Characterization of bacterial flora in persistent apical periodontitis lesions.

Introduction: Microorganisms are able to survive and induce persistent infection in periapical tissues. The aim of this study was to investigate the composition of the microflora of persistent apical periodontitis lesions.

Methods: Twenty apical lesion samples were obtained from 20 patients with chronic apical periodontitis by root end surgery and processed using aerobic or anaerobic culture techniques. All isolated strains were identified by 16S ribosomal DNA sequence analysis.

Results: Seventy-four strains were isolated, belonging to 31 bacterial species obtained from the 20 apical lesions that were isolated. The majority of the strains were facultative anaerobes (51.6%). Propionibacterium acnes, Staphylococcus epidermidis, Pseudomonas aeruginosa and Fusobacterium nucleatum were isolated from 16.2, 9.5, 6.8 and 5.4% of the samples, respectively. Fifteen samples harboured more than one species. The predominant association was P. acnes, S. epidermidis and F. nucleatum.

Conclusion: The microbiota of persistent apical periodontitis lesions is composed by diverse types of microorganisms with biofilm-forming capacity, including P. acnes, S. epidermidis and F. nucleatum.