EFFECTS OF METRONIDAZOLE ON PORPHYROMONAS-GINGIVALIS BIOFILMS

Subgingival bacteria exist within a biofilm consisting of cells and ex tracellular matrix which may afford organisms protection from both ant ibiotics and components of the host immune system. MIC values for plan ktonic Porphyromonas gingivalis treated with metronidazole were compar ed with those obtained for the same strain in biofilms associated with hydroxyapatite (HA) surfaces. The treated biofilms were examined for growth and studied by scanning electron microscopy. A broth assay resu lted in an MIC of 0.125 mu g/ml for metronidazole against P. gingivali s. P. gingivalis biofilms exhibited growth after treatment with 20 mu g/ml metronidazole, which was 160 times the MIC for planktonic organis ms. The results of this study indicate that biofilm-associated P. ging ivalis may be resistant to metronidazole at concentrations which are u sually attained by systemic administration.