Transmission electron micrographs of M. paratuberculosis-containing vacuoles in J774 macrophages. Infected macrophages were processed for transmission electron microscopy at 24 (A), 48 (B), 72 (C), and 96 (D) hours postinfection. The left column shows the infected macrophage and the right column shows an enlargement of the mycobacterial vacuole. Image magnification is shown beneath each column. Arrows point to the same mycobacterial cell in each magnification.