LAUSR

AIM To elucidate the presence of apical periodontitis in the root canal of teeth with secondary/persistent infection, including composition of microbiota, levels of endotoxins and lipoteichoic acid, and clinical implications of these findings. METHOD ology: Samples were collected from root canals of 50 patients who needed endodontic retreatment and had radiographic evidence of apical periodontitis. Microorganisms were identified by using the culture technique and biochemical tests. Nested PCR was used to identify 17 species of specific bacteria. Lipopolysaccharides (LPS) and lipoteichoic acids (LTA) were quantified by using, respectively, limulus amebocyte lysate (LAL) and enzyme-linked immunosorbent assay (ELISA) tests. RESULTS Bacteria were detected in all samples by culture and molecular methods. A total of 154 Gram-positive strains, out of 188 strains isolated, were found in the root canals by culture. E. faecalis and G. morbillorum were the most prevalent species identified by the biochemical tests, whereas molecular analyses (nested-PCR) showed a high frequency of P. gingivalis, E. faecalis and F. nucleatum. LPS and LTA were detected in all samples, with mean values being 3.52 EU/mL and 597.83 pg/mL, respectively. Significant statistical correlations were found between levels of LTA and clinical features. CONCLUSION Despite the prevalence of Gram-positives, the microbiota present in secondary/persistent infections showed a large variety of species. Within this diversity, associations were found between specific bacteria and clinical features. Additionally, higher levels of LTA were statistically associated with larger periapical radiolucent areas, but no correlation between this feature and LPS was found.