Ultrastructure of viable and inactivated Coxiella burnetii after inoculation of mice.

C3HA mice were inoculated intraperitoneally (i.p.) with viable Coxiella burnetii (C.b.) (strain Apodemus flavicollis-Luga, phase I) or C.b. antigen (formalin-inactivated C.b.); pieces of spleen, liver, omentum, kidney, and suspension of peritoneal macrophages were examined by electron microscopy at 1, 7, 14, 21, 28, and 42 days post-infection (p.i.). Two main types of viable C.b. cells--small dense (DC) and bacteria-like (BC)--were found in omentum, spleen, and peritoneal exudate cells beginning from the 1st day p.i. but maximal amount they reached in spleen at day 14. Some parasitophorous vacuoles contained damaged BC or lysing C.b. cells. C.b. corpuscular antigen was found in phagosomes in ultrathin sections of spleen macrophages until 28 days p.i. By 7 days p.i. in omentum 3 types of parasitophorous phagosomes were described which were supposed to be the sites of the antigen utilization. It is assumed that most BC are destroyed in omentum macrophages during the 1st week after i.p. injection of the antigen, and DC can persist in spleen at least for one month.