Metagenomic analysis of the periodontal and peri-implant microbiome: a link between health and disease status

The oral cavity has been becoming one of the most well-studied microbiomes after the introduction of new genomic technologies, including next-generation sequencing and bioinformatic analysis. Metagenomic studies of the oral microbial community have revealed the complexities of the oral cavity, that contains hundreds of different bacterial, viral and fungal species. Most species are commensal, but they can become pathogenic in responses to environmental changes. The oral microbiota analysis could provide a better understanding of the bacterial communities’ role in both physiology and pathophysiology, identifying micro-organisms that cause infections and others that are crucial for successful treatment and recovery of patients. The main focus of this project is to identify the healthy and disease profiles of the oral microbiome in periodontal and peri-implant diseases by 16S rRNA gene sequencing, to have a broader and more overall view of the trends of the oral microbial community. Data have shown the greatest bacterial richness in health sites, where Lautropia appeared as a health biomarker, while Olsenella, Mongibacterium and Dialister were the most discriminative taxa for disease groups. The identification of "healthy core microbiome" and a "diseased core" led us to the potential definition of specific biomarkers of health or disease. Moreover, we found a higher abundance of Streptococcus salivarius species in “healthy core microbiome”. This discovery led us to preliminary evaluate further properties of Streptococcus salivarius 24SMBc, which is an oral probiotic already commercialized and used in the prevention of recurrent acute otitis media, but that could represent also an oral probiotic candidate to be used in the prevention and treatment of these pathologies. The probiotic properties of this strain were tested against oral pathogens chose by supporting our background experience. Firstly, the absence of cytotoxicity on epithelial cell HEp-2 was confirmed, secondly, the ability to interfere in cellular adhesion and to co-aggregate with streptococcal pathogens was assessed. Moreover, a complete genome sequencing analysis of S. salivarius 24SMBc was performed by using Illumina sequencing technology to investigate the genetic background of the probiotic potential. Even if the efficacy of S. salivarius 24SMBc has to be proved against a wider sample of periodontal pathogens and in randomized clinical trials, it has responded positively to all test on the list, showing good adhesion interference of pneumococcal colonization and good co-aggregation ability with them. It is also free of streptococcal virulent factors and has got a bacteriocin-like protein (blp) locus. Thereby, the present work could improve the knowledge of the oral microbiome and its influence on host health and disease, providing fundamental information on wide-ranging interactions among oral bacteria in terms of positive and negative impacts on host health, enriching the literature in this regard and giving new potential diagnostic tools to the clinicians as well as new therapeutic options.