Movement of GFP-expressing M. marinum in a macrophage subsequently fixed and stained for F-actin. Time lapse images show motile bacteria first in phase contrast, and briefly in the green fluorescent channel for GFP. The same field is seen as the sample is fixed on the stage before permeabilization and F-actin staining (red). Finally, GFP and F-actin fluorescence were superimposed to show the relationship of the motile bacterium to actin.
