ABSTRACT
<p><b>OBJECTIVE</b>To compare the intraradicular bacterial community structures of teeth with or without post-treatment periapical periodontitis and to explore the suspicious microorganisms that is related to persistent periapical infection.</p><p><b>METHODS</b>The intraradicular biofilm samples were collected from 10 post-treatment periapical periodontitis teeth (apical periodontitis group) and 10 teeth without post-treatment periapical periodontitis (without apical periodontitis group). The V1-V3 hypervariable regions of bacterial 16S rRNA genes were amplified, and the high-throughput pyrosequencing was performed. The composition and structure characteristic of intraradicular microbiome were revealed by bioinformatic analysis.</p><p><b>RESULTS</b>Total sequences were taxonomically classified into 132 species-level bacteria belonging to 96 genera and 21 phyla. The most representive phyla in apical periodontitis group were Firmicutes [32% (18 534/58 688)], Proteobacteria [27% (15 626/58 688)], Actinobacteria [15% (8 685/58 688)], Bacteroidetes [11% (6163/58 688)], Fusobacteria [8% (4761/58688)] and Spirochaetes [3% (1 785/58 688)]. While the most representive phyla in without apical periodontitis group were Firmicutes [31% (16 941/55 480)], Proteobacteria [27% (14 748/55 480)], Bacteroidetes [18% (9 948/55 480)], Fusobacteria [10% (5 307/55 480)], Actinobacteria [9% (4 761/55 480)], Chloroflexi [3% (1 785/55 480)]. The abundance of actinobacteria in apical periodontitis group was significantly higher than without apical periodontitis group (P < 0.01). The detection rates of actinomycetes in apical periodontitis group and without apical periodontitis group were 100% and 50%.</p><p><b>CONCLUSIONS</b>The diversity of intraradicular bacterial community in teeth with apical periodontitis was higher than those without apical periodontitis. Actinomycetes may be related to post-treatment periapical periodontitis.</p>