Low Glucose Mediated Fluconazole Tolerance in Cryptococcus neoformans.

Area of Science:

• Mycology
• Antimicrobial Resistance
• Cell Biology

Background:

• Chronic meningoencephalitis is often caused by Cryptococcus neoformans.
• Fluconazole (FLC) monotherapy is a common treatment but frequently fails.
• Cryptococcus neoformans thrives in low glucose environments within the host.

Purpose of the Study:

• To investigate the impact of low glucose on FLC resistance in Cryptococcus neoformans.
• To elucidate the underlying mechanisms of FLC resistance under low glucose conditions.

Main Methods:

• Minimum inhibitory concentration (MIC) assays in varying glucose concentrations (0.05% vs. 2%).
• Gene expression analysis of efflux pump genes (AFR1, AFR2).
• Measurement of Nile Red accumulation, intracellular ATP, mitochondrial reactive oxygen species, and mitochondrial membrane potential (MMP).
• Fluorescence microscopy to visualize mitochondrial morphology.

Main Results:

• A >4-fold increase in FLC tolerance was observed in low glucose conditions.
• Upregulation of efflux pump genes (AFR1, AFR2) and decreased Nile Red accumulation indicated increased efflux.
• Elevated intracellular ATP and altered mitochondrial function, including fragmented mitochondria and preserved MMP in the presence of FLC, were noted.
• Low glucose conditions protected mitochondrial membrane potential against FLC treatment.

Conclusions:

• Low glucose significantly enhances FLC tolerance in Cryptococcus neoformans.
• Increased efflux pump activity and altered mitochondrial function contribute to this resistance.
• This mechanism is distinct from FLC heteroresistance associated with aneuploidy.