Safety of probiotics that contain lactobacilli or bifidobacteria

Application of genotypic and phenotypic analyses to commercial probiotic strain identity and relatedness

AIMS

The objective of this study was to generate strain-specific genomic patterns of a bank of 67 commercial and reference probiotic strains, with a focus on probiotic lactobacilli.

METHODS AND RESULTS

Pulsed-field gel electrophoresis (PFGE) was used as the primary method for strain differentiation. This method was compared with carbohydrate fermentation analysis. To supplement visual comparison, PFGE patterns were analysed quantitatively by cluster analysis using unweighted pair group method with arithmetic averages. SmaI, NotI and XbaI were found to effectively generate clear and easy-to-interpret PFGE patterns of a range of probiotic strains. Some probiotic strains from different sources shared highly similar PFGE patterns.

CONCLUSIONS

Results document the value of genotypic strain identification methods, combined with phenotypic methods, for determining probiotic strain identity and relatedness. No correlation was found between relatedness determined by carbohydrate fermentation profiles alone compared with PFGE analysis alone. Some commercial strains are probably derived from similar sources.

SIGNIFICANCE AND IMPACT OF THE STUDY

This approach is valuable to the probiotic industry to develop commercial strain identification patterns, to provide quality control of strain manufacturing production runs, to track use of protected strains and to determine the relatedness among different research and commercial probiotic strains.

Numbers and strains of lactobacilli in some probiotic products

The numbers and types of Lactobacillus strains in probiotic feed or food products for sale in Europe were compared with the information stated on the product labels. The labels of all 10 products gave information on the genus and species of Lactobacillus, and seven gave information on the numbers of a specified strain(s). Lactobacilli were recovered using a recently validated method, developed as part of the European Community Project SMT4 CT98-2235 for the official control of probiotic microorganisms used as feed additives. Polymerase chain reaction (PCR)-based methods were used to assess the accuracy of labelling with regard to genus and species, and pulsed-field gel electrophoresis (PFGE) was used to identify strains. Five products were mislabelled with respect to the numbers and three with respect to species of lactobacilli. In four cases, the specified strains were not detected. Four fermented milks sold under three trademarks contained the same strain, which was named differently on each label. As safety and functionality of probiotics are strain dependent, these results demonstrated the need to control lactobacilli present in commercially probiotic human food products, not only at the species but also at the strain level, to ensure their quality and protect the consumer. The usefulness of the official methods developed for animal feed additives to identify lactobacilli in probiotic foods for humans was demonstrated.

Lactobacillus sepsis associated with probiotic therapy

Probiotic strains of lactobacilli are increasingly being used in clinical practice because of their many health benefits. Infections associated with probiotic strains of lactobacilli are extremely rare. We describe 2 patients who received probiotic lactobacilli and subsequently developed bacteremia and sepsis attributable to Lactobacillus species. Molecular DNA fingerprinting analysis showed that the Lactobacillus strain isolated from blood samples was indistinguishable from the probiotic strain ingested by the patients. This report indicates, for the first time, that invasive disease can be associated with probiotic lactobacilli. This report should not discourage the appropriate use of Lactobacillus or other probiotic agents but should serve as a reminder that these agents can cause invasive disease in certain populations.

Antagonistic activities of lactobacilli and bifidobacteria against microbial pathogens

The gastrointestinal tract is a complex ecosystem that associates a resident microbiota and cells of various phenotypes lining the epithelial wall expressing complex metabolic activities. The resident microbiota in the digestive tract is a heterogeneous microbial ecosystem containing up to 1 x 10(14) colony-forming units (CFUs) of bacteria. The intestinal microbiota plays an important role in normal gut function and maintaining host health. The host is protected from attack by potentially harmful microbial microorganisms by the physical and chemical barriers created by the gastrointestinal epithelium. The cells lining the gastrointestinal epithelium and the resident microbiota are two partners that properly and/or synergistically function to promote an efficient host system of defence. The gastrointestinal cells that make up the epithelium, provide a physical barrier that protects the host against the unwanted intrusion of microorganisms into the gastrointestinal microbiota, and against the penetration of harmful microorganisms which usurp the cellular molecules and signalling pathways of the host to become pathogenic. One of the basic physiological functions of the resident microbiota is that it functions as a microbial barrier against microbial pathogens. The mechanisms by which the species of the microbiota exert this barrier effect remain largely to be determined. There is increasing evidence that lactobacilli and bifidobacteria, which inhabit the gastrointestinal microbiota, develop antimicrobial activities that participate in the host's gastrointestinal system of defence. The objective of this review is to analyze the in vitro and in vivo experimental and clinical studies in which the antimicrobial activities of selected lactobacilli and bifidobacteria strains have been documented.

Lactobacillus rhamnosus induces peripheral hyporesponsiveness in stimulated CD4+ T cells via modulation of dendritic cell function

BACKGROUND

Although it is widely recognized that the intake of so-called probiotic microorganisms is beneficial in chronic mucosal inflammation and topical allergic disease, the immunologic details explaining how such bacteria can exert these effects remain obscure.

OBJECTIVE

We determined whether Lactobacillus rhamnosus can modulate T cell responses in vitro and in vivo.

DESIGN

In vitro, human monocyte-derived dendritic cells (DCs) matured in the presence of L. rhamnosus were used to instruct naive CD4+ T cells; subsequently, the T cell response was assessed with the use of CD3/CD28 and interleukin (IL) 2. Cytokine production by ex vivo-stimulated naive cells and memory T cells was measured before and after oral supplementation with L. rhamnosus in 6 healthy volunteers and 6 patients with Crohn disease.

RESULTS

A decreased T cell proliferation and cytokine production, especially of IL-2, IL-4, and IL-10, was observed in CD3/CD28-stimulated T cells derived from L. rhamnosus-matured DCs. This T cell hyporesponsiveness was associated with enhanced DC-T cell interaction and normal responsiveness of T cells for IL-2. In vivo oral supplementation of L. rhamnosus for 2 wk induced a similar T cell hyporesponsiveness, including impaired ex vivo T helper subsets 1 and 2 responses without up-regulation of immunoregulatory cytokines in cohorts of both healthy volunteers and patients with Crohn disease.

CONCLUSIONS

We propose that L. rhamnosus modulates DC function to induce a novel form of T cell hyporesponsiveness; this mechanism might be an explanation for the observed beneficial effects of probiotic treatment in clinical disease.

Screening of Dairy Yeast Strains for Probiotic Applications

To evaluate the potential of yeasts of dairy origin as probiotics, we tested 8 species including Candida humilis, Debaryomyces hansenii, Debaryomyces occidentalis, Kluyveromyces lactis, Kluyveromyces lodderae, Kluyveromyces marxianus, Saccharomyces cerevisiae, and Yarrowia lipolytica, isolated from commercial blue cheese and kefir. Strains were randomly selected from each species and tested for their ability to adhere to human enterocyte-like Caco-2 cells in culture. Among the 8 species, K. lactis showed higher adhesive ability than K. marxianus, K. lodderae, and D. hansenii. The other 4 species were poorly adhesive. All species other than K. marxianus and C. humilis were resistant to acidic conditions. In the presence of bile acid, growth inhibition was undetectable when incubation was carried out at 27 degrees C; however, it was evident for C. humilis and a strain of D. occidentalis when incubated at 37 degrees C. Moreover, the influence of proteinase treatment of living cells of K. lactis and K. lodderae on their adhesion to Caco-2 cells was evaluated. Although a slight reduction was recognized when K. lactis was treated with proteinase K, the influence of intestinal protease treatments of pepsin followed by trypsin was negligible. These results indicated that a proteinaceous factor was unlikely to be involved in adhesion of K. lactis and K. lodderae to Caco-2 cells. No stimulation of IL-8 synthesis by Caco-2 cells was recognized in the presence of K. lactis. In conclusion, K. lactis was the most attractive to continue study for use as probiotic microorganisms.

Germ warfare: probiotics in defense of the premature gut

The potential benefits of a predominantly lactic acid bacterial flora include an improved balance of gut microbial ecology and decreased susceptibility of the gut mucosa to bacterial translocation via adherence to the intestinal mucosa, strengthening mucosal barrier function. These properties should be especially beneficial to the premature neonate with (1) delayed establishment of nor-mal flora, increasing the potential for proliferation of pathogenic bacteria and (2) immature development of the intestinal mucosa, rendering it more susceptible to the translocation of these pathogenic bacteria and leading to extra-intestinal spread and systemic disease. Early probiotic supplementation in preterm infants is theoretically sound and associated with minimal risk. Clinical data remain preliminary but are supportive of a reduction in feeding intolerance and NEC in this high-risk group.

Probiotics in relapsing and chronic diarrhea

Diarrhea is common in oncology patients; if it becomes chronic and relapsing, it can be debilitating, hinder planned management, and be difficult to treat. The authors describe two patients, one with leukemia who developed recurrent Clostridium difficile colitis and another who developed chronic diarrhea after bone marrow transplantation. In both patients, administration of antibiotics was suspected as the cause. In one patient, relapsing diarrhea resolved after probiotics were given with a 2-day course of metronidazole, and in the other patient, chronic diarrhea resolved after probiotics were given; resolution was maintained after the probiotics were stopped. Probiotics may offer a way to bring about resolution in antibiotic-associated chronic diarrhea.

Tolerance of probiotics and prebiotics

The clinical efficacy of probiotics and prebiotics has been proved in several clinical settings. The authors review their proved or potential side effects. Probiotics as living microorganisms may theoretically be responsible for 4 types of side effects in susceptible individuals: infections, deleterious metabolic activities, excessive immune stimulation, and gene transfer. Very few cases of infection have been observed. These occurred mainly in very sick patients who received probiotic drugs because of severe medical conditions. Prebiotics exert an osmotic effect in the intestinal lumen and are fermented in the colon. They may induce gaseousness and bloating. Abdominal pain and diarrhea only occur with large doses. An increase in gastroesophageal reflux has recently been associated with large daily doses. Tolerance depends on the dose and individual sensitivity factors (probably the presence of irritable bowel syndrome or gastroesophageal reflux), and may be an adaptation to chronic consumption.

Probiotics and the management of inflammatory bowel disease

The demonstration that immune and epithelial cells can discriminate between different microbial species has extended our understanding of the actions of probiotics beyond simple barrier and antimicrobial concepts. Several probiotic mechanisms of action, relative to inflammatory bowel disease, have been elucidated: (1) competitive exclusion, whereby probiotics compete with microbial pathogens for a limited number of receptors present on the surface epithelium; (2) immunomodulation and/or stimulation of an immune response of gut-associated lymphoid and epithelial cells; (3) antimicrobial activity and suppression of pathogen growth; (4) enhancement of barrier function; and (5) induction of T cell apoptosis in the mucosal immune compartment. The unraveling of these mechanisms of action has led to new support for the use of probiotics in the management of clinical inflammatory bowel disease. Though level 1 evidence now supports the therapeutic use of probiotics in the treatment of postoperative pouchitis, only levels 2 and 3 evidence is currently available in support of the use of probiotics in the treatment of ulcerative colitis and Crohn's disease. Nevertheless, one significant and consistent finding has emerged during the course of research in the past year: not all probiotic bacteria have similar therapeutic effects. Rigorously designed, controlled clinical trials are vital to investigate the unresolved issues related to efficacy, dose, duration of use, single or multi-strain formulation, and the concomitant use of probiotics, synbiotics, or antibiotics.

Probiotics and prebiotics in gastrointestinal disorders

PURPOSE OF REVIEW

This review summarizes the clinical efficacy of probiotics and prebiotics in gastrointestinal disorders and examines the mechanisms of action related to their therapeutic effect.

RECENT FINDINGS

The demonstration that immune and epithelial cells can discriminate between different microbial species has extended the known mechanism(s) of action of probiotics beyond simple barrier and antimicrobial effects. It has also confirmed that probiotic bacteria modulate mucosal and systemic immune activity and epithelial function. The progressive unraveling of these mechanisms of action has led to new credence for the use of probiotics and prebiotics in clinical medicine. Level I evidence now exists for the therapeutic use of probiotics in infectious diarrhea in children, recurrent Clostridium difficile-induced infections and postoperative pouchitis. Level II evidence is emerging for the use of probiotics in other gastrointestinal infections, prevention of postoperative bacterial translocation, irritable bowel syndrome, and in both ulcerative colitis and Crohn disease. Nevertheless, one consistent feature has emerged over the past year: Not all probiotic bacteria have similar therapeutic effects. Future clinical trials will need to incorporate this fact into trial planning and design.

SUMMARY

The use of probiotics and prebiotics as therapeutic agents for gastrointestinal disorders is rapidly moving into the "mainstream." Mechanisms of action explain the therapeutic effects and randomized; controlled trials provide the necessary evidence for their incorporation into the therapeutic armamentarium.

Relationship between interaction sites in the gut, hydrophobicity, mucosal immunomodulating capacities and cell wall protein profiles in indigenous and exogenous bacteria

AIMS

To investigate whether there is a relationship between interaction sites in the gut, hydrophobicity, mucosal immunomodulating capacities and cell wall protein profiles in lactobacilli, bifidobacteria and enterococci.

METHODS AND RESULTS

Hydrophobicity, cell wall protein profiles and sites of interaction in the gut (by using fluorescein isothiocyanate-labelled bacteria) were determined for Lactobacillus casei, L. acidophilus, L. fermentum, Bifidobacterium bifidum, B. animalis and Enterococcus faecalis. We also determined the number of immunoglobulin (Ig)A+, tumour necrosis factor (TNF)alpha+, interleukin (IL)-6+ and IL-10+ cells after oral administration of the above bacteria to BALB/c mice. All strains assessed were found to interact with the sites of induction of the immune response in the gut. No correlation with hydrophobicity was observed. When some strains at certain doses were administered to mice, bacterial translocation to liver was observed. The oral administration of indigenous (104 cells day(-1)) and exogenous (107 cells day(-1)) bifidobacteria and lactobacilli for 5 consecutive days activated the systemic and intestinal mucosal immune response in a strain-specific way, independently whether the strain was indigenous or exogenous in relation to the host. The differences in the immunopotentiating capacity of the various strains might be related to the differences in their cell wall protein profiles.

CONCLUSIONS

Indigenous bacteria activated the mucosal immune response at a dose significantly smaller than the one required for probiotic exogenous bacteria. However, probiotic exogenous bacteria can be used at high concentrations in fermented dairy products with a great impact on the immune system, favouring its immunomodulation.

SIGNIFICANCE AND IMPACT OF THE STUDY

The immunomodulation capacity of probiotic bacteria is strain specific and independent of the specificity of the host. The ability of certain strains to down-regulate the production and release of IL-6 by IL-10 may have potential implications in their use in cases in which cytokine deregulation or excessive production at the mucosal level can be the cause of tissue damage.

Effects of intestinal microflora and the environment on the development of asthma and allergy

The aim of previous research into the causes of allergic diseases, including asthma was mostly to identify potential risk factors in the environment. No major risk factors have been identified, however. Over the past 10 years, focus has, therefore, more been directed towards protective factors that could enhance the development of tolerance to allergens which were previously encountered early in life, but are now lost in modern affluent societies. In particular, the role of childhood infections has been discussed, but so far these studies have not been conclusive. Recent epidemiological studies and experimental research suggest that the microbial environment and exposure to microbial products in infancy modifies immune responses and enhances the development of tolerance to ubiquitous allergens. The intestinal microflora may play a particular role in this respect, as it is the major external driving force in the maturation of the immune system after birth, and animal experiments have shown it to be a prerequisite for normal development of oral tolerance. Recent studies have shown differences in the composition of the microflora between healthy and allergic infants in countries with a high and low prevalence of allergies and between healthy and allergic infants within such countries. These differences are apparent within the first week of life and thus precede clinical symptoms. The use of live microorganisms that might be beneficial to health has a long tradition and the safety is well documented. Very recently, several prospective intervention studies, modifying the gut flora from birth have yielded encouraging results and may suggest a new mode of primary prevention of allergy in the future.

Treatment and prevention of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common serious, acquired gastrointestinal disorder in the newborn infant. Although many variables are associated with development of NEC, only prematurity has been consistently identified in case-controlled studies. Traditionally, the diving seal reflex has been invoked as the mechanism responsible for ischaemic injury and necrosis. Intestinal ischaemia is likely to be the final common pathway in NEC; however, it is due to the release of vasoconstricting substances, such as platelet activating factor, rather than perinatal asphyxia. Bacteria and/or bacterial toxins are likely to have a key role in the pathogenesis of NEC by fostering production of inflammatory mediators. The role of feeding practices in the pathogenesis of NEC remains controversial. Treatment of infants with NEC generally includes a regimen of bowel rest, gastric decompression, systemic antibiotics and parenteral nutrition. Infants with perforation are generally operated upon; however, there has been recent interest in primary peritoneal drainage as an alternative. Prevention of NEC still remains elusive. Avoidance of preterm birth, use of antenatal steroids and breast-milk feeding are practices that offer the greatest potential benefits. Use of any other strategy should await further trials.