Survival of Trypanosoma cruzi metacyclic trypomastigotes within Coxiella burnetii vacuoles: differentiation and replication within an acidic milieu.

Coxiella burnetii, the etiological agent of Q fever, is an obligate intracellular bacterium that resides within acidified vacuoles with secondary lysosomal characteristics. Infective stages of Trypanosoma cruzi, the causative agent of Chagas' disease, actively invade a wide variety of cells, a process followed by lysosomal recruitment. Recently, we have investigated and characterized early events that occur in Vero cells persistently colonized with C. burnetii when doubly infected with T. cruzi trypomastigote forms. Kinetic studies of trypomastigote transfer indicated that parasitophorous vacuoles (PV) of metacyclic trypomastigotes are rapidly and efficiently fused to C. burnetii vacuoles. Based on these observations we have investigated the behavior of metacyclic trypomastigotes within C. burnetii vacuoles beyond 12 h of co-infection inside Vero cells. Using indirect immunofluorescence with MAb against different developmental stages, it was possible to follow the T. cruzi differentiation process within C. burnetii vacuoles after up to 96 h post-invasion. We observed that metacyclic trypomastigotes began to differentiate after 12 h of infection, and 24 h later amastigotes were the prevailing forms within C. burnetii vacuoles. T. cruzi amastigote replication within C. burnetii vacuoles was confirmed using video and time-lapse confocal microscopy and around 36 h of co-infection, cytokinesis took about 70 min to occur. After 72 h, we observed that amastigote forms seemed to escape from C. burnetii vacuoles. Labeling of amastigotes within C. burnetii vacuoles using a polyclonal antibody to C9 complement protein suggested that TcTOX (T. cruzi hemolysin) could play a role in parasite escape from C. burnetii. We concluded that T. cruzi has an outstanding adaptation capability and can survive within a hostile milieu such as C. burnetii vacuoles.