Listeria monocytogenes, a rod-shaped bacterium, is one of the world's deadliest foodborne pathogens. It causes listeriosis, a group of life-threatening diseases that include meningitis, encephalitis, pneumonia, septicemia, and intrauterine or cervical infections in pregnant women. The latter account for around 27 percent of the 500 listeria deaths that occur in the U.S. every year.
L. monocytogenes infects and moves through white blood cells using actin rockets, also known as "comet tails." The rockets work like this: A protein anchored to the bacterium's membrane triggers the rapid polymerization of the protein actin; this provides an explosive boost, so the bacterium can push through the membrane of white blood cells and burst out to infect another cell.
In this image, the bacteria (shown in red) are traveling around a cell using their bright actin rockets.