Fungal strains and the development of tolerance against natamycin

Area of Science:

• Mycology
• Antimicrobial Resistance
• Food Science

Background:

• Antimicrobial resistance is a growing concern for both antibacterial and antifungal agents.
• Natamycin is a widely used antifungal food preservative.
• Understanding potential fungal tolerance to natamycin is crucial for its continued efficacy.

Purpose of the Study:

• To investigate the development of fungal tolerance to the antifungal food preservative natamycin.
• To assess the impact of prolonged, increasing natamycin concentrations on fungal strains.
• To evaluate cross-tolerance to other polyene antifungals.

Main Methods:

• Twenty fungal species from medical and food sources were subjected to a "training" procedure with increasing natamycin concentrations.
• Minimum Inhibitory Concentrations (M.I.C.) were determined before and after the training period.
• Cross-tolerance to amphotericin B and nystatin was assessed in selected strains.

Main Results:

• While the overall range of M.I.C. did not significantly change, 13 out of 20 strains showed an increased M.I.C. after natamycin exposure.
• The average M.I.C. increased from 6.1μM to 8.6μM, with 4 strains exhibiting a >2-fold increase in tolerance.
• One strain of Aspergillus ochraceus showed cross-tolerance to amphotericin B and nystatin, while two Fusarium strains did not.

Conclusions:

• Continuous and prolonged increasing selection pressure can induce natamycin tolerance in individual fungal strains.
• This finding suggests that such selection pressures should be avoided in technical applications of natamycin.
• Avoiding selection pressure is essential to ensure the continued safe use of natamycin as a food preservative.