Microbial protection and virulence in periodontal tissue as a function of polymicrobial communities: symbiosis and dysbiosis

This review discusses polymicrobial interactions with the host in both health and disease. As our ability to identify specific bacterial clonal types, with respect to their abundance and location in the oral biofilm, improves, we will learn more concerning their contribution to both oral health and disease. Recent studies examining host– bacteria interactions have revealed that commensal bacteria not only protect the host simply by niche occupation, but that bacterial interactions with host tissue can promote the development of proper tissue structure and function. These data indicate that our host‐associated polymicrobial communities, such as those found in the oral cavity, co‐evolved with us and have become an integral part of who we are. Understanding the microbial community factors that underpin the associations with host tissue that contribute to periodontal health may also reveal how dysbiotic periodontopathic oral communities disrupt normal periodontal tissue functions in disease. A disruption of the oral microbial community creates dysbiosis, either by overgrowth of specific or nonspecific microorganisms or by changes in the local host response where the community can now support a disease state. Dysbiosis provides the link between systemic changes (e.g. diabetes) and exogenous risk factors (e.g. smoking), and the dysbiotic community, and can drive the destruction of periodontal tissue. Many other risk factors associated with periodontal disease, such as stress, aging and genetics, are also likely to affect the microbial community, and more research is needed, utilizing sophisticated bacterial taxonomic techniques, to elucidate these effects on the microbiome and to develop strategies to target the dysbiotic mechanisms and improve periodontal health.     

Dental plaque biofilm in oral health and disease

Dental plaque is an archetypical biofilm composed of a complex microbial community. It is the aetiological agent for major dental diseases such as dental caries and periodontal disease. The clinical picture of these dental diseases is a net result of the cross-talk between the pathogenic dental plaque biofilm and the host tissue response. In the healthy state, both plaque biofilm and adjacent tissues maintain a delicate balance, establishing a harmonious relationship between the two. However, changes occur during the disease process that transform this 'healthy' dental plaque into a 'pathogenic' biofilm. Recent advances in molecular microbiology have improved the understanding of dental plaque biofilm and produced numerous clinical benefits. Therefore, it is imperative that clinicians keep abreast with these new developments in the field of dentistry. Better understanding of the molecular mechanisms behind dental diseases will facilitate the development of novel therapeutic strategies to establish a 'healthy dental plaque biofilm' by modulating both host and microbial factors. In this review, the present authors aim to summarise the current knowledge on dental plaque as a microbial biofilm and its properties in oral health and disease.     

Biofilms of the oral cavity. Formation,development and involvement in the onset of diseases related to bacterial plaque increase

Biofilm is defined as a community of bacteria intimately associated with each other and included within an exopolymer matrix: this biological unit exhibits its own properties, quite different in comparison with those showed by the single species in planktonic form. The oral cavity appears as an open ecosystem, with a dynamic balance between the entrance of microrganisms, colonisation modalities and host defences aimed to their removal: to avoid elimination, bacteria need to adhere to either hard dental surfaces or epithelial surfaces. The oral biofilm formation and development, and the inside selection of specific microrganisms have been correlated with the most common oral pathologies, such as dental caries, periodontal disease and peri-implantitis. Many of these bacteria are usual saprophytes of the oral environment, that, in particular situations, can overcome and express their virulence factors: to better understand the mechanisms of these pathologies it's necessary to know the complex interactions between all the bacterial species inside the biofilm and host tissues and responses. The present paper is a review of the most significant studies on the biofilm development modalities, their correlations with either health or illness of the oral cavity, the bacterial co-aggregation strategies and the biofilm response to antimicrobial agents.     

人体口腔微生物组群与牙菌斑生物膜

牙菌斑是由多种微生物组成的生物膜结构,口腔微生物之间的相互作用可以影响牙菌斑生物膜的性质、形成、毒力,以及微生物在生物膜结构中的定位和定植。生物膜内细菌之间存在的信号传导对生物膜的形成及其毒力具有影响。本文重点介绍人体口腔微生物组群与牙菌斑生物膜关系的最新研究进展。     

Effect of xylitol on salivary β‐glucosidase in humans

Dental biofilm – in which a diverse set of microorganisms are embedded in a complex polysaccharide matrix that adheres to oral components – is one of the most complex microbial communities in the human body. As biofilm formation is related to oral infections, such as caries and periodontal diseases, strategies for biofilm control are crucial for maintaining oral health. Xylitol, a synthetic sugar used as a sucrose substitute, has been shown to reduce biofilm formation. However, its precise mechanism of action on biofilm reduction has so far not been elucidated. Previous studies demonstrate that bacterial β‐glucosidase action is crucial for biofilm formation. Here, we investigated the correlation between salivary β‐glucosidase activity and dental plaque occurrence. We found a positive correlation between enzymatic activity and the presence of dental biofilm. We observed that xylitol inhibits β‐glucosidase in human saliva. Kinetic studies also confirmed that xylitol acts as a mixed type inhibitor of salivary β‐glucosidase. Based on our data, we suggest that xylitol impairs oral biofilm formation by the inhibition of bacterial β‐glucosidase, which is essential for biofilm formation in the oral cavity.     

Acute focal infections of dental origin

This article describes the most important pus‐producing acute oral infections (dental infections) that can spread extra‐orally. Most of these infections are spread by bacteria entering the bloodstream. However, dental infections have a number of other pathways for dissemination. By forming abscesses or phlegmon they can reach facial spaces that communicate with each other and then spread downwards to the mediastinum or upwards to the brain. In such cases dental infections can become, if not properly treated, life‐threatening. It seems that early diagnosis and treatment are imperative, and potentially infectious foci should be traced and eliminated. Dental hygiene and prophylaxis to prevent dental biofilm formation are important measures to reduce the risk of these calamities. The more compromised the host defense is, the more importance should be put on these measures. Although commensal bacteria are often involved in these infections, attention should also be paid to specific periodontal pathogens, and a proper microbial diagnosis, obtained using molecular methods plus bacterial sensitivity testing, can provide the patient with optimal care. Drainage of pus must be established where possible so that the optimal effect of antibiotics can be achieved. Penicillin is still the drug of first choice in settings where suspicion of methicillin‐resistant Staphylococcus aureus is low.     

Using DGGE profiling to develop a novel culture medium suitable for oral microbial communities

More than 700 bacterial species have been detected in the human oral cavity. They form highly organized microbial communities and are responsible for many oral infectious diseases, such as dental caries and periodontal disease. The prevention and treatment of these diseases require a comprehensive knowledge of oral microbial communities, which largely relies on culture-dependent methods to provide detailed phenotypic and physiological analysis of these communities. However, most of the currently available laboratory media can only selectively support the growth of a limited number of bacterial species within these communities, and fail to sustain the original oral microbial diversity. In this study, using denaturing gradient gel electrophoresis (DGGE) as an index to systematically survey and analyse the selectivity of commonly used laboratory media, we developed a new medium (SHI medium) by combining the ingredients of several selected media that can support different subpopulations within the original oral microbial community derived from pooled saliva. DGGE and 454 pyrosequencing analysis showed that SHI medium was capable of supporting a more diversified community with a microbial profile closer to that of the original oral microbiota. Furthermore, 454 pyrosequencing revealed that SHI medium supported the growth of many oral species that have not before been cultured. Crystal violet assay and the confocal laser scanning microscope analysis indicated that, compared with other media, SHI medium is able to support a more complex saliva-derived biofilm with higher biomass yield and more diverse species. This DGGE-guided method could also be used to develop novel media for other complex microbial communities.     

In silico search of inhibitors of Streptococcus mutans for the control of dental plaque

Biofilm is an extremely complex microbial community arranged in a matrix of polysaccharides and attached to a substrate. Its development is crucial in the pathophysiology of oral infections like dental caries, as well as in periodontal, pulp, and periapical diseases. Streptococcus mutans is one of the most effective microorganisms in lactic acid production of the dental biofilm. Identifying essential Streptococcus mutans proteins using bioinformatics methods helps to search for alternative therapies. To this end, the bacterial genomes of several Streptococcus mutans strains and representative strains of other cariogenic and non-cariogenic bacteria were analysed by identifying pathogenicity islands and alignments with other bacteria, and by detecting the exclusive genes of cariogenic species in comparison to the non-pathogenic ones. This study used tools for orthology prediction such as BLAST and OrthoMCL, as well as the server IslandViewer for the detection of pathogenicity islands. In addition, the potential interactome of Streptococcus mutans was rebuilt by comparing it to interologues of other species phylogenetically close to or associated with cariogenicity. This protocol yielded a final list of 20 proteins related to potentially virulent factors that can be used as therapeutic targets in future analyses. The EIIA and EIIC enzymatic subunits of the phosphotransferase system (PTS) were prioritized, as well as the pyruvate kinase enzyme, which are directly involved in the metabolism of carbohydrates and in obtaining the necessary energy for the microorganism’s survival. These results will guide a subsequent experimental trial to develop new, safe, and effective molecules in the treatment of dental caries.     

Peptide and non‐peptide mimetics as potential therapeutics targeting oral bacteria and oral biofilms

The development of the oral biofilm requires a complex series of interactions between host tissues and the colonizing bacteria as well as numerous interspecies interactions between the organisms themselves. Disruption of normal host–microbe homoeostasis in the oral cavity can lead to a dysbiotic microbial community that contributes to caries or periodontal disease. A variety of approaches have been pursued to develop novel potential therapeutics that are active against the oral biofilm and/or target specific oral bacteria. The structure and function of naturally occurring antimicrobial peptides from oral tissues and secretions as well as external sources such as frog skin secretions have been exploited to develop numerous peptide mimetics and small molecule peptidomimetics that show improved antimicrobial activity, increased stability and other desirable characteristics relative to the parent peptides. In addition, a rational and minimalist approach has been developed to design small artificial peptides with amphipathic α‐helical properties that exhibit potent antibacterial activity. Furthermore, with an increased understanding of the molecular mechanisms of beneficial and/or antagonistic interspecies interactions that contribute to the formation of the oral biofilm, new potential targets for therapeutic intervention have been identified and both peptide‐based and small molecule mimetics have been developed that target these key components. Many of these mimetics have shown promising results in in vitro and pre‐clinical testing and the initial clinical evaluation of several novel compounds has demonstrated their utility in humans.     

The road to ruin: the formation of disease‐associated oral biofilms

Oral Diseases (2010) 16 , 729–739 The colonization of oral surfaces by micro‐organisms occurs in a characteristic sequence of stages, each of which is potentially amenable to external intervention. The process begins with the adhesion of bacteria to host receptors on epithelial cells or in the salivary pellicle covering tooth surfaces. Interbacterial cell–cell binding interactions facilitate the attachment of new species and increase the diversity of the adherent microbial population. Microbial growth in oral biofilms is influenced by the exchange of chemical signals, metabolites and toxic products between neighbouring cells. Bacterial cells on tooth surfaces (dental plaque) produce extracellular polymers such as complex carbohydrates and nucleic acids. These large molecules form a protective matrix that contributes to the development of dental caries and, possibly, to periodontitis. The identification of key microbial factors underlying each step in the formation of oral biofilms will provide new opportunities for preventative or therapeutic measures aimed at controlling oral infectious diseases.     

Dental calculus: the calcified biofilm and its role in disease development

Dental calculus represents the first fossilized record of bacterial communities as a testimony of evolutionary biology. The development of dental calculus is a dynamic process that starts with a nonmineralized biofilm which eventually calcifies. Nonmineralized dental biofilm entraps particles from the oral cavity, including large amounts of oral bacteria, human proteins, viruses and food remnants, and preserves their DNA. The process of mineralization involves metabolic activities of the bacterial colonies and strengthens the attachment of nonmineralized biofilms to the tooth surface. From a clinical point of view, dental calculus always harbors a living, nonmineralized biofilm, jeopardizing the integrity of the dento‐gingival or implanto‐mucosal unit. This narrative review presents a brief historical overview of dental calculus formation and its clinical relevance in modern periodontal practice.     

Influence of saliva on the oral microbiota

Saliva plays a major role in determining the composition and activity of the oral microbiota, via a variety of mechanisms. Molecules, mainly from saliva, form a conditioning film on oral surfaces, thus providing receptors for bacterial attachment. The attached cells use saliva components, such as glycoproteins, as their main source of nutrients for growth. Oral bacteria work sequentially and in a concerted manner to catabolize these structurally complex molecules. Saliva also buffers the pH in the biofilm to around neutrality, creating an environment which is conducive to the growth of many oral bacteria that provide important benefits to the host. Components of the adaptive and innate host defences are delivered by saliva, and these often function synergistically, and at sublethal concentrations, so a complex relationship develops between the host and the resident microbiota. Dysbiosis can occur rapidly if the flow of saliva is perturbed.     

菌斑微生物群落构成变化与儿童龋病相关研究进展

龋病作为多因素影响的疾病,细菌是龋病发生的始动因素,生态菌斑学说的提出以及现代分子生物学手段的应用,使得学者们能够从微生物角度对菌斑生物膜中细菌的种群分布、菌群多样性、菌斑微生物群落变化与儿童龋病之间的联系进行了更深入的探讨.菌群多样性的降低与龋病发生密切相关,早于龋病发生前的6个月就可以检测到菌群多样性水平的降低,这...     

口腔微生物组标志物——儿童龋齿防治的新策略

口腔中的微生物组在人类生长发育、疾病发生过程中扮演着重要角色。微生物在口腔的不同部位定植,形成生物膜结构,抵抗外部不良刺激的侵入。同时,菌群失调也增加了口腔疾病乃至全身性疾病的风险。龋齿是最常见的口腔疾病,低龄儿童最易发生,已成为全球学龄前儿童普遍存在的公共卫生问题。文章总结了人类口腔微生物组的最新研究进展,进一步介绍了儿童口腔菌群结构在生长发育各阶段的变化,以及患龋前后的菌群动态变化特征,并从中找到龋齿相关的微生物标志物。另外,从机制上探讨了微生物在口腔中形成生物膜并定植的影响因素（如细胞外基质）,阐述了关键细菌（如牙龈卟啉单胞菌）干预宿主免疫的可能机制。综上,文章确定了以微生物膜为靶标,在未来预防和治疗龋齿的意义和应用前景。     

龋齿、牙周炎患牙和健康牙的菌斑生物膜特征

目的研究牙面菌斑生物膜特征与口腔疾病的关系。方法选择牙周健康而牙冠严重龋坏的龋齿5颗、无龋损而极度松动的牙周炎患牙6颗及正畸原因拔除的健康牙4颗,在扫描电镜下,观察分析龈上、龈下及移行生态区的菌斑生物膜特征。结果龋齿、牙周炎患牙和健康牙的牙面均观察到细菌混合物组成的菌斑生物膜,健康牙菌斑生物膜以球菌为主,放线菌和短杆菌少量;龋齿牙的龋坏处为坏死组织和细菌,龋边缘及龈沟处的球菌和短杆菌较健康牙多;牙周炎患者牙菌斑生物膜的细菌种类多,在龈上、龈下移行处可见典型的玉米棒状菌斑或以杆菌为主的紧密附着菌斑,龈下可见球菌、杆菌、梭菌及螺旋体等构成的复杂菌斑。结论龋齿、牙周炎患牙和健康牙菌斑生物膜细菌组成、集聚秩序和立体结构不同,菌斑生物膜的形成与细菌的附着、集聚、生长有关,也与局部病变密切相关。     

牙菌斑生物膜研究模型的进展

口腔微生物群落是典型的生物膜,牙菌斑生物膜是多种菌属组成的三维结构,黏附在牙齿表面,具有生物膜结构和微生物生理学的功能。牙菌斑生物膜是龋病和牙周病的主要致病因素,已有多种生物膜模型用于研究龋病的病因、预防和治疗的研究。这些龋病生物膜模型有助于研究者用一种可控、简化的方式来预测龋病的临床进展结果。目前,研究龋病微生物的模型有体外单菌种生物膜模型和多菌种生物膜模型。本文将从研究龋病的生物膜体外模型建立做一综述。     

群体感应系统对牙周致病菌影响的研究进展

牙周炎是人类最好发的口腔疾病之一,牙菌斑细菌作为牙周炎的始动因子,是导致牙周炎的首要因素。群体感应系统依靠群体感应信号分子调节不同种类细菌之间的通信,加强细菌之间的交流,促进疾病的发生发展。群体感应系统亦对牙菌斑细菌形成生物膜起到重要的促进作用。近年来,许多研究表明群体感应抑制剂可以有效减弱细菌间的群体感应并抑制和降低细菌生物膜的形成和毒力因子的表达。该文就群体感应系统对牙周炎致病菌影响的研究进展进行综述。     

Early formation of Streptococcus sobrinus biofilm on various dental restorative materials.

OBJECTIVES: To examine the formation of dental biofilm by Streptococcus sobrinus on different types of restorative materials, using a model consisting of host and bacterial constituents. METHODS: The adsorption pattern of saliva to the restorative material was determined by means of gel electrophoresis coupled with computerized densitometry techniques. The amount of salivary proteins adsorbed onto the surfaces was measured using the Bradford method. Sucrose-dependent bacterial adhesion to the saliva-coated restorative material was tested by radioactive-labelled Streptococcus sobrinus, and viable counts of these bacteria in the biofilm was determined using bacterial culture techniques. RESULTS: Different adsorption patterns by salivary proteins to restorative materials were recorded. Durafil and acrylic dental materials demonstrated the most affinity to salivary proteins. A surface dependent adhesion profile was recorded, showing a high affinity of albumin and amylase to Acrylic and Durafil materials. Bacterial accumulation was the highest with Fuji LC and Fuji GC, which also demonstrated the highest bacterial viability. CONCLUSIONS: Our study demonstrates the specificity of biofilm formation on different brands of dental restorative materials. Formation of a variety of dental biofilms has a significant impact on the progression of dental diseases in the oral cavity.     

A practical guide to the oral microbiome and its relation to health and disease

The oral microbiome is incredibly complex with the average adult harboring about 50–100 billion bacteria in the oral cavity, which represent about 200 predominant bacterial species. Collectively, there are approximately 700 predominant taxa of which less than one‐third still have not yet been grown in vitro. Compared to other body sites, the oral microbiome is unique and readily accessible. There is extensive literature available describing the oral microbiome and discussing the roles that bacteria may play in oral health and disease. However, the purpose of this review is not to rehash these detailed studies but rather to educate the reader with understanding the essence of the oral microbiome, namely that there are abundant bacteria in numbers and types, that there are molecular methods to rapidly determine bacterial associations, that there is site specificity for colonization of the host, that there are specific associations with oral health and disease, that oral bacteria may serve as biomarkers for non‐oral diseases, and that oral microbial profiles may have potential use to assess disease risk.