title: Susceptibility of Actinobacillus actinomycetemcomitans to six antibiotics decreases as biofilm matures.
abstract: OBJECTIVE
  Actinobacillus actinomycetemcomitans is a major causative agent of chronic and aggressive periodontitis. Freshly isolated strains of A. actinomycetemcomitans display rough-type colonies and initiate biofilm formation on glass surfaces. The purpose of this study was to determine the antibiotic susceptibility of A. actinomycetemcomitans biofilm during different phases of maturation.
  
  
  METHODS
  Using 96-well microtitre plates, we determined the antibiotic susceptibility of rough-type strain 310a to concentrations from 0.1 to 10 mg/L each of erythromycin, ofloxacin, ampicillin, cefalexin, tetracycline and minocycline during biofilm formation. Antibiotics were added at the start of the culture (early phase) and after 24 h of cultivation (mature phase).
  
  
  RESULTS
  Adding 10 mg/L of ampicillin, 10 mg/L of cefalexin, 0.1 or 1 mg/L of tetracycline, or 0.1 mg/L of minocycline significantly inhibited 310a biofilm formation in the early phase, but not in the mature phase. Although adding 10 mg/L of erythromycin, tetracycline or minocycline reduced biofilm development in the early phase, it enhanced 310a biofilm development in the mature phase. Ofloxacin exerted a strong inhibitory effect in both the early and mature phases of biofilm formation throughout all experiments.
  
  
  CONCLUSIONS
  The present study demonstrated that the susceptibility of A. actinomycetemcomitans to many antibiotics decreased after biofilm maturation.
authors.affiliation: Department of Microbiology, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan.
authors.forename: Naoko
authors.initials: N
authors.lastname: Takahashi
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Ishihara
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Kato
authors.forename: Katsuji
authors.initials: K
authors.lastname: Okuda
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000187:drug effects* / Q000648:ultrastructure; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D008826:Microbial Sensitivity Tests; D008855:Microscopy, Electron, Scanning
chemical_list: D000900:Anti-Bacterial Agents