TRANSLATIONAL AND CLINICAL MEDICINE - Georgian Medical Journal

Abstract

Background: The human oral cavity harbors one of the most diverse microbial communities in the body, with the gingival sulcus representing a specialized ecological niche adjacent to the gingival margin and tooth surface. In health, this sulcus supports a complex but balanced microbiota that contributes to immune homeostasis and prevents pathogen overgrowth. Traditional culture‑based methods were limited in detecting the full breadth of microbial diversity, often overlooking fastidious and uncultivable taxa. The advent of 16S rRNA gene sequencing has revolutionized oral microbiome research by enabling high‑resolution, culture‑independent profiling of bacterial communities. This approach has improved our understanding of microbial ecology in the periodontal sulcus, particularly in distinguishing health‑associated taxa from those related to periodontal disease.

Aim: This article aims to synthesize current evidence from 16S rRNA gene sequencing studies on the composition of the gingival sulcus microbiome in clinically healthy individuals, highlighting dominant bacterial taxa and community structure associated with health.

Methods: A review of peer‑reviewed studies was conducted, focusing on 16S rRNA gene sequencing analyses of subgingival plaque or sulcus samples from periodontally healthy subjects. Eligible studies employed next‑generation sequencing platforms (e.g., Illumina MiSeq, 454‑pyrosequencing) and standard bioinformatics pipelines for taxonomic classification against reference databases such as HOMD (Human Oral Microbiome Database) and Green genes. Key metrics included alpha diversity (richness and evenness), beta diversity (community differences), and relative abundances of taxa at phylum, genus, and species levels.

Results: Across multiple 16S rRNA gene sequencing studies, the gingival sulcus microbiome in healthy individuals is characterized by high diversity and the predominance of several bacterial phyla:

• Firmicutes, Actinobacteria, Proteobacteria, Bacteroidetes, Fusobacteria, and Spirochaetes are consistently detected as dominant phyla in healthy sulcus communities.
• At the genus level, Streptococcus, Actinomyces, Corynebacterium, Veillonella, Neisseria, Haemophilus, and Capnocytophaga are frequently abundant in health, reflecting a community engaged in saccharolytic and homeostatic functions.
• Health‑associated taxa tend to show higher relative abundance and prevalence compared to disease‑associated pathogens such as Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola, which are rare or absent in healthy sulci.
• Alpha diversity measures in healthy subjects are generally higher than in individuals with periodontitis, suggesting that microbial richness and evenness may be protective against dysbiosis.
• Beta diversity analyses demonstrate distinct clustering of microbiome profiles between healthy and diseased groups, indicating that community structure shifts markedly with inflammation and periodontal breakdown.

Conclusions: Evidence from 16S rRNA gene sequencing studies has significantly advanced our understanding of the gingival sulcus microbiome in health. A diverse and balanced community dominated by specific Firmicutes, Actinobacteria, and Proteobacteria taxa appears characteristic of periodontal health. These communities differ markedly from those found in periodontal disease, supporting the concept that microbial community composition and diversity contribute to periodontal homeostasis. Future research integrating metagenomics, metatranscriptomics, and host immune profiling will further clarify microbial functions critical for maintaining gingival health. Continued longitudinal studies are needed to define health‑associated microbiome signatures that may inform preventive and therapeutic strategies.

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