Bacterial Internalization During Human Experimental Gingivitis: A Quasi-Longitudinal Study
Creators: Bhagirath, Anjali
Publisher: name: University of Alberta Library
Year: 2024

<p>Introduction: Bacterial invasion from subgingival plaque into gingival tissues is a critical aspect of periodontal disease pathogenesis. This invasion not only contributes to disease progression but also enables the pathogens to survive within the host and evade immune surveillance. While previous studies have identified some bacteria that penetrate host tissues in advanced periodontitis, the full spectrum in early gingivitis is not known. Our research breaks new ground by mapping out the bacteria originating from dental plaque that are capable of infiltrating host gingival tissues by leveraging a modification of the human experimental gingivitis model.  Materials and Methods: In our study (HREB: Pro00112019), 22 healthy participants underwent a three-phase Human Experimental Gingivitis investigation: baseline, induction, and resolution. Baseline was set post-professional cleaning before the start of the study. Using a partial-mouth approach with an acrylic stent, we induced gingivitis in randomly chosen mouth quadrants by pausing oral hygiene for up to 21 days, with the other quadrant as controls. This comprised the induction phase. Post-induction, regular hygiene was re-instituted and gingival health was restored. Clinical parameters with standard Indices such as PPD, BOP, PI, MQHPI, and PMA were recorded. Samples of subgingival plaque and gingival biopsies cleared of extracellular bacteria using gentamycin, underwent 16S rDNA sequencing for bacterial identification. The data were analyzed using systems biology approach to assess microbial taxonomy and functionality.Results: Over the 21-days PPD, BOP, PI, and MQHPI increased significantly (p&lt;0.05). The microbiome analysis reinforced the &#39;nepotism hypothesis’, indicating non-random clustering of plaque microbes (p&lt;0.05). Plaque showed higher microbial richness yet less uniformity in species distribution (p&lt;0.05). Both plaque and tissues saw a decline in Shannon diversity without an increase in strain numbers, suggesting selective microbial persistence (p&lt;0.05, Wilcoxon signed rank sum test). Plaque had more core taxa compared to tissues, and over time, beta-diversity within tissues diminished, denoting a more limited microbial community (p&lt;0.05, FDR post-hoc of Friedman’s test on PhILR distances). Specific plaque microbes significantly affected the diversity of gingival tissue taxa (p&lt;0.05, extended local similarity analysis). Other taxa modified these effects (p&lt;0.05, liquid association) indicating complex, non-linear inter-bacterial interactions.  Conclusions: Our findings reveal that variations in plaque and gingival microbiome are driven by shifts within existing microbial communities, rather than introductions of new species. Gingival tissues exhibit less diversity compared to plaque, indicating a selective environment that favors specific taxa early in the inflammation process. This highlights the pivotal role of microbial selection in shaping the progression of gingival inflammation.</p>