Objective: With a rise in multidrug resistant (MDR) bacterial isolates, search for antibiotics or compounds that could act synergistically with them is a significant area of research. Efflux-mediated resistance, in particular, is a great hurdle that needs to be overcome. In an effort to identify such synergistic compounds and potential efflux pump inhibitors (EPI), we analyzed the rind of Punica granatum (pomegranate) against MDR clinical Klebsiella pneumoniae isolates.Methods: Sequential fractionation of P. granatum rind ethanol (PGR) extract was carried out to obtain hexane, butanol and water fractions. Antibacterial activity of the plant extracts was confirmed, and synergistic interaction with antibiotics was determined by the checkerboard assay. Gas chromatography-mass spectrometry (GC-MS) analysis was performed to identify the phytochemical constituents of the hexane extract. To study EPI activity of the extracts, norfloxacin accumulation assay was carried out.Results: PGR ethanol extract was found to have synergistic activity with ciprofloxacin, levofloxacin, ceftazidime, cefoxitin, meropenem, and gentamicin resulting in fold decrease of minimum inhibitory concentration (MIC) ranging from 2 to 32 fold. The hexane fraction was found to have maximum synergistic activity resulting in a 32-fold reduction of ciprofloxacin MIC followed by butanol and water fractions. The PGR ethanol extract was also found to have efflux inhibition activity by the norfloxacin accumulation assay. Of the sequential fractions, the butanol fraction had maximum efflux inhibition activity.Conclusion: Therefore, our study shows that PGR extract can potentiate the effect of antibiotics on MDR bacteria, and the mode of action is likely to be due to EPI.

The study was performed to identify a potent antibacterial benzimidazole derivative using in vitro and in silico techniques. Benzimidazole and its derivatives were synthesized by reflux process. The derivatives were screened for antibiotic susceptibility test (AST) and minimum inhibitory concentration (MIC) against Gram-negative and Gram-positive clinical isolates and compared with the positive control Norfloxacin. Insilico molecular docking was performed to screen the binding potential of the derivatives with target enzymes topoisomerase II /DNA gyraseof Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) along with the control Norfloxacin.Totally fifty-four isolates were screened for antimicrobial supectibility test (AST) and minimum inhibitory concentration (MIC) and 35 clinical isolates of Gram-negative showed 86% resistance to Norfloxacin and 19 isolates of Gram-positive showed 90% resistance to Norfloxacin. However, these isolates were found to be sensitive to 1-(4-((1H–benzimidazol-1-yl) methylamino) phenyl) ethanone (3) (C2), and 2-methyl-1H-benzimidazole (C4) compounds, with MIC ranges from 6.25- 12.5 µg/ml. Molecular docking analysis revealed that the compound C2 exhibited better binding affinity towards topoisomerase II / DNA gyrase of E.coli and S.aureus when compared with C4 and control Norfloxacin. The antibacterial activity of these may due to the inactivation of these enzymes which is supported by the MIC results.The obtained in vitro and in silico results suggested that C2 showed better antimicrobial activity.