cultures; hence they are still not reflective of true probiotic products.

      BENEFICIAL HEALTH EFFECTS OF PROBIOTICS

      Although some of the effects of probiotics have been documented clearly, research is still ongoing in other areas, with important questions remaining unanswered. However, when considering the potential health benefits, it is crucial to remember that different probiotic strains are associated with different health benefits. The overall body of evidence suggests a beneficial effect with the use of certain probiotic microorganisms.

       Immunity

      One of the common claims used in the marketing of probiotic products is that they help boost immune status. Although in-vitro and in-vivo studies suggest that probiotics may modulate the immune response, the precise mechanisms involved remain unclear [
      • Reid G
      • Jass J
      • Sebulsky MT
      • McCormick JK
      Potential uses of probiotics in clinical practice.
      ], and studies with probiotic preparations in different laboratories have generated conflicting results. However, available data suggest that probiotic bacteria possess the ability to modulate the immune system by promoting the endogenous host defence systems. Studies have shown that probiotic bacteria can modify various immune parameters, including humoral, cellular and nonspecific immunity [
      • Matsuzaki T
      • Yamazaki R
      • Hashimoto S
      • Yokokura T
      The effect of oral feeding of Lactobacillus casei strain Shirota on immunoglobulin E production in mice.
      ,
      • Matsuzaki T
      • Chin J
      Modulating immune responses with probiotic bacteria.
      ,
      • Madsen K
      • Cornish A
      • Soper P
      • et al.
      Probiotic bacteria enhance murine and human intestinal epithelial barrier function.
      ,
      • Chiang BL
      • Sheih YH
      • Wang LH
      • Liao CK
      • Gill HS
      Enhancing immunity by dietary consumption of a probiotic lactic acid bacterium (Bifidobacterium lactis HN019): optimization and definition of cellular immune responses.
      ,
      • Gill HS
      • Rutherfurd KJ
      • Cross ML
      • Gopal PK
      Enhancement of immunity in the elderly by dietary supplementation with the probiotic Bifidobacterium lactis HN019.
      ,
      • Cross ML
      • Mortensen RR
      • Kudsk J
      • Gill HS
      Dietary intake of Lactobacillus rhamnosus HNOO1 enhances production of both Th1 and Th2 cytokines in antigen‐primed mice.
      ]. Emerging data also indicate that probiotics enhance the activity of natural killer cells in the elderly and modulate non-specific host defences [
      • Holzapfel WH
      • Haberer P
      • Geisen R
      • Bjorkroth J
      • Schillinger U
      Taxonomy and important features of probiotic microorganisms in food and nutrition.
      ,
      • Gill HS
      • Rutherfurd KJ
      • Cross ML
      • Gopal PK
      Enhancement of immunity in the elderly by dietary supplementation with the probiotic Bifidobacterium lactis HN019.
      ,
      • Sheih YH
      • Chiang BL
      • Wang LH
      • Liao CK
      • Gill HS
      Systemic immunity‐enhancing effects in healthy subjects following dietary consumption of the lactic acid bacterium Lactobacillus rhamnosus HN001.
      ,
      • Gill HS
      • Cross ML
      • Rutherfurd KJ
      • Gopal PK
      Dietary probiotic supplementation to enhance cellular immunity in the elderly.
      ]. A reversal of the age-related decline in cytokine production has been demonstrated in ageing mice fed with probiotic supplements [
      • Muscettola M
      • Massai L
      • Tanganelli C
      • Grasso G
      Effects of lactobacilli on interferon production in young and aged mice.
      ]. Although the mechanism of this reversal is unknown, it may be related to the selective adherence of probiotics to M-cells of Peyer's patches [
      • Erickson KL
      • Hubbard NE
      Probiotic immunomodulation in health and disease.
      ]. Immune-modulating mechanisms that have been demonstrated with probiotics include the induction of mucus production, macrophage activation by lactobacilli signalling, stimulation of secretory IgA and neutrophils, inhibition of release of inflammatory cytokines, and stimulation of elevated peripheral immunoglobulins [
      • Fukushima Y
      • Kawata Y
      • Hara H
      • Terada A
      • Mitsuoka T
      Effect of a probiotic formula on intestinal immunoglobulin A production in healthy children.
      ,
      • Perdigon G
      • Vintini E
      • Alvarez S
      • Medina M
      • Medici M
      Study of the possible mechanisms involved in the mucosal immune system activation by lactic acid bacteria.
      ,
      • Mack DR
      • Lebel S
      Role of probiotics in the modulation of intestinal infections and inflammation.
      ,
      • Miettinen M
      • Lehtonen A
      • Julkunen I
      • Matikainen S
      Lactobacilli and streptococci activate NF‐kappa B and STAT signaling pathways in human macrophages.
      ,
      • Kaila M
      • Isolauri E
      • Soppi E
      • Virtanen E
      • Laine S
      • Arvilommi H
      Enhancement of the circulating antibody secreting cell response in human diarrhea by a human Lactobacillus strain.
      ]. It has also been shown that probiotics may modulate dendritic cell surface phenotype and cytokine release [
      • Drakes M
      • Blanchard T
      • Czinn S
      Bacterial probiotic modulation of dendritic cells.
      ]. However, it is unclear whether these immunomodulatory effects are localised or systemic. It is not known whether these immunoregulatory effects are similar in healthy subjects and those with underlying disease, or whether all candidate probiotic organisms elicit similar effects on the immune system. Current evidence suggests that the regulatory effects on the immune system might be different in healthy subjects compared to those with underlying disease, since it has been reported that probiotics have a stimulatory effect on phagocytosis in healthy subjects, but cause downregulation in patients with allergy [
      • Pelto L
      • Isolauri E
      • Lilius EM
      • Nuutila J
      • Salminen S
      Probiotic bacteria down‐regulate the milk‐induced inflammatory response in milk‐hypersensitive subjects but have an immunostimulatory effect in healthy subjects.
      ]. In addition, other available data suggest that these immunomodulatory effects may depend on the immune status of the host and the dose of probiotics given, and that differences may exist between specific strains [
      • Matsuzaki T
      • Chin J
      Modulating immune responses with probiotic bacteria.
      ,
      • Cross ML
      • Mortensen RR
      • Kudsk J
      • Gill HS
      Dietary intake of Lactobacillus rhamnosus HNOO1 enhances production of both Th1 and Th2 cytokines in antigen‐primed mice.
      ,
      • Perdigon G
      • Vintini E
      • Alvarez S
      • Medina M
      • Medici M
      Study of the possible mechanisms involved in the mucosal immune system activation by lactic acid bacteria.
      ,
      • Gill HS
      • Rutherfurd KJ
      Viability and dose–response studies on the effects of the immunoenhancing lactic acid bacterium Lactobacillus rhamnosus in mice.
      ,
      • Yasui H
      • Shida K
      • Matsuzaki T
      • Yokokura T
      Immunomodulatory function of lactic acid bacteria.
      ]. Clearly, more research is required to characterise the immunomodulatory properties of candidate probiotic bacteria and to tailor their application for specific target populations.

       Diarrhoea

      The beneficial effect of probiotics in reducing the incidence or duration of certain diarrhoeal illnesses is perhaps the most substantiated health claim to date [
      • Reid G
      • Jass J
      • Sebulsky MT
      • McCormick JK
      Potential uses of probiotics in clinical practice.
      ,
      • Phuapradit P
      • Varavithya W
      • Vathanophas K
      • et al.
      Reduction of rotavirus infection in children receiving bifidobacteria‐supplemented formula.
      ,
      • Sullivan A
      • Nord CE
      Probiotics and gastrointestinal diseases.
      ]. This is especially true for the use of Lactobacillus rhamnosus GG, Bifidobacterium lactis BB-12 and Lactobacillus reuteri SD2222 in the prevention and treatment of rotavirus diarrhoea in children [
      • Shornikova AV
      • Isolauri E
      • Burkanova L
      • Lukovnikova S
      • Vesikari T
      A trial in the Karelian Republic of oral rehydration and Lactobacillus GG for treatment of acute diarrhoea.
      ,
      • Shornikova AV
      • Casas IA
      • Isolauri E
      • Mykkanen H
      • Vesikari T
      Lactobacillus reuteri as a therapeutic agent in acute diarrhea in young children.
      ,
      • Guandalini S
      • Pensabene L
      • Zikri MA
      • et al.
      Lactobacillus GG administered in oral rehydration solution to children with acute diarrhea: a multicenter European trial.
      ,
      • Guarino A
      • Canani RB
      • Spagnuolo MI
      • Albano F
      • Di Benedetto L
      Oral bacterial therapy reduces the duration of symptoms and of viral excretion in children with mild diarrhea.
      ,
      • Rosenfeldt V
      • Michaelsen KF
      • Jakobsen M
      • et al.
      Effect of probiotic Lactobacillus strains on acute diarrhea in a cohort of nonhospitalized children attending day‐care centers.
      ,
      • Rosenfeldt V
      • Michaelsen KF
      • Jakobsen M
      • et al.
      Effect of probiotic Lactobacillus strains in young children hospitalized with acute diarrhea.
      ]. A significant reduction in the duration of diarrhoea and earlier hospital discharge was demonstrated in several trials using L. rhamnosus GG [
      • Reid G
      • Jass J
      • Sebulsky MT
      • McCormick JK
      Potential uses of probiotics in clinical practice.
      ,
      • Sullivan A
      • Nord CE
      Probiotics and gastrointestinal diseases.
      ]. In addition, prophylactic use in hospitalised children resulted in a reduction in the risk of acquiring nosocomial diarrhoea [
      • Szajewska H
      • Kotowska M
      • Mrukowicz JZ
      • Armanska M
      • Mikolajczyk W
      Efficacy of Lactobacillus GG in prevention of nosocomial diarrhea in infants.
      ]. In undernourished children, the preventive effect was greatest in the group aged 18–29 months, and was seen mainly in non-breast-fed children [
      • Oberhelman RA
      • Gilman RH
      • Sheen P
      • et al.
      A placebo‐controlled trial of Lactobacillus GG to prevent diarrhea in undernourished Peruvian children.
      ]. Mechanisms that have been proposed for this protective effect include competitive blockage of receptor sites (resulting in inhibition of virus adherence and invasion), enhancement of the host immune system, and production of substances that inactivate virus particles [
      • Reid G
      • Jass J
      • Sebulsky MT
      • McCormick JK
      Potential uses of probiotics in clinical practice.
      ]. However, none of these mechanisms has been demonstrated conclusively. Nevertheless, it is now suggested that there is sufficient evidence to recommend the use of L. rhamnosus GG in milk or capsule form as an adjunct to oral rehydration therapy for the treatment of rotavirus diarrhoea [
      • Kaila M
      • Isolauri E
      • Soppi E
      • Virtanen E
      • Laine S
      • Arvilommi H
      Enhancement of the circulating antibody secreting cell response in human diarrhea by a human Lactobacillus strain.
      ,
      • Allen SJ
      • Okoko B
      • Martinez E
      • Gregorio G
      • Dans LF
      Probiotics for treating infectious diarrhoea.
      ,
      • D'Souza AL
      • Rajkumar C
      • Cooke J
      • Bulpitt CJ
      Probiotics in prevention of antibiotic associated diarrhoea: meta‐analysis.
      ]. It is estimated that a child dies every 15 s from diarrhoeal disease. The implementation of such a recommendation, particularly in developing countries, could contribute significantly to reducing the morbidity and mortality associated with diarrhoea.
      In contrast, the beneficial effect of probiotics for bacterial diarrhoea, particularly antibiotic-associated diarrhoea and travellers’ diarrhoea, remains unproven, as results from a number of studies are conflicting [
      • Pochapin M
      The effect of probiotics on Clostridium difficile diarrhea.
      ,
      • Rendi‐Wagner P
      • Kollaritsch H
      Drug prophylaxis for travelers' diarrhea.
      ,
      • Thomas MR
      • Litin SC
      • Osmon DR
      • Corr AP
      • Weaver AL
      • Lohse CM
      Lack of effect of Lactobacillus GG on antibiotic‐associated diarrhea: a randomized, placebo‐controlled trial.
      ,
      • Lewis SJ
      • Potts LF
      • Barry RE
      The lack of therapeutic effect of Saccharomyces boulardii in the prevention of antibiotic‐related diarrhoea in elderly patients.
      ,
      • Vanderhoof JA
      • Whitney DB
      • Antonson DL
      • Hanner TL
      • Lupo JV
      • Young RJ
      Lactobacillus GG in the prevention of antibiotic‐associated diarrhea in children.
      ,
      • Sullivan A
      • Nord CE
      Probiotics in human infections.
      ]. While L. rhamnosus GG has been shown to be useful in the prevention of antibiotic-associated diarrhoea in children, similar effects were not observed in adults [
      • Thomas MR
      • Litin SC
      • Osmon DR
      • Corr AP
      • Weaver AL
      • Lohse CM
      Lack of effect of Lactobacillus GG on antibiotic‐associated diarrhea: a randomized, placebo‐controlled trial.
      ,
      • Vanderhoof JA
      • Whitney DB
      • Antonson DL
      • Hanner TL
      • Lupo JV
      • Young RJ
      Lactobacillus GG in the prevention of antibiotic‐associated diarrhea in children.
      ]. A number of studies have evaluated the effect of Saccharomyces boulardii in the prevention of antibiotic-associated diarrhoea, but the results have been inconclusive, as the reduced incidence seen in some studies was not demonstrable in others [
      • Sullivan A
      • Nord CE
      Probiotics in human infections.
      ]. In addition, a beneficial effect in Clostridium difficile infection was demonstrable only when S. boulardii was combined with highdose vancomycin [
      • Surawicz CM
      • McFarland LV
      • Greenberg RN
      • et al.
      The search for a better treatment for recurrent Clostridium difficile disease: use of high‐dose vancomycin combined with Saccharomyces boulardii.
      ].
      Necrotising enterocolitis is a cause of morbidity and mortality in pre-term babies. In a retrospective comparison study, the treatment of pre-term babies with a combination of two probiotic strains (Lactobacillus acidophilus and Bifidobacterium infantis) was effective in reducing the occurrence of necrotising enterocolitis and associated mortality [
      • Hoyos AB
      Reduced incidence of necrotizing enterocolitis associated with enteral administration of Lactobacillus acidophilus and Bifidobacterium infantis to neonates in an intensive care unit.
      ]. However, another study using Lactobacillus alone did not show a statistically significant reduction in the occurrence of necrotising enterocolitis [
      • Dani C
      • Biadaioli R
      • Bertini G
      • Martelli E
      • Rubaltelli FF
      Probiotics feeding in prevention of urinary tract infection, bacterial sepsis and necrotizing enterocolitis in preterm infants. A prospective double‐blind study.
      ]. A number of commercial infant milk formulas contain added probiotics. While there may be beneficial effects, the use of probiotics so early in life, and at a time when the gut microbiota has not yet been established, might result in long-term colonisation with these organisms. The implications of modifying the complex intestinal microbial ecosystem are still unclear, and a better understanding of the effects of these interventions on the infant gut microbiota is needed.

       Other gastrointestinal conditions

      Various studies have assessed the efficacy of probiotics for the prevention and treatment of other common gastrointestinal conditions, including Helicobacter pylori infection and inflammatory bowel diseases, such as Crohn's disease and irritable bowel syndrome [
      • Sullivan A
      • Nord CE
      Probiotics and gastrointestinal diseases.
      ,
      • Hamilton‐Miller JM
      The role of probiotics in the treatment and prevention of Helicobacter pylori infection.
      ,
      • Schultz M
      • Timmer A
      • Herfarth HH
      • Sartor RB
      • Vanderhoof JA
      • Rath HC
      Lactobacillus GG in inducing and maintaining remission of Crohn's disease.
      ,
      • Sen S
      • Mullan MM
      • Parker TJ
      • Woolner JT
      • Tarry SA
      • Hunter JO
      Effect of Lactobacillus plantarum 299v on colonic fermentation and symptoms of irritable bowel syndrome.
      ,
      • Niedzielin K
      • Kordecki H
      • Birkenfeld B
      A controlled, double‐blind, randomized study on the efficacy of Lactobacillus plantarum 299V in patients with irritable bowel syndrome.
      ]. Although animal studies and preliminary human studies have shown promising results, large double-blinded randomised trials are required to verify the benefits of probiotic products in treating these conditions. In addition, there is evidence to suggest that the intestinal microbiota play a critical role in the pathogenesis of bowel inflammatory disease, and it appears that the use of a combination rather than a single probiotic strain might be effective in alleviating the symptoms [
      • Reid G
      • Jass J
      • Sebulsky MT
      • McCormick JK
      Potential uses of probiotics in clinical practice.
      ].

       Cancer

      There is accumulating evidence to suggest that some members of the intestinal microbiota influence the onset of carcinogenesis by producing enzymes, such as glycosidase, azoreductase, nitroreductase and β-glucoronidase, which transform pre-carcinogens into active carcinogens [
      • Gorbach SL
      • Goldin BR
      The intestinal microflora and the colon cancer connection.
      ,
      • Nalini N
      • Manju V
      • Menon VP
      Effect of coconut cake on the bacterial enzyme activity in 1,2‐dimethyl hydrazine induced colon cancer.
      ]. Preliminary data suggest that probiotic products may protect against this carcinogenic activity [
      • Hosoda M
      • Hashimoto H
      • He F
      • Morita H
      • Hosono A
      Effect of administration of milk fermented with Lactobacillus acidophilus LA‐2 on fecal mutagenicity and microflora in the human intestine.
      ,
      • Hosoda M
      • Hashimoto H
      • Morita H
      • Chiba M
      • Hosono A
      Antimutagenicity of milk cultured with lactic acid bacteria against N‐methyl‐N′‐nitro‐N‐nitrosoguanidine.
      ]. Human studies have shown that the ingestion of L. acidophilus or Lactobacillus casei results in reduced levels of the above enzymes in the stools of volunteers [
      • Hayatsu H
      • Hayatsu T
      Suppressing effect of Lactobacillus casei administration on the urinary mutagenicity arising from ingestion of fried ground beef in the human.
      ,
      • Lidbeck A
      • Nord CE
      • Gustafsson JA
      • Rafter J
      Lactobacilli, anticarcinogenic activities and human intestinal microflora.
      ]. Whether the ingestion of probiotics will actually lead to a reduced incidence of cancer is still unknown, and such anti-cancer effects must to be demonstrated in clinical trials involving the use of recognised cancer markers. A study investigating the impact of probiotic intake on cancer has shown promising results [
      • Aso Y
      • Akaza H
      • Kotake T
      • Tsukamoto T
      • Imai K
      • Naito S
      Preventive effect of a Lactobacillus casei preparation on the recurrence of superficial bladder cancer in a double‐blind trial. The BLP Study Group.
      ]. This study demonstrated that use of L. casei Shirota (present in ‘Yakult’ preparation) reduced the recurrence rate of superficial bladder cancer. However, more efficacy studies in humans are required before definitive conclusions can be reached regarding the beneficial effects of probiotic products in the prevention of cancer.

       Allergy

      There is evidence to suggest that the composition of the vaginal microbiota can influence the eventual asthmatic status of children. Benn et al. [
      • Benn CS
      • Thorsen P
      • Jensen JS
      • et al.
      Maternal vaginal microflora during pregnancy and the risk of asthma hospitalization and use of antiasthma medication in early childhood.
      ] demonstrated that vaginal colonisation with either Ureaplasma urealyticum or staphylococci during pregnancy was associated with the development of wheezing and/or asthma by the fifth year of life. However, the use of probiotics in pregnancy appears to have the effect of reducing the development of atopic disease in childhood. A clinical study has shown that giving L. rhamnosus GG to pregnant women for 4 weeks before delivery, and then to the newborn infant, caused a significant reduction in the occurrence of early atopic disease [
      • Kalliomaki M
      • Salminen S
      • Arvilommi H
      • Kero P
      • Koskinen P
      • Isolauri E
      Probiotics in primary prevention of atopic disease: a randomised placebo‐controlled trial.
      ]. The findings from this double-blinded placebo-controlled study, as well as from other studies [
      • Vanderhoof JA
      • Young RJ
      Role of probiotics in the management of patients with food allergy.
      ], have given more weight to the possible beneficial effects of probiotics for allergy sufferers. Furthermore, data from the 4-year follow-up of the same cohort of infants also suggest that this protective effect extends beyond infancy [
      • Kalliomaki M
      • Salminen S
      • Poussa T
      • Arvilommi H
      • Isolauri E
      Probiotics and prevention of atopic disease: 4‐year follow‐up of a randomised placebo‐controlled trial.
      ]. Although the precise mechanism(s) is yet to be elucidated, it has been suggested that lactobacilli may reverse increased intestinal permeability, as well as promote gut barrier function, via the restoration of normal microbiota [
      • Kalliomaki M
      • Salminen S
      • Arvilommi H
      • Kero P
      • Koskinen P
      • Isolauri E
      Probiotics in primary prevention of atopic disease: a randomised placebo‐controlled trial.
      ,
      • Kalliomaki M
      • Isolauri E
      Role of intestinal flora in the development of allergy.
      ]. In addition, enhancement of the gut-specific IgA response and production of cytokines, which promote IgE antibody production, may occur [
      • Kalliomaki MA
      • Isolauri E
      Probiotics and downregulation of the allergic response.
      ,
      • Isolauri E
      • Sutas Y
      • Kankaanpaa P
      • Arvilommi H
      • Salminen S
      Probiotics: effects on immunity.
      ]. With the incidence of allergic conditions, especially asthma and atopic eczema, increasing, particularly in industrialised nations, further research designed to obtain conclusive results regarding this promising beneficial effect is needed.

       Genitourinary tract infection

      Many women with genitourinary tract infection may be asymptomatic, and yet be at risk of severe complications, especially during pregnancy. A strong link exists between the absence of vaginal lactobacilli and the risk of sexually transmitted infection [
      • Reid G
      • Jass J
      • Sebulsky MT
      • McCormick JK
      Potential uses of probiotics in clinical practice.
      ,
      • Reid G
      • Devillard E
      Probiotics for mother and child.
      ]. Indeed, a correlation has been demonstrated between the absence of lactobacilli in the vagina and positive results for carriage of Neisseria gonorrhoeae and Chlamydia trachomatis [
      • Wiesenfeld HC
      • Hillier SL
      • Krohn MA
      • Landers DV
      • Sweet RL
      Bacterial vaginosis is a strong predictor of Neisseria gonorrhoeae and Chlamydia trachomatis infection.
      ]. Both animal and human studies have shown that local instillation of lactobacilli resulted in marked inhibition of Escherichia coli growth, as well as a reduction in both the severity of inflammation and the risk of recurrent urinary tract infection [
      • Reid G
      • Jass J
      • Sebulsky MT
      • McCormick JK
      Potential uses of probiotics in clinical practice.
      ,
      • Reid G
      • Bruce AW
      • Tejada‐Simon MV
      Instillation of Lactobacillus and stimulation of indigenous organisms to prevent recurrence of urinary tract infections.
      ,
      • Asahara T
      • Nomoto K
      • Watanuki M
      • Yokokura T
      Antimicrobial activity of intraurethrally administered probiotic Lactobacillus casei in a murine model of Escherichia coli urinary tract infection.
      ]. Furthermore, oral intake of probiotic lactobacilli has been shown to reduce the risk of urinary tract infection, bacterial vaginosis and candidiasis [
      • Reid G
      • Jass J
      • Sebulsky MT
      • McCormick JK
      Potential uses of probiotics in clinical practice.
      ,
      • Reid G
      • Devillard E
      Probiotics for mother and child.
      ]. Although the mechanism by which ingested lactobacilli cause a reduction in the risk of these infections is unclear, a multifactorial scenario has been hypothesised in which it has been suggested that ingested lactobacilli could ascend from the rectal skin to the vagina, or alternatively, prevent the ascent of pathogens [
      • Reid G
      • Jass J
      • Sebulsky MT
      • McCormick JK
      Potential uses of probiotics in clinical practice.
      ]. However, an overall influence of the immune or host system in the reduction of susceptibility to pathogens could also be involved. Unfortunately, the evidence for the efficacy of probiotics in urogenital infections is still not conclusive, partly because there are still reports in the scientific literature that fail to demonstrate a protective effect against urogenital infections with the use of probiotics [
      • Kontiokari T
      • Sundqvist K
      • Nuutinen M
      • Pokka T
      • Koskela M
      • Uhari M
      Randomised trial of cranberry‐lingonberry juice and Lactobacillus GG drink for the prevention of urinary tract infections in women.
      ,
      • Baerheim A
      • Larsen E
      • Digranes A
      Vaginal application of lactobacilli in the prophylaxis of recurrent lower urinary tract infection in women.
      ,
      • Jerse AE
      • Crow ET
      • Bordner AN
      • et al.
      Growth of Neisseria gonorrhoeae in the female mouse genital tract does not require the gonococcal transferrin or hemoglobin receptors and may be enhanced by commensal lactobacilli.
      ]. However, the overwhelming body of evidence remains in support of a beneficial effect.

      PROBIOTICS IN HEALTHY INDIVIDUALS

      Many probiotic products are used routinely by healthy individuals; indeed, the marketing of many probiotic food products is targeted at healthy individuals. The claims that regular ingestion will contribute to a healthy lifestyle, promote general wellbeing, and protect against or reduce the risk of developing chronic gastrointestinal, respiratory or cardiac problems in the long-term, has induced many people to undertake regular consumption of these products. However, there is no precise measure of ‘health', and there are no studies that have verified the claims that long-term use of probiotics helps to maintain good health. In addition, there are no measurements of the impact of probiotics on the immune system of healthy individuals, or their innate resistance to disease. It is worth considering whether probiotic intake has any advantages over other healthy lifestyle factors such as diet, exercise or stress reduction. It is known that ingestion of probiotic strains has not been associated with long-term colonisation and survival in the host, as probiotic strains are only retained for days or weeks after discontinuation of ingestion [
      • Alander M
      • Satokari R
      • Korpela R
      • et al.
      Persistence of colonization of human colonic mucosa by a probiotic strain, Lactobacillus rhamnosus GG, after oral consumption.
      ,
      • De Champs C
      • Maroncle N
      • Balestrino D
      • Rich C
      • Forestier C
      Persistence of colonization of intestinal mucosa by a probiotic strain, Lactobacillus casei subsp. rhamnosus Lcr35, after oral consumption.
      ,
      • Tannock GW
      • Munro K
      • Harmsen HJ
      • Welling GW
      • Smart J
      • Gopal PK
      Analysis of the fecal microflora of human subjects consuming a probiotic product containing Lactobacillus rhamnosus DR20.
      ]. Therefore, their effects appear to be transient, and continuous long-term intake is necessary. This raises the question of the impact of regular probiotic intake on the intestinal flora of healthy individuals. It is known that there are gut commensal microorganisms that benefit the host, and the impact of regular intake of probiotics on these microbes is unknown. Although current evidence does not indicate loss or depletion of these beneficial organisms [
      • Tannock GW
      • Munro K
      • Harmsen HJ
      • Welling GW
      • Smart J
      • Gopal PK
      Analysis of the fecal microflora of human subjects consuming a probiotic product containing Lactobacillus rhamnosus DR20.
      ], the questions regarding the long-term effects of probiotic intake on otherwise healthy individuals remain unanswered. Well-designed studies are still needed to investigate the perception that healthy people benefit from regular intake of probiotics.

      SAFETY OF PROBIOTICS

      As viable probiotic bacteria have to be consumed in large quantities, and over an extended period of time for there to be beneficial effects, the issue of the safety of these organisms becomes a primary concern. The traditional use of probiotics, particularly lactobacilli in food processing, without significant adverse effects in humans, has long attested to their safety. In recent years, there have been reports of isolated cases of opportunistic infections caused by certain probiotics, such as Enterococcus and Saccharomyces spp. Enterococci are of particular medical relevance because of their increasing importance as a cause of nosocomial infection, coupled with evolving antimicrobial resistance. Certain Enterococcus strains have a long history of safe use as starter cultures in dairy fermentation and are therefore being promoted as probiotics. However, the potential for genetic transfer of virulence factors from medical strains to culture starter strains via a natural conjugation process has now been demonstrated [
      • Eaton TJ
      • Gasson MJ
      Molecular screening of Enterococcus virulence determinants and potential for genetic exchange between food and medical isolates.
      ]. Current FAO/WHO guidelines [
      • FAO/WHO
      ] recommend that probiotic strains should be evaluated for a number of parameters, including antibiotic susceptibility patterns, toxin production, metabolic and haemolytic activities, infectivity in immunocompromised animal models, side-effects and adverse incidents in humans.

      CHOICE OF PROBIOTIC PRODUCT AND REGULATORY ISSUES

      Although there are guidelines regarding the choice of probiotic strains and the assessment of their efficacy and safety [
      • FAO/WHO
      ,
      • FAO/WHO
      ], there is still no international regulatory consensus, particularly concerning probiotic food products. Studies evaluating products on supermarket shelves have found that the contents do not always correspond with the label claims in terms of the type, number and viability of probiotic microorganisms [
      • Weese JS
      Evaluation of deficiencies in labeling of commercial probiotics.
      ,
      • Hamilton‐Miller JM
      • Shah S
      • Winkler JT
      Public health issues arising from microbiological and labelling quality of foods and supplements containing probiotic microorganisms.
      ,
      • Weese JS
      Microbiologic evaluation of commercial probiotics.
      ,
      • Weese JS
      • Arroyo L
      Bacteriological evaluation of dog and cat diets that claim to contain probiotics.
      ]. In addition, there is inadequate information available regarding the stability of probiotics in powdered milk (including infant formula), especially as the production process is known to cause cell damage and loss of viability of the probiotic cultures [
      • Selmer‐Olsen E
      • Sorhaug T
      • Birkeland SE
      • Pehrson R
      Survival of Lactobacillus helveticus entrapped in Ca‐alginate in relation to water content, storage and rehydration.
      ]. Appropriate labelling should therefore state the species and strain of probiotic bacteria in the product as well as the viable concentration present at the end of the shelf-life.

      CONCLUSIONS

      There is scientific evidence that specific strains of probiotic microorganisms confer benefits to the health of the host and are safe for human use. However, these cannot be extrapolated to other strains, as such effects are strain-specific. Use of probiotics has potential benefits for conditions such as gastrointestinal infections, genitourinary infections, allergies and certain bowel disorders, all of which afflict a considerable proportion of the global population. However, considerable work is required to affirm these benefits. A systematic approach based on the guidelines recommended by the Joint FAO/WHO Expert Consultation should be adopted by researchers.
      Much work is still needed before credibility can be given to health claims regarding the use of probiotic products in healthy individuals. Internationally uniform regulatory procedures for probiotic foods are urgently required to ensure appropriate labelling, manufacturing and handling procedures, as well as the health claims that are made for these products.

      ACKNOWLEDGEMENTS

      This work was supported by the Arabian Gulf University, Manama, Kingdom of Bahrain as part of a project entitled ‘Pathogenetic mechanisms and mucosal immune defences of Campylobacter and rotavirus associated with diarrhoea in children'.

      References

        • FAO/WHO
        Evaluation of health and nutritional properties of powder milk and live lactic acid bacteria. Food and Agriculture Organization of the United Nations and World Health Organization Expert Consultation Report, Cordoba, Argentina2001: 1-34
        • Metchnikoff E
        Lactic acid as inhibiting intestinal putrefaction.
        in: Chalmers Mitchell P The prolongation of life: optimistic studies. Heinemann, London1907: 161-183
        • Lilly DM
        • Stillwell RH
        Probiotics: growth promoting substances produced by microorganisms.
        Science. 1965; 147: 747-748
        • Stanton C
        • Gardiner G
        • Meehan H
        • et al.
        Market potential for probiotics.
        Am J Clin Nutr. 2001; 73: 476S-483S
        • Anonymous
        Pro‐ and prebiotics gain popularity in a large US market for gut health.
        Nutr Bus J. 2001; xi: 19-20
        • Anonymous
        LGG at Ten.
        New Nutr Bus. 2000; 5: 6-7
        • Elliot E
        • Teversham K
        An evaluation of nine probiotics available in South Africa, August 2003.
        S Afr Med J. 2004; 94: 121-124
        • Weese JS
        Evaluation of deficiencies in labeling of commercial probiotics.
        Can Vet J. 2003; 44: 982-983
        • Hamilton‐Miller JM
        • Shah S
        • Winkler JT
        Public health issues arising from microbiological and labelling quality of foods and supplements containing probiotic microorganisms.
        Pub Health Nutr. 1999; 2: 223-229
        • Holzapfel WH
        • Haberer P
        • Geisen R
        • Bjorkroth J
        • Schillinger U
        Taxonomy and important features of probiotic microorganisms in food and nutrition.
        Am J Clin Nutr. 2001; 73: 365S-373S
        • Rolfe RD
        The role of probiotic cultures in the control of gastrointestinal health.
        J Nutr. 2000; 130: 396S-402S
        • Ishibashi N
        • Yamazaki S
        Probiotics and safety.
        Am J Clin Nutr. 2001; 73: 465S-470S
        • Donohue C
        • Salminen S
        Safety of probiotic bacteria.
        Asia Pacific J Clin Nutr. 1996; 5: 25-28
        • Eaton TJ
        • Gasson MJ
        Molecular screening of Enterococcus virulence determinants and potential for genetic exchange between food and medical isolates.
        Appl Environ Microbiol. 2001; 67: 1628-1635
        • Ibnou‐Zekri N
        • Blum S
        • Schiffrin EJ
        • Von Der Weid WT
        Divergent patterns of colonization and immune response elicited from two intestinal Lactobacillus strains that display similar properties in vitro.
        Infect Immun. 2003; 71: 428-436
        • FAO/WHO
        Guidelines for the evaluation of probiotics in food. Food and Agriculture Organization of the United Nations and World Health Organization Working Group Report, London, Ontario2002: 1-11
        • Pestka JJ
        • Ha CL
        • Warner RW
        • Lee JH
        • Ustunol Z
        Effects of ingestion of yogurts containing Bifidobacterium and Lactobacillus acidophilus on spleen and Peyer's patch lymphocyte populations in the mouse.
        J Food Prot. 2001; 64: 392-395
        • Tejada‐Simon MV
        • Lee JH
        • Ustunol Z
        • Pestka JJ
        Ingestion of yogurt containing Lactobacillus acidophilus and Bifidobacterium to potentiate immunoglobulin A responses to cholera toxin in mice.
        J Dairy Sci. 1999; 82: 649-660
        • De Vrese M
        • Stegelmann A
        • Richter B
        • Fenselau S
        • Laue C
        • Schrezenmeir J
        Probiotics—compensation for lactase insufficiency.
        Am J Clin Nutr. 2001; 73: 421S-429S
        • Reid G
        • Jass J
        • Sebulsky MT
        • McCormick JK
        Potential uses of probiotics in clinical practice.
        Clin Microbiol Rev. 2003; 16: 658-672
        • Matsuzaki T
        • Yamazaki R
        • Hashimoto S
        • Yokokura T
        The effect of oral feeding of Lactobacillus casei strain Shirota on immunoglobulin E production in mice.
        J Dairy Sci. 1998; 81: 48-53
        • Matsuzaki T
        • Chin J
        Modulating immune responses with probiotic bacteria.
        Immunol Cell Biol. 2000; 78: 67-73
        • Madsen K
        • Cornish A
        • Soper P
        • et al.
        Probiotic bacteria enhance murine and human intestinal epithelial barrier function.
        Gastroenterology. 2001; 121: 580-591
        • Chiang BL
        • Sheih YH
        • Wang LH
        • Liao CK
        • Gill HS
        Enhancing immunity by dietary consumption of a probiotic lactic acid bacterium (Bifidobacterium lactis HN019): optimization and definition of cellular immune responses.
        Eur J Clin Nutr. 2000; 54: 849-855
        • Gill HS
        • Rutherfurd KJ
        • Cross ML
        • Gopal PK
        Enhancement of immunity in the elderly by dietary supplementation with the probiotic Bifidobacterium lactis HN019.
        Am J Clin Nutr. 2001; 74: 833-839
        • Cross ML
        • Mortensen RR
        • Kudsk J
        • Gill HS
        Dietary intake of Lactobacillus rhamnosus HNOO1 enhances production of both Th1 and Th2 cytokines in antigen‐primed mice.
        Med Microbiol Immunol (Berl). 2002; 191: 49-53
        • Sheih YH
        • Chiang BL
        • Wang LH
        • Liao CK
        • Gill HS
        Systemic immunity‐enhancing effects in healthy subjects following dietary consumption of the lactic acid bacterium Lactobacillus rhamnosus HN001.
        J Am Coll Nutr. 2001; 20: 149-156
        • Gill HS
        • Cross ML
        • Rutherfurd KJ
        • Gopal PK
        Dietary probiotic supplementation to enhance cellular immunity in the elderly.
        Br J Biomed Sci. 2001; 58: 94-96
        • Muscettola M
        • Massai L
        • Tanganelli C
        • Grasso G
        Effects of lactobacilli on interferon production in young and aged mice.
        Ann NY Acad Sci. 1994; 717: 226-232
        • Erickson KL
        • Hubbard NE
        Probiotic immunomodulation in health and disease.
        J Nutr. 2000; 130: 403S-409S
        • Fukushima Y
        • Kawata Y
        • Hara H
        • Terada A
        • Mitsuoka T
        Effect of a probiotic formula on intestinal immunoglobulin A production in healthy children.
        Int J Food Microbiol. 1998; 42: 39-44
        • Perdigon G
        • Vintini E
        • Alvarez S
        • Medina M
        • Medici M
        Study of the possible mechanisms involved in the mucosal immune system activation by lactic acid bacteria.
        J Dairy Sci. 1999; 82: 1108-1114
        • Mack DR
        • Lebel S
        Role of probiotics in the modulation of intestinal infections and inflammation.
        Curr Opin Gastroenterol. 2004; 20: 22-26
        • Miettinen M
        • Lehtonen A
        • Julkunen I
        • Matikainen S
        Lactobacilli and streptococci activate NF‐kappa B and STAT signaling pathways in human macrophages.
        J Immunol. 2000; 164: 3733-3740
        • Kaila M
        • Isolauri E
        • Soppi E
        • Virtanen E
        • Laine S
        • Arvilommi H
        Enhancement of the circulating antibody secreting cell response in human diarrhea by a human Lactobacillus strain.
        Pediatr Res. 1992; 32: 141-144
        • Drakes M
        • Blanchard T
        • Czinn S
        Bacterial probiotic modulation of dendritic cells.
        Infect Immun. 2004; 72: 3299-3309
        • Pelto L
        • Isolauri E
        • Lilius EM
        • Nuutila J
        • Salminen S
        Probiotic bacteria down‐regulate the milk‐induced inflammatory response in milk‐hypersensitive subjects but have an immunostimulatory effect in healthy subjects.
        Clin Exp Allergy. 1998; 28: 1474-1479
        • Gill HS
        • Rutherfurd KJ
        Viability and dose–response studies on the effects of the immunoenhancing lactic acid bacterium Lactobacillus rhamnosus in mice.
        Br J Nutr. 2001; 86: 285-289
        • Yasui H
        • Shida K
        • Matsuzaki T
        • Yokokura T
        Immunomodulatory function of lactic acid bacteria.
        Ant v Leeuw. 1999; 76: 383-389
        • Phuapradit P
        • Varavithya W
        • Vathanophas K
        • et al.
        Reduction of rotavirus infection in children receiving bifidobacteria‐supplemented formula.
        J Med Assoc Thai. 1999; 82: S43-S48
        • Sullivan A
        • Nord CE
        Probiotics and gastrointestinal diseases.
        J Intern Med. 2005; 257: 78-92
        • Shornikova AV
        • Isolauri E
        • Burkanova L
        • Lukovnikova S
        • Vesikari T
        A trial in the Karelian Republic of oral rehydration and Lactobacillus GG for treatment of acute diarrhoea.
        Acta Paediatr. 1997; 86: 460-465
        • Shornikova AV
        • Casas IA
        • Isolauri E
        • Mykkanen H
        • Vesikari T
        Lactobacillus reuteri as a therapeutic agent in acute diarrhea in young children.
        J Pediatr Gastroenterol Nutr. 1997; 24: 399-404
        • Guandalini S
        • Pensabene L
        • Zikri MA
        • et al.
        Lactobacillus GG administered in oral rehydration solution to children with acute diarrhea: a multicenter European trial.
        J Pediatr Gastroenterol Nutr. 2000; 30: 54-60
        • Guarino A
        • Canani RB
        • Spagnuolo MI
        • Albano F
        • Di Benedetto L
        Oral bacterial therapy reduces the duration of symptoms and of viral excretion in children with mild diarrhea.
        J Pediatr Gastroenterol Nutr. 1997; 25: 516-519
        • Rosenfeldt V
        • Michaelsen KF
        • Jakobsen M
        • et al.
        Effect of probiotic Lactobacillus strains on acute diarrhea in a cohort of nonhospitalized children attending day‐care centers.
        Pediatr Infect Dis J. 2002; 21: 417-419
        • Rosenfeldt V
        • Michaelsen KF
        • Jakobsen M
        • et al.
        Effect of probiotic Lactobacillus strains in young children hospitalized with acute diarrhea.
        Pediatr Infect Dis J. 2002; 21: 411-416
        • Szajewska H
        • Kotowska M
        • Mrukowicz JZ
        • Armanska M
        • Mikolajczyk W
        Efficacy of Lactobacillus GG in prevention of nosocomial diarrhea in infants.
        J Pediatr. 2001; 138: 361-365
        • Oberhelman RA
        • Gilman RH
        • Sheen P
        • et al.
        A placebo‐controlled trial of Lactobacillus GG to prevent diarrhea in undernourished Peruvian children.
        J Pediatr. 1999; 134: 15-20
        • Allen SJ
        • Okoko B
        • Martinez E
        • Gregorio G
        • Dans LF
        Probiotics for treating infectious diarrhoea.
        Cochrane Database Syst Rev. 2004; (CD003048.)
        • D'Souza AL
        • Rajkumar C
        • Cooke J
        • Bulpitt CJ
        Probiotics in prevention of antibiotic associated diarrhoea: meta‐analysis.
        BMJ. 2002; 324: 1361
        • Pochapin M
        The effect of probiotics on Clostridium difficile diarrhea.
        Am J Gastroenterol. 2000; 95: S11-S13
        • Rendi‐Wagner P
        • Kollaritsch H
        Drug prophylaxis for travelers' diarrhea.
        Clin Infect Dis. 2002; 34: 628-633
        • Thomas MR
        • Litin SC
        • Osmon DR
        • Corr AP
        • Weaver AL
        • Lohse CM
        Lack of effect of Lactobacillus GG on antibiotic‐associated diarrhea: a randomized, placebo‐controlled trial.
        Mayo Clin Proc. 2001; 76: 883-889
        • Lewis SJ
        • Potts LF
        • Barry RE
        The lack of therapeutic effect of Saccharomyces boulardii in the prevention of antibiotic‐related diarrhoea in elderly patients.
        J Infect. 1998; 36: 171-174
        • Vanderhoof JA
        • Whitney DB
        • Antonson DL
        • Hanner TL
        • Lupo JV
        • Young RJ
        Lactobacillus GG in the prevention of antibiotic‐associated diarrhea in children.
        J Pediatr. 1999; 135: 564-568
        • Sullivan A
        • Nord CE
        Probiotics in human infections.
        J Antimicrob Chemother. 2002; 50: 625-627
        • Surawicz CM
        • McFarland LV
        • Greenberg RN
        • et al.
        The search for a better treatment for recurrent Clostridium difficile disease: use of high‐dose vancomycin combined with Saccharomyces boulardii.
        Clin Infect Dis. 2000; 31: 1012-1017
        • Hoyos AB
        Reduced incidence of necrotizing enterocolitis associated with enteral administration of Lactobacillus acidophilus and Bifidobacterium infantis to neonates in an intensive care unit.
        Int J Infect Dis. 1999; 3: 197-202
        • Dani C
        • Biadaioli R
        • Bertini G
        • Martelli E
        • Rubaltelli FF
        Probiotics feeding in prevention of urinary tract infection, bacterial sepsis and necrotizing enterocolitis in preterm infants. A prospective double‐blind study.
        Biol Neonate. 2002; 82: 103-108
        • Hamilton‐Miller JM
        The role of probiotics in the treatment and prevention of Helicobacter pylori infection.
        Int J Antimicrob Agents. 2003; 22: 360-366
        • Schultz M
        • Timmer A
        • Herfarth HH
        • Sartor RB
        • Vanderhoof JA
        • Rath HC
        Lactobacillus GG in inducing and maintaining remission of Crohn's disease.
        BMC Gastroenterol. 2004; 4: 5
        • Sen S
        • Mullan MM
        • Parker TJ
        • Woolner JT
        • Tarry SA
        • Hunter JO
        Effect of Lactobacillus plantarum 299v on colonic fermentation and symptoms of irritable bowel syndrome.
        Dig Dis Sci. 2002; 47: 2615-2620
        • Niedzielin K
        • Kordecki H
        • Birkenfeld B
        A controlled, double‐blind, randomized study on the efficacy of Lactobacillus plantarum 299V in patients with irritable bowel syndrome.
        Eur J Gastroenterol Hepatol. 2001; 13: 1143-1147
        • Gorbach SL
        • Goldin BR
        The intestinal microflora and the colon cancer connection.
        Rev Infect Dis. 1990; 12: S252-S261
        • Nalini N
        • Manju V
        • Menon VP
        Effect of coconut cake on the bacterial enzyme activity in 1,2‐dimethyl hydrazine induced colon cancer.
        Clin Chim Acta. 2004; 342: 203-210
        • Hosoda M
        • Hashimoto H
        • He F
        • Morita H
        • Hosono A
        Effect of administration of milk fermented with Lactobacillus acidophilus LA‐2 on fecal mutagenicity and microflora in the human intestine.
        J Dairy Sci. 1996; 79: 745-749
        • Hosoda M
        • Hashimoto H
        • Morita H
        • Chiba M
        • Hosono A
        Antimutagenicity of milk cultured with lactic acid bacteria against N‐methyl‐N′‐nitro‐N‐nitrosoguanidine.
        J Dairy Sci. 1992; 75: 976-981
        • Hayatsu H
        • Hayatsu T
        Suppressing effect of Lactobacillus casei administration on the urinary mutagenicity arising from ingestion of fried ground beef in the human.
        Cancer Lett. 1993; 73: 173-179
        • Lidbeck A
        • Nord CE
        • Gustafsson JA
        • Rafter J
        Lactobacilli, anticarcinogenic activities and human intestinal microflora.
        Eur J Cancer Prev. 1992; 1: 341-353
        • Aso Y
        • Akaza H
        • Kotake T
        • Tsukamoto T
        • Imai K
        • Naito S
        Preventive effect of a Lactobacillus casei preparation on the recurrence of superficial bladder cancer in a double‐blind trial. The BLP Study Group.
        Eur Urol. 1995; 27: 104-109
        • Benn CS
        • Thorsen P
        • Jensen JS
        • et al.
        Maternal vaginal microflora during pregnancy and the risk of asthma hospitalization and use of antiasthma medication in early childhood.
        J Allergy Clin Immunol. 2002; 110: 72-77
        • Kalliomaki M
        • Salminen S
        • Arvilommi H
        • Kero P
        • Koskinen P
        • Isolauri E
        Probiotics in primary prevention of atopic disease: a randomised placebo‐controlled trial.
        Lancet. 2001; 357: 1076-1079
        • Vanderhoof JA
        • Young RJ
        Role of probiotics in the management of patients with food allergy.
        Ann Allergy Asthma Immunol. 2003; 90: 99-103
        • Kalliomaki M
        • Salminen S
        • Poussa T
        • Arvilommi H
        • Isolauri E
        Probiotics and prevention of atopic disease: 4‐year follow‐up of a randomised placebo‐controlled trial.
        Lancet. 2003; 361: 1869-1871
        • Kalliomaki M
        • Isolauri E
        Role of intestinal flora in the development of allergy.
        Curr Opin Allergy Clin Immunol. 2003; 3: 15-20
        • Kalliomaki MA
        • Isolauri E
        Probiotics and downregulation of the allergic response.
        Immunol Allergy Clin North Am. 2004; 24 (viii.): 739-752
        • Isolauri E
        • Sutas Y
        • Kankaanpaa P
        • Arvilommi H
        • Salminen S
        Probiotics: effects on immunity.
        Am J Clin Nutr. 2001; 73: 444S-450S
        • Reid G
        • Devillard E
        Probiotics for mother and child.
        J Clin Gastroenterol. 2004; 38: S94-S101
        • Wiesenfeld HC
        • Hillier SL
        • Krohn MA
        • Landers DV
        • Sweet RL
        Bacterial vaginosis is a strong predictor of Neisseria gonorrhoeae and Chlamydia trachomatis infection.
        Clin Infect Dis. 2003; 36: 663-668
        • Reid G
        • Bruce AW
        • Tejada‐Simon MV
        Instillation of Lactobacillus and stimulation of indigenous organisms to prevent recurrence of urinary tract infections.
        Microecol Ther. 1995; 23: 32-45
        • Asahara T
        • Nomoto K
        • Watanuki M
        • Yokokura T
        Antimicrobial activity of intraurethrally administered probiotic Lactobacillus casei in a murine model of Escherichia coli urinary tract infection.
        Antimicrob Agents Chemother. 2001; 45: 1751-1760
        • Kontiokari T
        • Sundqvist K
        • Nuutinen M
        • Pokka T
        • Koskela M
        • Uhari M
        Randomised trial of cranberry‐lingonberry juice and Lactobacillus GG drink for the prevention of urinary tract infections in women.
        BMJ. 2001; 322: 1571
        • Baerheim A
        • Larsen E
        • Digranes A
        Vaginal application of lactobacilli in the prophylaxis of recurrent lower urinary tract infection in women.
        Scand J Prim Health Care. 1994; 12: 239-243
        • Jerse AE
        • Crow ET
        • Bordner AN
        • et al.
        Growth of Neisseria gonorrhoeae in the female mouse genital tract does not require the gonococcal transferrin or hemoglobin receptors and may be enhanced by commensal lactobacilli.
        Infect Immun. 2002; 70: 2549-2558
        • Alander M
        • Satokari R
        • Korpela R
        • et al.
        Persistence of colonization of human colonic mucosa by a probiotic strain, Lactobacillus rhamnosus GG, after oral consumption.
        Appl Environ Microbiol. 1999; 65: 351-354
        • De Champs C
        • Maroncle N
        • Balestrino D
        • Rich C
        • Forestier C
        Persistence of colonization of intestinal mucosa by a probiotic strain, Lactobacillus casei subsp. rhamnosus Lcr35, after oral consumption.
        J Clin Microbiol. 2003; 41: 1270-1273
        • Tannock GW
        • Munro K
        • Harmsen HJ
        • Welling GW
        • Smart J
        • Gopal PK
        Analysis of the fecal microflora of human subjects consuming a probiotic product containing Lactobacillus rhamnosus DR20.
        Appl Environ Microbiol. 2000; 66: 2578-2588
        • Weese JS
        Microbiologic evaluation of commercial probiotics.
        J Am Vet Med Assoc. 2002; 220: 794-797
        • Weese JS
        • Arroyo L
        Bacteriological evaluation of dog and cat diets that claim to contain probiotics.
        Can Vet J. 2003; 44: 212-216
        • Selmer‐Olsen E
        • Sorhaug T
        • Birkeland SE
        • Pehrson R
        Survival of Lactobacillus helveticus entrapped in Ca‐alginate in relation to water content, storage and rehydration.
        J Indust Microbiol Biotechnol. 1999; 23: 79-85