False-colour transmission electron micrograph of the whooping cough bacterium, Bordetella pertussis. The micrograph shows the bacterium's surface covered in fine hairs called pili or frimbriae. Several types of pili have been identified, based on shape & function. Generally, pili cause bacteria to stick together & attach to foreign cells in the body. The fragments around the bacterium are bits of the growth medium. The whooping cough bacteria parasitise only humans, causing a respiratory tract infection characterised by fits of coughing that end in loud inspiratory whoops. It is potentially fatal in infancy. Magnification: x30,500 at 6x4.5cm size.