Microbial Biomarkers of EArly Pseudomonas Aeruginosa Colonization in CHildren With Cystic Fibrosis

Inclusion criteria: * Infants aged 6 months maximum at inclusion with a confirmed diagnosis of cystic fibrosis in its classical form (positive sweat test and/or two mutations of the CFTR gene from class I to III) -Children free from any antecedent of colonization to P. aeruginosa at the time of inclusion (certified by the microbiological history supplemented by a molecular test by qPCR according to the diagram of Le gal et al., 2013)--- * Affiliation to the social security system * Consent signed by the holders of parental authority or the sole parent holding parental authority / and "oral" agreement of the second holder Exclusion criteria: * Severe acute illness (other than cystic fibrosis) ongoing, or requiring surgery * Children unable to undergo the tests required by the protocol * Children whose parent(s) is/are minors * Children whose legal guardians do not have sufficient command of the French language * Children under exclusive parenteral nutrition * Refusal to participate in the study