Whooping cough (pertussis) is caused by the bacterium Bordetella pertussis. B. pertussis  is a very small Gram-negative aerobic coccobacillus that appears singly or in pairs. Its metabolism is respiratory, never fermentative, and taxonomically, Bordetella is placed among the "Gram-negative Aerobic Rods and Cocci" in Bergey's Manual. Bordetella is not assigned to any family. The bacteria are nutritonally fastidious and are usually cultivated on rich media supplemented with blood. They can be grown in synthetic medium, however, which contains buffer, salts, an amino acid energy source, and growth factors such as nicotinamide, for which there is a strict requirement. Even on blood agar the organism grows slowly and requires 3-6 days to form pinpoint colonies.

Bordetella pertussis colonizes the cilia of the mammalian respiratory epithelium (Figure 1). Generally, it is thought that B. pertussis does not invade the tissues, but some recent work has shown the bacterium sequestered in alveolar macrophages. The bacterium is a pathogen for humans and possibly for higher primates, and no other reservoir is known. Whooping cough is a relatively mild disease in adults but has a significant mortality rate in infants. Until immunization was introduced in the 1940s, whooping cough was one of the most frequent and severe diseases of infants in the United States.