These organisms land in the thin layer of liquid, called airway surface liquid, that overlays the cells lining the inside of the lungs. The airway cells produce a host of natural antibiotic substances and secrete them into the airway surface liquid where they kill the invading bacteria. However, in the lungs of people with CF the system breaks down, allowing the bacteria to get a foothold and eventually develop into the chronic infections that are the leading cause of death in CF patients. UI scientists have suggested that the natural defense system in CF patients is disrupted because a genetic defect results in an increase in the salt concentration of the airway surface liquid. Zabner and his colleagues knew that they needed a substance called an osmolyte that would not be easily absorbed by the cells and would lower the salt concentration to favor the antimicrobial agents.
Simple sugars fit the bill.
However, airway bacteria can use many sugars as an energy source to aid their growth. This information and the fact that xylitol has been used for years in Europe as a safe sugar substitute, made me think that xylitol might be a good choice for our studies. The UI team used a series of experiments to prove that xylitol was not used by airway bacteria to grow, and that the sugar did lower the salt concentration of the airway surface liquid, thereby enhancing the bacteria-killing activity of the natural antibiotics. The UI team then used human volunteers to test the principle that xylitol helps the body to fight against airborne bacteria. The amount of a particular bacterium, commonly found in nasal passages, was assessed for 21 healthy volunteers.