Electron microscopic studies on the in vitro proliferation of spotted fever group rickettsia isolated in Japan.

Rickettsia was isolated from a patient with Japanese spotted fever, and its proliferation in cultured green monkey kidney cells was observed by electron microscopy. In the course of this study, we observed fusion of infected cells to uninfected cells which may be a way of spreading the rickettsiae from a cell to another. On the other hand, whirlpool-like, multilayer membranous structures, similar to the mesosomes of gram-negative bacteria, were sometimes seen in the rickettsial cells. The other profiles common to the other rickettsiae in spotted fever group were observed, such as the electron-lucent halo zone around the rickettsiae, and external fibrous materials on their surface, but intranuclear multiplication was rarely observed.