Fig. 1. Neisseria meningitidis induces localized cellular membrane protrusions. SEM examination of HUVEC monolayers infected with the ROU strain of N. meningitidis. Bars represent 1µm. (A) After 4 hours of infection, adhering bacteria proliferate and form small colonies at their site of attachment (localized adhesion). During this step, small protrusions of the cellular membrane are induced underneath bacterial colonies. (B) Detail showing cellular protrusions engulfing a bacterium during the localized adhesion step of the infection. (C) After 6 hours, meningococci start to spread over the apical cell surface (diffuse adhesion). (D) Higher magnification showing that the membrane protrusions have disappeared at the late stage of infection.

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