The objective of this study is to evaluate the predictive nature of the biomarker Porphyromonas catoniae measured at the age of 12 months in the occurrence of colonization with Pseudomonas aeruginosa at 36 months of age in children with cystic fibrosis.

This is a multicentric study in 3 phases:

• Pre-inclusion: at the first visit to the CRCM (support for a positive screening confirmed by sweat test and genotyping CFTR)
• Inclusion: possible between the 2nd visit to the CRCM (about 2 months old) and the 6th month
• Follow-up: up to 36 months old. The pace of visits will be based on the usual follow-up rate of CF infants

The clinical data as well as samples (expectorations, stools) will be collected on a monthly basis up to 6 months old and then every 2 months until one year old and finally quarterly until 3 years old.

• Tracheo-bronchial secretions will be collected at the CRCM
• Stools samples will be carried out by the parents prior to consultation with the CRCM
• A blood collection will be carried out annually in an annual report.

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

All collected data that underlie results in a publication

Data will be available after the publication of result and ending fifteen years following the last visit of the last patient

Data access requests will be reviewed by the internal committee of Brest UH. Requestors will be required to sign and complete a data access agreement.