FIG. 7.

The mhqR mutant is resistant to rifampicin and norfloxacin but impaired in survival after lapachol stress. (A, C, E) For the growth curves, S. aureus COL wild type, the mhqR and qsrR mutants, and the mhqR complemented strain (mhqR) were grown in RPMI until an OD₅₀₀ of 0.5 and treated with 0.05 μM rifampicin, 62.6 μM norfloxacin, and 300 μM lapachol. (B, D, F) Survival assays were performed by treatment with sublethal and lethal doses and plating 100 μL of 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 mhqR mutant is significantly more resistant to rifampicin and norfloxacin, which could be restored in the mhqR complemented strain back to wild-type level. However, the mhqR mutant is significantly more susceptible to the naphthoquinone lapachol than the wild type. The results are from four biological replicates. Error bars represent the standard deviation. *p < 0.05; **p < 0.01; ***p < 0.001.