Phylogenetic relationship of Ornithobacterium rhinotracheale isolated from poultry and diverse avian hosts based on 16S rRNA and rpoB gene analyses

Background: Ornithobacterium (O.) rhinotracheale is an emerging bacterial pathogen in poultry and not fully understood to date. Because of its importance particularly for the global turkey meat industry, reliable diagnostic and characterization methods are needed for early treatment and in future for better vaccine production. The host range of birds infected by O. rhinotracheale or carrying the bacterium in their respiratory tract has constantly increased raising important epidemiological and taxonomic questions for a better understanding of its diversity, ecology and transmission cycles. The purpose of this study was to introduce partial rpoB gene sequencing for O. rhinotracheale into routine diagnostics to differentiate strains isolated from poultry and more diverse avian hosts (i.e., birds of prey, corvids and pigeons) and to compare phylogenetic relationships with results from 16S rRNA gene analysis and multilocus sequence typing (MLST).
Results: Partial 16S rRNA gene analysis revealed a high level of homogeneity among the 65 investigated O. rhinotracheale sequences with similarity values ranging from 98.6 to 100% between sequences from non-galliform and poultry species. The corresponding rpoB gene sequences were heterogeneous and ranged in their similarity values from 85.1 to 100%. The structure of the rpoB tree was in strong correlation with previous MLST results revealing three main clusters A (poultry and birds of prey), B (poultry, birds of prey and corvids) and C (pigeons), which were clearly separated from each other.
Conclusions: By using partial sequences from a single gene, the rpoB gene analysis is in good agreement with MLST results with a slight decrease in resolution to distinguish more similar strains. The present results provide strong evidence that traditional phenotypic and genetic methods may not properly represent the heterogeneous group of bacteria classified as O. rhinotracheale. From housekeeping gene analyses, it is very likely that the genus Ornithobacterium includes additional species and partial rpoB gene sequencing can be recommended as fast, costeffective and readily available method to identify strains and differentiate between O. rhinotracheale and Ornithobacterium-like bacteria.