口腔醫學工程留學essay：口腔疾病研究

Oral disease is the most common and costly forms of infections in humans. Only a few studies have been conducted in probiotics for oral health compared with gastrointestinal tract in the past few years. Oral probiotics are likely to have the same mechanisms with the probiotics of gastrointestinal tract, when considering the fact that mouth is first organ consisting of gastrointestinal tract. This review aims to describe current knowledge with respect to probiotic bacteriotheraphy and its safety in the aspect of oral and dental health. Furthermore, the possibility of Kimchi, Korean fermented food, as new reservoir for the purpose of finding probiotic candidates will be discussed in this review paper.
 
Introduction
 
Oral disease is the most common and costly forms of infections in humans. Dental caries and periodontal disease reach to almost 95% in general public. There has been limitation on capacity to control the actual infection, in spite of contribution of fluoride and other preventive method to dramatic decline in oral disease [28, 30, 31].
 
Probiotics have been extensively studied in the gastrointestinal tract. However, probiotics have been studied for promoting oral health as well in the past few years, which is the topic of present review. Highly possibly, it is likely that putative probiotic mechanisms are the same in the mouth with their mode of action in the gastroinstestinal tract, when considering the fact that mouth is first organ consisting of gastrointestinal tract [2].
 
The concept of the microbial ecological change as a mechanism for oral disease provides radical method for prevention of dental caries through probiotic bacteriotheraphy. Bacteriotheraphy using probiotics can be considered alternative and promising way to get rid of pathogenic members of the microflora. Combat of harmless bacteria with oral pathogens leads to replace resident pathogenic micro biota [3]. However, data is still sparse on the probiotic action in oral cavity. Further studies are needed on the putative probiotic mechanisms of action and their possible effects on oral biofilms.
 
The safety needs to be investigated thoroughly in administration of probiotics for promoting oral health, even though the cases of infection due to probiotics such as bifidobacteria andlactobacillus are extremely rare [4]. The needs for further studies on safety becomes evident when considering that the increased consumption of probiotic products inevitably results in increased concentration of these microbial inhabitants in the host body.
 
For the purpose of finding probiotic candidates, Kimchi, Korean fermented food might be considered as new reservoir of probiotics. Both substrates and temperature fermentation of Kimchi are different from the dairy fermented products and other fermented vegetable foods; as a result, the microbial community of Kimchi is quite different from other fermented foods [10]. In spite of its well known health booting functions, only a few studies have been conducted for probiotics regarding promoting oral health. Weissella cibaria is a good example of oral probiotics to inhabit in Kimchi when considering its inhibitory ability in the formation of S. mutans biofilm and its high ecological pH (above pH 5.5) [12].#p#分頁標題#e#
 
Present review aims at summarizing the literature published up to now with respect to probiotic bacteriotheraphy and its safety in the aspect of oral and dental health. Furthermore, the possibility of Kimchi as new reservoir for the purpose of finding probiotic candidates will be discussed in this review paper.
 
New method for dental prevention: Bacteriotheraphy
 
The causes of change in oral environment, such as illness, diet, or medications, interferes the balance from homeostasis and results in susceptibility to endogenous or exogenous infections. The ecosystem of resident oral micro biota consists of diverse species which need differentiated conditions; that is, nutritional (saccharolytic, proteolytic, secondary feeders), atmospheric (aerobic, anaerobic, facultative, micro-aerophilic, capnophilic) and physico-chemical (pH, co-factors) requirements [29]. The environmental changes mentioned above may lead to dental disease. If there disturbances occur in local environment, potential pathogens acquire a competitive advantage under their favorable conditions, which subsequently disturbs homeostasis in balance and it may lead to dental disease [3].
 
The insight of the microbial ecological change as a mechanism for oral disease provides radical method for prevention of dental disease by probiotic bacteriotheraphy [3]. Bacteriotheraphy using probiotics can be considered alternative and promising way to get rid of pathogenic members of the microflora. Combat of harmless bacteria with oral pathogens leads to replace resident pathogenic micro biota [3].
 
Mechanisms of oral probiotic action
 
The expected roles of oral probiotics are inferred thoroughly from results on gastrointestinal research. The application of probiotics for oral use needs further studies. In spite of limited studies of probitics for oral use, probiotics of gastrointestinal tract may have least the same roles in the eco physiology of oral micro biota, considering the fact that mouth is first organ which consists of gastrointestinal tract [2].
 
The oral probiotics may have functions in the microbial ecosystem of oral biofilms, as well as in the development of formation of dental plaque. There have been a few anticipated mechanisms for oral probiotic roles.
 
Adhesion of bacteria to mucous is initial step in pathogenesis and its binding leads to the colonization. The one of the probiotic functions lies in competition with pathogenic microorganisms for nutritional substrates and binding sites. The combat, using harmless bacteria, can replace pathogen and it may achieve the homeostasis of microbial ecosystem [3].
 
The some of probiotics produce antimicrobial substance, such as organic acids, hydrogen peroxide, carbon peroxide, diacetyl, bacteriocins, and adhesion inhibitors, and these components can inhibit growth of pathogens and binding to host’s epithelia cells [6, 9].#p#分頁標題#e#
 
Probiotics are known to enhance the colonization resistance to pathogenic bacteria by reinforcing the mucosal barrier in the gut [5]. Also, probiotics normalize an increased permeability of the biofilm. Probiotics have capacity to activate and control the immune system [44]; also, they can use immune exclusion, immune elimination, and immune regulation to enhance the gut defense [8].
 
To summarize with probiotics’ mechanisms, their roles of action include 1) competition with potential pathogens for binding sites and nutritional substrates and 2) production of antimicrobial substrates, and 3) local and systemic immunomodulation. Figure 1 illustrates the hypothetical mechanisms of probiotics in oral disease.
 
Probiotic bacteria for oral application
 
There are a numerous miroorganisms classified as probiotics and most of probiotics belong to the genera Lactobacillus and Bifidobacterium [1]. The studies regarding probiotics focus intensively on L. acidophilus, L. casei, L. reuteri and Bifidobacterium bifidum [3]. For oral application, L. rhamnosous GG and L. reuteri have been reported to reduce counts of S. mutans, thereby both may play the important role, as oral probiotics, in careis prophylaxis [15, 23, 25]. Recently, L. rhamnosous GG is found to reduce oral Candida counts as well, and this finding suggests alternative approach to eliminate oral yeast [19]. 
 
Clinical studies
 
Only a few researches have been conducted to assess the roles and effects of probiotics for promoting oral and dental health. In Helsinki, Finland, it was found that administration of L. rhamnosous GG to children reduced their dental caries and initial caries process. 594 children were offered probiotic milk and normal milk with meals, and which was practiced for 5 days per week during 7 months. The results of caries risk, calculated by clinical and microbiological data relevant to S.mutans level of dental plaque and saliva, showed lower counts of S.mutans and less dental caries [7].
 
Another study was conducted in Finland again, and which reported that an inhibitory effect of L. rhamnosous GG and bifidobacteria on S. mutans and yeast are shown in young adults who consumed cheese containning a combination of L. rhamnosous GG and bifidobacteria by short term intervention. These subjects consisted of 74 people and 18-35 year old, and it was double-blinded, randomized, placebo-controlled study. While the significant reduction of S. mutans counts was observed in the intervention group during the post treatment period, any significant difference between the intervention group and control group regarding S. mutanslevel [45].
 
Recently, one study was carried out with application of Weissella cibaria belonging to new genus for oral probiotics in South Korea. The authors demonstrated that two W. cibaria isolates from human saliva have inhibitory activities on the formation of biofilm, both in vitro and in vivo.72 healthy subjects between the ages of 20 and 30 were volunteered to participate into this study. Plaque scoring was measured based on the debris index of the simplified oral hygiene index (OHI-S).In the study, to determine the effects of W. cibaria isolates on biofilm formation in human adult, the plaque scores before and after mouth rinsing with suspensions of W. cibariawere assessed. The result showed the significant reduction in the plaque scores of the adults by application of CMS1. This study attempted the first trial to demonstrate a strain in genusWeissella may be used as a probiotic for oral health. Also, W. cibaria has not, up to date, been reported to have association with any evidence of pathogenicity [12].#p#分頁標題#e#
 
Study about the effect of Lactobacillus reuteri on chronic periodontitis was conducted in Malmö, Sweden, and which showed that Lactobacillus reuteri was efficacious in reducing gingivitis and decreasing gum bleeding. It was practiced for 2 weeks, and was conducted by randomized, placebo-controlled, double blind study. 59 patients with gingivitis were received one of two different Lactobacillus reuteri formulations (LR-1 or LR-2). Among 59 patients, 20 patients were randomly chosen to LR-1, 21 to LR-2 and 18 to placebo. Significant reductions in gingival index were observed in all 3 groups. Significant reductions in plaque index were observed in LR-1 and in LR-2 from the 0 day to 14th day, but not in the placebo group. At 14th day, colonization of Lactobacillus reuteri was observed with 65% patients in LR-1 and 95% patients in the LR-2 group [21].
 
Safety aspect of probiotics: Lactobacilli and Bifidobacteria
 
During last several years, the safety issue has become special concern because of the increased probiotic use as supplementation in the food products. For the proper use of probiotics, the following criteria should be satisfied; 1) putative probiotics should not pathogenic. 2) probiotic candidate should not have any growth factors for pathogenic bacteria. 3) probiotic candidates should not contain easily transferable antibiotic resistance genes to other genera [18].
 
The increased consumption of probiotic products unavoidably results in increased concentration of these microbial inhabitants in the host body [1]. The cases of infection with bifidobacteria and lactobacillus are tremendously rare and there have been approximately 180 reported cases during last 30 years [58]. Most of the rare cases of infection due to lactobacilli occur in the patients with immunocompromised or underlying diseases such as diabetes, cardiovascular disease, gastrointestinal disorder, malignancies, or organ transplant patients [4].
 
However, there has not been any reported evidence that consumption of either lactobacilli orbifidobacteria exert increased risk of opportunistic infections among immunocompromised patients who are more vulnerable to pathogenic bacterial infection or have more risk of opportunistic infections. There have been several clinical studies conducted to assess the safety of probiotics in patients with HIV infection and these studies support the safety of consumption of probiotics in these immunocompromised patients [49, 50].
 
The absence of acquired antibiotic resistance is another important criterion in safety use of probiotics. Some of probiotics are closely related to opportunistic pathogens and these probiotics may transfer their antimicrobial resistance genes to potential pathogens [22]. The antibiotic resistance (nonsusceptibility) is regarded to have no risk when it does not render probiotics untreatable infections in rare cases or when any transferal of antimicrobial resistance genes do not occur to the potential pathogens.#p#分頁標題#e#
 
Numerous strains of lactobacilli have vancomycin resistance. The vancomycin resistance genes of lactobacillus are thought to be stably located in the chromosome so that their transferals are not likely to happen between microorganisms [51].
 
For the purpose of preventing antibiotic resistance, further studies need to be done when considering that the number of species which develop antibiotic resistance has been increased and it is now growing concern [1].
 
Appropriate vehicles for administration of probiotics
 
Probiotics should be able to adhere to dental tissue to incorporate biofilm and compete with cariogenic bacteria [32]. In order to achieve the goal, the installation of probiotics in oral tissue is primarily done. However, the interaction time between probiotics and plaque is important factor because the activity of probiotics is more increased if the probiotics are installed in the dental plaque for longer duration of contact time [3]. Furthermore, in order for prevention or treatment of dental disease, specially designed formulas, device, or carriers delivering probiotics slowly into oral environment may be considered [1]. In this point of view, appropriate vehicles for oral probiotics are discussed here.
 
Dental research result showed that the consumption of the probiotic yoghurt has nothing to do with installation of lactobacilli in the oral environment. Up to date, it is uncertain about the ability of probiotics to colonize in the oral tissue. Any residual antibacterial activity after cession of consumption was not observed whereas regular consumption of yoghurt containing probiotics can reduce the number of salivary lactobacilli and S. mutans.[33, 34].
 
Lactic acid bacteria (LAB) have been thought as opportunistic pathogens due to their production of ferment sugars and acid. Of these bacteria, both lactobacilli and mutans streptococci have been considered detrimental to oral health [47]. In spite of its contribution to low pH environment, the good buffering capacity of milk exerts appropriate pH level, when LAB are administrated in means of milk [48]. Moreover, calcium and other substances may play important role in protection of tooth surface and inhibition of adherence of harmful micro-flora in the mouth.
 
In a recent study, Lactobacilli were orally administrated both in capsules and liquid form to determine the role of direct contact with oral cavity and examine whether administrated probiotics exerts reduction cariogenic S. mutans level. In that study, administration oflactobacilli in liquid and in capsule form contributes to increase the counts of lactobacilli while any significant difference was not observed in the S. mutans counts [24].
 
It is worthy to be noted that reduced demineralization of teeth can be due to high concentration of Ca rather than putative probiotics, lactobcilli, in the case of consumption of the dairy products containing both high Ca and putative probiotics [3].#p#分頁標題#e#
 
Cheese might be an ideal carrier for delivery of probiotics to oral to promote dental health [2]. Cheese is reported to exert beneficial effect on oral health in the way that its administration prevents demineralization and promotes remineralization of enamel and reduce the salivary S. mutans counts in significant level [46].
 
Chewing gums containing L. reuteri Prodentis is a way of prevention for dental caries. Practice of chewing gums twice a day is known to remarkably reduce S. mutans counts in the oral cavity. Moreover, a straw containing probiotics is another effective way of non-dairy delivery, and its delivery method showed significant level of reduction in salivary S. mutans in placebo-control study [54].
 
Table 2 illustrates the variety means of carrier facilitated up to date for the delivery of probiotics to dental tissue [1].
 
Weissella cibaria: new potential candidate for oral probioics
 
Weissella species belongs to Lactic acid bacteria, and the genus Weissella has recently been separated from the genus Lactobacillus due to 16S rRNA phylogenetic analyses. (fig 2) [39].Weissella cibaria is Gram-positive and heterofermentative, non-spore-forming, non-motile bacillus which is isolated from fermented foods, including Kimchi. This species is known to produce dextran from sucrose [38]. In spite of characterization of this species, its effect on dental health has been studied very recently.
 
Lactic acid bacteria (LAB) inhabit mainly in gastrointestinal tract (GI tract) and some of them have been reported to exert beneficial health in human due to their protective roles against a number of pathogenic infections [36,37]. Nevertheless, the most of lactic acid bacteria are known to play the opportunistic role in the pathogenesis of dental caries because their production of lactic acid causes demineralization of the enamel of tooth and extracellular polysaccharides can cause contributes to elevate their adherence to teeth [35].
 
Recently, Chung et al 2006 demonstrated the inhibitory ability of Weissella cibaria in the formation of S. mutans biofilm, both in vitro and in vivo. In this study, two W. cibaria strains, CMS1 and CMS2, were isolated and selected based on their inhibitory effect on the formation ofS. mutans biofilm. As a result, two W. cibaria isolates are showed to remarkably suppress the proliferation of S. mutans.W. cibaria isolates reduced the proliferation of S. mutans by 22 and 44-fold in the groups administrated with two W. cibaria isolates compared to the control group (table 3). However, any inhibitory activity of S. mutans on growth of W. cibaria was not observed. The culture supernatant (CS) of two W. cibaria isolates did not show any apparent inhibitory effects on the S. mutans proliferation (table 3), whereas the CS of W. cibaria stains reduced biofilm formation by S. mutans (fig. 2). Therefore, the authors concluded that the inhibitory effects associate with W. cibaria CMS1 and CMS3 may be resulted primarily from the substance with the capacity to directly suppress the formation of S. mutans biofilm rather than the inhibition of S. mutans biofilm by antibacterial materials [12].#p#分頁標題#e#
 
Adherence to the oral tissue and surface of teeth is an important prerequisite for the colonization of probiotics, providing a competitive advantage in this ecosystem of micro biota [57]. Previous studies showed that the aggregation ability has strong association with the cell adherence properties. Kang et al (2005) demonstrate co-aggregation ability of W. cibaria withFusobacteruum nucleatum as well as the adherence property of W. cibaria to epithelial cells [14]. Fusobacterium nucleatum, as a bridge-organism, enables the colonization of other bacteria by co-aggregation [55]. There have been many studies showing that the co-aggregation abilities of lactobacilli species prevents colonization of pathogenic bacteria by formation of a barrier of lactobacilli [27, 56], and growth of pathogens is also inhibited by various substances from Lactobacillus species [14].
 
Kang et al (2005) characterized the W. cibaria components mediating the adherence to F. nucleatum by various pretreatment of the bacterial cells. Pronase-treated F. nucleatum did not inhibit the coaggregation; however, in case of W. cibaria, it led to additional reduction in co-aggregation between both species, thus suggesting the proteinaceus nature of the interspecies interaction. Heat-resistant components firmly attached to the cell surface of W. cibaria were responsible for their co-aggregation with F. nucleatum. The results of this study also showed the important role of the S-layer proteins of W. cibaria in cell wall adherence to the epithelial cells. The adhesiveness of W. cibaria to the epithelial cells was investigated. All three W. cibariaisolates were strongly attached to both KB cells and HeLa cells, but the numbers of W. cibariaadhered to epithelial cells remarkably reduce after the LiCl treatment (Fig. 4). These results implied that the surface layer proteins of the W. cibaria strains are strongly associated with the adhesion process [14].
 
It is remarkable that ecological pH of Weissella cibaria is high (above pH 5.5) in no conjunction with lactobacilli, thereby the possibility of opportunistic role in development of dental caries due to production of lactic acid may be ruled out [12]. These characteristics of the W. cibariastrongly suggest their possibility of probiotic candidate appropriate for oral cavity.
 
Kimchi: New reservoir of probiotics
 
Kimchi is well known traditional Korean food fermented from variety of vegetables. It is the product of lactic acid fermentation of Chinese cabbage stuffed with various different spices, including hot pepper, garlic, and ginger [11].
 
The microbial community of Kimchi is quite different from other fermented vegetable foods when considering that Kimchi fermentation is governed by the distinct population dynamics of subsets of Weissella, Leuconostoc, Lactobacillus species [10]. In general, lactic acid bacteria play the important role in fermented vegetable foods [11]. Lactobacilli play the important role in the fermentation process of Mexican pozol, acid beverage produced by fermentation of nixtamal [42, 43]. Lb. plantaum and Lb. manihotivonrans are predominant species in fermentation process of cassava sour starch [41]. Lc. mesenterteroides, P. pentosaceus, Lb. brevis and Lb. plantrarum play the important role in fermentation of saukeraut [40].#p#分頁標題#e#
 
In case of Kimchi fermentation, Weissella cibaria as well as two Leuconostoc species, specificallyLeuconostoc citreum and Leuconostoc gasicominatum are predominant species during early stages (pH>4.6), and then microbial diversity reduced remarkably, namely Weissella koreensisbecomes predominant species in the later stages. (15℃ program: Temperature decreased to -1 ℃ (at day 3) from 15 ℃ over 24 h) [10]. Weissella koreensis, a psychrophilic bacterium, can be dominating species because of its ability to grow in stressful conditions, e.g. -1℃ and pH<4.3, under which majority of other existing species are deprived of the capacity to grow. (fig 5) Table 4 presents the composition of lactic acid bacterial species during kimchi fermentations at 15℃ program [10].
 
The fermentation temperature, one of the crucial factors to determine microbial populations, in Kimchi is different from the dairy products other fermented vegetable foods, when considering the fact that proper fermentation temperature for Kimchi is 15℃ rather than 37~ 45 ℃ where dairy products are properly fermented [10].
 
Conclusion
 
Oral disease is the most common and costly forms of infections in humans [3]. There has been limitation on capacity to control the actual infection, in spite of contribution of fluoride and other preventive method to dramatic decline in oral disease. Bacteriotheraphy using probiotics may provide alternative and promising way to get rid of pathogenic member of bacteria, and which results in balanced homeostasis in ecosystem of micro biota [3].
 
Most possibly, it is likely that putative probiotic mechanisms are the same in the mouth with their mode of action in the gastrointestinal tract, when considering the fact that mouth is first organ consisting of gastrointestinal tract [2]. Up to date, data is still sparse on the probiotic action in oral cavity. Further studies are needed on the putative probiotic mechanisms of action and their possible effects on oral biofilms.
 
The safety of probiotics needs further investigation, even though the cases of infection due to probiotics such as bifidobacteria and lactobacillus are extremely rare [52, 53]. The needs for further studies on safety becomes evident when considering that the increased consumption of probiotic products inevitably results in increased concentration of these microbial inhabitants in the host body [1].
 
Lactic acid bacteria (LAB) inhabit mainly in gastrointestinal tract (GI tract) and some of them have been reported to exert beneficial health in human due to their protective roles against a number of pathogenic infections [36, 37]. Nevertheless, the most of lactic acid bacteria are known to play the opportunistic role in the pathogenesis of dental caries because their production of lactic acid causes demineralization of the enamel of tooth and extracellular polysaccharides contributes to elevate their adherence to teeth [35].#p#分頁標題#e#
 
For the purpose of finding probiotic candidates, Kimchi, Korean fermented food might be considered as new reservoir of probiotics. Unlike dairy fermented product, Kimchi is the product of lactic acid fermentation of Chinese cabbage with variety of vegetables. The fermentation temperature, one of the crucial determinants to microbial populations, is 15℃ rather than 37~ 45℃. As result, the microbial community of Kimchi is quite different from fermented dairy foods as well as other fermented vegetable foods when considering the fact that Kimchi fermentation is governed by the distinct population dynamics of subsets of Weissella, Leuconostoc, Lactobacillus species [10].
 
Weissella cibaria is a good example of oral probiotics to inhabit in Kimchi. The inhibitory ability of Weissella cibaria was shown in the formation of S. mutans biofilm both in vitro and in vivo [12]. The adhesiveness of W. cibaria, an important prerequisite for the colonization of probiotics [57], to the epithelial cells was demonstrated and it may provide a competitive advantage in this ecosystem of micro biota [11]. Futhermore, ecological pH of Weissella cibariais high (above pH 5.5) in no conjunction with lactobacilli; therefore, the possibility of opportunistic role in development of dental caries due to production of lactic acid may be excluded [12]. These characteristics of the W. cibaria strongly suggest their possibility of probiotic candidate appropriate for oral cavity.
 
The possibility of Kimchi as new reservoir is worth to be considered for the purpose of finding probiotic candidates that may have new characteristics.
 
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