Figure 3.

Determination of the molecular basis of N. meningitidis adhesion under liquid flow and the optimal flow for efficient adhesion. (A) Testing of different mutants deficient for pili biogenesis and function shows that Tfp are necessary for adhesion under flow. After introduction in the flow chamber containing the endothelial cells in the presence of 0.04 dynes/cm², the number of bacteria per mm² was determined. Compared with the wild-type strain (WT), the pilE-deficient mutant (PilE) does not express the Tfp major subunit, the pilC1-deficient strain (PilC1) expresses nonfunctional pili, and the pilT mutant (PilT) fails to retract its pili. (B) The ability of N. meningitidis to adhere to an endothelial cell monolayer at different flow velocities was determined to show that increased shear stress strongly inhibits adhesion. The concentration of the bacterial suspension introduced in the chamber is constant throughout each experiment and only the shear stress levels varied. The number of bacteria per mm² is plotted as a function of shear stress level. Squares represent the results on HUVEC cells and circles on the brain-derived hCMEC/D3 endothelial cell line. (C) Comparison of adhesion behavior for three pilin variants at 0.04 (white bars) and 0.2 dynes/cm² (black bars) shows that adhesion is also inhibited by shear stress increase in these variants. Results are expressed as the percentage of the number of bacteria adhering at 0.04 dynes/cm².