pH is decreased by the CFTR (cystic fibrosis transmembrane conductance regulator) bicarbonate channel defect (12, –, 14), and the pH can be further reduced during periods of decline in CF lung function, known as pulmonary exacerbations (15, –, 17), potentially due to both host and microbial production of acidic molecules, such as lactic acid (16). Here, CFTR is linked to cystic fibrosis.