Phytochemical Analysis, Antibacterial Activity and Mode of Action of the Methanolic Extract of Scutellaria barbata Against Various Clinically Important Bacterial Pathogens

The objective of the current study was to evaluate the phytochemical composition and antibacterial effect of methanolic extract of Scutellaria barbata (S. barbata) against a panel of clinically important bacterial pathogens along with deciphering the mode of action of the extract. Liquid chromatography-mass spectrometry was performed to evaluate the phytochemical constituents of the bioactive extract. Disc diffusion assay and microdilution assay were used to test the antibacterial efficacy of the extract. Scanning Electron Microscopy (SEM) was used to evaluate the morphological changes induced by the extract. The 2', 7'-dichlorofluorescein diacetate (DCFDA) was used to detect the Reactive Oxygen Species (ROS) generation in these six bacterial strains induced by the methanol extract of 5. barbata. The extract inhibited cell growth of all tested bacteria dose-dependently with S. typhimurium being the most susceptible pathogen. The percentage of bacterial cells killed within a 40-min contact time between the bacterial cells and the extract was around 24.7% which increased to 44.5% after 60-min time. The extract also induced potent ROS generation as well is intracellular protein leakage in all bacterial cultures with maximum peak in S. typhimurium. The SEM results revealed that the extract induces deleterious morphological changes in the bacterial cell membrane of S. typhimurium indicating that ROS generation can lead to membrane damage in bacterial cells. The present findings indicate that S. barbata has potential antibacterial effect against a variety of bacterial strains and the antibacterial effect is mediated via ROS generation, intracellular protein leakage and rupture of bacterial cell membrane.