TEM analysis of murine placentas infected with F. nucleatum 12230. (A) At 24 h postinfection. R, red blood cells in the blood vessel. The solid arrows point to bacteria internalized in the endothelial cells lining the veins. The open arrow points to an organism attached to the endothelial cells. Magnification, 6,000×. (B) At 72 h postinfection. Arrows indicate bacteria that have proliferated in the cytoplasm or outside the cells. Magnification, 1,500×. (C) Enlarged view of the area boxed in panel B. Arrows indicate bacteria in the nucleus.