Characterisation and mechanistic insights into antifungal drug tolerance in the human pathogen Nakaseomyces glabratus (Candida glabrata)

Abstract

Antifungal drug tolerance (AFDT) remains largely unexplored in clinically relevant non-albicans species such as N. glabratus. Thus, the broader focus of this research isunderstanding the mechanistic pathways associated with drug tolerance in this species andassessing the universality of this trait, as observed in C. albicans by Berman’s group. Partsof this thesis are presented in a thesis-by-publication format. Chapter 2, drafted as amanuscript, focuses on optimising robust assays to quantify tolerance levels in N. glabratuswild-type (ATCC) strains and clinical isolates from the Royal Victoria Hospital, UK. Thesechapters explore the impact of various environmental factors, such as temperature, drugtype, media, and pH combinations, on tolerance modulation. Based on environmentalconstraints and optimised statistical quantification protocols, we were able to reproduciblyclassify the strains into high-, low-, and moderate-tolerant phenotypes. These robustphenotypes tested on the in-vitro Galleria model revealed its clinical significance andtherefore further motivated the rationale of undertaking a transcriptomic approach toelucidate the key factors behind such robust phenotypes in the followingchapter. Chapter 3, presented as a publication draft, centres on in-depth transcriptomicanalysis, including an assessment of differentially expressed genes and molecular pathwaysdistinguishing tolerant from non-tolerant states in N. glabratus, with a comparison to C.albicans. Briefly, our initial insights presented a strategy undertaken by N. glabratustolerant cells to undergo metabolic re-wiring and emerge into a state of metabolicdormancy. Hence, through Chapter 4, we investigated the variances in growth metrics usingboth bulk analyses as well as single-cell level drug responses in high- and low-tolerantstrains, allowing to compare the differences in parameters such as growth rate, lag time,doubling time, overall viability as well as metabolic activity. Overall, this thesis contributesto increasing the knowledge base of this complex and clinically relevant phenomenon ofAFDT with a particular focus on the less-explored species Nakaseomyces glabratus.

Thesis is embargoed until 31 July 2027.

Date of Award	Jul 2026
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Edel Hyland (Supervisor) & Fionnuala Lundy (Supervisor)