The project is intended to be realised in two phases. In the first stage, a case control study will be performed. In the second phase, double-blind, placebo controlled cross-over study will be conducted. The first stage it to compare innate immunity activation and Pseudomonas aeruginosa (Pa) expression between Pa positive and negative patients. In the second phase the effects of inhaled lactizole- TAS3R inhibitor will be assessed.

Three visits have been planned during the entire study. During the first visit, all patients included in the study will have the following procedures: questionnaire tests, lung function tests, taste perception tests (gustometry) and exfoliative cytology of the nasal mucosa.

Patients with confirmed Pseudomonas aeruginosa presence in the airways will be randomly assigned to the Lactizole-Placebo group and the Placebo-Lactizole group, with a recommendation to take laktizol (3 ml) for 3 weeks at the concentration determined during the preliminary examination, in the nebulization 2 times per day) or placebo (3ml 0.9% NaCl solution in nebulization 2 once a day). The first nebulization of the solution issued during the visit will take place during the visit; each patient will undergo a clinical and spirometric assessment after 20 minutes of observation from completed nebulization.

During the second visit (after 4 weeks from visit 1), the first visit procedures will be repeated for all patients. Patients in the Lactizole-Placebo group will be recommended to take a placebo for 4 weeks (3 ml of 0.9% NaCl solution in nebulization 2 once a day); on the other hand, patients from the Placebo-Lactizole group will be advised to take lactisol for 4 weeks (3 ml of the solution in the concentration determined during the preliminary examination, in the nebulization 2 once a day). The first nebulization of the solution issued during the visit will take place during the visit; each patient will undergo a clinical and spirometric assessment after 20 minutes of observation from completed nebulization.

During the third visit (after 4 weeks from visit 2), the first visit procedures will be repeated for all patients.

Inclusion Criteria:

• ulmonary manifestations of cystic fibrosis

Exclusion Criteria:

• first positive result of inoculation from the airways, which according to the standard is associated with the need for antibiotic therapy
• contraindication to a biopsy of the nasal mucosa
• exacerbation requiring antibiotics
• diabetes, exposure to tobacco smoke
• other chronic diseases and clinical conditions which, according to the researcher, may influence the assessed parameters and the course of the study.

Temporary exclusion criteria

- acute respiratory infection within 2 weeks from 1, 2 and 3 visits of the study.