THE EFFECT OF PLASMID ACQUISITION ON POTENTIAL VIRULENCE ATTRIBUTES OF PASTEURELLA-MULTOCIDA

Several plasmids that were isolated from complement-resistant Pasteure lla multocida or Escherichia coli were evaluated for phenotypic marker s. Plasmid p2267, isolated from a tetracycline-resistant, complement-r esistant fowl cholera field isolate of P. multocida (PM2267), was used to transform a K-12 E. coli (C600); this resulted in increased comple ment resistance, which was eliminated by curing. Either of two plasmid s (p1870 or p70-1, isolated from P. multocida and E. coli, respectivel y) conferred an increase in complement resistance and invasiveness to turkey epithelial cells when expressed in the Clemson University (CU) vaccine strain of P. multocida. Additionally, the CU strain containing p1870 was more virulent in turkey challenge, and the plasmid appeared amplified in vivo. No detectable differences in major outer-membrane proteins, capsule, or carbohydrate fermentation were found to be assoc iated with the acquisition of these plasmids.