Study of Herbal Extracts for Antibacterial Activity and Type Three Secretion System Inhibitor in Bacteria

Abstract

Nowadays, Thai herbal extracts including garlic, turmeric, chantaleela and king of bitters have been used widely for basic spice in Thai food or traditional medicine in Thailand. These herbs were reported that they have antibacterial activity. However, the previous study showed that some herbs are potential as not only antibacterial activity but also anti-T3SS activity for interruption of bacterial pathogenesis. Therefore, the aim of this study is to study Thai herbs including garlic, chantaleela, turmeric, and king of bitters for being as T3SS inhibitors. The SPI-1 T3SS of Salmonella Typhimurium was used as a model in this study. First of all, anti-T3SS activity of herbs were screened and determining of the minimal concentration of the herbs for inhibition of SPI-1 T3SS effector protein secretion from engineering S. Typhimurium by Western blotting. The result showed that garlic, turmeric and Chantaleela inhibited the secretion of SipA-strep tag protein from engineered Salomonella in a dose-dependent manner. The minimal concentrations of garlic, turmeric and Chantaleela were 100 µg/ml, 75 µg/ml and 150 µg/ml, respectively. Moreover, result of invasion assay showed that herbs were able to inhibit invasion activity of S. Typhimurium into host cells. In addition, effective dose from 3 herbs did not affect bacterial growth and harm to HeLa cells, respectively. For anti-T3SS mechanism, RNA transcriptional level in regulatory cascade of SPI-1 T3SS illustrated that herbs suppressed the transcription of SPI-1 T3SS regulator gene, HilD. As this reason, the reduction of HilD expression affected the ability for SPI-1 T3S. Therefore, garlic, turmeric and chantaleela were identified as potential for novel T3SS inhibitors against SPI-1 T3SS of S. Typhimurium.

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