Investigation of the Antibacterial Activity and Efflux Pump Inhibitory Effect of R.Br. Extract against Clinical Isolates.

The vast spread of multidrug-resistant bacteria has encouraged researchers to explore new antimicrobial compounds. This study aimed to investigate the phytochemistry and antibacterial activity of R.Br. leaves extract against clinical isolates. The minimum inhibitory concentration (MIC) values of extract ranged from 4 to 32 µg/mL. The impact of the treatment of the isolates with sub-inhibitory concentrations of extract was investigated on the bacterial growth, membrane integrity, inner and outer membrane permeability, membrane depolarization, and bacterial morphology using a scanning electron microscope (SEM) and on the efflux activity using qRT-PCR. Interestingly, most isolates treated with extract showed growth inhibition-a decrease in membrane integrity. In addition, we observed various morphological changes, a significant increase in inner and outer membrane permeability, a non-significant change in membrane depolarization, and a decrease in efflux activity after treatment. The phytochemical investigation of extract revealed the isolation of one new biflavonoid, 5,7,7″,4‴-tetra--methyl-hinokiflavone (), and five known compounds, stigmasterol (), naringenin (), 2,3-dihydrobilobetin (), 4',4‴-dimethyl amentoflavone (), and hinokiflavone (), for the first time. Moreover, the pure compounds' MICs' ranged from 0.25 to 2 µg/mL. Thus, could be a potential source for new antimicrobials.