Brucella Egresses from Host Cells Exploiting Multivesicular Bodies

Host cell egress is a critical step in the life cycle of intracellular pathogens, especially in microbes capable of establishing chronic infections. The Gram-negative bacterium Brucella belongs to such a group of pathogens. Even though much has been done to understand how Brucella avoids killing and multiplies in its intracellular niche, the mechanism that this bacterium deploys to egress from the cell to complete its cycle has been poorly studied. In the manuscript, we quantify the kinetics of bacterial egress and show that Brucella exploits multivesicular bodies to exit host cells. For the first time, we visualized the process of egress in real time by live video microscopy and showed that a population of intracellular bacteria exit from host cells in vacuoles containing multivesicular body-like features. We observed the colocalization of Brucella with two multivesicular markers, namely, CD63 and LBPA, both during the final stages of the intracellular life cycle and in egressed bacteria. Moreover, drugs that either promote or inhibit multivesicular bodies either increased or decreased the number of extracellular bacteria, respectively. Our results strongly suggest that Brucella hijacks multivesicular bodies to exit the host cells to initiate new infection events.