The electron transport chain plays a minor role in survival of L. monocytogenes within macrophages. (A) ΔmenD, cydA::Tn, qoxA::Tn, and atpH::Tn strains were grown in aerated BHI cultures at 37°C and monitored for OD600. Data are representative of results from three independent experiments. (B) ΔmenD, cydA::Tn, qoxA::Tn and atpH::Tn strains 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 presented as mean percent ± SEM of results from three independent experiments. (C and E) ΔmenD, cydA::Tn, qoxA::Tn, and atpH::Tn strains (C) or ΔmenD, ΔcydAB, ΔqoxA, and ΔcydAB/ΔqoxA strains (E) (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 means ± SEM of results from three independent experiments. ND, not detected. (D and F) ΔmenD, cydA::Tn, qoxA::Tn, and atpH::Tn strains (D) or ΔmenD, ΔcydAB, ΔqoxA, and ΔcydAB/ΔqoxA strains (F) (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 five independent experiments.