FIG 4.

Tolerance of persister cells to ciprofloxacin is reduced in the presence of cis-DA. Persister cell subpopulations of P. aeruginosa planktonic populations (A), P. aeruginosa biofilms (B), E. coli planktonic populations (C), and E. coli biofilms (D) were exposed to saline, cis-DA in saline, ciprofloxacin in saline, and ciprofloxacin with cis-DA in saline. Biofilm and planktonic populations were exposed to 150 μg/ml and 20 μg/ml of ciprofloxacin, respectively. Experiments were performed for a period of 24 h, and cell viability was determined throughout the experiment. Experiments with persister cells derived from biofilms had one additional control, a total biofilm population treated with cis-DA in saline (control). P. aeruginosa cells were exposed to 100 nM cis-DA, and E. coli cells were exposed to 310 nM cis-DA. The averages of data from 3 experiments are shown. Error bars indicate standard deviations (*, P < 0.001; **, P < 0.01 [significantly different from persister cells treated with ciprofloxacin, saline, and cis-DA, as indicated by one-way ANOVA]).