Secondary metabolite compounds from Morus nigra (MN), has been shown to have antioxidant and antimicrobial activities. moreover, phenolics and flavonoids contained in this species are partly responsible for those activities. This study aims to evaluate the mode of action of MN stem bark extract and its antibacterial activity against Streptococcus mutans. The stem bark of MN was macerated using ethanol as a solvent for 72 h. Furthermore, the antibacterial activities of the extract were evaluated using Agar diffusion and microdilution methods, by determining the zone of inhibition and the minimum inhibitory concentration (MIC). Scanning electron microscopy (SEM) was used to observe the morphological changes induced by the extract. The protein and ion leakage from the bacterial cells were analyzed spectrophotometrically. The extract exhibited antibacterial activity against Streptococcus mutans, at a MIC value of 8mg/mL. Furthermore, it discovered via SEM that at 4xMIC, this extract could damage the membrane cell of Streptococcus mutans. Finally, protein and ion leakage were observed in bacterial cells of Streptococcus mutans induced with this extract. MN stem bark extract is a potential herbal medicine, which has antibacterial activity against Streptococcus mutans.
