Meta-analyses on the Periodontal Archaeome.

Recently, we have published a scoping review on the oral archaeome, showing that these microorganisms inhabit various oral niches, including periodontal sites. In order to reinforce the importance of the Archaea domain and alert the scientific community about the importance of inter-domain relationships in oral dysbiosis, we have performed meta-analyses evaluating the prevalence of archaea in periodontal diseases (PROSPERO protocol: CRD42020213109). A systematic search in the literature was conducted in several databases and in grey literature, retrieving 30 reports on periodontal archaeome, published from 1980 to 2020. The methodological quality of included studies and the certainty of evidence were evaluated by using validated tools. Most studies focused on the detection of methanogens, revealing that the diversity of the periodontal archaeome is currently underestimated. Two meta-analyses concluded that individuals with periodontitis are prone to have archaeal-positive subgingival biofilms when compared to periodontally healthy individuals (OR 6.68, 95% CI 4.74-9.41 for 16S rRNA gene analysis and OR 9.42, 95% CI 2.54-34.91 for mcrA gene analysis). Despite the archaeal enrichment in sites with periodontitis, less than half of the individuals with periodontitis tested positive for archaeal DNA (general estimative of 46%; 95% CI 36-56%). Conventional treatment for periodontitis reduced the archaeal population, but systemic antibiotics used as adjunctive therapy did not increase its effectiveness. Hence, it could conceivably be hypothesised that archaea are secondary colonizers of areas with dysbiosis, probably flourishing in the inflammatory environment. Due to their lower prevalence, archaeal cells are probably underestimated by the current detection protocols. It may also be speculated that archaea do not have a single central role in the infection, with bacterial cells directly involved in that role. New studies are necessary, with different methodological approaches, to explore the underestimated diversity of the oral archaeome.