FIG. 1.

The nlpI deletion decreased the ability of E. coli K1 strain RS218 to interact with HBMECs. (A) The RS218-ΔnlpI isogenic mutant showed significantly decreased HBMEC association and invasion frequencies in comparison with the wild-type RS218. (B) The defects of the mutant were restored by complementation with the nlpI gene. pNI1, which was derived from the vector plasmid, pCL1920, harbors the nlpI gene. Hatched and filled bars indicate relative association and invasion frequencies, respectively, compared to the wild-type strain RS218, which was set at 100%. The association frequencies of the wild-type RS218 (A) and the pCL1920-harboring wild-type RS218 (B) were 25% ± 2% and 19% ± 3% of the original inoculum, respectively, while their invasion frequencies were 0.97% ± 0.13% (A) and 1.09% ± 0.06% (B) of the original inoculum. The data shown are representative of three independent experiments done in triplicate. The results were shown as means ± the standard deviations (SD). *, P values of ≤0.01 between the nlpI mutant and the wild-type strain as determined by ANOVA. +, P values of ≤0.01 between the nlpI mutant strains harboring pNl1 and pCL1920 as determined by ANOVA.