! " #$% &’ ( " #)* ’ $!) $ *( ’ + 1 Institute of Microbial Technology, Sector39A, Chandigarh160036, India 2 Department of Natural Products, National Institute of Pharmaceutical Education and Research, Sector67, S.A.S. Nagar160062 , India Email: sonika2007@gmail.com & & Efflux pump inhibitors (EPIs) are expected to block the efflux of antibiotics from the site of action and provide complete antimicrobial effect. Emerging evidence indicates that secondary metabolites from plants as well as microbes combat effluxmediated microbial resistance either by modulating the antimycobacterial activity of known antiTB drugs or exhibiting EPI activity. So, in search of new modulators for anti mycobacterial activity, lipophilic extracts of were investigated. Previous report revealed high antimicrobial activity of lipophilic extract of against Grampositive and anaerobic bacteria. Here in, we investigated Minimum Inhibitory Concentration (MIC) of eight isolated pure compounds and their modulating effect on ethidium bromide (EtBr) against mc 2 155 (ATCC 700084). MICs of putative EPIs were determined previously described 3 and tested for synergistic effects with EtBr in a “modulation assay” using mc²155 (ATCC 70084). The concentration of the modulators remained the same throughout the experiment, whereas the EtBr was serially diluted for MIC determination with and without modulator, respectively. The extent of MIC (EtBr)modulation is expressed by the Modulation Factor (MF) Table:1. Structure of modulators, their MIC values, modulation factors and FICI against mc²155. (*EtBr’s antimycobacterial activity was modulated) MF= MIC (EtBr) / MIC (EtBr + modulator)r) Fractional Inhibitory Concentration Index (FICI) expressed the effect of combination of antibacterial agents: FICI= FIC (A)+ FIC (B) FIC(A)=MIC (A in presence of B)/MIC (A alone) FIC(B)=MIC (B in presence of A)/MIC (B alone) Synergism, ≤ 0.5; Antagonism, FICI≥4.0; and no interaction, FICI> 0.54.0 Compounds # MIC (Eg/ml) Conc used in modulatory activity (ug/ml) MF (EtBr) FICI 1´1´acetoxychavicol acetate 6.26 2.5 64 0.41 coumaryl diacetate 50 6.25 64 0.14 The change in modulation activity may be due to methoxy group at C5 position of phenyl ring in ACA. Further, designing of structural variants by QSAR and possible synthetic derivatives may add potential drug candidate which can be used as promising modulator and EPI for TB drugs, in future. Those compounds which were found to be active in modulation assay will be further tested for EtBr accumulation and efflux assays. Significance of these compounds for reducing drugresistance in clinical TB (INH, Ofloxacin, etc.) drugs either as modulator or EPI is under experimental trials. 1. Lechner, D., Gibbons, S. & Bucar, F. (2008). Plant phenolic compounds as ethidium bromide efflux inhibitors in J Antimicrob Chemother 62, 345348 2. De Rossi, E., Ainsa, J. A. & Riccardi, G. (2006). Role of mycobacterial efflux transporters in drug resistance: an unresolved question. FEMS Microbiol Rev 30, 3652 3. Stavri, M., Schneider, R., Donnell G., Lechner, D et al. (2004). The antimycobacterial components of Hops ( and their Dereplication. Phytother Res, 8, 774776 All compounds (18) exhibited MIC values of ≤ 50 Eg/ml (See table 1). Reserpine is wellknown EPI with MIC ≥ 128 Eg/ml but not potent modulator (MF≤ 2) of antimycobacterial activity. Compound 1, 2 and 3 were found to be better modulator as compared to reserpine and modulated EtBr’s antimycobacterial activity by 64 fold at 2.5 to 6.25 Eg/ml. i.e. reduced the MIC of EtBr by 64 fold. 1´1´acetoxyeugenol acetate 50 5 64 0.12 1´1´hydroxychavicol acetate 50 5 4 0.35 4()3´hydroxyprop1´ enylphenyl acetate 50 5 1 1.2 hydroxycinnamaldehyde 50 8.75 1 1.2 hydroxycinnamaldehyde acetate 50 8.75 1 1.2 coumaryl alcohol 50 8.75 1 1.2 Reserpine 128 40 2 0.8 *MIC of EtBr = 16 Eg/ml