FIG. 5.

Enhanced intramacrophage killing of the Δctu mutant is NO dependent. (A) Culture supernatants from the invasion assay were analyzed for nitrite levels, using a commercial Griess reagent. The detection limit of the Griess reaction was 2.5 μM. The results are expressed as the means ± SEs from four replicate samples tested in triplicate and are representative of the results of two independent experiments conducted. (B) BMDMs derived from C57BL/6 WT and inos^−/− mice were stimulated with IFN-γ (100 ng/ml) for 16 h prior to and after infection with the F. tularensis Schu S4, Δctu, or Δctu+pctu strain at a multiplicity of infection of 100. The infected BMDMs were lysed 24 h PI, and the bacterial numbers were quantitated. The results are expressed as the means ± standard deviations. The statistical analysis was performed using unpaired Student's t test. **, P < 0.01; and ***, P < 0.001.