Tilney and Portnoy were the first to show that Listeria monocytogenes hijacks the actin machinery of infected cells to invade neighbouring cells. Since then, many examples have been found of bacteria and viruses that generate actin comets in host cells (Goley and Welch, 2006).
Movie of an epithelial PtK2 cell infected with Listeria monocytogenes (phase contrast optics; by courtesy of Antonio Sechi)
The smallest known member of the class of pathogens propelled by actin is an insect baculovirus (Ohkawa et al., 2010).
Movie (fluorescence optics) shows a fish fibroblast that was infected with baculovirus. The cell was transfected with baculovirus tagged with mCherry and with GFP-VASP and mCherry-actin.
The relative sizes of Listeria and baculovirus are depicted in this schematic diagram. Baculovirus is only 40nm in diameter, compared to 500nm for Listeria and 300nm for Vaccinia virus, which also hijacks the actin cytoskeleton (Link to Way lab).