Abstract
Oxidative treatment is one of the strategies for preventing Penicillium contamination in crops/foods. The antifungal efficacy of hydrogen peroxide (H2O2; oxidant) was investigated in Penicillium strains by using kojic acid (KA) as a chemosensitizing agent, which can enhance the susceptibility of pathogens to antifungal agents. Co-application of KA with H2O2 (chemosensitization) resulted in the enhancement of antifungal activity of either compound, when compared to the independent application of each agent alone. Of note, heat enhanced the activity of H2O2 to a greater extent during chemosensitization, whereby the minimum inhibitory or minimum fungicidal concentrations of H2O2 was decreased up to 4 or 13 fold, respectively, at 35–45 °C (heat), when compared to that at 28 °C (normal growth temperature). However, heat didn’t increase the antifungal activity of KA, indicating specificity exists between heat and types of antifungals applied. The effect of chemosensitization was also strain-specific, where P. expansum (both parental and fludioxonil-resistant mutants) or P. italicum 983 exhibited relatively higher susceptibility to the chemosensitization, comparing to other Penicillium strains tested. Collectively, chemosensitization can serve as a potent antifungal strategy to lower effective dosages of toxic antifungal substances, such as H2O2. This can lead to coincidental lowering of environmental and health risks.
Highlights
Kojic acid (5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one, kojic acid (KA), Figure 1), is a natural compound produced by certain filamentous fungi (Aspergillus, Penicillium) or Acetobacter ([1,2] and references therein)
Unlike in H2O2, heat did not enhance the activity of KA, suggesting specificity exists between heat and types of antifungal compounds applied for the enhancement of antifungal activity
Levels of interactions between biotic (KA) and abiotic (H2O2) stressors were determined for the enhancement of antifungal efficacy as follows: With chemosensitization (KA + H2O2), (1) Minimum Inhibitory Concentrations (MICs) or Minimum Fungicidal Concentrations (MFCs) of KA or H2O2 was lowered during chemosensitization depending on types of strains or culture conditions (See Table 3 for summary)
Summary
Kojic acid (5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one, KA, Figure 1), is a natural compound produced by certain filamentous fungi (Aspergillus, Penicillium) or Acetobacter ([1,2] and references therein). The filamentous fungi in the genus Penicillium are frequently involved in food contamination or postharvest decay. Development of strategies for early intervention of mycotoxin production or fungal contamination in crops or foods is urgently needed. Various environmental factors, such as fluctuation of temperature, humidity or pH, etc., can be sources of “abiotic” stress to fungal pathogens. Heat or oxidative treatment is one of the strategies to prevent contamination by Penicillium in foods or crops. Antifungal chemosensitization is investigated for effective control of pathogenic strains of Penicillium (See Table 1) by co-applying KA with H2O2, which mimics host reactive oxygen species. : NRRL, National Center for Agricultural Utilization and Research, USDA-ARS, Peoria, IL, USA
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