A Selective Medium for Actinobacillus actinomycetemcomitans and the Incidence of the Organism in Juvenile Periodontitis

Abstract

A selective medium, malachite green bacitracin agar, was developed for the isolation of Actinobacillus actinomycetemcomitans from subgingival plaque of periodontally diseased patients. The medium consisted of Trypticase soy agar 40 gm/liter, bacitracin 128 μg/ml, malachite green 8 μg/ml and 5% defibrinated sheep blood. The medium, when incubated in an atmosphere of air plus 10% CO₂ for 5 days, permitted greater than 80% recovery of pure cultures of A. actinomycetemcomitans when compared with a nonselective medium. The most frequent contaminant in plaque samples from different clinical conditions was Haemophilus aphrophilus. Decomposition of H₂O₂ was useful in differentiating these two species. Clinical studies employing the malachite green bacitracin medium revealed a significant association between the presence of the organism, A. actinomycetemcomitans and juvenile periodontitis.