Confocal images of uninfected and S. typhimurium (ST)-infected B cells. The actin filaments were labelled with rhodamine-phalloidin and the bacteria were stained with fluorescein isothiocyanate (FITC). a) Uninfected cells present peripheral and homogeneous fluorescent staining. b) One h after infection, S. typhimurium induced actin cytoskeletal rearrangements that are responsible for membrane ruffling; in addition, a bacillus that is attached to these structures was observed (upper right corner). c-d) After 3 h of infection, longer actin projections and actin redistribution were observed, and some bacilli were found inside the B cell (c) or surrounded by actin organisations (d).