Characterisation of dermonecrotic toxin-producing strains of Pasteurella multocida subsp multocida isolated from man and swine

Thirty-six isolates, from man or swine, of Pasteurella multocida subsp, mul tocida producing (n = 13) or not producing (n = 23) the dermonecrotic toxin (DNT) were studied by numerical analysis, capsular typing and ribotyping. Toxigenic strains were also characterised by restriction fragment length po lymorphism (RFLP) of the toxA gene and pulsed-field gel electrophoresis (PF GE), Numerical analysis differentiated the Pasteurella species and subspeci es, but did not discriminate between toxigenic and nontoxigenic strains. RF LP demonstrated that toxA was located in a conserved part of the chromosome of all toxigenic strains. Ribotyping provided evidence of a close associat ion between DNT production and one of the sir EcoRI ribotypes designated as E2. In contrast, PFGE provided evidence for significant DNA polymorphism a mongst the toxigenic strains. Results of phenotypic and genotypic studies s uggested that toxigenic strains do not form a clone within the subspecies m ultocida. No difference was found between toxigenic strains of porcine or h uman origin by biochemical characterisation, capsular serotyping or genomic typing methods.