FIG 4.
Antibiotics stimulate an iron starvation response. (A) Diagram depicting the function of PryhB-lacZ as an intracellular reporter of the response of bacteria to iron depletion. When the intracellular free iron levels are low, Fur will not repress the transcription of lacZ. (B, C) E. coli CP9 was cultured in BHI medium in the presence or absence of an antibiotic (VAN at 250 μg/ml or CTX at 62.5 ng/ml), DFP (150 μg/ml), or both, and β-galactosidase activity was measured at 8 h in both the cell pellet fraction (B) and the culture supernatant fraction (C). Data are the mean values and standard deviations from three independent experiments. P values were determined by Student's t test.