Anti-cryptococcal activity of ethanol crude extract and hexane fraction from Ocimum basilicum var. Maria bonita: mechanisms of action and synergism with amphotericin B and Ocimum basilicum essential oil.

BACKGROUND

Ocimum basilicum L. (Lamiaceae) has been used in folk medicine to treat headaches, kidney disorders, and intestinal worms.

OBJECTIVE

This study evaluates the anti-cryptococcal activity of ethanol crude extract and hexane fraction obtained from O. basilicum var. Maria Bonita leaves.

METHODS

The MIC values for Cryptococcus sp. were obtained according to Clinical and Laboratory Standards Institute in a range of 0.3-2500 μg/mL. The checkerboard assay evaluated the association of the substances tested (in a range of 0.099-2500 μg/mL) with amphotericin B and O. basilicum essential oil for 48 h. The ethanol extract, hexane fraction and associations in a range of 0.3-2500 μg/mL were tested for pigmentation inhibition after 7 days of treatment. The inhibition of ergosterol synthesis and reduction of capsule size were evaluated after the treatment with ethanol extract (312 μg/mL), hexane fraction (78 μg/mL) and the combinations of essential oil + ethanol extract (78 μg/mL + 19.5 μg/mL, respectively) and essential oil + hexane fraction (39.36 μg/mL + 10 μg/mL, respectively) for 24 and 48 h, respectively.

RESULTS

The hexane fraction presented better results than the ethanol extract, with a low MIC (156 μg/mL against C. neoformans T444 and 312 μg/mL against C. neoformans H99 serotype A and C. gattii WM779 serotype C). The combination of the ethanol extract and hexane fraction with amphotericin B and essential oil enhanced their antifungal activity, reducing the concentration of each substance needed to kill 100% of the inoculum. The substances tested were able to reduce the pigmentation, capsule size and ergosterol synthesis, which suggest they have important mechanisms of action.

CONCLUSIONS

These results provide further support for the use of ethanol extracts of O. basilicum as a potential source of antifungal agents.