Thai herbal extracts from Garlic and Turmeric suppress the type 3 secretion system of Salmonella Typhimurium

In Thailand, garlic and turmeric have been used widely as basic spices in Thai food and traditional medicine. Previous studies reported that both of them had antibacterial activities. A few data have shown that extracts from both herbs are type 3 secretion system (T3SS) inhibitors. Therefore, this study aimed to investigate anti-T3SS in garlic and turmeric extracts and identify their specific mechanisms.

Salmonella Typhimurium containing chromosomally infusion between the gene encoding SipA effector protein and strep-tag epitope was used for the determination of anti-T3SS in garlic and turmeric extracts. The mechanism of inhibition was identified by the determination of mRNA expression of T3SS genes with semiquantitative RT-PCR.

Garlic and turmeric extracts contained T3SS inhibitory activity at the concentrations of 100 μg/mL and 75 μg/mL, respectively. These extracts reduced the ability of bacterial invasion into epithelial cell cultures. However, the effective dose of both extracts did not affect bacterial growth or toxic effects on HeLa cells. Moreover, the results from RNA transcriptional levels illustrated that these extracts suppressed the transcription of the T3SS regulation genes.

It may conclude that garlic and turmeric extracts blocked T3S activity for the secretion of effector proteins and bacterial invasion by interfering the expression of the T3SS regulatory cascade. Therefore, the extracts from garlic and turmeric might be potential sources for the development of new anti-T3SS therapeutic agents.