Antibacterial, Synergistic and β-lactamase Inhibitory Activity of Oroxylem indicum: An In vitro and Molecular Interaction Study

Aims: The study was aimed to evaluate the antibacterial, synergistic and β-lactamase inhibitory potential of O. indicum against ampicillin resistant and Extended Spectrum β-lactamase (ESBL) producing bacterial strains.
Methods: Bacterial strains were screened for ampicillin resistance and ESBL production by disk diffusion method and modified double disc synergy test respectively. Antibacterial and synergistic activities of O. indicum methanol extract and ethyl acetate sub fraction of methanol extract were explored by agar well diffusion method and Checkerboard method respectively. Extracts were subjected to Gas chromatography and Mass spectroscopy (GC-MS) analysis to identify the bioactive compounds. Molecular docking studies were carried out to verify the β-lactamase inhibitory potential of the bioactive compounds.
Results: All bacterial strains were found to be resistant to ampicillin and only one strain was detected as ESBL positive. Ethyl acetate sub fraction exhibited strong antibacterial and synergistic activity than the methanol extract. Zone of inhibition and Minimum inhibitory concentration for ethyl acetate sub fraction was 16 mm and 15mg/ml respectively. In vitro interactions between plant extracts and ampicillin evaluated in terms of fractional inhibitory concentration (FIC) indices revealed synergistic effects of plant extracts. The molecular docking studies of major bioactive compounds depicted by GC-MS analysis revealed that Wogonin, a flavonoid (GLIDE Score-5.77) possessed the best inhibitory profile against β–lactamase.
Conclusion: Synergistic activity of O. indicum may be attributed to the β–lactamase inhibitory potential of the bioactive compounds present in the extract. The findings provide substantial basis for the future use of O. indicum crude extracts as potential antibacterial and antibiotic modulating agent.