A Noble Selective Medium for Isolation of Actinobacillus actinomycetemcomitans

Objective: Actinobacillus actinomycetemcomitans is an important pathogen in juvenile periodontitis and occasionally nonoral infections. Several selective media have been described for the isolation of A. actinomycetemcomitans though their selectivities are low. The present study is undertaken with the purpose of improving the selectivity of a new medium for detection of A. actinomycetemcomitans. Methods: The most suitable based medium and the sensitivity of antibiotics were examined using reference strains (serotypes a~e) of A. actinomycetemcomitans. The recovery of the new selective medium were calculated and compared with nonselective blood agar and TSBV medium, which is the most widely used. Results: This bacterium requires nutritionally complex media for growth, and the media usually include blood or serum in their base. The globulin powder was the better for supplement to base medium. We tested tryptic soy, brain heart infusion, GC agar base, Brucella etc. for base medium. However, there are not so big differences among them. Bacitracin and vancomycin are well known to resistant to A. actinomycetemcomitans. Our new selective medium contains limited antibiotic for selective A. actinomycetemcomitans from other oral bacteria. Strains of serotype d grew in TSBV with low level, but their recoveries were almost 100% growth in the new selective medium. The recovery of the medium was 80-100% by referent strains. Culture condition anaerobically at 37°C for 3 days in a CO₂ incubator in air-5% CO₂ was better than in anaerobic chamber in an atmosphere of 80% N₂-10%H₂-10%CO₂ or in candle jars. Conclusion: The new selective medium was highly selective for A. actinomycetemcomitans serotype from a through e and eliminated possible false-positive or-negative results caused by visually interpreting non-A. actinomycetemcomitans and Haemophilus aphrophilus . This study was supported in part by a Grant-in-Aid for FRONTIER 2003 from MEXT.