A genus of gram-negative, immotile and nonspore-forming, oval to rod-shaped, often pleomorphic bacteria which occur as parasites or pathogens in mammals (including humans), birds, and reptiles. They are facultatively aerobic, capable of fermenting carbohydrates (without production of gas) and of reducing nitrates. Most species are oxidase- and catalase-positive. Some cultures tend to stick on the surface of agar media, particularly on primary isolation. The genome deoxyribonucleic acid contains between 40 and 47 mol % guanine plus cytosine. The actinobacillus group shares many biological properties with the genus Pasteurella. At least two of the following features or combinations of features differentiate members of the Actinobacillus group from Pasteurella: hemolysis, delayed or lacking fermentation of D-galactose or D-mannose, fermentation of inositol, positive reactions for both urease and β-galactosidase, hydrolysis of salicin or esculin, and fermentation of maltose together with negative reactions for trehalose fermentation and ornithine decarboxylase.