New Bacterial Combinations in Secondary Endodontic Infections of Patients with a Recent Systematic Antibiotic Therapy.

Introduction: To date, the microbiota associated with persistent endodontic infections has only been analyzed in patients who did not receive any antibiotic therapy for at least 3 months before endodontic treatment. In this clinical study, secondary endodontic infections of patients who recently received systematic antibiotic therapy before endodontic treatment were analyzed and compared with the actual data available in the literature.

Methods: Root canal-filled teeth with periradicular lesions of 20 patients who were under systematic antibiotic therapy which ended 1-21 days before the endodontic treatment were studied. A wide range of antibiotics was administered, including amoxicillin, amoclav, amoxicillin/metronidazole, ampiclox (ampicillin and cloxacillin), doxycycline, tetracycline, ciprofloxacin, and azithromycin. Microorganisms were isolated according to standard protocols and identified using MALDI-TOF-MS. A narrative review of the literature was conducted to compare the results of this study with the data reported so far.

Results: The presence and concentrations of bacteria isolated from the infected root canals were comparable with those depicted in the literature, although the total colony-forming units number in saliva was rather low. The number of different bacterial species isolated and identified in each patient as well as the diversity over all patients did not show signs of any influence of the administered antibiotics. Weissella hellenica and Cellulomonas spp. were detected in root canals for the first time. Granulicatella adiacens and Dietzia spp., previously isolated from primary endodontic infections, were detected for the first time in persistent root canal infections in this patient group.

Conclusions: The bacterial diversity reported to date in secondary endodontic infections should be extended with the new microbial composition revealed in endodontic patients who had recently received systematic antibiotic therapy.