CHARACTERIZATION OF NEWLY ISOLATED PLASMIDS FROM ACTINOBACILLUS-PLEUROPNEUMONIAE

The genetic basis of drug-resistant strains of Actinobacillus pleuropn eumoniae in Japan was studied. The A pleuropneumoniae strains AV277 an d AV281 that belong to serotype 2 were resistant to streptomycin (SM) and sulfonamide (SA). Both strains had an 8.1-kilobase (kb) SM-SA plas mid that was previously classified in the H1 group. The AV177 (serotyp e 1) strain was resistant to SM, SA, ampicillin, and kanamycin (KM), b ut did not have any plasmids. The AV319 and AV324 (serotype 1) strains were resistant to SM, SA, tetracycline (TC), and chloramphenicol (CP) . The AV318 (serotype 12) strain was resistant to SM, SA, TC, minocycl ine, and CP. These 3 strains (AV319, AV324, and AV318) had a 4.3-kb SM -SA plasmid and a 5.2-kb CP plasmid. The 4.3-kb plasmid was classified in the H2 group. The AV263 (serotype 1) strain was resistant-to SM, S A, KM, TC, and cp. It had a 5.2-kb CP plasmid and a 6.6-kb SM-SA-KM pl asmid. Both plasmids did not replicate stably in Escherichia coli stra ins. The former 5.2-kb plasmid was mobilized in E coli strains by plas mid RP4, which belonged to incompatibility P with broad host range, bu t the latter 6.6-kb plasmid was not so mobilized. Three 5.2-kb CP plas mids isolated from strains AV319, AV324, and AV318, had the same restr iction endonuclease pattern after digestion with Ava I and EcoRI. They coexisted with Hl group plasmids in the incompatibility test, and coe xisted also with H2 group plasmids of the original A pleuropneumoniae strains. Results indicated that the 5.2-kb CP plasmids could be classi fied in a new incompatibility group, H3. In this study, 4 types of pla smids were isolated, but no plasmids encoded TC and minocycline resist ance.