Dendrogram grouping based on the composite RAPD electrophoretic band patterns of representative H. parasuis strains and outgroup strains. Band patterns from all three single-primer experiments were combined to obtain a composite-primer RAPD dendrogram. Reference strains are designated A-O (Table 1), field isolates are designated 1–31 (Table 2), and outgroups are Pasteurella multocida (PM), Mannheimia haemolytica (MH), Pasteurella trehalosi (PT) and Actinobacillus pleuropneumoniae (AP). Three clade designations are shown. Reference strains were obtained between 1978 and 1990. Field strains 1–24, 25–29, 30–31 were obtained in 2004, 1999, and 1984, respectively. Numbers at the nodes indicate percentages of bootstrap values after 1000 replicates.