Low Glucose Mediated Fluconazole Tolerance in .

Chronic meningoencephalitis is caused by and is treated in many parts of the world with fluconazole (FLC) monotherapy, which is associated with treatment failure and poor outcome. In the host, propagates predominantly under low glucose growth conditions. We investigated whether low glucose, mimicked by growing in synthetic media (SM) with 0.05% glucose (SM), affects FLC-resistance. A > 4-fold increase in FLC tolerance was observed in seven strains when minimum inhibitory concentration (MIC) was determined in SM compared to MIC in SM with normal (2%) glucose (SM). In SM, cells exhibited upregulation of efflux pump genes (8.7-fold) and (2.5-fold), as well as decreased accumulation (2.6-fold) of Nile Red, an efflux pump substrate. Elevated intracellular ATP levels (3.2-fold and 3.4-fold), as well as decreased mitochondrial reactive oxygen species levels (12.8-fold and 17-fold), were found in the presence and absence of FLC, indicating that low glucose altered mitochondrial function. Fluorescence microscopy revealed that mitochondria of grown in SM were fragmented, whereas normal glucose promoted a reticular network of mitochondria. Although mitochondrial membrane potential (MMP) was not markedly affected in SM, it significantly decreased in the presence of FLC (12.5-fold) in SM, but remained stable in SM-growing cells. Our data demonstrate that increased FLC tolerance in low glucose-growing is the result of increased efflux pump activities and altered mitochondrial function, which is more preserved in SM. This mechanism of resistance is different from FLC heteroresistance, which is associated with aneuploidy of chromosome 1 (Chr1).