ANTIMICROBIAL SUSCEPTIBILITY TESTING,THERAPY (POSTER PRESENTATION) In vitro Activity of Amoxicillin,Tetracyclines, Azithromycin, O£oxacin and Metronidazole Against Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum strains E. Carrasco* , M. Martinez, M. Calbacho, and M.Wilckens Faculty of Dentistry, University of Concepcio Ân, Concepcio Ân, Chile Key Words: amoxicillin, tetracycline Introduction Antibiotics are frequently used as adjuncts to con- ventional periodontal therapy and have been reported to be effective in the treatment of several periodontal disease entities. Perhaps due to the increased usage of antibiotics by dentists, there has been a dramatic increase in the incidence of bacterial resistance in the periodontal flora. The spectrum of antimicrobials known to be effective in treating anaerobic infections has changed significantly in recent years, and some agents previously regarded as therapeutically effec- tive are no longer considered useful. Although susceptibility testing is not recommended for all anaerobic bacteria, determination of in vitro activity can be important in certain situations, for example, to monitor patterns of susceptibility and resistance in the population or for using antimicrobial agents as adjuncts to mechanical treatment of refractory period- ontitis patients. In Chile there is no previous research about the resistance levels in periodontal flora to antibiotics used. It is important to know the antibacterial susceptibility in countries where there is no control or education about the use of antibiotics in the population. The purpose of this study was therefore to examine the susceptibility of predominant cultivable anaerobic periodontal bacteria in adult periodontitis ot the most commonly used antibiotics in periodontal therapy and dental practice in Chile. Materials and Methods Bacterial strains The antibiotic susceptibilities were determined for 25 characterized clinical strains of Porphyromonas gingi- valis, 20 of Prevotella intermedia and 10 of Fusobacterium nucleatum. *Corresponding author. Tel./Fax: +56 41 243 311. E-mail: ecarrasc@udec.cl 1075±9964/99/030443 + 03 $30.00/0 # 1999 Academic Press Anaerobe (1999) 5, 443±445 Article No. anae.1999.0270