複雑な組織内細菌叢が歯周病巣にバイオフィルムを形成している

Complex Intratissue Microbiota Forms Biofilms in Periodontal Lesions.

抄録

歯周炎は歯肉縁下の細菌群集が異常になることで発症し，歯肉組織への細菌侵入が増加すると考えられている．健康状態から歯周炎への移行に伴う細菌群集構造の変化はよく知られているが，歯周病巣の歯肉組織内に存在する細菌の性質は不明である．歯周病組織内の細菌叢を明らかにし，プラーク細菌叢と比較するために，慢性歯周炎患者7名の歯肉組織および歯肉縁下プラークを採取した．16S rRNA遺伝子の塩基配列解析の結果，種の豊富さおよび多様性は2群間で有意差は認められなかった．しかし，組織内群集の被験者間変動はプラーク群集のそれよりも小さかった．また，組織内群集は，プラーク群集と比較して，Firmicutesが減少し，FusobacteriaとChloroflexiが増加する特徴を有していた。特に、Fusobacterium nucleatumとPorphyromonas gingivalisは組織内で非常に濃縮されており、全菌数の15%から40%を占めていた。さらに、結合組織繊維の分解が顕著な組織内では、アルシアンブルー染色と原子間力顕微鏡で可視化されたバイオフィルムが観察された。以上より，歯周病巣の歯肉組織内には非常に複雑な細菌群集がバイオフィルムとして存在し，持続的な感染のリザーバーとなる可能性があることがわかった．この新しい知見は，歯周炎の治療戦略に関する新たな研究を促進する可能性がある．

Periodontitis is caused by dysbiotic subgingival bacterial communities that may lead to increased bacterial invasion into gingival tissues. Although shifts in community structures associated with transition from health to periodontitis have been well characterized, the nature of bacteria present within the gingival tissue of periodontal lesions is not known. To characterize microbiota within tissues of periodontal lesions and compare them with plaque microbiota, gingival tissues and subgingival plaques were obtained from 7 patients with chronic periodontitis. A sequencing analysis of the 16S rRNA gene revealed that species richness and diversity were not significantly different between the 2 groups. However, intersubject variability of intratissue communities was smaller than that of plaque communities. In addition, when compared with the plaque communities, intratissue communities were characterized by decreased abundance of Firmicutes and increased abundance of Fusobacteria and Chloroflexi. In particular, Fusobacterium nucleatum and Porphyromonas gingivalis were highly enriched within the tissue, composing 15% to 40% of the total bacteria. Furthermore, biofilms, as visualized by alcian blue staining and atomic force microscopy, were observed within the tissue where the degradation of connective tissue fibers was prominent. In conclusion, very complex bacterial communities exist in the form of biofilms within the gingival tissue of periodontal lesions, which potentially serve as a reservoir for persistent infection. This novel finding may prompt new research on therapeutic strategies to treat periodontitis.