Invasion potentials fluorescence tagged L. monocytogenes. Numbers of Colony Forming Units (CFU) of fluorescent L. monocytogenes strains and its inlA' mutant, which were internalized per well of Caco-2 cells. Counts were normalized to a concentration of 107 L. monocytogenes per ml in the bacterial cultures prior to infection of Caco-2 cells. Each point represents the average of data from two experiments. Error bars represent standard deviations. Statistical analysis (Dunnet's test) confirmed that the infection potentials of the labelled strains were not different from that of the wt (p < 0.05).