FIG. 5.

Expression of OmpX in E. coli K-12 TOP10 promotes adherence, internalization, and serum resistance. (A) Cell association. Bacteria were grown to mid-exponential phase at 37°C and coincubated for 1 h with Hep-2 monolayers at 37°C (MOI = 20 to 50). Hep-2 host cells were disrupted and plated on LB agar or incubated with gentamicin for 1.5 h to kill extracellular bacteria before plating. Open bars represent the number of cell-associated bacteria (extracellular and intracellular), and filled bars represent the number of intracellular bacteria. Results are means ± SEM from assays performed in duplicate on two separate days (n = 8). (B) Serum resistance. Bacteria were grown as described above and incubated in 50% normal human serum (NHS) or heat-inactivated serum (HIS) for 1 h at 37°C and plated on LB agar. Results are means ± SEM from two assays performed on separate days (n = 8 for cell association assay; n = 4 for serum resistance assay). The asterisk indicates a difference (ANOVA, P < 0.0001, for cell association assay; Kruskal-Wallis, P < 0.001, for serum resistance assay) between the strain expressing OmpX [TOP10(pOmpX)] and the two controls [cell TOP10 and plasmid control TOP10(pTA) strains).