Plaque assay and cloning of scrub typhus rickettsiae in irradiated L-929 cells

Abstract
.gamma.-irradiated L-929 cells support plaque formation by 3 strains of Rickettsia tsutsugamushi and representative species of the spotted fever and typhus group rickettsiae. Sensitivity of the plaque assay for detection of viable scrub thyphus rickettsiae was similar to that achieved with i.p. inoculation of random-bred mice. The concentration of irradiated cells and the temperature and length of incubation all affected plaque size. A technique combining terminal dilution and plaque purification was used to obtain clones of 3 strains of scrub typhus rickettsiae.