Subgingival microbial changes in Down Syndrome adults with periodontitis after chlorhexidine adjunct non-surgical therapy and monthly recalls–A 12-month case series study

•Porphyromonas, Tannerella, Desulfobulbus, and Saccharibacteria (TM7) appeared to be key pathogenic genera in Down syndrome adults with periodontitis.•Non-surgical periodontal treatments adjunct with chlorhexidine resulted in favorable responses in Down syndrome adults with periodontitis.•The therapy led to microbial transitions in subgingival plaque composition, shifting from periodontal-related bacteria to health-related bacteria, with the relative abundance of Desulfobulbus sp. HMT 041, Saccharibacteria (TM7) [G-1] bacterium HMT 346 or 349, and Tannerella forsythia significantly reduced after treatment.•The relative abundance of Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans showed no significant reduction in the subgingival after the treatment. Down Syndrome (DS) adults are at risk for periodontitis. Previous reports indicated difficulties in periodontopathogen reduction or eradication in DS individuals after periodontal treatment. This case series follows the subgingival microbial changes in adult DS individuals with periodontitis who received chlorhexidine adjunct non-surgical therapy plus 12-month recalls. Twenty periodontitis DS participants (7 females; 25.5 ± 5.6 years of age; 3 with generalized periodontitis) partook in a study involving non-surgical mechanical periodontal therapy, twice daily chlorhexidine gel toothbrushing, chlorhexidine mouthwash, and monthly recalls. The subgingival microbiota profile was followed at baseline, 6-, and 12-months post-operation. Desulfobulbus, Saccharibacteria (TM7), Tannerella, and Porphyromonas were the major subgingival genera in this DS cohort. Favorable chlorhexidine adjunct non-surgical treatment outcomes were observed, with the relative abundance of Desulfobulbus sp. HMT 041, Saccharibacteria (TM7) [G-1] bacterium HMT 346 or 349, and Tannerella forsythia significantly reduced at the end of the study, but no significant reduction of Porphyromonas gingivalis or Aggregatibacter actinomycetemcomitans could be observed. Relative abundance of Desulfobulbus sp. HMT 041 and T. forsythia were also found to be significantly associated with plaque, bleeding on probing, and probing pocket depth (PPD, in mm) at a site level, while the relative abundance of Halomonas pacifica was negatively associated with PPD. Successful chlorhexidine adjunct non-surgical treatment with hygiene care was accompanied by a subgingival microbial shift involving certain periodontopathogenic species, except P. gingivali