Cystic fibrosis is the most common genetic inherited disease in the European Caucasian population. It is due to mutations in the gene CFTR (for Cystic Fibrosis transmembrane conductance regulator) which encodes a chloride channel involved in electrolytic exchanges through the plasma membrane of numerous epithelial cell types. Several organs, therefore, are involved, but prognosis essentially depends on the severity of the lesions of the lungs. In the respiratory tract, mutations in the gene CFTR lead to a defect in the mucociliairy clearance and a thickening of the bronchial mucus, thus enabling the entrapment of the inhaled bacteria and fungal spores and  the  subsequent  colonization  of  the  airways  by  these microorganisms.
Besides bacteria which are by far the most common cause of respiratory infections in this clinical context, several mold species may also colonize the respiratory tract of the patients. Although the clinical significance of their isolation from respiratory secretions has raised much controversy, the prevalence of fungal colonization of the airways is regularly increasing along with the increase in life expectancy. Moreover, this fungal colonization of the airways may also lead to true respiratory infections, including allergic broncho-pulmonary mycosis and pneumonia. Finally, due to their propensity to disseminate in an immunocompromised host and to their low susceptibilty or innate resistance to current antifungal drugs, one should be cautious if a lung transplantation is required, particularly in case of chronic colonization of the airways. Appropriate treatment, therefore, should be initiated as early as possible, which implies improved detection, identification and typing methods. Additionally, beside moulds, the respiratory tract of patients with CF often is colonized by yeasts, and a large variety of yeast species has been described in the CF context, Candida albicans, Candida glabrata and Candida parapsilosis being the most prevalent. Long considered completely devoid of clinical relevance, recent works on the airway colonization by Candida albicans as well as some clinical reports about the newly described Trichosporon mycotoxinivoranshave revived discussion about the pathogenic role of yeasts.