Microbial nanofactories for production of silver nanoparticles utilising locally-isolated Malaysian bacterial strain as an alternative source of antimicrobial agents

The over prescription and misuse of antibiotics contribute to the rise of bacterial resistance to antibiotics, limiting the efficacy of antibiotic treatments for infectious diseases and necessitating the exploration of new strategies. Therefore, silver nanoparticles are proposed as promising candidates for alternative antimicrobial agent due to their superior antimicrobial efficiency, attributed to their excellent surface-to-volume ratio. This study focuses on extracellular synthesis of silver nanoparticles using a locally isolated bacterial strain from Bagan Lalang, Selangor, chosen for its potential cost-effectiveness, fast reduction properties, and leave environmentally friendly residues. The phylogenetic identification of the silver nanoparticles-producing bacteria using 16S rRNA sequencing resulted in a high homology to Bacillus genus. Preliminary screening of bacterial-synthesised silver nanoparticles using UV-vis spectroscopy indicated nanoparticle formation through surface plasmon resonance (SPR), with a distinct absorption peak at 420 nm. Size and polydispersity analysis using dynamic light scattering (DLS) revealed low polydispersity (0.20 value), with an average size of 139.73±13.63 nm. Field emission scanning and transmission electron microscopy images showed spherical and uniformly distributed nanoparticles with the average diameter of less than 25 nm. The extracellular biofilm layer observed in transmission electron microscopy (TEM) suggests a capping agent maintaining nanoparticle integrity. Elemental analysis through elemental dispersive x-ray (EDX) confirmed the presence of 27.41% silver, with minimal biological residues. Antimicrobial testing against Escherichia coli (E. coli) DH5α strain using disk diffusion assay demonstrated that bacterial-synthesised silver nanoparticles exhibit inhibitory effects, with a 0.87±0.12 cm inhibition zone, showcasing their potential as antimicrobial agents. Further testing through bacterial growth inhibition assay revealed that a 10% (v/v) concentration of bacterial-synthesised silver nanoparticles inhibits bacterial growth in suspension culture by 50%. Despite exhibiting a lower inhibitory effect compared to other antimicrobial agents, the study systematically compares the antimicrobial properties of bacterial-synthesised silver nanoparticles, revealing an efficiency 1.5 times higher than non-nano silver derived from silver nitrate (AgNO3), with an efficiency rate of 150.5% at a normalised concentration. In conclusion, the locally isolated bacteria serve as a promising biofactory for synthesising silver nanoparticles, offering a scalable and antimicrobially potent solution that may complement or address antibiotic resistance.

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