Antifungal Properties of Protein Extracts from Thai Medicinal Plants to Opportunistic Fungal Pathogens

Abstract

Antifungal proteins or peptides (AFPs) are the natural products produced by several life forms including plants as the first-line defenses to infections. The AFPs from Thai plants can be used as new therapeutic agents in the world with growing resistance to conventional antifungals. This study determined the antifungal activities of protein extracts from Thai medicinal plants against important human opportunistic fungi, Candida albicans, Cryptococcus neoformans, Aspergillus fumigatus, and Talaromyces marneffei. Total crude protein supernatants and their precipitated proteins from 10 Thai medicinal plants with the historical usage for treatment of fungal infection were prepared. Most of the protein extracts showed antifungal activities to the tested fungi. The most effective reactivity found in the extracts from Rhinacanthus nasutus, Andrographis paniculata, and Psidium guajava by showing highest activity to T. marneffei ATCC200051 (yeast phase), followed by C. neoformans ATCC90112, C. albicans ATCC90028, T. marneffei ATCC200051 (mold phase), and A. fumigatus NCPF7367. The precipitated proteins from R. nasutus and A. paniculata containing antifungal properties were selected for partial purification by size cut-off membrane centrifugation and tested for antifungal activities. A colorimetric broth microdilution method was used to determine the minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) to anti-T. marneffei. The partially purified fractions from A. paniculata, and R. nasutus showed anti-T. marneffei activity with the MIC and MFC values ranged from 2 to 128 μg/mL and 16 to >128 μg/mL, respectively. Therefore, A. paniculata and R. nasutus can be further subjected to the study of the therapeutic antifungals.