Genetic analysis of actinobacillus pleuropneumoniae, and comparison with Haemophilus spp. Taxon “Minor Group” and Taxon C

The genetic diversity among 52 field isolates, mainly from Australia, and 15 reference strains of Actinobacillus pleuropneumoniae was examined using multilocus enzyme electrophoresis. Thirty three electrophoretic types (ETs) were recognised, with a mean genetic diversity per locus of 0.312. Australian strains of serovars 1, 2, 5 and 7 belonged to the same clonal lines as strains of these serovars in other countries, but distinct clones of serovars 3, 7, 11 and 12 were also identified. The type strains of serovars 1, 9 and 11 were placed in the same ET. Strains of A. pleuropneumoniae biovar 2 were closely related to biovar 1 strains. Twenty three isolates which did not react with the typing sera or could not be assigned to a single serovar were divided into seven clonal groups. Five strains of Haemophilus sp. Taxon “minor group” which were included in the study were distinct from A. pleuropneumoniae, and were diverse, being divided into at least two major genetic groupings. Two strains of Haemophilus sp. Taxon C were placed in another distinct ET.