H Christensen1, M Bisgaard. 1. Department of Veterinary Disease Biology, Faculty of Life Sciences, University of Copenhagen, Frederiksberg C, Denmark. hech@life.ku.dk
Abstract
AIMS: The aims of the present investigation were to characterize and identify serovars of Riemerella anatipestifer and Riemerella-like isolates genetically and to test the specificity of PCR tests reported for the identification of R. anatipestifer. METHODS AND RESULTS: A total of 50 isolates from poultry tentatively classified with Riemerella anatipestifer were characterized genetically by partial sequencing of rpoB and by nearly full sequencing of the 16S rRNA gene for selected isolates. The results obtained were compared with the data from 13 reference strains by phylogenetic analysis. A total of 41 isolates were identified as R. anatipestifer, three as Wautersiella falsenii like, a single isolate as Pelistega europaea, while five isolates were classified as new, unnamed taxa. None of the reported PCR tests for identification of R. anatipestifer were found specific. CONCLUSIONS: Characterization of R. anatipestifer and related bacteria by traditional methods is often inconclusive because of inconsistent reactions and phenotypic diversity. For the same reason, gene sequencing and phylogenetic analysis are essential to allow proper classification and identification as demonstrated in the present study. SIGNIFICANCE AND IMPACT OF THE STUDY: The present investigations demonstrated that isolates of R. anatipestifer are often misidentified, and that new serovars should not be accepted unless they have been properly characterized by relevant genetic methods such as gene sequencing. In addition, we showed that the published PCR tests are not specific for this species. Finally, two new taxa were outlined, the final taxonomic positions of which remain to be identified.
AIMS: The aims of the present investigation were to characterize and identify serovars of Riemerella anatipestifer and Riemerella-like isolates genetically and to test the specificity of PCR tests reported for the identification of R. anatipestifer. METHODS AND RESULTS: A total of 50 isolates from poultry tentatively classified with Riemerella anatipestifer were characterized genetically by partial sequencing of rpoB and by nearly full sequencing of the 16S rRNA gene for selected isolates. The results obtained were compared with the data from 13 reference strains by phylogenetic analysis. A total of 41 isolates were identified as R. anatipestifer, three as Wautersiella falsenii like, a single isolate as Pelistega europaea, while five isolates were classified as new, unnamed taxa. None of the reported PCR tests for identification of R. anatipestifer were found specific. CONCLUSIONS: Characterization of R. anatipestifer and related bacteria by traditional methods is often inconclusive because of inconsistent reactions and phenotypic diversity. For the same reason, gene sequencing and phylogenetic analysis are essential to allow proper classification and identification as demonstrated in the present study. SIGNIFICANCE AND IMPACT OF THE STUDY: The present investigations demonstrated that isolates of R. anatipestifer are often misidentified, and that new serovars should not be accepted unless they have been properly characterized by relevant genetic methods such as gene sequencing. In addition, we showed that the published PCR tests are not specific for this species. Finally, two new taxa were outlined, the final taxonomic positions of which remain to be identified.