Bordetella pertussis
the usual cause of pertussis (whooping cough), found only in the human respiratory tract. Virulent strains are encapsulated with smooth colonies (Phase I); prolonged laboratory culture produces loss of surface K antigens and altered colonial morphology (Phases II, III, and IV) progressing to obviously rough strains that are avirulent. Called also Bordet-Gengou bacillus.
Medical dictionary.
2011.