Purpose: To evaluate the anticandidal activity of the ethanol extracts of 12 herbs from Thailand.

Methods: The herbs studied were Alpinia galanga, Curcuma longa, Curcuma zedoaria, Mentha cordifolia, Ocimum africanum, Ocimum basilicum, Ocimum sanctum, Piper betle, Piper chaba, Piper nigrum, Piper sarmentosum and Zingiber officinale. Various Candida spp. were examined for minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) using microdilution method; time-kill assay was also used to assess the plants. Antibiofilm activity was investigated using a 3-[4, 5-dimethyl-2-thiazolyl]-2, 5-diphenyl-2H-tetrazolium-bromide (MTT assay). Gas chromatography mass spectrometry (GC-MS) analysis, thin layer chromatography (TLC) fingerprinting and TLC-bioautography were used to determine the active anticandidal compounds.

Results: All tested herbs, except extracts of P. nigrum and Limiaceae family, showed varying zones of inhibition against Candida albicans ATCC 90028. P. betle revealed the strongest anticandidal activity against all tested strains with MIC ranging from 1.56 to 3.13 mg/ml, and MFC from 3.13 to 8.33 mg/ml. Killing activity depended on time and concentrations of the extract. The concentration of P. betle extract required to inhibit ≥ 90 % biofilm formation of C. albicans ATCC 90028 was 3.13 ± 0.15 mg/ml, while that to remove ≥ 90 % biofilm growth was 12.50 ± 0.69 mg/ml. The result of GC-MS analysis showed the major compound of P. betle extract responsible for anticandidal activity as 4-chromanol.

Conclusion: P. betle extract contains 4-chromanol which is a good potential anticandidal agent for the treatment of oral infectious diseases caused by certain Candida spp.