A promising agent against wild-type and antibiotic-resistant bacteria using biogenic silver nanoparticles from...

The antibiotic resistance (AR) crisis has intensified and overshadowed efforts to develop new antibiotics and treatments. Biogenic silver nanoparticles (AgNPs) synthesised using Marphysa moribidii extract offer a promising solution because of their broad-spectrum antibacterial activity and ease of synthesis. However, concerns regarding the physicochemical properties of AgNPs may vary, and the optimal dosage for bacterial inhibition must be determined. This study addresses these gaps by evaluating the physicochemical properties, antibacterial efficacy, and mechanisms of action of biogenic AgNPs against selected bacteria, including wild-type strains (Escherichia coli and Staphylococcus aureus) and antibiotic-resistant strains (ESBL-E. coli and MRSA). Silver nitrate reduction by bioactive compounds in polychaete extract, such as amino acids and fatty acids, resulted in the formation of stable spherical AgNPs. These nanoparticles exhibited surface plasmon resonance peak at 397 nm and zeta potential of -36.48 mV. The AgNPs effectively inhibited the growth of both wild-type and antibiotic-resistant bacteria at concentrations ranging from 0.05-0.40 μg/mL and 0.10-0.40 μg/mL, respectively. Bactericidal effects were observed against wild-type bacteria and bacteriostatic effects against antibiotic-resistant bacteria. Electron microscopies revealed membrane damage in wild-type and AR bacteria, whereas leakage assays confirmed increased membrane permeability. Furthermore, reactive oxygen species detection assay demonstrated that AgNPs induced oxidative stress, suggesting a multifaceted mechanism of action. These findings highlight the potential of M. moribidii-derived AgNPs as effective broad-spectrum antibacterial agents, particularly against AR bacteria, and pave the way for the development of standardised biogenic AgNPs synthesis methods for future applications.