Vibrio cholerae is a Gram-negative aquatic bacterium responsible for the severe diarrheal disease cholera, which is still prevalent in many developing countries (Sack et al., 2004). Among >200 serogroups of V. cholerae, O1 (El Tor and classical biotypes) and O139 serogroups
are responsible for cholera epidemics (Ramamurthy et al., 2003). The strains belonging to other serogroups are called non-O1/non-O139, which are associated with sporadic cases of diarrhea (Chatterjee et al., 2009). Recently, a new variant of the V. cholerae O1 El Tor biotype, with attributes of the classical biotype, has been isolated from hospitalized patients with more severe diarrhea than typical El Tor strains (Das et al., 2007). This type of strains has been Compound Library in vitro designated as El Tor variants (Raychoudhuri et al., 2008). The major virulence factors in V. cholerae are cholera Venetoclax toxin (CT) and toxin-coregulated pili (TCP), encoded by the ctxAB and tcpA genes, respectively. CT is
composed of two subunits: A and B. However, the B subunit of CT of El Tor differs from that of the classical one in two amino acid positions. The El Tor variants produce classical type CT-B instead of El Tor (Nair et al., 2006). Expressions of CT and TCP are regulated by TcpP/TcpH and ToxR/ToxS, which activate the expression of ToxT, the master regulator of virulence gene expression. ToxT subsequently regulates the expression of CT and TCP (DiRita et al., 1991; Hase & Mekalanos, 1998). In contrast, histone-like nucleoid structuring protein (H-NS) encoded by the hns gene, a global prokaryotic gene regulator, has been shown to repress the transcription of several virulence genes including toxT, ctxAB and tcpA (Nye et al., 2000). The uses of antimicrobial agents are generally accepted as a key therapeutic for bacterial diseases. The majority of epidemic V. cholerae strains, however, Thymidylate synthase have also become resistant
to multiple antimicrobial agents via mutations, horizontal gene transfer, etc. (Mwansa et al., 2007). Antimicrobial agents are generally bacteriocidal or bacteriostatic and thus most likely have no effect on virulence gene expression. Moreover, antimicrobial agents such as mitomycin C and fluoroquinolone can induce Stx1 and Stx2 production in enterohemorrhagic Escherichia coli (Wu et al., 2005). Therefore, alternate approaches are needed to overcome this hurdle in combating infectious diseases. Screening of bioactive compounds from natural sources, including compounds that can specifically target bacterial virulence cascade without affecting their growth, is one such approach that could be used as novel therapeutic interventions. Since ancient times, natural products such as spices, herbs, etc. have been used to treat diarrheal diseases (Low Dog, 2006). Red chilli (Capsicum annuum) is also a common pungent spice used for many purposes including pharmaceutical preparations (Barceloux, 2008).
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