Candida Infection Biology – fungal armoury, battlefields ... - FINSysB

Poster number: 42
The role of fungal cell wall composition and remodelling in
echinocandin drug tolerance
Louise Walker, Kerstin Nather, Laura Selway, David Stead, Keunsook Lee,
Alistair Brown, Carol Munro
Institute of Medical Sciences, School of Medical Sciences, University of Aberdeen, Aberdeen, UK
Echinocandins are antifungal agents, which affect fungal cell wall integrity by
inhibiting (1,3)-glucan synthesis. Assembly of the fungal cell wall is a dynamic
process. Echinocandin treatment below the MIC activates compensatory
mechanisms that upregulate chitin biosynthesis and result in altered cross-linking
and changes in the cell wall proteome, in an attempt to reinforce the cell wall.
Proteomic analysis and transcript profiling have identified cell wall proteins (CWP)
and genes that are more abundant and have elevated expression in response to
treatment with sub-MIC caspofungin. These include transglycosidases and crosslinking
proteins involved in modifying cell wall polysaccharides (Utr2, Crh11, Phr1,
Cht2), as well as novel proteins (Pga31). Changes in cell wall architecture and
composition can alter a cell’s sensitivity to the echinocandins. Using a tetracycline
inducible promoter, genes of CWPs which were upregulated in response to
caspofungin treatment, were overexpressed to determine whether this altered
susceptibility to caspofungin. Overexpression of CHT2 lead to reduced
susceptibility whereas overexpression of UTR2 and PHR1 resulted in increased
sensitivity to caspofungin. To determine whether altered susceptibility to
caspofungin was observed in vivo, larvae of Galleria mellonella were used as a
preliminary screening model. Overexpression of UTR2 lead to reduced susceptibility
to caspofungin in G. mellonella. Treatment with caspofungin increased the survival
time of larvae infected with the UTR2 overexpression strain compared to larvae
infected with the wild-type. Fungal burdens were significantly reduced in infected
larvae treated with caspofungin and this reduction was greater in larvae infected
with the UTR2 overexpression strain. The number of immune cells also determines
the fitness of G. mellonella. Larvae infected with wild-type and UTR2 overexpression
strain had more immune cells after treatment with caspofungin, indicating an
increase in fitness. Therefore, overexpression of fungal cell surface proteins can
affect the susceptibility of C. albicans to caspofungin in vitro and in vivo.
200