FIG. 4.

Invasion of HBMEC by L. monocytogenes EGD after preincubation of either the bacteria or the HBMEC with HS. Prior to infection, either the bacteria (left) or the HBMEC (right) were incubated in RPMI medium containing 10% HS for 1 h at 37°C. Preincubated HBMEC were washed once and infected with untreated L. monocytogenes for 60 min as described in Materials and Methods. Preincubated listeriae were collected by centrifugation, resuspended in RPMI medium, and used for infection of untreated HBMEC for 60 min as described in Materials and Methods. Intracellular bacteria were enumerated after an additional 60 min of incubation in the presence of gentamicin. The numbers of bacteria recovered (expressed as percentages of the number recovered for the untreated control, taken as 100%) are shown. Values are means and standard deviations (error bars) of the results of a representative experiment. Open versus shaded bars are explained in the legend to Fig. 1.