Drug Resistance and R Plasmids inPasteurella multocidaIsolates from Swine

Abstract
A total of 163 strains of Pasteurella multocida isolated from swine were examined for drug resistance and R plasmids. Strains resistant to sulfadimethoxine (Sar), ampicillin (Apr), streptomycin (Smr) kanamycin (Kmr), and chloramphenicol (Cpr) were found in 93.9, 1.8, 16.6 , 1.2, and 10.4%, respectively. There were two patterns of drug resistance (Sar and SarCpr) in isolates from nasal cavities, and five patterns (Sar, SarSmr, SarSmrCpr, SarSmrApr, and SarSmrKmrCpr) in isolates from pneumonic lung specimens. Two isolates studied were proved to carry a nonconjugative R plasmid PJY2 or PJY8 with other unidentified plasmids, respectively. PJY2 (3.6 megadaltons) encoding resistance to SarSmr had one cleavage site for EcoRI or HindIII endonuclease and two sites for PstI endonuclease. PJY8 (5.5 megadaltons) encoding resistance to SarSmrKmrCpr had one EcoRI site and two PstI sites.