Effects ofMoraxella(Branhamella)ovisCulture Filtrates on Bovine Erythrocytes, Peripheral Mononuclear Cells, and Corneal Epithelial Cells

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Abstract
Infectious bovine keratoconjunctivitis (IBK) is a highly contagious ocular disease that affects cattle of all ages and that occurs worldwide. Piliated hemolyticMoraxella bovisis recognized as the etiologic agent of IBK. According to data from the Nebraska Veterinary Diagnostic Laboratory System, however,Moraxella(Branhamella)ovishas been isolated with increasing frequency from cattle affected with IBK. The objective of this study was, therefore, to examineM. ovisfield isolates for the presence of the putative virulence factors ofM. bovis. Culture filtrates from selectedM. ovisfield isolates demonstrated hemolytic activity on bovine erythrocytes and cytotoxic activity on bovine peripheral blood mononuclear cells and corneal epithelial cells. The hemolytic activity of the culture filtrates was attenuated after heat treatment. Polyclonal antibodies raised against theM. bovishemolysin-cytotoxin also recognized a protein of approximately 98 kDa in a Western blot assay. These data indicate that theM. ovisfield isolates examined produce one or more heat-labile exotoxins and may suggest thatM. ovisplays a role in the pathogenesis of IBK.

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