Siti Aisyah binti Abd Ghafar [Supervisor]Siti Nor Asma binti Musa2024-06-112024-06-112023-12Siti Nor Asma binti Musa (2023). Antimicrobial Activities of Silver Nanoparticles-Strobilanthes Crispus (Agnp-Sc) Against Selected Bacteria [Master’s thesis, Universiti Sains Islam Malaysia]. USIM Research Repository.https://oarep.usim.edu.my/handle/123456789/19102Matric: 3192584 (FPG)The emerging of resistant bacteria strains against current drugs has raised worldwide concern. This situation has led to invention of many alternative plant-based treatments which is effective, safer, and economical. One of it is through biosynthesis of silver nanoparticles combined with plant extract. This study is aimed to determine the ability of silver nanoparticle-Strobilanthes crispus (AgNP-SC) as an antimicrobial agent against selected bacteria. S. crispus extract was chosen based on the previous studies that have shown various medicinal benefits. Effectiveness of AgNP-SC at various concentrations have been tested on seven selected bacteria namely Escherichia coli O157, Pseudomonas aeruginosa, Streptococcus mutans, Staphylococcus aureus, Streptococcus pyogenes, Bacillus cereus and Salmonella enterica newport. Preliminary tests have been conducted to determine the susceptibility of the bacteria against AgNPSC through disc diffusion assay (DDA), followed by minimum inhibitory concentration assay (MIC) and minimum bactericidal concentration assay (MBC). Results from these three susceptibility tests have shown that AgNP-SC have highest antibacterial effects on E. coli, P. aeruginosa and S. mutans at lower concentration compared to silver nanoparticles (AgNPs) and S. crispus aqueous (SC) extract. Thus, AgNP-SC was further tested using time-kill assay to confirm bactericidal effect against all three bacteria. In time-kill assay, AgNP-SC was found to has better effect on antibacterial activity compared to AgNPs and SC only. AgNP-SC was found to show bactericidal properties within four hours incubation period on E. coli and P. aeruginosa, whilst showing bacteriostatic property against S. mutans. Morphological changes of treated bacteria had been determined by scanning electron microscopy (SEM). From SEM analysis E. coli, P. aeruginosa and S. mutans morphologies have been distorted by AgNP-SC. Gene expression of treated bacteria had been studied by Real-time PCR analysis. In gene expression analysis, AgNP-SC affected the gene that encodes for adhesin protein in E. coli and genes that involve in biofilm formation in P. aeruginosa and S. mutans. As conclusion, AgNP-SC has great potential as antimicrobial agent against all three bacteria by disturbing the cell membrane and interrupting the genes that regulating virulence factors in bacteria.en-USEscherichia coliPseudomonas aeruginosaSilver nanoparticlesStreptococcus mutansStrobilanthes crispusAntibacterialBacteriatext::thesis