Relationship between polyene resistance and sterol compositions in Cryptococcus neoformans

Area of Science:

• Mycology
• Molecular Biology
• Antifungal Resistance

Background:

• Cryptococcus neoformans is an opportunistic fungal pathogen.
• Polyene antifungals like nystatin, pimaricin, and amphotericin B are crucial for treating fungal infections.
• Understanding the mechanisms of antifungal resistance is vital for developing effective therapies.

Purpose of the Study:

• To investigate the sterol composition of Cryptococcus neoformans mutants resistant to nystatin, pimaricin, and amphotericin B.
• To correlate specific sterol alterations with the level of antifungal resistance.
• To assess the impact of sterol changes on fungal virulence and growth characteristics.

Main Methods:

• Isolation of drug-resistant mutants using ultraviolet irradiation.
• Analysis of major sterol profiles in wild-type and mutant strains using chromatographic techniques.
• Assessment of antifungal resistance levels.
• Evaluation of fungal growth rates at different temperatures (25°C and 37°C).
• In vivo virulence studies in a mouse model.

Main Results:

• Six nystatin/pimaricin-resistant mutants and three amphotericin B-resistant mutants were generated.
• Nystatin/pimaricin-resistant mutants displayed altered sterol profiles, including loss of ergosterol and production of novel sterols (Delta(7, 22)-ergostadien-3beta-ol, Delta(7)-ergosten-3beta-ol, Delta(8(9))-ergosten-3beta-ol, Delta(5, 8(9), 22)-ergostatrien-3beta-ol).
• Mutants producing Delta(8(9))- and Delta(5, 8(9), 22)- sterols showed high resistance to nystatin/pimaricin, while those with Delta(7, 22)- and Delta(7)- sterols showed lower resistance.
• Amphotericin B-resistant mutants had wild-type sterol compositions, suggesting resistance via non-sterol mechanisms.
• Mutants with altered sterols exhibited reduced virulence, impaired growth at 37°C, and slower growth at 25°C.

Conclusions:

• Alterations in sterol biosynthesis pathways are a key mechanism for resistance to nystatin and pimaricin in Cryptococcus neoformans.
• Specific sterol changes correlate with varying degrees of resistance.
• Resistance to amphotericin B can occur independently of major sterol modifications.
• Sterol alterations leading to polyene resistance can compromise fungal fitness, affecting virulence and thermotolerance.