Investigating the antimicrobial activity of sphingosine as a novel therapy against respiratory infection and the epidemiology of nontuberculous mycobacteria in children with cystic fibrosis

Abstract

Airway infection in children with cystic fibrosis (CF) remains a major issue despite the advent of modulator therapies targeting the underlying defect. Sphingosine deficiency has been implicated in pulmonary infection susceptibility in CF. Previous studies have demonstrated sphingosine’s broad-spectrum antimicrobial properties, though its mechanism remains poorly elucidated. This thesis investigated sphingosine’s in vitro antimicrobial activity against lab and clinical strains of Staphylococcus aureus and Pseudomonas aeruginosa and its mechanism of action. Sphingosine had in vitro antimicrobial activity against S. aureus but not P. aeruginosa. Sphingosine’s effect on S. aureus’ membrane permeability and potential was investigated using electron microscopy and fluorescence microscopy techniques. Antimicrobial susceptibility testing against mutant strains were performed investigating inhibition of the electron transport chain and cardiolipin-binding as specific mechanisms. Anti-staphylococcal activity of sphingosine was primarily mediated by membrane depolarisation with no evidence to support specific mechanisms described above. Sphingosine has potential as an anti-staphylococcal agent though lack of efficacy against P. aeruginosa suggests caution in its use in CF. Additionally presented in this thesis is an epidemiological study on nontuberculous mycobacteria (NTM) in children with CF. Using UK CF registry data between 2010 and 2018, descriptive analysis of epidemiological trends in NTM infection was performed. Logistic regression was performed to identify associated clinical factors. Annual prevalence of NTM infection increased from 2010 to 2018 but plateaued between 2016-2018. However, 2018 had the highest annual prevalence (3.6%), substantially higher than in 2010 (2%). Out of those who had isolated NTM at least once between 2014 and 2018, Mycobacterium abscessus complex (55.9%) was most commonly isolated followed by Mycobacterium avium complex (27.7%). NTM infection was associated with older age, lower lung function and allergic bronchopulmonary aspergillosis. This study highlights the significance of NTM in

children with CF. Well-designed trials are urgently needed to identify the most effective management strategies.