Undergraduate Student Report 2021
Adaptation to a potent anti-fungal metabolite by the pathogen, Candida auris
Emily Rowlands worked with Dr Alex Brand, University of Exeter, to investigate differences between clades of the human fungal pathogen, Candidia auris.
I am a second year Biomedical Sciences student at the University of Bristol, with a keen interest in microbiology and laboratory studies. This summer (2021), I was thrilled to be awarded a Summer Bursary by the BMS to undertake an exciting 8-week placement in Dr Alex Brand’s lab at the University of Exeter. My project was to test the efficacy of a fungal secondary metabolite against Candida auris, an emerging fungal pathogen, and to explore its mode of action.
C. auris was first identified in 2009 as a new species that was difficult to treat due to its multi-drug resistance. The 4 clades of this fungus are categorised by their geographical location, and there is emerging evidence that each clade has distinct phenotypes from the others. Previous studies of C. auris by the Brand group have investigated the growth rates of each clade in various media and compared the Minimum Inhibitory Concentrations of antifungal drugs required to suppress its growth.
My initial role on this summer placement was to compare the growth rates of all four clades of C. auris in different growth media to quantify the differences between clades. I then analysed how this was affected by application of increasing concentrations of a specific fungal metabolite. From these data, I planned further experiments aiming to discover the mode of action of the compound and how it was affecting the growth of C. auris. It was hypothesised that the compound interfered with cell-membrane homeostasis by inhibiting an enzyme in a lipid biosynthetic pathway. Therefore, I investigated whether cell growth inhibition in the presence of this compound could be rescued by supplementing the growth medium with these lipids.
Figure 1: Cells of the four C. auris clades were grown in different media in a 96-well plate, in the presence and absence of a fungal metabolite. Once the growth responses were characterised, it was found that supplementation of the medium with specific lipids completely rescued the growth inhibition observed.
I found that the growth rates of the 4 C. auris clades were different in the media types tested. In addition to this, their susceptibility to the fungal metabolite also differed in a medium-dependent manner. Some clades exhibited growth inhibition at high concentrations of the compound, while in others growth inhibition was only temporary. This indicated that these clades were capable of adaptation, potentially through changes in gene expression changes. However, other clades grew slowly but steadily throughout, suggesting that slow growth itself constituted a resistance mechanism. My last experiments established that growth inhibition was completely alleviated on supplementation with specific lipids, therefore supporting the view that the compound acted by inhibiting a lipid biosynthetic pathway and not by uptake of precursors from the medium. Although, in its native form, the metabolite tested did not have a consistent effect on all 4 clades, future work will investigate the underlying mechanisms of their differences in order to better understand how to develop this compound and others as antifungal drugs that are effective against all 4 C. auris clades.
I would like to thank the BMS for offering me and the Brand lab a Summer Bursary that allowed this project to take place despite the COVID-19 pandemic, which has severely reduced the lab training opportunities available. The project enabled me to learn a range of general laboratory skills and how to work with fungal cultures. I also learned how to carry out antifungal drug testing techniques, data analysis and statistics. These skills are invaluable and have expanded my laboratory knowledge well beyond what I have been taught on my degree course. Not only this, but I have had to develop a good understanding of the research question and cell biology in order to plan experiments and decide on the best approach, which I have not been required to do before in undergraduate practical work. This personal development has given me the confidence to do well my final year, especially for my lab project, and also support my career-development through post-graduate education and training. The help of all in Alex Brand’s group, her Research Technician, Debra Carter, and members of the MRC Centre for Medical Mycology generally, have ensured that I have benefited as much as possible from this experience.