Deoxyribonucleic Acid-Deoxyribonucleic Acid Hybridization Analysis of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus

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Abstract
DNA were isolated and purified from 20 strains of A. actinomycetemcomitans, 6 strains of H. aphrophilus, 2 strains of H. paraphrophilus, 2 strains of H. pleuropneumoniae, 2 strains of H. paraphrohaemolyticus, 2 strains of H. influenzae and 1 strain each of A. lignieresii, A. suis, H. aegyptius, H. parainfluenzae and H. parahaemolyticus. The guanine-plus-cytosine contents of the DNA were determined and they agreed closely with previous estimates. DNA-DNA hybridization analyses revealed that all of the strains identified as A. actinomycetemcomitans were at least 69% homologous to DNA probes from 2 A. actinomycetemcomitans strains (strains NCTC 9710T [T = type strain] and Y4). The H. aphrophilus and H. paraphrophilus strains were homologous to the 2 A. actinomycetemcomitans probes at levels of 25-37%. The DNA of all A. actinomycetemcomitans strains were homologous to a DNA probe from H. aphrophilus strain NCTC 5906 at levels of 30-39%. The 2 strains of H. paraphrophilus tested were homologous to the H. aphrophilus probe at levels of 73 and 77%, indicating a very close relationship between these groups of organisms. H. parainfluenzae strain ATCC 9796 DNA seemed to be homologous to the H. aphrophilus and A. actinomycetemcomitans probes at low but significant levels (12-16%). All of the other strains of haemophili and actinobacilli tested gave .ltoreq. 10% homology with the 3 test probes.

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