Drug resistance plasmids of Actinobacillus (Haemophilus) pleuropneumoniae serotype 2 strains isolated from swine.

Drug resistance plasmids were detected in two drug resistant strains of Actinobacillus (Haemophilus) pleuropneumoniae serotype 2 isolated in Japan. One strain, Hpn25, was resistant to ampicillin, kanamycin, streptomycin and sulfonamides, and harbored two plasmids with a molecular size of 3.7 and 4.1 kilobases (kb). The other strain, Hpn18, which was resistant to streptomycin, tetracycline, and chloramphenicol, harbored three plasmids with a molecular size of 2.2, 12, and 35 kb. The resistance of Hpn 25 to streptomycin and sulfonamides is mediated by a 4.1 kb plasmid and that of Hpn 18 to streptomycin and chloramphenicol by one or more of the 2.2, 12, and 35 kb plasmids.