Fig. 2.

Isogenic mutants for purR are highly cytotoxic and cause rapid death. (A) Mutants for purR secrete a greater number of proteins compared with wild-type USA300 and a mutant complemented in trans with purR. Asterisks indicate loading controls, which are nonspecific bands recognized by the antibodies. (B) Five percent culture filtrates obtained from the purR mutant are highly cytotoxic against primary human PMNs compared with wild-type USA300 or the complemented mutant (n = 5 donors). Statistical significance was done using a one-way ANOVA and post hoc Holm–Sidak correction of multiple comparisons. Error bars indicate SEM. **P < 0.01, ***P < 0.001. (C) Mice infected i.v. (2.5 × 10⁷ CFUs) with the purR mutant are acutely susceptible to death compared with wild-type USA300 or the complemented mutant (n = 10 mice per strain). Statistical analysis for survival was performed using the Gehan–Breslow–Wilcoxon test with P values adjusted for multiple comparisons. ****P < 0.0001. (D) Mice administered an i.v. infection (2.5 × 10⁷ CFUs) exhibit no differences in bacterial burden at 4 h postinfection (n = 10 mice per strain; n = 5 kidneys per strain). (E) Mice infected i.v. (2.5 × 10⁷ CFUs) with the purR mutant exhibit significantly higher levels of bacterial burden at 20 h postinfection compared with wild-type S. aureus or the complemented mutant (n = 10 mice per strain). Dotted lines represent the limit of detection in these organs. Statistical significance was done using a one-way ANOVA and post hoc Holm–Sidak correction of multiple comparisons. **P < 0.01, ***P < 0.001, ****P < 0.0001.