Probiotics – A New Paradigm in Oral Health:
Lactobacillius Reuteri
©Juliette Reeves 2010 

The most commonly used species of lactic acid bacteria in probiotic preparations include Lactobacillus, Bifidobacterium, Enterococcus and Streptococcus species. Organisms other than lactic acid bacteria, which are currently being used in probiotic preparations, include Bacillus yeasts (e.g. Saccharomyces boulardii) and filamentous fungi (e.g. Aspergillus oryzae).  

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Lactobacillus  

 

The Lactobacillus genus has over 125 species and are a major part of the lactic acid bacteria group, named as such because most of the strains convert lactose into lactic acid. Their primary mode of action involves lowering gut pH thereby limiting the proliferation of pathogenic bacteria, competing for pathogen binding and receptor sites, and modulation of the local and systemic inflammatory immune response (1,2). 

 

The GI tract serves as an interface between the gut and immune system, with the intestinal lining functioning as a barrier, decreasing the passage of bacteria from the gut into the bloodstream. The background thinking is that harmless microorganisms, such as species of lactobacilli and bifidobacteria, can preferentially occupy a space or a biofilm that otherwise would be colonized by a pathogen.  When inflammed, the GI tract becomes permeable and serves as a link between inflammatory diseases of the GI tract and extra-inflammatory disorders such as arthritis. Modulation or down regulation of the immune system and subsequent reduction in GI tract permeability can result from consuming probiotics (3,4)

 

Oral Health Benefits

 

Probiotics have been extensively studied for their health-promoting effects. The main field of research has been the gastrointestinal tract. However, in the past decade probiotics have also been investigated in the oral health perspective. Due to  their mechanisms of bacterial adhesion, competitive colonization of bioflim, and possible effects on immunomodulation,  probiotic treatment of oral diseases such as dental caries and periodontal disease is under investigation.

 

Lactobacilli in particular  have gained interest in dental research over the last decade. This is due to their ability to inhibit a wide range of bacterial species including oral Streptococci (5), Aggregatibacter actinomycetemcomitans, and Porphyromonas gingivalis (6).

 

Caries

 

Dairy microorganisms have been tested in vitro for their ability to become a part of the supragingival dental biofilm and for their ability to compete with cariogenic microorganisms, and promising results have been obtained for some strains (7).In addition, milk fermented with Lactobacillus GG was recently shown to reduce the adherence of Streptococcus mutans to saliva-coated hydroxyapatite beads. The preventive effect of Lactobacillus GG in milk has been evaluated in a clinical study of caries involving nearly 600 pre-school children over a period of 7 months (9). Statistically significant differences were found in the development of caries between children treated with the probiotic strain compared with those given a placebo milk product. A further separate study also demonstrated decreased counts of yeast and Streptococcus mutans in saliva (10).  

 

Periodontal Disease

 

More recently a number of probiotics have been studied with reference to the prevention and treatment of periodontal disease. Koll et al (6) studied 10 species of oral lactobacilli and reported suppression in the growth of Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis (AA, PG) and Streptococcus mutans.  

 

A further study also identified Lactobacillus brevis as having anti-inflammatory effects on periodontal disease (11). After exposure to L.brevis containing lozenges, salivary concentration of pro inflammatory markers was markedly reduced. This suggests a new innovative approach to the treatment of chronic periodontal disease.  

 

Halitosis

 

Other areas under investigation include the use of probiotics in the treatment of halitosis and reduction of volatile sulphur compounds. The primary treatment for oral malodour is the reduction of bacterial populations, especially those present on the tongue, by use of a variety of antimicrobial agents or mechanical devices. However, shortly after treatment the problematic bacteria can quickly repopulate the tongue and the malodour returns.Encouraging results have been shown using Streptococcus salivarius (12,13) and Weissella cibaria (14) respectively. The outcome of these preliminary studies indicates that the replacement of bacteria implicated in halitosis by colonization with competitive bacteria such as S. salivarius may provide an effective strategy to reduce the severity of halitosis. It may be that probiotic bacterial strains originally sourced from the indigenous oral microbiotas of healthy humans may have potential application as adjuncts for the prevention and treatment of halitosis.  

 

Oral Colonization

 

Colonization of the oral cavity however is mixed, with some strains colonizing more effectively than others. Lactobacillus GG was found to colonize the oral cavity in one week, with lactobacilli present for up to two weeks after discontinuation (15).  No installation was found after one week with L. acidophilus, L.casei or B. bifidum (16).  The most effective colonization appears to be from L. reuteri with 95% colonization after 14 days.  For a probiotic to be effective they should  adhere to dental tissues as a part of the biofilm (or plaque) and compete with the growth of cariogenic bacteria or periodontal pathogens (8).  None of the studies were able to demonstrate permanent colonization. This could be due to the relatively short exposure time. Daily intake, therefore, may be required for continuance of action. 

 

Lacobacillus reuteri  

 

Gerhard Reuter first isolated L. reuteri from human faecal and intestinal samples in the 1960s, and this work was later repeated by other researchers (18). L. reuteri is now well-established as one of the most ubiquitous members of the lactic acid producing bacteria (19). In the late 1980s Dobrogosz and Casas et al (20), discovered that L. reuteri produced a novel broad-spectrum antibiotic substance via the organism's fermentation of glycerol. They named this substance "reuterin", also after Gerhard Reuter.  

 

Reuterin, it was found, inhibits the growth of some harmful Gram-negative and Gram-positive bacteria, along with yeasts, fungi, and protozoa (21). Researchers found that L. reuteri can indeed secrete sufficient amounts of reuterin to cause the desired anti-microbial effects. Furthermore, since about 4-5 times the amount of reuterin is needed to kill bifido("good") gut bacteria (i.e. L. reuteri and other Lactobacillus species) as bacteroides ("bad") bacteria, this would allow L. reuteri to remove pathogenic species while keeping normal gut flora intact.   Oral intake of L. reuteri has been shown to effectively colonize the intestine of healthy people; colonization begins rapidly within days of ingestion, although the amount of the bacterium present in the body returns to low levels within several months after intake is stopped (23). Once present in the body, L. reuteri benefits its host in a variety of ways, in general health, immunomodulation and disease protection (22).  

 

L.reuteri and Oral Health

 

Due to the versatility of L.reuteri,  increasing attention is being given to this probiotic with reference to oral colonization and prevention of both caries and periodontal disease.  

 

In a number of recent studies L. reuteri has been shown to colonize the oral cavity and significantly reduce salivary concentrations of Streptococcus mutans(24)and inhibit a number of pathogens associated with periodontal disease, most notably AA and PG(25).  

 

Nikawa et al (24) found that the consumption of yogurt containing L. reuteri resulted in a significant growth inhibition of Streptococcus mutans, which was in contrast with other probiotic lactobacilli strains. In the study mentioned above, dairy products such as milk, yogurt, and cheese were selected as delivery vehicles for the selected bacteria. Caglare et al (26) investigated the effect of the probiotic bacterium L. reuteri on the levels of salivary mutans streptococci and lactobacilli in young adults when ingested via two different non-dairy delivery systems (straws and tablets). A significant reduction of the mutans streptococci levels was recorded after ingestion of the probiotic bacteria via both straw and tablets, which was in contrast to the placebo controls. Recently, new research has evaluated the effect of probiotic chewing gums containing two strains of L. reuteri on the levels of salivary mutans streptococci and lactobacilli in young adults (27) . Daily chewing of the gum containing probiotic bacteria reduced the levels of salivary mutans streptococci significantly.  

 

Probiotics can also be delivered by lozenges, powder, gelatine, straw, or tablets. It has been suggested that slowly melting tablets would allow a more thorough contact between the probiotic and oral environment, however, the best vehicle for probiotic delivery has yet to be identified (28).    

 

L.reuteri and Periodontal Disease.

 

More recently studies have shown the ability of L. reuteri  to inhibit the proliferation of the main periodontal pathogens including AA and PG (25).  Krasse et al (17) have also been able to demonstrate the ability of L. reuteri to colonize the oral cavity within two weeks of exposure. In addition a reduction in both gingivitis and plaque levels was observed. In this study two strains of L reuteri were trialed, (L.reuteri ATCC 55730/ L. reuteri ATCC PTA 5289) both strains were shown to have sucessfully colonized the oral cavity. A 59% reduction in gingivitis levels was recorded and a 42% reduction in plaque levels after 4weeks of treatment.        

 

Probiotics and Immune Function

 

Probiotics can enhance both specific and nonspecific immune responses. These effects are believed to be mediated through activating macrophages, increasing levels of cytokines, increasing natural killer cell activity and/or increasing levels of immunoglobulins (29,30). Probiotics have also been found to upregulate anti-inflammatory cytokines.(31) This is seen both as an immunostimulatory effect in healthy subjects and as a down regulation effect of immunoinflammatory responses in hypersensitive patients. Moreover, probiotics might prevent infection because they compete with pathogenic viruses or bacteria for binding sites on epithelial cells (32,33).  Probiotics might also inhibit the growth of pathogenic bacteria by producing bacteriocins such as reuterin.  

 

The ability of a probiotic to influence immune function, colonize the gut ,oral cavity and plaque biofilm, is only as good as it’s adhesion factor.  The ability of these microorganisms to adhere to mucosal surfaces is potentially a major distinguishing feature for selection of bacteria as probiotic strains. Close interaction with host tissues  provide probiotics with a distinct advantage when establishing residence in the gastrointestinal tract or interacting with cells of the mucosa. Not all probiotics have the same adhesion factors, however. L.reuteri has been shown to have superior adhesion and ability to colonize the entire digestive tract ( including the oral cavity) when compared to other lactobacilli (34).    

 

New emerging evidence suggests that L. reuteri may be able to modulate the immune system in the gastrointestinal tract (35,36).  Valeur et al (37) observed a significant increase in CD4+ T cells and B lymphocytes. Furthermore Mao et al (38) found that L.reuteri  could increase sIgA levels in addition to CD4+ T cells. It is suggested that the stimulation of T-helper cells by L. reuteri may be a central mechanism of symbiosis for improving the health of the host gut and a key mechanism of action for this probiotic. In conclusion, Valeur showed colonization of the human gastrointestinal tract by L. reuteri ATCC 55730 delivered in a tablet formulation and consequent modulation of local immune cell populations. It seems likely that this response to exogenous L. reuteri may be involved in maintaining gastrointestinal well-being and defense against bacterial pathogens.  

 

L.reuteri prodentis

 

In a number of studies two strains of L reuteri were trialed, (L.reuteri ATCC 55730/ L. reuteri ATCC PTA 5289) both strains are shown to have sucessfully colonized the oral cavity. A multistrain probiotic  L.reuteri prodentis has been developed as a combination of two complementary stains of L.reuteri,(L.reuteri ATCC 55730 and L. reuteri ATCC PTA 5289).While a monostrain has to overcome barriers presented by the host and its endogenous microflora, multistrain probiotics have a greater divergency, and the enhanced chance of survival of at least one strain (39).  

 

The safety of consuming L reuteri on a daily basis has been well established through a number of studies on diverse populations, including adults (40), children (41), newborn infants (42), premature infants (43) and immunocompromised adults (44).     

 

Conclusion  

 

The oral administration of probiotic therapies may be beneficial in a multitude of disorders both inside and outside the GI tract. Their application in the treatment and prevention of oral disease appears to be both local (colonization of plaque biofilm) and systemic (modulation of the immune system).   

 

The direct effects of probiotics in the GI tract are well documented and include upregulation of immunoglobulins such as IgA, downregulation of inflammatory cytokines, and enhancement of gut barrier function. New research evidence supports indirect, systemic effects of probiotics for a widely divergent set of disorders, including atopic disease, immune compromise and now it also appears to affect caries and chronic inflammatory periodontal disease.  

 

Unfortunately, the concentration of probiotics in food products varies  tremendously and there are currently no national standards of identity for levels of bacteria required in yogurt or other fermented products. Presented as L.reuteri prodentis, PerioBalance is able to provide a multistrain L.reuteri probiotic  dose with a consistent potency of 200 million active micro organisms. Taken as a slowly melting lozenge once a day after brushing and flossing, ensures  consistent exposure to L.reuteri on a daily basis.  

 

There is obviously considerable potential for the benefits of probiotics over a wide range of clinical conditions. As oral  health professionals we are  in an ideal position to guide the consumer towards appropriate uses of probiotics to deliver the desired beneficial oral health effects. 

 

 

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