Fig. 7

Intracellular abundance and distribution of N. meningitidis. A NSC34 neuronal cells were infected with either N. meningitidis wild type strain B1940 or B1940ΩhrpA derivative mutant as indicated. Immunofluorescence microscopy shows green and red stained extracellular bacteria (yellow in merged image), while intracellular bacteria are only stained in red. Bars,10 µm. B Quantification of intracellular wild type and hrpA-defective mutant meningococci. Extracellular and intracellular bacteria were counted in at least 50 cells per sample in different fields. Then, we calculated the percentage of intracellular bacteria on the total number of bacteria scored. Data shown are the mean ± SEM of three independent experiments. C Results of the gentamicin protection assay. Number of wild type or hrpA-defective mutant surviving and growing in NSC-34 cells 3, 5 and 7 h post-infection. Values are the mean ± SEM of three different experiments. *P < 0.05 **P < 0.01 ***P < 0.001. D Quantification of the intracellular distribution of wild type and mutant bacteria in cell body and neurites. Measures were obtained by analyzing at least 50 cells/sample in three independent experiments E, F Immunostaining of NSC-34 neuronal cells with anti-DYNLT1 (green) and with anti-N. meningitidis (red) antibodies shows co-localization (yellow) between DYNLT1 and intracellular meningococci and clustering of meningococci in neurites. White dashed boxes indicate zoomed areas on the right. Scale bar: 10 μm