Scutellaria baicalensis Polysaccharide-Mediated Green Synthesis of Smaller Silver Nanoparticles with Enhanced Antimicrobial and Antibiofilm Activity

Silver nanoparticles (AgNPs) have attracted widespread attention in multidrug-resistant bacterial infections. However, the application of AgNPs synthesized by conventional methods is restricted by its high costs, toxicity, and poor stability. Herein, a water-soluble polysaccharide (Scutellaria baicalensis polysaccharide, SBP) rich in reducing sugars was used as both the reductant and stabilizer to greenly synthesize spherical AgNPs@SBP with smaller particle sizes (11.18 ± 2.50 nm) and higher negative zeta potential (−23.05 ± 2.76 mV), which was favorable to enhance its antimicrobial activity and improve pH and thermal stability. Besides, SBP facilitated the adhesion and penetration of AgNPs@SBP to methicillin-resistant Staphylococcus aureus (MRSA) and carbapenem-resistant Escherichia coli (CREC), thus significantly enhancing its antibacterial activity (increased by 32-fold and 64-fold, respectively). Likewise, AgNPs@SBP at a low concentration (7.8 μg/mL) could effectively penetrate and inhibit nearly 90% of MRSA and CREC biofilm formation. Antimicrobial mechanism studies showed that AgNPs@SBP could lead to more severe cell membrane damage and genetic material leakage by upregulating reactive oxygen species and depolarizing mitochondrial membrane potential, ultimately resulting in the apoptosis of bacteria. Overall, the wrapping of SBP significantly enhanced the antibacterial and antibiofilm activity of AgNPs, which possessed great potential in the prevention and treatment of multidrug-resistant bacterial infections.