Actinobacillus organisms are mainly pathogens of farm animals and commensals of the mucosa of upper respiratory tract and oral cavity. They cannot survive for long in the environment, so carrier animals are important in their transmission. Actinobacillus organisms are small Gram negative coccobacilli that are oxidase negative, non-motile facultative anaerobes that ferment carbohydrates to produce acid. They do not grow on MacConkey Agar. Clinically, they cause granulomatous inflammation.