Differentiation of toxigenic from nontoxigenic isolates of Pasteurella multocida by PCR.

A PCR assay was developed for the differentiation of toxigenic Pasteurella multocida subsp. multocida strains, the major etiologic agent for progressive atrophic rhinitis in pigs, from nontoxigenic strains. The PCR targeted a toxA gene encoding a 143-kDa dermonecrotic toxin that is considered to be the central etiologic factor in progressive atrophic rhinitis. toxA fragments were amplified from toxigenic P. multocida isolates but not from nontoxigenic isolates or other bacteria isolated from pigs. The sensitivity of the reaction was as low as 10 pg of chromosomal DNA from a toxigenic strain. The results obtained by PCR of the DNAs of 187 field isolates of P. multocida were consistent with those obtained by the guinea pig skin test and Western blot (immunoblot) analysis. Restriction fragment analysis of the PCR-amplified fragments from 67 field isolates and comparison of the DNA sequences of fragments from capsular serotype A and D strains suggest that the PCR-amplified region, which is considered to encode the major immunologic determinants of the toxin, would be the same among P. multocida strains. The PCR that we describe should be useful for the diagnosis and the etiologic survey of progressive atrophic rhinitis.