Histamine production by Haemophilus

Eight Haemophilus influenzae and four Haemophilus parainfluenzae strains, all freshly isolated from patients, were examined for histamine production. Histamine was produced by all the H. influenzae (0.06 microgram-2.6 micrograms/100 ml) and by two of the H. parainfluenzae strains (46.5-47.9 micrograms/100 ml). It is concluded that histamine which plays an important role in the pathogenesis of chronic aspecific respiratory diseases, may derive not only from degranulation of mast cells, but also produced by Haemophilus.