Analysis of Actinobacillus pleuropneumoniae and related organisms by DNA-DNA hybridization and restriction endonuclease fingerprinting.

The objective of this study was to determine the degree of genetic relatedness of Actinobacillus pleuropneumoniae to selected members of the family Pasteurellaceae, with particular emphasis on species commonly associated with swine. Free-solution DNA-DNA hybridization studies revealed that representative strains of all 12 serotypes of A. pleuropneumoniae formed a homogeneous group, sharing 74 to 90% sequence homology with A. pleuropneumoniae serotype 1. All serotypes of A. pleuropneumoniae tested demonstrated a high degree of genetic relatedness (66 to 79%) to the type species of the genus Actinobacillus, A. lignieresii. Little homology (less than 20%) was detected between A. pleuropneumoniae strains and selected Haemophilus spp. and Pasteurella spp. Since free-solution hybridization methods are technically demanding and require large amounts of highly purified DNA, restriction endonuclease fingerprinting (REF) was examined to determine whether it could be a useful taxonomic tool for classification of members of the family Pasteurellaceae. REF profiles were compared, and the degree of similarity between organisms was quantitated by calculating Jaccard similarity coefficients. There was a significant positive relationship between the REF Jaccard coefficients and the DNA homology values determined from free-solution hybridization experiments.