Sublethal concentrations of ciprofloxacin induce bacteriocin synthesis in Escherichia coli

Abstract

Antibiotics that interfere with DNA replication, as well as cell wall synthesis, induce the SOS response. In this report, we show that ciprofloxacin induces synthesis of colicins, narrow-spectrum antibiotics frequently produced by Escherichia coli strains, in an SOS-dependent manner.

FIG. 1.

Expression of the cka-lacZ fusion with and without ciprofloxacin in RW118 and in the recA-defective mutant RW464. Levels of β-galactosidase activity in Miller units in RW118 (solid symbols) without ciprofloxacin (squares), with ciprofloxacin added at 1/8 MIC (circles), and with ciprofloxacin added at 1/16 MIC (triangles). Levels of β-galactosidase activity in Miller units in RW464 (open symbols) without ciprofloxacin (squares), with ciprofloxacin added at 1/8 MIC (circles), and with ciprofloxacin added at 1/16 MIC (triangles). The dotted lines represent growth of both strains with and without ciprofloxacin. The experiment was performed three times, and the means ± standard errors of the mean (error bars) are shown.

FIG. 2.

Expression of the sulA-lacZ and bolA-lacZ fusions with and without ciprofloxacin in strains VIP36 and ENZ1257, respectively. Levels of β-galactosidase activity in Miller units from the sulA-lacZ fusion (solid symbols) without ciprofloxacin (squares), with ciprofloxacin added at 1/8 MIC (circles), and with ciprofloxacin added at 1/16 MIC (triangles). Levels of β-galactosidase activity in Miller units from bolA-lacZ (open symbols) without ciprofloxacin (squares), with ciprofloxacin added at 1/8 MIC (circles), and with ciprofloxacin added at 1/16 MIC (triangles). The dotted lines represent growth of both strains without and with ciprofloxacin. The experiment was performed three times, and the means ± standard errors of the mean (error bars) are shown.

FIG. 3.

Colicin production assay of cells harboring colicin-encoding plasmids with and without ciprofloxacin. The indicated concentrations of ciprofloxacin added to the colicin-producing cultures are 0 (none), 1/8, and 1/16 MIC. Aliquots (10 μl) of twofold serial dilutions of colicin extracts were placed into wells in an LB plate and overlaid with soft agar harboring the indicator strain, as described in the text. (a) colicin N, (b) colicin K, (c) colicin E1, (d) colicin K expression in recA-defective strain RW464, (e) colicin E7, and (f) colicin A.