Figure 6.

Effect of airway surface liquid pH on clearance of S. aureus CIP 76.25 in WT and F508del Human Bronchial Epithelial primary cells. Human Bronchial Epithelial (HBE) primary cells were apically infected with S. aureus CIP 76.25 (3,000 CFU/ml). The apical fluid was collected at the end of the experiments and plated on Petri dishes to count surviving bacteria. To investigate the effect of pH on bacterial clearance, pH of inoculum medium was changed by different HCO₃⁻ concentrations. In WT HBE cells, HCO₃⁻ concentrations at 5 mM and 25 mM corresponded respectively to a pH of apical supernatant at 6.90 and 7.45. In F508del HBE cells, HCO₃⁻ concentrations at 25 mM and 40 mM corresponded respectively to a pH at 7.20 and 7.45. Surviving bacteria detected at the end of experiment in apical fluid under test conditions are expressed as ratio (%) to the control condition of 25 mM HCO₃⁻ inoculum solution. (A) F508del HBE cells. % of surviving bacteria after 2 hours in 40 mM HCO₃⁻ condition vs. 25 mM HCO₃⁻ control condition: 66 ± 18%, p = 0.02. For all conditions, n = 3 in triplicate. (B) WT HBE cells. % of surviving bacteria after 2 hours in 5 mM HCO₃⁻ condition vs. 25 mM HCO₃⁻ control condition: 145 ± 12%, p = 0.01. For all conditions, n = 3, 4 filters per experiment. (C) WT HBE cells. % of surviving bacteria after 6 hours in 5 mM HCO₃⁻ condition vs. 25 mM HCO₃⁻ control condition: 368 ± 117%, p = 0.01. For all conditions, n = 3 in triplicate. Data are presented as mean ± SEM. Statistical significance from unpaired nonparametric Wilcoxon test. *p < 0.05.