FIG. 4.

The Δctu mutant of Schu S4 is deficient for intramacrophage survival. A macrophage cell culture invasion assay was performed on BMDMs and the MH-S cells untreated (left panels) or treated with IFN-γ (right panels). The intracellular replication was quantitated at the indicated times and expressed as CFU/ml. The values represent the means ± standard errors (SE) of quadruplicate samples and are cumulative of the results of three experiments conducted. P values were determined using one-way ANOVA. *, P < 0.05; **, P < 0.01; and ***, P < 0.001.