Cos-1 cells were infected with C. jejuni and or S. typhimurium invA (invasin), as indicated. At the designated times, cells were fixed and processed for immunofluorescence using antibodies directed to C. jejuni or S. typhimurium and to the endocytic markers EEA-1 and lamp-1 (A and B), or cathepsin B (G and H). Alternatively, Cos-1 cells were transfected with plasmids expressing PX-GFP (a probe for phosphoinositide 3 phosphate) (C), Rab4-GFP (D), Rab5-GFP (E), or Rab7-GFP (F) , and subsequently infected with C. jejuni or S. typhimurium invA (invasin) as indicated. Cells were fixed and processed for immunofluorescence using antibodies directed to C. jejuni or S. typhimurium. At the indicated times, the number of bacteria-containing vacuoles that colocalized with the different markers was quantified by immunofluorescence microscopy as indicated in Materials and Methods. Results are the means and standard deviation of three independent experiments. For each experiment at least 100 vacuoles were counted for acquisition of each marker.