Cultivation of viable but non-culturable bacteria present in the oral microbiota using quorum sensing inhibitors

Quorum sensing (QS) is a phenomenon by which bacteria communicate between intra- and interspecies. In the human oral cavity, nearly 700 species are found. Although approximately 220 species were identified using molecular techniques, they have not yet been cultured. This is thought to be caused by the fact that they cannot be cultured because of bacterial QS mechanism which controls their population density in their natural environment, and they also continue this process under laboratory conditions. In this study, it was aimed to cultivate viable but non-culturable bacteria in oral microbiota by interrupting their QS signal molecules, which are capable of controlling their population densities, with known QS inhibitor substances. Five groups of QS inhibitors were formed and tested on the bioindicator strains. Oral cavity samples from six healthy individuals were seeded on agar media with and without QS inhibitors. The cultures were incubated up to 35 days and examined periodically for growth. The strains grown only in media containing QS inhibitors were evaluated as potential cultivated strains for the first time. Among the strains which appeared only on the QS inhibitors containing medium, 121 strains were picked and subcultured on media without inhibitors.These strains were then grouped by standard bacteriological methods, 28 representative strains were further identified by 16S rRNA sequence analysis. According to the 16S rRNA sequence analysis, 28 strains were found to be homologous with taxa belonging to phyla of Actinobacteria, Firmicutes and Proteobacteria. Three strains showed homology with unnamed and cultured Streptococcus species. One of these was found to show high homology with Streptococcus species with a culture lost status according to the gene bank. The other 25 strains were found to be officially named and have been cultured before. However, the results showed that QS inhibitors used in this study altered the population density of oral microbiota. The co-cultures with QS inhibitors allow to isolate more variety of bacteria compared to cultures on control media. The results show that this method is applicable to increase diverse species of bacteria from any ecosystems, and from different regions of human body.