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, cost-effective and readily available method to identify strains and differentiate between O. rhinotracheale and Ornithobacterium-like bacteria.

Multilocus sequence typing of Ornithobacterium rhinotracheale isolated from pigeons and birds of prey revealed new insights into its population structure.

The sudden emergence of Ornithobacterium rhinotracheale (ORT) in commercially raised poultry species and its presence in non-galliform birds raise important epidemiological issues about the role of interspecies transmission. In the present study, 21 ORT strains isolated from pigeons and from birds of prey were analyzed using the recently established multilocus sequence typing (MLST) scheme. Results were compared to MLST sequence data available from ORT strains isolated mainly from turkeys and chickens, but also single strains from pheasant, guineafowl and rook. The pigeon-derived ORT strains (n=11) were closely related amongst themselves representing their own cluster distant from ORT strains of non-columbiform avian hosts. ORT strains isolated from birds of prey (n=10) revealed a higher genetic heterogeneity that corresponded well to their host family relationships but grouped within the two mainly poultry-based clusters. None of these strains had a sequence type identical to strains investigated previously. However, three strains isolated from common kestrels and a single strain from a turkey vulture shared one or two out of seven gene loci, respectively, with strains of turkey and chicken origin. The MLST results of ORT isolated from pigeons and birds of prey likely reflect evolutionary bacterial host adaptations but might also indicate a potential for interspecies transmission. Definite conclusions should be drawn carefully as so far a few strains from non-galliform birds were analyzed by MLST. By extending the number of ORT isolates and the range of potential avian hosts, the MLST database can provide a valuable resource in understanding transmission dynamics.