Ticarcillin Hypersusceptibility in Pseudomonas Aeruginosa in Cystic Fibrosis

Background: A subpopulation of Pseudomonas aeruginosa (PsA) exists in cystic fi brosis (CF) patients that is hypersusceptible to ticarcillin, a carboxypenicillin, in vitro (Tichs strain) defi ned as a minimum inhibitory concentration (MIC) ≤4μg/ml. Methods: In a retrospective cohort study, isolates of PsA from CF (23), non-cystic fi brosis 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. Results: Prevalence of the Tichs strain in PsA was 48%, 76% and 0% in the CF, NCFB and control cohorts respectively. A statistically signifi cant difference in geometric mean MIC was seen between the Tichs and non-Tichs cohorts in CF for ticarcillin (as expected) and temocillin (p=0.041and p=0.036 respectively). A similar trend was observed in NCFB for ticarcillin (p=0.038) and temocillin (p=0.067), although statistical signifi cance was not reached for the latter. In CF, the Tichs strain demonstrated lower MICs to all antibiotics tested apart from gentamicin compared to their non-Tichs counterparts. Those who had the Tichs strain in CF had fewer antibiotics (13.9 days versus 23.5 days, Tichs and non-Tichs respectively) although this result was not statistically signifi cant p=0.202. Conclusion: Our data supports the existence of a Tichs strain of PsA in our CF and NCFB patient populations. This strain correlated with reduced MICs to temocillin in CF, to which PsA would normally be resistant, which may be of clinical relevance. Research Article Ticarcillin Hypersusceptibility in Pseudomonas Aeruginosa in Cystic Fibrosis IT Hettiarachchi1*, T O’Sullivan2, M Wootton1, A Smith2, J Duckers3 and R Dhillon1 1Public Health Wales, Microbiology, Cardiff University Hospital of Wales, Heath Park, Cardiff, UK 2Cardiff University, Cardiff, UK 3All Wales Adult Cystic Fibrosis Centre, University Hospital of Llandough, UK Dates: Received: 27 April, 2017; Accepted: 12 September, 2017; Published: 13 September, 2017 *Corresponding author: Irasha Hettiarachchi, Public Health Wales Microbiology Cardiff, University Hospital of Wales, Heath Park, Cardiff, CF14 4XW, UK, E-mail: