Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2008
Publication Date: 10/15/2008
Citation: Tabatabai, L.B., Zehr, E.S., Zimmerli, M.K., Nagaraja, K.V. 2008. Iron acquisition by Ornithobacterium rhinotracheale. Avian Diseases. 52(3):419-425. Interpretive Summary: Ornithobacterium rhinotracheale (ORT) is an emerging respiratory pathogen of poultry in North America causing millions of dollars of economic losses to the poultry industry, and is the causative agent of pleuritis, pneumonia and airsacculitis of turkeys, chickens and wild birds. Little is known about the molecular mechanisms of infection, or the type of virulence factors that may play a role in the pathogenesis of this organism. Acquisition of iron is one of the mechanisms pathogens use to survive and, colonize and infect the host animal. There are three mechanisms pathogens can use to acquire this important nutrient, a) passive membrane regulated uptake of ferrous iron; b) a gene (fur)-regulated uptake of iron that uses secreted low molecular weight iron chelators, and c) a fur-regulated uptake of iron through outer membrane receptor proteins for hemoglobin, heme-hemopexin, transferrin and possibly other iron-containing proteins the organism encounters while infecting its host. By using selective media that was rendered iron restricted to mimic the host environment, we found that Ornithobacterium rhinotracheale takes up iron passively, as expected, and takes up iron through outer membrane receptor proteins specific for various hemoglobins and ovotransferrin. It does not, however, secrete low molecular weight iron chelators. We also found that of 72 field strains of Ornithobacterium, 22 were able to grow well in the iron-restricted medium, suggesting that these filed strains maybe potentially more virulent. This is the first report on the identification of the iron acquisition mechanism of O. rhinotracheale. The information obtained in this study allows us to design strategies for the control of O. rhinotracheale infection of poultry.
Technical Abstract: Ornithobacterium rhinotracheale (ORT) is an emerging respiratory pathogen of poultry in North America causing millions of dollars of economic losses to the poultry industry. O. rhinotracheale is associated with airsacculitis, pleuritis, pneumonia and consolidation of lungs. Little is known about the molecular mechanisms of infection. In this study we explore the mechanism of iron acquisition by O. rhinotracheale. O. rhinotracheale grown under iron deprivation in brain heart infusion broth containing 200 µM 2,2’-dipyridyl did not secrete siderophores into the growth medium nor on chromazurol (CAS)-agar. Filter disks impregnated with inorganic iron salts of Fe(III) and Fe(II) and various protein-bound iron compounds placed on iron-restricted agar inoculated with a lawn of O. rhinotracheale supported growth from Fe(III) and Fe (II), bovine, sheep and porcine hemoglobins, ovotransferrin, but did not support growth from bovine transferrin, bovine apo-transferrin, bovine lactoferrin, and hemin. A putative hemoglobin-binding protein was identified, along with three additional proteins involved in iron acquisition. Seventy two field strains of ORT obtained from various turkey flocks were tested for their sensitivity to the iron chelator, 2,2’-dipyridyl, in a microtiter plate assay. Results showed that 22 of 72 strains tested were resistant to the iron chelator at concentrations of 50 and 100 µM, suggesting the presence of an inducible iron acquisition mechanism. This is the first report on the identification of the iron acquisition mechanism of O. rhinotracheale.