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JAC Advance Access originally published online on November 20, 2006
Journal of Antimicrobial Chemotherapy 2007 59(1):59-65; 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

Susceptibility of Actinobacillus actinomycetemcomitans to six antibiotics decreases as biofilm matures

Naoko Takahashi1,2, Kazuyuki Ishihara1,2,*, Tetsuo Kato1,2 and Katsuji Okuda1

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

Received 16 June 2006; returned 4 August 2006; revised 14 September 2006; accepted 13 October 2006

*Corresponding author. Tel: +81-43-270-3742; Fax: +81-43-270-3744; E-mail: ishihara{at}tdc.ac.jp

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


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