Achromobacter xylosoxidans is frequently isolated in sputum samples from CF patients. Although its clinical role is not fully clear yet, chronic infection has been associated with lung inflammation, increased frequency of exacerbations and decline of the respiratory function, and is usually complicated by multidrug resistance. The pathogenic potential of 54 A. xylosoxidans clinical strains isolated from 26 CF patients will be first evaluated in Galleria mellonella larvae. After whole genome sequencing, the presence of virulence genes will be investigated to identify markers associated with pathogenicity as assessed in G. mellonella. Cytotoxicity and epithelial disruption by representative strains will be evaluated in vitro on human CF bronchial epithelial cells; pro-inflammatory effects will be assessed in vivo in infected CF mice. Clinical data (infection status, lung function, pulmonary exacerbations, transplantation, genotype) of the carrier patients will be correlated to the pathogenic features of the infecting strains. Researchers expect to identify genetic virulence markers associated with A. xylosoxidans pathogenicity and to link these features to the clinical conditions of carrier patients.