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The purpose of present investigation was to understand the drug resistance reversal mechanism of 4-hydroxy- α-tetralone ( 1) isolated from Ammannia spp. along with its semi-synthetic derivatives ( 1a- 1e) using multidrug resistant Escherichia coli ( MDREC). The test compounds did not show significant antibacterial activity of their own, but in combination, they reduced the minimum inhibitory concentration ( MIC) of tetracycline ( TET). In time kill assay, compound 1 and its derivative 1e in combination with TET reduced the cell viability in concentration dependent manner. Compounds 1 and 1e were also able to reduce the mutation prevention concentration of TET. Both compounds showed inhibition of ATP dependent efflux pumps. In real time polymerase chain reaction ( RT- PCR) study, compounds 1 and 1e alone and in combination with TET showed significant down expression of efflux pump gene ( yojI) encoding multidrug ATP binding cassettes ( ABC) transporter protein. Molecular mechanism was also supported by the in silico docking studies, which revealed significant binding affinity of compounds 1 and 1e with YojI. This study confirms that compound 1 and its derivative 1e are ABC efflux pump inhibitors which may be the basis for development of antibacterial combinations for the management of MDR infections from inexpensive natural product. [ABSTRACT FROM AUTHOR]

Fast centrifugal partition chromatography (FCPC) was successfully applied in the separation of close Rfcomplex bioactive iridoid, loganetin directly from the ethyl acetate extract ofAlstonia scholaris. The experiment was performed with a two-phase solvent system composed of methyltert-butyl ether (MtBE)/ACN/Water (3:1.5:3 v/v/v) where the lower phase of the biphasic system, the aqueous layer containing 8 mM HCl, was the stationary phase, while the upper organic layer supplemented with 15 mM triethylamine TEA was designated as the mobile phase. From 1.5 g of EtOAc extract, 48 mg of loganetin (1) was obtained in 94.4% purity as determined by HPLC. The isolated compound (1) was characterized on the basis of its1H,13C–NMR, and ESI-MS spectroscopic data. Although loganetin does not possess antibacterial activity of its own, but in combination, it appreciably reduces the minimum inhibitory concentration (MIC) of nalidixic acid (NA) against nalidixic acid resistant (NAREC) and nalidixic acid sensitive (NASEC) strains ofEscherichia coli. Loganetin, a very common, inexpensive, and non-toxic natural product may finds its application in the antibacterial drug development for treating multidrug-resistant Gram negative infections. [ABSTRACT FROM AUTHOR]

Objective • To evaluate the antimicrobial activity potential of the essential oil of rosemary specifically for its efficacy against the drug-resistant mutants of Mycobacterium smegmatis, Escherichia coli, and Candida albicans. Method • Antibacterial, antifungal, and drug resistance—modifying activity was evaluated both qualitatively and quantitatively following disc diffusion and broth dilution assay procedures. Results • The rosemary essential oil was found to be more active against the gram-positive pathogenic bacteria except E faecalis and drug-resistant mutants of E coli, compared to gram-negative bacteria. Similarly, it was found to be more active toward non-filamentous, filamentous, dermatophytic pathogenic fungi and drug-resistant mutants of Candida albicans. Conclusion • Our findings suggest that characterization and isolation of the active compound(s) from the rosemary oil may be useful in counteracting gram-positive bacterial, fungal, and drug-resistant infections. [ABSTRACT FROM AUTHOR]