Ornithobacterium rhinotracheale North American Field Isolates Express a Hemolysin-Like Protein

Ornithobacterium rhinotracheale is a gram-negative bacterium responsible for the sporadic outbreaks of airsacculitis in poultry, accounting for millions of dollars in losses to the poultry industry annually. Although the organism was originally classified as non–β-hemolytic, recent North American field isolates of O. rhinotracheale obtained from pneumonic lungs and air sacs indicated hemolytic activity on blood agar plates upon extended incubation for 48 hr at room temperature in air after initial incubation at 37 C for 48 hr under 7.5% CO2. This report characterizes the β-hemolytic activity of O. rhinotracheale isolates by using in vitro kinetic hemolysis assays with sheep red blood cells, western blotting with leukotoxin-specific monoclonal antibodies, and isobaric tagging and relative and absolute quantitative (iTRAQ) analysis of O. rhinotracheale outer membrane protein digest preparations. The kinetic analyses of the hemolytic activity with red blood cells indicated that the protein is a pore former. iTRAQ analysis with membrane preparations revealed four peptides with homology to Mannheimia haemolytica leukotoxin and two peptides with homology to Actinobacillus actinoacetemcomitans leukotoxin. This is the first report that North American field isolates of O. rhinotracheale may express a hemolysin-like activity.