306 MA isolated from 62 FC patients of 4 Italian CF centers were studied. In the large majority of patients persistently infected by the same MA, the subspecies genetic analysis was carried out by VNTR profile and/or resorting to whole genome sequencing. It demonstrated that the genotype remained unchanged in the same patient and the same strain of MA was invariably responsible for the infection. In contrast, the isolates from different patients belonged to different strains. Only in a couple of patients, nine strains were shared and the patient-to-patient transmission cannot be excluded. The epidemiological investigation undertaken by the researchers will help to make clear this question. The antimicrobial susceptibility testing confirmed that, with the exception of a single strain, all the others strains were characterized by inducible resistance to macrolides. The confirmation or the exclusion of patient-to-patient transmission may heavily impact on cross-infection prevention measures.