Vaccine potential of recombinant Ornithobacterium rhinotracheale antigens.

Ornithobacterium rhinotracheale is a pathogen involved in respiratory infection and systemic disease in poultry. Previously, eight potential vaccine candidates were identified that induced cross-protective immunity when administered to chickens as a multi-component vaccine. In this study, we analyzed the immunogenicity of these eight recombinant proteins by subunit vaccination, and characterized the different proteins and corresponding genes more thoroughly by sequencing, in vitro expression analysis, and cellular localization experiments. We found, that all genes encoding the eight antigens were highly conserved among different O. rhinotracheale serotypes, but the different antigens were not expressed by all serotypes. Cellular fractionation experiments indicated that the majority of the antigens are predominantly located in the outer membrane fraction. Vaccination of chickens with single-antigen vaccines demonstrated that the Or77 antigen was protective against serotypes that expressed Or77 in vitro, suggesting that the protein has strong potential as a vaccine antigen. Furthermore, immunization with four-component subunit vaccines indicated the existence of immunogenic synergism between the candidate vaccine antigens.

Successful selection of cross-protective vaccine candidates for Ornithobacterium rhinotracheale infection.

Ornithobacterium rhinotracheale is a bacterial pathogen known for causing respiratory disease in poultry. In this study, we demonstrate for the first time that cross-protective immunity against different O. rhinotracheale serotypes can be induced by live vaccination. Sera from these live-vaccinated and cross-protected birds were used to identify new vaccine targets by screening an O. rhinotracheale expression library. Out of 20,000 screened plaques, a total of 30 cross-reactive clones were selected for further analysis. Western blot analysis and DNA sequencing identified eight different open reading frames. The genes encoding the eight cross-reactive antigens were amplified, cloned in an expression vector, and expressed in Escherichia coli. Purified recombinant proteins with a molecular mass ranging from 35.9 kDa to 62.9 kDa were mixed and tested as a subunit vaccine for (cross-)protection against challenge with homologous and heterologous O. rhinotracheale serotypes in chickens. Subunit vaccination resulted in the production of antibodies reactive to the recombinant proteins on Western blot, and this eight-valent vaccine conferred both homologous and heterologous protection against O. rhinotracheale challenge in chickens.

Passive immunization of immune-suppressed animals: chicken antibodies protect against Ornithobacterium rhinotracheale infection.

Unravelling of the protective immunity acquired during a natural infection may contribute to vaccine development. To assess the role of antibody-mediated immunity in protection against Ornithobacterium rhinotracheale infection in chickens, a novel experimental method was applied that combined immune depletion and passive transfer of immunity within the same host. Administration of cyclophosphamide (CY) to broiler chickens successfully suppressed B lymphocyte development, and therefore humoral immunity, as confirmed by histological and serological analysis. Challenge of CY-treated birds with O. rhinotracheale revealed a significantly higher pathology score in comparison to immune-competent birds that received the same bacterial challenge. Measurement of serum immunoglobulin levels of immune-competent birds revealed a positive correlation between IgA and/or IgG production and protection against infection. Passive transfer of O. rhinotracheale-specific antiserum to the immune-suppressed birds prior to pathogen challenge significantly decreased morbidity. This protective effect was not observed after administration of control sera containing similar concentrations of immunoglobulins. Together, these results provide firm evidence that chicken humoral immunity to O. rhinotracheale is a key component in protection against infection. Our data confirm that the applied immune depletion and reconstitution approach is an attractive tool to analyse the nature of the protective immune response.

Ornithobacterium rhinotracheale: A review.

Ornithobacterium rhinotracheale is a relatively recently discovered bacterium of the rRNA superfamily V. It is of worldwide distribution in commercial poultry, in which it is associated with respiratory diseases, and it is also found in wild birds. Airsacculitis and pneumonia are the most common features of infection with O. rhinotracheale. These signs can be induced by aerosol in intra-tracheal or intra-thoracic administration of the organism, and can be aggravated by other factors, such as respiratory viruses, bacteria or climatic conditions. Osteitis, meningitis and joint-infections, which can be induced by intravenous application, have been associated with O. rhinotracheale, but it remains uncertain whether the organism should be regarded as a primary pathogen. The infection can be transmitted horizontally by aerosol, as well as vertically through eggs, which probably accounts for its rapid and worldwide spread. Although O. rhinotracheale is difficult to identify, some commercial identification systems have been found to be suitable, although the media used in such systems will not always support its growth. A PCR assay was also found to be suitable for identification purposes. Twelve serotypes can be distinguished within the species O. rhinotracheale, of which serotype A is the most prevalent. Genetic investigation has revealed that more species or subspecies probably exist within the genus Ornithobacterium. Therapeutic treatment of the disease can be difficult because acquired resistance against the regular antibiotics is very common within the genus. Vaccination with autogenous inactivated vaccines has been successful in reducing clinical signs, but success depends on the adjuvant used. Only potent oil adjuvants are effective in young birds with maternal antibodies, but the use of these adjuvants is known to induce some local reactions. Live vaccination is feasible, but up to now, no avirulent strains of O. rhinotracheale have been found. Vaccination of broiler breeders induced protection against experimental infection of the progeny to at least 3 weeks of age.

[Respiratory problems, growth retardation and arthritis in turkeys and broilers caused by a Pasteurella-like organism: Ornithobacterium rhinotracheale or 'Taxon 28']. / Ademhalingsproblemen, groeivertraging en gewrichtsontsteking bij kalkoenen en vleeskuikens door een Pasteurella-achtige bacterie: Ornithobacterium rhinotracheale of 'Taxon 28'.

Since August 1993 moderate to serious respiratory problems with necrotic pneumonia, growth depression and fast increasing mortality are seen in commercial turkeys (2-8 weeks of age) and broilers (4-6 weeks of age). An unidentified pleiomorphic Gram-negative rod was isolated from affected tissues. This Pasteurella-like organism, with yet unknown taxonomy, is recently named Ornithobacterium rhinotracheale gen. nov. sp. nov. or 'Taxon 28'. Experimentally severe growth depression and arthritis could be evoked in commercial turkeys and chickens. Respiratory signs caused by O. rhinotracheale could not (yet) be reproduced experimentally. This is the first report of the isolation of this organism in poultry in the Netherlands findings.