A longitudinal study of the oral microbiome during the onset and resolution of experimentally-induced gingivitis

Gingivitis is a mild and treatable form of periodontal disease characterized by gingival inflammation in response to plaque accumulation. Without treatment, gingivitis can lead to a more severe and irreversible form of the disease known as periodontitis, which accompanies the progressive loss of supporting bone and periodontal ligament that anchor teeth. Here, using weekly sampling and 16S V4-V5 sequencing, we aimed to obtain the most comprehensive snapshots of oral bacterial ecology by analyzing the dental (both supragingival and subgingival regions), tongue and salivary microbiome of 15 subjects using an experimental gingivitis model. Gingivitis was induced in all subjects by discontinuation of any form of oral hygiene procedures for three weeks, whereas its resolution was implemented by the resumption of oral hygiene for an additional two weeks. An increase in alpha diversity was observed during gingivitis induction, which returned to baseline levels after oral hygiene was resumed. Disease onset was accompanied by an increased abundance in members of the *Porphyromonas*, *Tannerella*, *Selenomonas*, *Fusobacterium*, and *Prevotella* genera, while inflammation resolution was accompanied by an increase in members belonging to *Streptococcus*, *Rothia*, *Haemophilus*, *Actinomyces*, and *Granulicatella* genera. Amplicon sequence variants with significant abundance trends were mapped to the expanded Human Oral Microbiome Database, thus highlighting potential strains that can be harnessed for surveillance to allow disease progression to be curbed at a milder (and reversible) stage. Evidence for intra-oral dipersal of *Streptococcus*, *Selenomonas*, *Granulicatella*, and other taxa was observed during gingivitis onset. We highlight the possibility that oral microorganisms that have been labelled commensal or even "health-associated" on the basis of decreased abundance in a disease set (such as *Streptococcus* spp., *Haemophilus parainfluenzae*, *Rothia aeria*, *Actinomyces* spp., and *Filifactor* spp.) are dipsersing to unmonitored sites in the body.