title: Combinatorial effects of amoxicillin and metronidazole on selected periodontal bacteria and whole plaque samples.
abstract: OBJECTIVE
  The aim of the present study was to analyze in vitro the combinatorial effects of the antibiotic combination of amoxicillin plus metronidazole on subgingival bacterial isolates.
  
  
  METHODS
  Aggregatibacter (Actinobacillus) actinomycetemcomitans, Prevotella intermedia/nigrescens, Fusobacterium nucleatum and Eikenella corrodens from our strain collection and subgingival bacteria isolated from patients with periodontitis were tested for their susceptibility to amoxicillin and metronidazole using the Etest. The fractional inhibitory concentration index (FICI), which is commonly used to describe drug interactions, was calculated.
  
  
  RESULTS
  Synergy, i.e. FICI values ≤ 0.5, between amoxicillin and metronidazole was shown for two A. actinomycetemcomitans (FICI: 0.3), two F. nucleatum (FICI: 0.3 and 0.5, respectively) and one E. corrodens (FICI: 0.4) isolates. Indifference, i.e. FIC indices of >0.5 but ≤4, occurred for other isolates and the 14 P. intermedia/nigrescens strains tested. Microorganisms resistant to either amoxicillin or metronidazole were detected in all samples by Etest.
  
  
  CONCLUSIONS
  Combinatorial effects occur between amoxicillin and metronidazole on some strains of A. actinomycetemcomitans, F. nucleatum and E. corrodens. Synergy was shown for a few strains only.
authors.affiliation: Department of Preventive Dentistry and Oral Microbiology, School of Dental Medicine, University of Basel, Switzerland. Electronic address: eva.kulik@unibas.ch.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Kulik Kunz
authors.affiliation: Department of Periodontology, Endodontology and Cariology, School of Dentistry, University of Basel, Switzerland.
authors.forename: Krystyna
authors.initials: K
authors.lastname: Lenkeit
authors.affiliation: Department of Preventive Dentistry and Oral Microbiology, School of Dental Medicine, University of Basel, Switzerland.
authors.forename: Tuomas
authors.initials: T
authors.lastname: Waltimo
authors.affiliation: Department of Periodontology, Endodontology and Cariology, School of Dentistry, University of Basel, Switzerland.
authors.forename: Roland
authors.initials: R
authors.lastname: Weiger
authors.affiliation: Department of Periodontology, Endodontology and Cariology, School of Dentistry, University of Basel, Switzerland.
authors.forename: Clemens
authors.initials: C
authors.lastname: Walter
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000187:drug effects; D000658:Amoxicillin / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003773:Dental Plaque / Q000382:microbiology*; D024881:Drug Resistance, Bacterial; D004357:Drug Synergism; D016124:Eikenella corrodens / Q000187:drug effects; D016967:Fusobacterium nucleatum / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D008795:Metronidazole / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D010518:Periodontitis / Q000382:microbiology*; D045242:Prevotella nigrescens / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D008795:Metronidazole; D000658:Amoxicillin
keywords: Aggregatibacter (Actinobacillus) actinomycetemcomitans; Amoxicillin; Combinatorial effect; Eikenella corrodens; Etest; Metronidazole