To cause an infection, the human specific pathogen Neisseria meningitides must first colonize the nasopharynx. Upon tight interaction with the mucosal epithelium, N. meningitidis may cross the epithelial cellular barrier, reach the bloodstream and cause sepsis and/or meningitis. Since N. meningitidis niche is restricted to humans the availability of relevant animal models to study host-pathogen interactions are limiting. Therefore, most findings that involve N. meningitidis colonization derive from studies using cultured human cell lines. Human epithelial cells have been successfully used to examine and identify molecular effectors involved in initial adherence of the pathogen. Here, we describe a standard protocol to quantify the adherence of N. meningitidis to epithelial pharyngeal FaDu cells. Colony counts of cell lysates collected after infection are used to quantify adherence to the epithelial cells.

To efficiently colonize the nasopharyngeal epithelium, the human restricted pathogen Neisseria meningitidis follows a multistep adhesion cascade. First, the bacteria adhere to host cells and aggregate into spherical shaped structures called microcolonies. Several hours later, single bacteria start dispersing from the microcolonies and form a monolayer on top of the host cells. Once in proximity to host cells meningococci can adhere tightly to the epithelial surface or become internalized. This can eventually result in invasion of the mucosal surfaces and gain access to the bloodstream, causing a life-threatening disease. Lactate, a metabolite derived from human epithelial cells, has been previously shown to induce rapid dispersal of N. meningitidis from microcolonies. Here, we describe a host-cell free method based on live-cell imaging to examine the effect of host derived lactate on the timing of N. meningitides microcolony dispersal. Although in this protocol we use lactate, it can be easily modified to test the effects of other molecules.