Some ultrastructural effects of persistent infections by the rickettsia Coxiella burnetii in mouse L cells and green monkey kidney (Vero) cells.

Mouse fibroblasts (L-929) and Vero (green monkey kidney) cells were infected with the rickettsia Coxiella burnetti, and persistent infections developed and were studied over a 6- to 10-month period. Ultrastructural comparisons were made between the two infected cell types, and both were tested cytochemically for the presence of acid phosphatase, a marker enzyme of lysozymes. Rickettsiae were always observed within vacuoles, and some infected L cells showed flattened endoplasmic reticulum as compared with uninfected cells. Rickettsiae in Vero cells were most often seen in vacuoles containing whorls of membranes ("myelin configurations") which were also seen in uninfected cells. Rickettsiae in Vero cells were pleomorphic, with acid phosphatase reaction product in their periplasmic space. This suggests either rickettsial degradation by lysosomal enzymes which penetrated the cell envelope or a penetration after the rickettsiae were dead. Vacuoles of infected Vero cells showed much more reaction product than that in infected L cells, and most rickettsiae in L cells had a normal appearance and showed no reaction product in their periplasmic space.