POSSESSION OF IDENTICAL NONCONJUGATIVE PLASMIDS BY DIFFERENT ISOLATES OF PASTEURELLA-MULTOCIDA DOES NOT IMPLY CLONALITY

Experiments were performed to test the hypothesis that possession of the same nonconjugative R plasmid by different isolates of Pasteurella multicida implied that they were of the same clone. Seven isolates of P. multicida were studied, two possessed an identical nonconjugative R plasmid (pVM109), four possessed another (pVM110), and one isolate possessed a nonconjugative R plasmid related to pVM110. Phenotypic and genotypic characteristics of the isolates were determined and compared. Isolates possessing the same nonconjugative R plasmid were shown to be different, and isolates possessing a different nonconjugative R plasmid were shown to be the same. We conclude that possession of an identical nonconjugative R plasmid by two isolates of P. multocida does not imply clonality. © 1990.