The Composition Of Oral Microbiome And Its Relationship With Human Diseases

Oral cavity is the initial part of the digestive tract,which offers many different binding sites for microbial adhesion and colonization,served as an important habitat for the microorganisms.It was reported that bacteria could co-aggregate on the surfaces of oral cavity and then form biofilms.In a mature oral biofilm,through the bacteria-bacteria interaction,the community structure maintains stable,and the inhabitants also show a dynamic ecological balance with the host,thus playing an import role to the body health.When the environment of the oral cavity changes,the balance of the microbial community structure will be destroyed and some opportunistic pathogens will be enriched,which may in turn influence the oral and even the whole body health of the host.Accumulated clinical studies have shown that the oral microbiota closely linked to several oral health problems or diseases,such as bad breath,caries and periodontal diseases,and may have relationship to the occurrence of several systemic system diseases like diabetes,cardiovascular disease.The oral microbiota may also play an important role in the development of pneumonia,chronic gastritis,colorectal cancer,etc.Exploring the structural changes of the oral microbiota in different oral habitats from different individuals under different disease states and digging the relationship between bacteria and diseased condition,will be helpful to better understanding the etiology of a disease and provide theoretical basis for the prevention,diagnosis and treatment of it.In the current research,three different works targeting three different human diseases using different oral samples were involved.First,we used 16 S rRNA gene pyrosequencing to profile the microbiota of saliva,supragingival and subgingival plaque from periodontitis patients and periodontally healthy volunteers.Different oral habitats harbored significantly different microbiota,and segregation of microbiota composition between periodontitis and health was observed as well.Two-step redundancy analysis identified twenty-one OTUs,including Porphyromonas gingivalis,Tannerella forsythia and Filifactor alocis,as potential pathogens that were significantly associated with periodontitis and two periodontitis diagnostic parameters(pocket depth and attachment loss)in both saliva and supragingival plaque habitats.Interestingly,pairwise correlation analysis among the 21 OTUs revealed that Filifactor alocis was positively correlated with seven other putative pathogens(R>0.6,P<0.05),forming a co-occurrence group that was remarkably enriched in all three habitats of periodontitis patients.This bacterial cluster showed a higher diagnostic value for periodontitis.Thus,our study identified a potential synergistic ecological pattern involving eight co-infecting pathogens across various oral habitats.Next,we compared the structure of microbiota in infected root canals obtained from thirty-three apical periodontitis patients,including 27 patients of primary infection and 6 patients of secondary infection.The results showed that Bacteroidetes(47.2%),Firmicutes(25.6%),Synergistetes(6.3%),Actinobacteria(5.7%)and Fusobacteria(5.3%)were the most predominant phyla in the microbiota of root canal.And several genera,including Pseudomonas,Prevotella,Porphyromonas,Dialister and Fusobacteria,showed high prevalence in infected root canals,thus could be regarded as the core taxa of the microbiota.As revealed by univariate statistical analysis,we found Tannerella and Streptococcus displayed a higher abundance in the root canal of the secondary infection than that of the primary infection.In addition,our work also revealed Treponema maltophilum,Porphyromonas endodontalis and Solobacterium moorei were significantly enriched in individuals with sinus tract,swelling or pain,respectively,indicating that these bacteria may be associated with the different clinical symptoms of apical periodontitis,thus might be potential targets for the disease treatment.We also investigated the tongue coating microbiota of 70 gastritis patients and 48 healthy controls through pyrosequencing and DGGE.Distinct segregation of the microbiota between the gastritis and the healthy was observed by both methods.Redundancy analysis identified 52 OTUs which were significantly different between those two groups.Particularly,Prevotella pallens,P.veroralis and Veillonella parvula/disparas were significantly enriched in the tongue coating microbiota of patients compared with those of healthy ones,thus were regarded as the key phylotypes associated with gastritis.Correlation analysis revealed the gastritis-enriched phylotypes showed more remarkable co-abundant behavior.Further studies revealed neither the tongue coating microbiota between white and yellow fur nor those between thin and thick fur,the different tongue appearance representing the different types of TCM syndromes,were significantly different.This implied the relationship between tongue coating microbiota and TCM syndromes is still unclear.However,the microbiota between greasy fur and non-greasy fur,two types of gastritis patients seeming to have different degree of the disease,showed significant difference with each other.Two OTUs,which were both closely to Megasphaera micronuciformis,increased their relative abundance in patients compared with healthy controls,and showed the highest abundance in patients with greasy fur.This bacterium might be the critical organism associated with the development of gastritis and worth to be further studied.In conclusion,the oral microbiome structure in diverse oral habitats(including saliva,supragingival plaque,subgingival plaque,root canal and tongue coating)form periodontitis,apical periodontitis and chronic gastritis patients were investigated comprehensively through high-throughput sequencing technologies.Integrating the data from the three studies,we found the oral microbiome in different oral habitats were significantly different.For a certain oral habitat,the characteristic disease-associated communities can be found by comparing the microbiome in this oral habitat between diseased and healthy cohorts.The results of this study will help to deepen the understanding of disease pathogenesis and provide theory basis for the intervention of the disease.