Cystic fibrosis (CF) is a complex systemic disease that mainly involves the respiratory and gastrointestinal (GI) tracts. The polymicrobial community composition of respiratory and GI tracts is influenced by both genetic and environmental factors. Children with CF may harbor an abnormal intestinal microflora, because of altered Cystic fibrosis transmembrane conductance regulator (CFTR) function and heavy drug load (antibiotics, pancreatic enzymes and acid suppressors). The investigators previously demonstrated that intestinal inflammation is highly frequent in CF children, being a major feature of intestinal involvement. In addition, specific probiotics significantly improved airway and GI inflammation in a preliminary trial. The aim of the study is to characterize intestinal and respiratory microflora in CF patients and to investigate the effects of daily Lactobacillus GG (LGG) supplementation on both GI and airway microflora and the eventual relationship between probiotic assumption and clinical and inflammation markers. The aim is to study the effect of microflora modification on intestinal and extraintestinal inflammation to eventually improve the quality of life of CF patients, who often suffer from intestinal and respiratory progressive disease, through a non invasive intervention consisting in the supplementation of probiotic bacteria.

Inclusion Criteria:

• Diagnosis of CF documented by sweat chloride test over 60 mmol/L and confirmed by genotype analysis with the presence of F508del/F508del or F508del/other;
• Boys and girls between 2 and 16 years of age;
• Clinical stability at enrolment, defined as no clinical evidence of acute exacerbation, no modifications in the therapeutic regimen and no hospitalization in the last 2 weeks;
• Pancreatic insufficiency;
• Basal Forced expiratory volume 1 second (FEV1) above 50% of predicted value.

Exclusion Criteria

• Colonization of respiratory tract with Burkholderia cepacia spp.;
• Steroid therapy within one month before enrolment;
• Pregnancy and fertile women taking oral contraceptives;
• Parenteral or oral antibiotics therapy within 2 weeks before enrolment;
• Regular assumption of probiotics;
• Regular assumption of azythromycin.