In vitro studies of bacterial growth often reveal antibacterial activity of fungi. That is how Penicillin was discovered. This phenomenon dates back to Fleming in 1940 when he was growing staphylococcus and discovered a fungal contaminant on the plate. The areas surrounding fungal colonies had no staphylococcal growth. There may be other fungi that have this attribute. However introducing a fungus into the CF lung would be dangerous. The substance from the fungus must be isolated and tested. This is a good lead.