Comparison of Bacterial Prevalence in Saliva of Edentulous Patients with or without Complete Dentures by 16S rRNA Gene Based Metagenomic Analysis Identifies a Novel Bacterial Signature in Denture Patients

The aim of this study was to investigate the bacterial flora in the saliva of edentulous patients with or without complete dentures, and relate the occurrence of bacteria with denture biofilm.

Saliva samples from four edentulous patients who had been wearing denture (EdD) for at least 10 years and four edentulous patients who had been so without complete dentures (Ed) for at least 10 years were collected in a sterile 1.5ml microfuge tube. Biofilm samples from the mucosal surface of both upper and lower complete dentures from two of the above patients were scrapped with a disposable synthetic swab and collected in a 1.5ml microfuge tube containing lysis buffer. All the samples were processed simultaneously to extract total genomic DNA, and were subjected to 16S rRNA gene sequencing analysis on a next generation sequencer, the PGS-Ion Torrent. Those bacterial genera with read counts greater than 1000 were considered as significant in the respective subjects and used to associate the occurrence in other subjects.

Metagenomic analysis identified a higher prevalence of Streptococcus, Veillonella, Rothia, Lachnospiraceae, Prevotella and Alteromonas in the saliva of EdD patients. Four other bacterial species namely, Actinomyces, Haemophilus, Neisseria and Vibrio showed comparative pattern in the saliva of both EdD and Ed patients. Comparison of the read counts of bacteria identified in the saliva of two EdD patients with the biofilm bacterial population in their respective complete dentures showed a relatively higher prevalence of all the six bacterial species in the biofilms than in saliva. These findings clearly indicate that: 1) bacterial flora still exists, albeit at a lower level, in edentulous patients even in the absence of complete dentures, and 2) the biofilm on mucosal surface of complete dentures serve as niche areas for bacterial species.