Cystic Fibrosis Microbiome-determined Antibiotic Therapy Trial in Exacerbations: Results Stratified

Inclusion Criteria: * Written and informed consent, and assent where required. * Age 16 years or older at enrolment * Diagnosis of CF by standard sweat test and/or genetic analysis * Persistent pulmonary Pseudomonas aeruginosa colonization confirmed on at least 2 occasions in the preceding 12 months * Screening FEV1 predicted of \>25% * Able to perform spirometry reproducibly prior to enrolment * Able to expectorate and provide a sputum sample at least once daily * ≥1 non-elective course of intravenous antibiotics in the preceding year * Able to understand and comply with protocol requirements, restrictions and instructions and likely to complete the study as planned, as judged by the investigator Exclusion Criteria: * Life expectancy less than 6 months * They are a solid organ transplant recipient * Have a requirement for immunosuppression ≥10mg corticosteroids per day * Previous positive culture of non-tuberculosis mycobacteria species M.avium, M.abscessus or M.intracellulare within the last 12 months or undergoing active therapy * Positive culture of any Burkholderia cepacia species within the last 12 months or undergoing active therapy * Allergic bronchopulmonary aspergillosis on treatment * Known allergies to more than 3 different classes of antibiotics, and intolerance or allergy to tobramycin. * Liver portal hypertension, determined by identification of oesophageal varices * Advanced kidney disease requiring a dose reduction of ceftazidime or contraindicating aminoglycosides * History of any illness that in the opinion of the investigator, might confound the results of the study or pose an additional risk in administering study drug to the subject * If patient undergoes a pulmonary exacerbation before the Microbiome analysis is reviewed by the Consensus Treatment Panel and i.v. antibiotics are administered. In this case, a repeat sputum will be sent for analysis 4 weeks after end of antibiotic treatment. * Pregnant or breast-feeding at time of eligible pulmonary exacerbation