Bordetella pertussis Tohama I. This strain was originally isolated from a patient with whooping cough and has been studied extensively for over 40 years. The chromosome contains a type IV secretion system for export of the pertussis toxin, a typical AB type toxin. The B subunits are involved in attachment to host cells, and the A subunit, the ADP-ribosylating factor, interferes with cell signalling pathways by increasing intracellular cAMP concentrations. The result is an inability of phagocytes to kill foreign invaders such as the bacterium.