Bordetella is a genus of small (0.2 - 0.7 µm), Gram-negative coccobacilli of the phylum Proteobacteria. Bordetella species, with the exception of B. petrii, are obligate aerobes, as well as highly fastidious, or difficult to culture. Three species are human pathogens (B. pertussis, B. parapertussis, B. bronchiseptica); one of these (B. bronchiseptica) is also motile.