5-fluorocytosine resistance in Cryptococcus neoformans.

Area of Science:

• Medical Mycology
• Antimicrobial Resistance
• Pharmacology

Background:

• 5-fluorocytosine (5-FC) is a key antifungal agent.
• Cryptococcus neoformans infections can be challenging to treat.
• Acquired drug resistance limits therapeutic options.

Purpose of the Study:

• To investigate the mechanisms of 5-fluorocytosine (5-FC) resistance in Cryptococcus neoformans.
• To analyze the genetic basis of acquired antifungal drug resistance.
• To compare in vivo and in vitro resistance development.

Main Methods:

• Isolating Cryptococcus neoformans from patients before and after 5-FC therapy.
• Employing fluctuation analysis to determine mutation rates.
• Measuring intracellular uptake and incorporation of radiolabeled cytosine and 5-FC.
• Assessing cross-resistance to 5-fluorouracil (5-FU).

Main Results:

• Post-therapy isolates showed massive and stable 5-FC resistance.
• Spontaneous 5-FC resistant mutants occurred at low frequencies (<0.001%) in susceptible isolates.
• Reduced intracellular uptake of 5-FC was observed in most resistant isolates.
• Resistance was linked to defects in uridine-5'-monophosphate pyrophosphorylase or cytosine permease.

Conclusions:

• Cryptococcus neoformans can rapidly acquire high-level resistance to 5-FC.
• Mechanisms include impaired drug uptake and enzymatic alterations.
• Understanding these mechanisms is crucial for optimizing antifungal strategies.