FIG. 8.

The mhqR mutant is impaired in survival inside J-774.1 murine macrophages after 24 h and growth sensitive under sublethal ROS and NaOCl but resistant to long-term infections and toxic ROS and NaOCl. (A, B) The survival of S. aureus strains was analyzed 2, 4, 24, and 48 h postinfection (p.i.) of the murine macrophage cell line J-774A.1 and the CFUs were determined. (A) The percentages in survival of the wild type (WT), WT pRB473, mhqR deletion mutant, and the mhqR complemented strain (mhqR) were calculated, and the survival at the 2 h time point was set to 100%. (B) The average percentage in survival was calculated for each mutant and complemented strains in relation to the WT or WT pRB473, which was set to 100%. Results of four biological replicates are presented as scatter dots in (A) and mean values (B). (C, D) For growth curves, S. aureus COL wild type, the mhqR deletion mutant, and the mhqR complemented strain were grown in RPMI until an OD₅₀₀ of 0.5 and treated with sublethal 10 mM H₂O₂ and 1.5 mM NaOCl. (E) Survival assays were performed by treatment with lethal 80 mM H₂O₂ and 3.5 mM NaOCl and plating serial dilutions onto LB agar plates after 4 h of stress exposure. The survival rates of CFUs for the treated samples were calculated relative to the control, which was set to 100%. The results are from three biological replicates. Error bars represent the standard deviation. ns, p > 0.05; *p < 0.05; **p < 0.01; ***p < 0.001; ****p ≤ 0.0001. H₂O₂, hydrogen peroxide; ROS, reactive oxygen species.