Cryo-SEM image of a rapid frozen parasite-host interaction. Here Shigella bacteria (in red) attacking a He-La cell, which in a defence reaction forms F-actin induced wide membrane ruffles on its surface (bright blue). The bacterium interacts with the host cell membrane by injecting its invasins, which act to choreograph a local actin-rich membrane ruffle at the host cell surface (Niebuhr and Sansonetti, 2000). The ruffle engulfs the bacterium and eventually disassembles, internalising the bacterium.

Image: Roger Wepf, Philippe Sansonetti, and Ariel Blocker, Electron Microscopy ETH Zurich

(Source: cimst.ethz.ch)

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