Salmonella typhimurium growing within a macrophage.
The image shows the bacterial pathogen Salmonella typhimurium, the most common cause of food poisoning, dividing within a macrophage. Macrophages normally destroy bacteria, but Salmonella is able to takes over the cell and create a hospitable environment for its own replication. At 24-hours post-infection the bacteria (dark ovals, surrounded by white vacuolar space) can be seen growing within macrophages to very high numbers by transmission electron microscopy.
These images were taken in the Robert D. Ogg Electron Microscope Laboratory (a research unit of the College of Letters and Sciences) by Nicholas Arpaia (Barton Lab, Department of Molecular and Cell Biology).