Characterization and analysis of the bioactivity of the Piper rivinoides Kunth essential oil and its components myristicin and elemicin, against opportunistic fungal pathogens.

Candidiasis is an infectious disease caused by some fungi of the genus Candida. In Brazil, the incidence rate is higher than in European countries and the United States, and health problems occur mainly due to the virulence factors of the fungi, which have made treatment with commercial drugs difficult. Considering the context, plants rich in phenolic compounds, such as those of the genus Piper, have been studied due to their antimicrobial properties. Thus, the objective of this study was to isolate and characterize the essential oil of Piper rivinoides Kunth, as well as to analyze the bioactivity of this essential oil and the myristicin and elemicin isolates against opportunistic fungal pathogens. The broth microdilution method was used to identify the intrinsic activity of the isolated natural products alone and combined with fluconazole to obtain the 50 % inhibitory concentration of the fungi (IC). Microdilution subculture assays were performed to determine the minimum fungicidal concentration. The results revealed moderate antifungal activity of P. rivinoides oil against C. tropicalis (512 μg/mL), C. albicans (1024 μg/mL), and P. kudriavzevii (512 μg/mL). Myristicin also showed moderate activity against C. albicans, C. tropicalis and P. kudriavzevii at 1024 μg/mL. As for elemicin, inhibition occurred at a concentration of 512 μg/mL for both strains, except against P. kudriavzevii, which was from 128 μg/mL. Combined with fluconazole, the products modified the drug's action, increasing its efficacy at concentrations ranging from 0.007 to 20.78 μg/mL, except for elemicin, which antagonized the drug's effect, modifying its action from 32.17 to 74.18 μg/mL against P. kudriavzevii. The antifungal effect of compounds, alone or in combination with fluconazole, was fungistatic, except for P. kudriavzevii, which was fungicidal in the isolated test with elemicin at concentrations starting from 128 μg/mL. Therefore, P. rivinoides and its isolated compounds have the potential for combination therapy with antifungals.