Are γ-terpinene, 1,8-cineole, p-coumaric acid, and quercetin active against wild-type and non-wild-type Sporothrix brasiliensis to itraconazole?

The emergence of itraconazole (ITZ)-resistant Sporothrix brasiliensis in feline and canine cases in southern Brazil has hampered the clinical cure of animal sporotrichosis, encouraging the search for therapeutic alternatives. The promising use of plants extracts from Lamiaceae family is known; however, there are no studies with its major compounds, as gamma-terpinene (gamma TER), 1,8-cineole (1,8CIN), p-coumaric acid (pCOU), and quercetin (QUER). For the first time, we evaluated the antifungal, synergistic, cytotoxic activities and action mechanism of these compounds against S. brasiliensis. For this, 28 S. brasiliensis from cats (n= 24) and dogs (n=4) and standard strains of S. brasiliensis and S. schenckii (n=4) were tested by M38-A2 (CLSI), revealing non-wild-type (WT) isolates to ITZ on 54.2% (13/24) and 75% (03/04) of feline and canine isolates, respectively. Of the compounds, gamma TER stood out against all isolates (MIC/MFC 0.75 to > 3 mg/ml; MIC50 3 mg/ ml). However, 1,8CIN, pCOU, and QUER showed little or no activity (MIC50 > 3 mg/ml). Thus, gamma TER was selected for checkerboard assay, whose combination with ITZ showed synergistic (WT isolates) and indifferent (non-WT isolates) interaction. For action mechanism (sorbitol protection and ergosterol effect), gamma TER acted in membrane by complexing with fungal ergosterol and at the cell wall level, showing two possible pathways as antifungal target. Finally, cytotoxicity (MTT assay) showed that gamma TER was the safest compound on MDBK cells, even at a concentration of 3 mg/ml (90.16%). Our findings support that gamma TER is a potent antifungal candidate for the control of sporotrichosis, including against non-WT S. brasiliensis.

Automated summary

The emergence of itraconazole (ITZ)-resistant Sporothrix brasiliensis in southern Brazil has hindered the treatment of animal sporotrichosis, leading to the search for alternative therapies. The compound gamma-terpinene (gamma TER) from Lamiaceae family plants showed potent antifungal activity against S. brasiliensis, making it a promising candidate for the control of sporotrichosis.