Effects of cytochalasin D on internalization of L. monocytogenes, S. typhimurium, P. mirabilis, and E. coli by nonconfluent HeLa and HEp-2 epithelial cells and by nonconfluent and confluent HT-29 enterocytes. Horizontal lines indicate lower limit of assay detection. Error bars are not apparent if <0.1. Significant change in the numbers of bacteria internalized in the presence of cytochalasin compared to those internalized in the absence of cytochalasin: ∗, P < 0.01; †, P < 0.05.