RICKETTSIA-CONORII ENTRY INTO VERO CELLS

The entry of rickettsiae into eukaryotic cells is mediated by an induc ed phagocytosis, but rickettsiae have never been observed in a closed phagocytic vacuole. In this study, Rickettsia conorii entry into Vero cells was observed by transmission electron microscopy during a period of 3 to 20 min after bacterium-cell contact. The entry occurred withi n 3 min after bacterium-cell contact, and R. conorii was observed in t he process of engulfment, within a phagocytic vacuole, or free in the cytosol. Escape from the phagosome is a very rapid step since phagosom e lysis was only occasionally observed. By 12 min, 90% of bacteria wer e internalized and half were free in the cytosol. This report confirms that rickettsiae penetrate nonphagocytic cells by induced phagocytosi s and is the first demonstration of rickettsiae within a complete phag ocytic vacuole.