Abstract
Background: Systemic antibiotics are often used as adjunctive treatment modalities for periodontal diseases. Testing of antimicrobial efficacy can be relevant only if the bacteria are in the form of biofilms rather than in planktonic state, and at concentrations of physiological relevance i.e. reachable in the periodontal pocket. The aim of the present study was to test on a multi-species in vitro biofilm model the antimicrobial efficacy of five different antibiotic schemes, at physiologically relevant concentrations. Methods: A 10-species in vitro "subgingival" biofilm model was exposed to metronidazole (15 µg/ml), amoxicillin (15 µg/ml), their combination, doxycycline (2 µg/ml) and azithromycin (10 µg/ml), over 24 h. Species-specific bacterial numbers were determined by culture on selective agar media, or by epifluorescence microscopy. Results: Metronidazole alone did not affect biofilm composition. Total bacterial counts were significantly reduced by doxycycline, azithromycin and amoxicillin, or its combination with metronidazole, albeit by less than 1-log. On the species-specific level, these regimens significantly reduced the numbers of Streptococcus anginosus, Porphyromonas gingivalis, Fusobacterium nucleactum and Campylobacter rectus (except from amoxicillin). The strongest effects were displayed by the combination of amoxicillin and metronidazole. Conclusions: Antibiotics at concentrations detectable in gingival crevicular fluid do not dramatically reduce total bacterial loads in this in vitro biofilm model, but cause species-specific reductions, which may disrupt the biofilm unity.
Belibasakis, Georgios N