ΔmenD and ΔmenF strains are deficient for generation of the membrane potential and intracellular survival. (A and B) Genetic (A) or chemical (B) complementation of ΔmenD and ΔmenF strains grown in aerated cultures in BHI media at 37°C and monitored at OD600. Data are representative of results from three independent experiments. (C) ΔmenD and ΔmenF cultures grown to exponential phase in BHI media at 37°C were examined for membrane potential generation. Data are normalized to the wild-type red/green fluorescence ratios and represented as mean percent ± SEM of results from three independent experiments. MFI, median fluorescence intensity; PMF, proton motive force. (D) ΔmenD and ΔmenF strains (MOI of 0.5) were examined for plaque formation in L2 fibroblasts 6 days postinfection. Data are normalized to wild-type plaque size and represent mean percent ± SEM of results from three independent experiments. ND, not detected. (E) ΔmenD and ΔmenF strains (MOI of 10) were tested for bacteriolysis in iIFNAR−/− macrophages over 6 h. All data are normalized to wild-type levels of bacteriolysis and presented as means ± SEM of results from four independent experiments.