Carrasco,E.*
Faculty of dentistry, University of Concepción, Chile

One of the causes for failures in periodontal chemotherapy has been the inappropriate choice of antibacterial agents used. It is important to determine their activity against periodontopathic bacteria. The aim of this study was to determine the susceptibility of periodontal bacteria to commonly used antibiotics in periodontal therapy. Twenty-five clinical strains of Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum were tested for their susceptibility to doxycycline, tetracycline, metronidazole, ofloxacin, amoxicillin and azithromycin by their minimal inhibitory concentration (MIC) which were determined through E-Test method. The 90% of strains of F.nucleatum and P.intermedia showed MICs values of < 0.002 ug/ml for metronidazole and < 0.016 ug/ml for tetracyclines and amoxicillin. The 90% of strains of P.gingivalis showed MICs values of 0.25 ug/ml for tetracyclines, 4.0 ug/ml for ofloxacin and 0.094 ug/ml for azithromycin and metronidazole. Metronidazole had good inhibitory effect almost equivalent to tetracyclines and amoxicillin against all the strains tested. Ofloxacin was less active against P.gingivalis than P.intermedia and F.nucleatum.