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An In Vitro Study of the Antimicrobial Effects of Indigo Naturalis Prepared from Strobilanthes formosanus Moore
Biodiversity Research Center, Academia Sinica, Taipei 115, Taiwan
Graduate Institute of Natural Products, College of Medicine, Chang Gung University, Taoyuan 333, Taiwan
Research Center for Industry of Human Ecology, Chang Gung University of Science and Technology, Taoyuan 333, Taiwan
Department of Traditional Chinese Medicine, Chang Gung Memorial Hospital, Keelung 204, Taiwan
School of Traditional Chinese Medicine, Chang Gung University, Taoyuan 303, Taiwan
* Author to whom correspondence should be addressed.
Received: 10 September 2013; in revised form: 24 October 2013 / Accepted: 25 October 2013 / Published: 21 November 2013
Abstract: Indigo naturalis is effective in treating nail psoriasis coexisting with microorganism infections. This study examines the antimicrobial effects of indigo naturalis prepared from Strobilanthes formosanus Moore. Eight bacterial and seven fungal strains were assayed using the agar diffusion method to examine the effects of indigo naturalis and its bioactive compounds. The bioactive compounds of indigo naturalis were purified sequentially using GFC, TLC, and HPLC. Their structures were identified using mass spectrometry and NMR spectroscopy. UPLC-MS/MS was applied to compare the metabolome profiles of indigo naturalis ethyl-acetate (EA) extract and its source plant, Strobilanthes formosanus Moore. The results of in vitro antimicrobial assays showed that indigo naturalis EA-extract significantly (≥1 mg/disc) inhibits Gram-positive bacteria (Staphylococcus aureus, S. epidermis and methicillin-resistant S. aureus (MRSA)) and mildly inhibits non-dermatophytic onychomycosis pathogens (Aspergillus fumigates and Candida albicans), but has little effect on dermatophyes. Isatin and tryptanthrin were identified as the bioactive compounds of indigo naturalis using S. aureus and S. epidermis as the bioassay model. Both bioactive ingredients had no effect on all tested fungi. In summary, indigo naturalis prepared from Strobilanthes formosanus Moore exhibits antimicrobial effects on Staphylococcus and non-dermatophytic onychomycosis pathogens. Tryptanthrin and isatin may be its major bioactive ingredients against Staphylococcus and the inhibitory effect on MRSA may be due to other unidentified ingredients.
Keywords: indigo naturalis; Strobilanthes formosanus Moore; tryptanthrin; isatin; nail psoriasis; onychomycosis
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Chiang, Y.-R.; Li, A.; Leu, Y.-L.; Fang, J.-Y.; Lin, Y.-K. An In Vitro Study of the Antimicrobial Effects of Indigo Naturalis Prepared from Strobilanthes formosanus Moore. Molecules 2013, 18, 14381-14396.
Chiang Y-R, Li A, Leu Y-L, Fang J-Y, Lin Y-K. An In Vitro Study of the Antimicrobial Effects of Indigo Naturalis Prepared from Strobilanthes formosanus Moore. Molecules. 2013; 18(11):14381-14396.
Chiang, Yin-Ru; Li, Ann; Leu, Yann-Lii; Fang, Jia-You; Lin, Yin-Ku. 2013. "An In Vitro Study of the Antimicrobial Effects of Indigo Naturalis Prepared from Strobilanthes formosanus Moore." Molecules 18, no. 11: 14381-14396.