MK biosynthesis intermediates are required for cytosolic survival of L. monocytogenes. (A) Major intermediates and enzymes present in the MK biosynthesis pathway of L. monocytogenes according to the KEGG database (http://www.genome.jp/kegg/). Specific men mutants examined in this study are highlighted in red. (B and E) MK biosynthesis mutants (B) or ΔmenB, ΔmenA, and ΔmenB/ΔmenA strains (E) (MOI of 10) were tested for bacteriolysis in iIFNAR−/− macrophages using the bacteriolysis assay. Data are normalized to wild-type levels of bacteriolysis and presented as means ± SEM of results from four to six independent experiments. (C) The menD::Tn, menB::Tn, ΔmenA, and menG::Tn strains were grown to exponential phase in BHI media at 37°C of stained and measured for membrane potential generation. Data are normalized to wild-type red/green fluorescence ratios and presented as mean percent ± SEM of results from three independent experiments. (D and F) The menB::Tn, ΔmenA, and menG::Tn strains (D) or ΔmenB, ΔmenA, and ΔmenB/ΔmenA strains (MOI of 0.5) were examined for plaque formation in L2 fibroblasts at 6 days postinfection. Data are normalized to wild-type plaque size and represent means ± SEM of results from three independent experiments.