Introduction: Silver nanoparticles has been proven to be an effective agent for antimicrobial efficacy against bacteria, viruses and other eukaryotic microorganisms. Green synthesis is one of the methods that has been developed to synthesize silver nanoparticles in environmentally-friendly conditions. It uses plant extracts as reducing and capping agents. Besides act as reducing and capping agents, bioactives such as phenolic compounds may bind to silver nanoparticles and enhance its medicinal properties. Strobilanthes crispus is a Malaysian native plant. Previous studies had shown that S. crispus contains polyphenols, catechins, alkaloids, caffeine, tannins and vitamins. Therefore, the aim of this study is to determine antibacterial activities of silver nanoparticles-Strobilanthes crispus (AgNP-SC) against clinically important pathogens such as Escherichia coli, Pseudomonas aeruginosa and Streptococcus mutans. Methods: The disc diffusion assay (DDA) was performed to investigate the inhibition zone of AgNps-Sc towards E. coli, P. aeruginosa and S. mutans. Minimum inhibition concentration (MIC) and minimum bactericidal concentration (MBC) was used to determine bactericidal/bacteriostatic profile of AgNP- SC against E. coli, P. aeruginosa and S. mutans. Results: AgNP-SC (40mg/mL) shows the greatest inhibition properties (12.67±0.6mm) against S. mutans when compared to Strobilanthes crispus leaves extract (6.0±0.001mm) and blank silver nanoparticles (6.0±0.001mm). MIC values for AgNP-SC against S. mutans and E. coli were at 0.625 mg/mL and 1.25 mg/mL, respectively. Whereas the MIC value of AgNP- SC against P. aeruginosa was at 2.5 mg/mL. MBC values of AgNP-SC against E. coli, P. aeruginosa and S. mutans were at 1.25, 2.5 mg/mL respectively. Results are concentration-dependent, with higher concentration demonstrating better inhibition property. Conclusion: It can be concluded that AgNP-SC possesses bactericidal properties against S. mutans, E. coli and P. aeruginosa.

The aim of this study was to isolate lactic acid bacteria (LAB) from fermented food, to determine its antibacterial activity, and to identify the LAB in order to select candidate probiotic strains for preventing caries. The probiotic strains were isolated from eight fermented food which are tapai ubi, tapai pulut, rebung, tauchu, kimchi, incalok, tempeh and tempoyak, taucu. Ten-fold serial dilutions of the fermented food samples were made in sterile peptone water before plating on de Man Rogosa and Sharpe (MRS) agar. The pure cultures were then randomly picked and biochemically identified. Then, the antibacterial activity of LAB against Streptococcus mutans was assessed by using the disk diffusion method. A total of 120 LAB were isolated from eight different fermented foods. The morphologies of the isolates were circular, convex, dull opaque white or translucent white. Gram staining identification showed that the isolates were Gram-positive rods. Of the 120 LAB isolates, five strains displayed moderate to strong antibacterial activity against S. mutans with the inhibition zones ranging from 7- 12 mm. The antibacterial activity demonstrated from LAB isolated from fermented foods suggests that the isolates from fermented foods possess antibacterial properties against a pathogen which responsible for causing dental caries. These strains are currently investigated in depth to assess whether they can be fully characterized as probiotics.