FIG 3.

Response of P. aeruginosa to electrophilic stress. (A) The bioluminescence of strain PA14::PA2048-lux was monitored at defined time points after exposure to increasing concentrations of glyoxal (GO) and is expressed as the ratio of relative light units (RLU) to bacterial density (A₆₀₀). Nontreated bacteria were used as the control (CTRL). Results are mean values ± standard deviations from three independent experiments. (B) Expression levels of genes mexE and PA2048 were determined by RT-qPCR in strain PA14 exposed to 200 μg ml⁻¹ GO and compared with those of a nontreated control (CTRL). Results are mean values of four determinations from two independent experiments. (C) Induction of pump MexEF-OprN with glyoxal was assessed by a double-disk antagonism test using strain PA14 and negative-control strain PA14ΔmexEF-oprN. Paper disks were loaded with 8,000 μg glyoxal (GO), 5 μg ciprofloxacin (CIP), 1,000 μg chloramphenicol (CHL), or 240 μg trimethoprim (TMP). Antagonism is visible between GO and all the tested MexEF-OprN substrates in strain PA14 (left) but not in mutant PA14ΔmexEF-oprN (right).