Brucella abortus transits through the autophagic pathway and replicates inthe endoplasmic reticulum of nonprofessional phagocytes

Brucella abortus is an intracellular pathogen that replicates within a memb rane bounded compartment. In this study, we have examined the intracellular pathway of the virulent B. abortus strain 2308 (S2308) and the attenuated strain 19 (S19) in HeLa cells. At 10 min after inoculation, both bacterial strains are transiently detected in phagosomes characterized by the presenc e of early endosomal markers such as the early endosomal antigen 1. At simi lar to 1 h postinoculation, bacteria are located within a compartment posit ive for the lysosome-associated membrane proteins (LAMPs) and the endoplasm ic reticulum (ER) marker sec61 beta but negative for the mannose 6-phosphat e receptors and cathepsin D. Interestingly, this compartment is also positi ve for the autophagosomal marker monodansylcadaverin, suggesting that S2308 and S19 are located in autophagic vacuoles. At 24 h after inoculation, att enuated S19 is degraded in lysosomes, while virulent S2308 multiplies withi n a LAMP- and cathepsin D-negative but sec61 beta- and protein disulfide is omerase-positive compartment. Furthermore, treatment of infected cells,vith the pore-forming toxin aerolysin from Aeromonas; hydrophila causes vacuola tion of the bacterial replication compartment. These results are compatible ,vith the hypothesis that pathogenic B. abortus exploits the autophagic mac hinery of HeLa cells to establish an intracellular niche favorable for its replication within the ER.