False-colour shadow transmission electron micrograph (TEM) of an individual bacterium of genus Rickettsiae, a group of very small, non- motile, rod-like, Gram-negative bacteria. Like viruses, Rickettsiae are obligate intracellular parasites, ie they cannot live outside of the host's cells. Rickettsiae infect ticks & mites, through whom they may infect mammals (including man), causing serious diseases. Rickettsia akari causes rickettsial pox, several rickettsial species cause different forms of typhus, & R. rickettsii is responsible for Rocky Mountain spotted fever. Magnification: X 38,000 at 35mm size.