The low availability of antifungal agents, emergence of resistant fungi, pharmacokinetic difficulties, toxicity, adverse effects and lack of production of new drugs, highlight the need for the finding/development of new bioactive molecules such as antifungal agents. The great diversity of ethnopharmacologically used plants in the Northeast Argentina, are potential sources of research on substances with biological activity. Acanthospermum australe (Loefl.) Kuntze (A. australe), commonly known as "tapekué" in Argentina, is a medicinal plant widely distributed in South America used by the indigenous peoples for skin infetions, among other dermal conditions. On the other hand, the skin diseases associated with Malassezia spp. are often chronic, recurrent and topical and systemic antifungal therapies not always with have successful outcome, so a large proportion of patients seek alternative natural options, obtaining in many cases excellent results.
The objective of this work was to evaluate the in vitro inhibitory activity of the A. australe essential oil against clinical isolates of Malassezia furfur and Malassezia sympodialis.
Plants of A. australe collected on Riachuelo locality, Corrientes province (Argentina) were identified by Instituto de Botánica del Nordeste (IBONE), Universidad Nacional del Nordeste (Argentina) where a voucher specimen was deposited. Plants were air dried and then the leaves were separated. Essential oil of the leaves were obtained by steam distillation and stored at 4°C until bioassayed. In order to evaluate the inhibitory activity of the essential oil, using broth microdilution method in accordance with CLSI M27-A3 with the modifications proposed by Rojas et al. (2014), the minimum inhibitory concentrations (MIC) were determined against 20 M. furfur and 10 M. sympodialis clinical isolates. CBS M. furfur and M. sympodialis reference strains were included. Range, arithmetic mean, mode, MIC50 and MIC90 values defined as the lowest concentration at which 90 and 50% of the isolates were inhibited, were obtained.
A. australe essential oil against M. furfur showed values ranged 0.5-2 mg/mL; arithmetic mean: 1.5 mg/mL; mode: 2 mg/mL; MIC50: 2 mg/mL; MIC90: 2 mg/mL. In contrast, essential oil against M. sympodialis showed values ranged 0.25-2 mg/mL; arithmetic mean: 1 mg/mL; mode: 1 mg/mL; MIC50: 1 mg/mL; MIC90: 2 mg/mL.
Essential oil of A. australe leaves showed in vitro inhibitory activity against clinical isolates of M. furfur and M. sympodialis causing malasseziosis. Essential oil was more active against M. sympodialis than M. furfur. These results contribute to the scientific explanation of the empirical use of A. australe in treating several skin infections and with the revaluation of the traditional ethnomedical knowledge. This is the first report where the inhibitory activity of the A. australe essential oil against Malassezia is evaluated and contributes to the knowledge about the antifungal activity of new compounds against Malassezia.

In vitro inhibitory activity of the Acanthospermum australe essential oil against Malassezia furfur and Malassezia sympodialis