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JAC Advance Access first published online on November 20, 2006
This version published online on November 24, 2006
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkl452
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© The Author 2006. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
Received June 16, 2006
Revised September 14, 2006
Accepted October 13, 2006

Original article

Susceptibility of Actinobacillus actinomycetemcomitans to six antibiotics decreases as biofilm matures

Naoko Takahashi 1, Kazuyuki Ishihara 1 *, Tetsuo Kato 1, and Katsuji Okuda 2

1 Department of Microbiology, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan; Oral Health Science Center, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan
2 Department of Microbiology, Tokyo Dental College, 1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan

* To whom correspondence should be addressed.
Kazuyuki Ishihara, E-mail: ishihara{at}tdc.ac.jp


  Abstract

Objectives: 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.

Keywords: periodontitis; bacterial biofilm; antibiotic resistance; antibiotic therapy; A. actinomycetemcomitans.
The originally published version of this article is incorrect. The last author's name was incorrectly shown. The authors apologize for this error.
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