Capsaicin inhibitory effects on Vibrio cholerae toxin genes expression

Cholera is an acute secretory diarrhea caused by the Gram-negative bacterium, Vibrio cholerae mostly through production of cholera toxin (CT) and zonula occludens toxin (Zot). Isolates of V. cholerae have acquired resistance elements during the last decade. One of the most promising ways to treat resistant strains is to use antivirulence agents instead of killing the causative agent with conventional antibiotics. In this study, we examined whether different concentrations of capsaicin - the pungent fraction of red chili- can act as an antivirulence agent and inhibit V. cholerae toxin production. Two standard strains namely, V. cholerae ATCC 14035 and V. cholerae PTCC 1611 were used in this study. Minimum Inhibitory Concentration (MIC) of capsaicin was determined by broth microdilution method. Based on MIC results, the bacteria were cultured in the presence of sub-MIC concentrations of capsaicin and a negative control without capsaicin. Real-time PCR (RT-PCR) was carried out to determine the expression level of V. cholerae toxin genes at each concentration. MIC test showed that 200 mg/mL of capsaicin in 2% dimethyl sulfoxide (DMSO) could inhibit the growth of the two standard strains of V. cholerae. The expression of V. cholerae toxin genes was significantly reduced following treatment with sub-MIC concentrations of capsaicin as assessed by RT-PCR. Capsaicin showed great inhibitory effect against cholera toxin and reduced Zot production in the tested strains of V. cholerae. The results showed promising insights into antivirulence effects of capsaicin.