Haemophilus

            Small, non-motile, non-sporing, Gram-negative bacilli that are parasitic on human beings and animals.  They are characterized by their requirement of one or both of two accessory growth factors present in blood, ie., X and V.  It was isolated in 1892 by Pfeiffer, hence known as Pfeiffer's bacillus. The genus name is derived from the Greekwords meaning 'blood loving'. H. influenzae is an exclusively human pathogen whose complete genome has sequenced. The important  species are   Haemophilus influenzae, H. aegyptius, H. ducreyi