Gold nanoparticles functionalised with vancomycin enhance antibacterial activity and inhibit Streptococcus pneumoniae...

Streptococcus pneumoniae (S. pneumoniae) is a leading cause of respiratory infections, with increasing antibiotic resistance posing a major challenge. While gold nanoparticles (AuNPs) functionalised with antibiotics have been explored, their impact on bacterial adherence and invasion remains underexplored. This study presents a vancomycin-conjugated AuNP formulation designed to enhance antibacterial efficacy and prevent S. pneumoniae colonisation. The nano-formulation was characterised using UV-Vis spectroscopy and TEM, confirming successful conjugation and a uniform spherical size of 23 ± 1 nm. Minimum inhibitory concentration (MIC) assays demonstrated a significant reduction in the required concentrations of AuNPs (from 512 to 32 µg ml^-1) and vancomycin (from 0.5 to 0.125 µg ml^-1) compared to their individual use. Unlike previous studies that focused solely on bacterial viability, our work demonstrates that the nano-antibiotic effectively inhibits bacterial adherence and invasion in human alveolar epithelial cells (A549). Mechanistically, vancomycin weakens the bacterial cell wall, facilitating AuNP penetration, membrane disruption, and oxidative stress-induced bacterial death. This dual-action mechanism not only enhances bactericidal effects but also prevents bacterial colonisation-an aspect not extensively explored in prior studies. Toxicity assays confirmed that the formulation was non-toxic to A549 cells, supporting its potential for clinical applications. These findings highlight the synergistic antibacterial and anti-infective properties of vancomycin-functionalised AuNPs, offering a promising strategy to combat S. pneumoniae infections while mitigating antibiotic resistance.