Pistachio Hull Essential Oil May Combat Candida sp.

In immunocompetent subjects, Candida sp. are generally responsible for mucosal infections, including thrush and vaginitis, which can lead to invasive candidiasis in immunocompromised patients, with emerging species becoming multi-drug resistant. Candida sp. represent the most common cause of fungal infections worldwide. In this work, researchers evaluated the activity of an essential oil extracted from pistachio hulls against a number of standard and clinical strains of Candida sp.

Methods / C. albicans ATCC 64550, C. parapsilosis ATCC 22019, 4 clinical strains of C. albicans, 3 clinical strains of C. parapsilosis and 3 clinical strains of C. glabrata were used. All clinical isolates were identified by species-specific PCR-based methods.

Susceptibility studies were performed using pistachio hull essential oil alone or in combination with antifungal compounds. The interactions between pistachio hull essential oil and selected antifungal compounds were also evaluated using the checkerboard method and the mechanisms of interaction investigated by droplet size distribution.

Results / Pistachio hull essential oil was fungicidal at the concentrations between 2.50 and 5.0 mg/ml. D-limonene and 3-Carene were the components with major activity. An antagonistic effect was observed with all combinations tested.

Pistachio hull EO was active against all strains tested, C. parapsilosis strains being the most sensitive (complete inhibition achieved with a concentration of 1.25–2.50 mg/ml), followed by C. glabrata strains (complete inhibition achieved with a concentration of 1.25–5.0 mg/ml) and C. albicans strains (complete inhibition achieved with a concentration of 5.0 mg/ml). The effect of pistachio hull EO was fungicidal against all tested strains. Interestingly, all clinical strains of C. albicans and1 strain of C. glabrata (strain 33) were resistant to both voriconazole and fluconazole.

Killing curves for pistachio hull EO against C. albicans strain 16 (a), C. glabrata strain 9 (b) and C. parapsilosis strain 26 (c). Control, ♦; 1/4xMIC, ×; 1/2xMIC, ▲; 1xMIC, ■. Mean of three experiments. MIC = minimum inhibitory concentration

Conclusion / The antifungal activity of pistachio hull essential oil could be used to help control resistance in Candida species. More studies need to be performed to elucidate the mechanisms responsible for the activity of pistachio hull essential oil.

Source: Manuela D’Arrigo, et al. In vitro evaluation of the activity of an essential oil from Pistacia vera L. variety Bronte hull against Candida sp. BMC Complementary and Alternative Medicine 2019 19:6. https://doi.org/10.1186/s12906-018-2425-0