Ticarcillin Hypersusceptibility in Pseudomonas Aeruginosa in Cystic Fibrosis

Background: A subpopulation of Pseudomonas aeruginosa (PsA) exists in cysticfibrosis (CF) patients that is hypersusceptible to ticarcillin, a carboxypenicillin, in vitro (Tichs strain) defined as a minimum inhibitory concentration (MIC) ≤4μg/ml. Methods: In a retrospective cohort study, isolates of PsA from CF (23), non-cystic fibrosis bronchiectasis (NCFB) (17) and control (18) patients were analysed. MICs for each isolate were determined using agar dilution against six antibiotics and interpreted using EUCAST breakpoints. Prevalence of Tichs in each cohort was calculated. A point prevalence survey was conducted in CF to review the patients' clinical progress following PsA isolation.