Peculiarities of Rickettsia prowazekii in the cell culture as revealed by cryoultramicrotomy.

Ultrastructure of Rickettsia prowazekii has been followed in L-929 cells 4 days post-infection (p.i.) by cryoultramicrotomy. Groups of rickettsiae were present in the cytoplasm outside of vacuoles forming microcolonies. The size of rickettsiae amounted to 400 X 700 nm, the average thickness of the cell wall was 5 nm, that of periplasmic space and cytoplasmic membrane 14 and 6 nm, respectively. Within intracytoplasmic colonies the rickettsiae were tightly packed and their cell walls were closely adjacent to each other. No halo or capsule-like coating around them was detected. No ultrastructural details were observed in the light translucent spaces between cells. Marginal rickettsiae of the microcolonies were often in close contact with the host cell mitochondria.