Bacterial genera in the fluid from apical periodontitis-related radicular cysts: an observational study

Aim This study aimed to evaluate bacteriome profiles (diversity, composition, and relative abundances of bacterial genera) of the fluids from apical periodontitis (AP)-related radicular cysts (RCs). Methods This observational study included 29 patients with AP and RC with complete sample triplets (supragingival plaque, cryopulverized tooth, and cystic fluid). The bacteriome profiles of each matrix as well as of negative controls (NCs) were examined using 16S rRNA amplicon sequencing. Results Bacteriome profiles of cystic fluids differed from NCs in 79 % of cases. The number of distinct amplicon sequence variants and Shannon index detected in cystic fluids and cryopulverized teeth were significantly lower than in paired supragingival plaque samples. Gramnegative genera and anaerobic genera were more abundant in cystic fluids than in paired cryopulverized teeth or their supragingival plaques. The relative abundances of the genera Prevotella_7/Prevotella, Fusobacterium, and Porphyromonas were higher in cystic fluids than in paired cryopulverized teeth and NCs; their relative abundances dominated (> 20 %) in individual cystic fluids. Also, DNA from the genus Fretibacterium was significantly more commonly found in cryopulverized teeth and cystic fluids than in supragingival plaque samples. The relative abundances of this gramnegative bacterial genera in cryopulverized teeth differed from NCs; the difference from cystic fluids was borderline insignificant. Conclusions Although the alpha diversity in the cystic fluids is much lower compared to supragingival plaques, most cystic fluids are not sterile. DNA from specific anaerobic gramnegative bacterial genera dominated the fluids from AP-related RCs. Mock spike-in Samples were spiked with internal MOCK standard of Allobacillus and Imtechella.