Bacteriological characteristics of Histophilus ovis and its relationship to similar bacteria

Seventeen strains of Histophilus ovis were obtained from a variety of pathological conditions and geographical areas and were examined to determine the bacteriological characteristics of the organism. All were Gram-negative pleomorphic rods which only grew under micro-aerophilic conditions in media enriched with blood, serum or meat particles. All strains were catalase negative, indole positive and nitrate positive while most produced acid from glucose, fructose, galactose, mannose, xylose, mannitol and sorbitol. Eight strains were examined serologically and compared with two strains of Actinobacillus seminis. In agglutination and precipitation tests, all strains of H ovis appeared antigenically identical and showed antigenic relationships to A seminis. Results of complement fixation tests confirmed the close, if not identical, antigenic relationship of H ovis and A seminis. It is suggested that H ovis and A seminis are biochemical variants of the same organism.