Fig. 1.

P. aeruginosa HQNO induces S. aureus STX production. (A–G) USA300 or crtM::Tn was grown at increasing distances from designated P. aeruginosa strains, PQS, HQNO, or the solvent in which the molecules were dissolved, on solidified media in a macrocolony proximity assay. Yellow arrows point to USA300 with no pigment change, orange arrows point to USA300 with increased yellow pigmentation, and the white arrow indicates white crtM::Tn colonies. The black arrows point to S. aureus growth inhibition by P. aeruginosa. (H) STX production in LB-grown USA300 treated with (+) or without (−) 5% filter-sterilized spent media (sup) of designated P. aeruginosa strains, or 5 μM of HQNO or PQS. STX production was quantified by absorbance at OD₄₆₂. The results were normalized to the untreated group. Data are presented as mean ± SD from the results of at least three biological replicates, each with two technical replicates. ***P < 0.001; ****P < 0.0001; ns, not significant, compared to the untreated group, determined by one-way ANOVA.