agents target bacterial virulence determinants including toxin production, adhesion to host cells, specialized secretion systems such as TTSS . Application of anti-virulence agents is speculated to allow host immune system to prevent or clear the bacterial infection. Several synthetic and natural molecules with anti-virulence properties have been discovered [20, 21] and at least one molecule, LED209, was shown to be effective in animal models . However, none of the molecules have entered wide-scale clinical trial as of yet, owing to various concerns such as their toxicity and safety. Therefore, there is an urgent need to identify a more diverse pool of molecules with anti-virulence activities. Availability of such a pool will ensure better drug designing strategies,
to combat bacterial infections like EHEC. Secondary metabolites produced by plants present very diverse scaffolds, which have been SBE-��-CD molecular weight used for designing novel drugs including antimicrobials. In nature, secondary metabolites contribute to systemic and induced plant defense system against insect, bacterial and fungal infestation . Several secondary metabolites belonging to classes such as coumarins, flavonoids, terpenoids and alkaloids demonstrate inhibitory properties against numerous microorganisms. Recently our group and others identified QS inhibitory properties of several very plant secondary metabolites and extracts rich in phytochemicals [23–28]. Citrus species contain a unique class of secondary metabolites known as limonoids. Chemically, limonoids are triterpenoids with relatively high degree of oxygenation . Several studies have reported anticancer, cholesterol lowering, antiviral and antifeedant activities
of citrus limonoids [29–35]. Recently, we demonstrated that certain limonoids such as obacunone, nomilin, isolimonic acid and ichangin interfere with QS in V. harveyi[23, 36]. In addition, obacunone and nomilin seems to modulate type III secretion system (TTSS) and biofilm formation in EHEC and Salmonella Typhimurium [23, 37]. The present work was carried out to understand effect of five citrus limonoids (Figure 1), viz. isolimonic acid, ichangin, isoobacunoic acid, isoobacunoic acid glucoside (IOAG) and deacetyl nomilinic acid glucoside (DNAG) on EHEC biofilm and TTSS. Figure 1 HPLC chromatograms and structures of limonoids. The limonoids were analyzed using HPLC. Purity was determined by calculating percentage area under curve for the given limonoids. The figure depicts chromatogram and structure of (A) ichangin, (B) isoobacunoic acid, (C) isolimonic acid, (D) DNAG, (E) IOAG. Methods Materials Previously purified isolimonic acid, ichangin, isoobacunoic acid, IOAG and DNAG were used in the present study .