Fig. 5: Effect of potentiators on resistance selection in PAO1.

a Frequency of resistance to ciprofloxacin and rifampicin after 24 h of incubation with each antibiotic at 4 x MIC, in control conditions (antibiotic alone) or in the presence of alexidine (ALE, 2.5 µM), polymyxin B nonapeptide (PMBN, 30 µM), colistin (CST, 0.5 µM), PAβN (38 µM), NV731 and NV716 (2.5 µM). All data are mean ± SEM (triplicates from three independent experiments). Statistical analysis: one-way ANOVA with Dunnett’s post-hoc test comparing each combination with antibiotic alone (*p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001). b Quantitative real-time PCR of transcripts of the gene recA in the absence of or in the presence of antibiotics at ½ MIC, NV716 alone at 2.5 µM or their combinations. Data, expressed in fold change vs. control samples, are means ± SEM of three independent experiments. Statistical analysis: one-way ANOVA with Tukey post hoc test (only relevant significant differences are shown on the graph). c, d Evolution of the MIC of ciprofloxacin or rifampicin over passages in the presence of each antibiotic at ½ MIC (with daily readjustment of the concentration) alone or combined with potentiators at the same concentrations as in panel a. All data are mean ± SEM (duplicates from three independent experiments). e Evolution of the MIC of alexidine, colistin, and NV716 over passages in the presence of each antibiotic at ½ MIC (with daily readjustment of the concentration). After 52 passages, MICs were measured for all compounds after 1 culture on agar in the absence of compounds (beige box in panel e and values in panel f).