Identification of the capsule type of Pasteurella multocida isolates from cases of fowl cholera by multiplex PCR and comparison with phenotypic methods

The ability of Pasteurella multocida to invade and multiply in its host is enhanced by the presence of the capsule, one of the most important virulence factors for this bacterium. Capsular typing methods are often used in epidemiological and pathogenesis studies of this agent. Five different serogroups have been identified based on serological typing. However, such tests are laborious, and agglutination of homologous antiserum may fail. The aim of this study was to develop a multiplex PCR protocol for the identification of the hyaD-hyaC and dcbF genes specific to serogroups A and D, respectively, and to compare these results with those of phenotypic tests for 54 strains isolated from fowl cholera cases in southern Brazil. The kappa coefficient and chisquare statistics were calculated to assess the agreement between the diagnostic methods and to determine the significance of the results, respectively. The multiplex PCR was able to detect the evaluated genes. Forty-nine strains (90.74%) were classified into serogroup A, and only two isolates (3.7%) were not identified as belonging to any of the serogroups analyzed. In contrast, with the phenotypic tests, only 41 strains (75.93%) were classified into serogroup A and 11 samples (20.37%) were unidentifiable. Of the strains analyzed, 70.37% were classified into the same serogroup (A) by both methods, and the kappa coefficient (k = 0.017) indicated poor agreement between the tests. Thus, multiplex PCR is an alternative for P. multocida capsular typing, as it allows the simultaneous and rapid detection of genes and also provides a greater strain-typing capacity