| There are many kinds of microorganisms living in various parts of the human body,including oral cavity,intestinal tract and skin.The number of these microorganisms is about equal to the number of human cells,and their genetic informations are considered as the second genome of the human body.As one of the most important ecological colonization sites for microbes,there are about 1000 kinds of microorganisms in oral cavity.The interaction between them and the host is closely related to the health and disease status of oral cavity and whole body,so it has always been one of the focuses of human microbiology researches.About half of the oral microbes can’t be cultivated by now,so the researches relying on the traditional culture methods have been curbed and we can’t shed light on the links between oral microbial community and health from an overall perspective.The advent of high-throughput sequencing has enabled examination of oral microbiota and provided necessary conditions for us to study microbial community as a whole.The composition and structure of human microbiota are affected by many factors,including age,genes,symbiotic sites and other physiological factors,as well as diseases,diet and other factors.The study of influencing factors is also conductive to deepen our understanding of human microorganisms.We collected saliva sample from preschool children with deciduous teeth dentition and studied the microbial community using Illumina MiSeq high-throughput sequencing technologies,in order to reveal the effects of caries and probiotics on oral microbiota.We expected these researches would deepen our understanding and provide novel information and ideas for salivary microbiota in preschool children.Objective:The aim of this research is to study the composition and structure of salivary microbiota in caries-free preschool children with deciduous dentition and the changes of microbiota caused by dental caries,and to evaluate the effect of probiotics on salivary microbiota in caries-free preschool children.Methods:1.Thirty-five saliva samples was collected from caries-free preschool children with deciduous dentition,the total DNA of the microorganisms was extracted and 16S rRNA coding gene was amplified and then sequenced using Illumina MiSeq sequencing platform.The sequence readings were compared with the Silva Datebase to obtain sequence information and bioinformatics’ analysis was conducted to analyze the salivary microbiota from the whole structure to the taxonomic levels.2.Sixty caries-free preschool children with deciduous dentition were included at the beginning,followed up for two years.A total of 23 children completed the follow-up and saliva samples were collected every six months.All samples were sequenced using Illumina MiSeq sequencing platform to obtain sequence information.Twelve of the children developed caries eventually.The subjects were divided into caries-free group and caries-transformed group,and cross-sectional comparisons were conducted at every time points to explore the changes of diversity,structure and taxonomic information in salivary microbiota before and after the occurrence of caries.3.Twenty caries-free preschool children with deciduous dentition were included at the beginning,and then were given probiotic yogurt every day and followed up for one year.A total of 6 children completed the follow-up and saliva samples were collected every six months.All samples were sequenced using Illumina MiSeq sequencing platform to obtain sequence information.The changes of diversity,structure and taxonomic information in salivary microbiota after the intake of probiotic yogurt were discussed.Results:1.There was no statistical difference in composition diversity and structure of salivary microbiota between male and female caries-free preschool children with deciduous dentition.When it came to the comparison of taxonomic information,it was found that the relative abundance of Neisseria was significantly higher in the salivary microbiota of male children than that of female children.There were core microbiomes at phylum and genus levels respectively,including the phyla of Actinobacteria,Bacteroidetes,Firmicutes,and Proteobacteria and the subordinated genera of Actinomyces,Rothia,Capnocytophaga,Porphyromonas,Streptococcus,Gemella,Granulicatella,Lachnoanaerobaculum,and Neisseria.2.It was found that the composition diversity of salivary microbiota did not change significantly after the occurrence of caries,but the structure of microbial community did change significantly.The relative abundance of Rothia and Shuttleworthia was negatively correlated with the occurrence of dental caries.On the contrary,the relative abundance of Atopobium,Afegasphaera,and Veillonella was positively correlated with the occurrence of caries.The salivary core microbiomes of caries-free and caries-transformed children were highly similar but different.3.By comparing the samples among different time points,it was found that the intake of probiotics caused significant changes in the microbial community structure of saliva.There were differences in the relative abundance of 11 genera among the groups,with 7 genera,including Campylobacter,Haemophilus,Lautropia,Bacillus,Catonella,Lactococcus,and Solibacillus showed an upward trend.On the other hand,Gemella and Streptococcus showed a downward trend.Conclusion:1.There are a variety of dominant microorganisms in the saliva of caries-free preschool children with deciduous dentition,as well as core microbial species;there was no statistical difference in the diversity and community structure of salivary microbiota between male and female children.2.The occurrence of dental caries did lead to significant changes in the structure of bacterial community;the microorganism with significant changes in relative abundance may be closely related to the occurrence and development of caries.3.The intake of probiotic yoghurt caused significant changes in the structure of the oral microbial community,as well as significant changes in the relative abundance of microbial species,which suggested that the composition and structure of salivary microbiota can be influenced by probiotics,and the effects of these changes are possible beneficial to oral health,such as tooth and periodontal tissue. |
