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