Fig. 2.

STX induction protects both S. aureus and P. aeruginosa from H₂O₂-mediated killing. (A) S. aureus USA300 and crtM::Tn were pre-treated with or without 5% filter-sterilized spent media (sup) from designated P. aeruginosa strains overnight and then subjected to 3% H₂O₂-mediated killing for 2 h. The dotted line indicates 100% survival. (B) PAO1, alone (−) or mixed with an equal amount of S. aureus, was subjected to 3% H₂O₂-mediated killing for 1 h. USA300 and crtM::Tn were pre-treated with 50 μg/mL flavone (+F) to inhibit STX production and serve as controls. (C) PAO1 mixed with an equal amount of S. aureus with various treatments was subjected to 3% H₂O₂-mediated killing for 1h in LB. USA300 and crtM::Tn were pre-treated with or without (−) 5% filter-sterilized P. aeruginosa spent media (sup), or 5 μM HQNO or PQS overnight. Bacterial survival is presented as CFUs normalized to the starting CFUs at 0 h. Data are presented as mean ± SD from the results of at least three biological replicates, each with three technical replicates. **P < 0.01; ***P < 0.001; ****P < 0.0001; ns, not significant, compared to the P. aeruginosa alone group (B) or the no treatment group (A and C). Statistical differences are determined by two-way ANOVA (A and C) or one-way ANOVA (B).