Fig. 6

Effects of DSF and C23 on antibiotic resistance of P. aeruginosa strains. a Effect of addition of DSF, C23, and DSF together with C23 on tolerance of P. aeruginosa to polymyxins. Time-courses of killing of P. aeruginosa by 4 μg/ml polymyxin B were established for bacteria suspended in sodium phosphate buffer. Bacteria for these experiments were grown in BM2 medium with glucose supplemented with 2 mM Mg²⁺. DSF and C23 were added to these cultures to a final concentration of 50 μM. Values are the average of three technical repeats (mean± standard deviation). The observed values of addition of DSF and C23 were significantly different from the addition of DSF alone (p < 0.05, ANOVA). b Effect of addition of DSF, C23, and DSF with C23 on antibiotic resistance gene expression in clinical isolates of P. aeruginosa as compared to the laboratory strain PAO1. Transcript levels of PA4775 in PAO1, the isogenic ΔPA1396, and a selection of clinical isolates of P. aeruginosa (CF3, CF9, CF14, CF21, and CF 22) were examined using qRT–PCR as described in Methods. The qRT–PCR data were normalized to proC and are presented as the fold change relative to the wild type for each gene in each strain with no addition. Data (means ± standard deviation) are from one representative experiment (n = 3). A p-value of <0.05 was considered statistically significant and is designated in the figures with an asterisk. Double asterisks indicate p-values of <0.01. c Effect of administration of C23 on P. aeruginosa clearance by tobramycin treatment in the mouse airway. C57BL/6 mice were infected intranasally with 1 × 10⁷ CFU P. aeruginosa PAO1 and treated by inhaling PBS with or without 50 μM C23. Tobramycin was administered at a concentration of 30 mg /kg 1 h after infection. After 24 h of infection, the mice were harvested, and bacterial loads were determined in lung homogenates. Each data point shows the results from an individual mouse. A p-value of <0.05 was considered statistically significant and is designated in the figures with an asterisk. Double asterisks indicate p-values of <0.01