[Determination of DNA base composition and levels of DNA-DNA hybridization of Actinobacillus actinomycetemcomitans].

Using the strains of Actinobacillus actinomycetemcomitans (Aa) and Haemophilus aphrophilus (Haph) in experiments, the mole percent quanine plus cytosine content (mol% G + C) and level of DNA-DNA hybridization (DNA homology) were determined for the first time in oral microbiologic study in China. DNA was extracted by Marmur's method. The mol% G + C of DNA was determined by thermal denaturation method (Tm). DNA-DNA hybridization was carried out by De Ley's optical procedure (initial renaturation rate). The results are as follows: 1. The mol% G + C of DNA of Aa is different from that of Haph. 2. 2 strains of Aa had high DNA homology (73.8%) and the DNA homology between Aa and Haph was low (33.9%). It was confirmed that Aa and Haph are different species. In order to identify the bacteria in periodontal pockets accurately, it is necessary to carry out the nucleic acid study in bacterial classification.