Honey weed leaf–derived silver nanoparticles for disruption of Staphylococcus aureus biofilms: In vitro efficacy and mechanistic characterization

Biofilm-mediated infections caused by Staphylococcus aureus are difficult to treat because the recalcitrant biofilms shield the sessile bacterial cells from the conventional antibiotics leading to the development of persistent infection and antibiotic resistance. Plant-mediated nanoparticles have evolved as one of the most promising alternative approaches for eradicating these biofilm-associated infections and overcoming the global concern of antibiotic resistance. This study involves the use of Leonurus sibiricus leaf extract for green synthesis of silver nanoparticles (AgNPs) and thereby assessed the potential of these AgNPs in removal of biofilms formed by S. aureus . The AgNPs showed a minimum inhibitory concentration of 20 µg/ml and removed around 82.66% of S. aureus biofilm, which was further optimized by response surface methodology. Mode of action of the AgNPs was analysed using Fourier-transformed infrared spectroscopy, flow cytometric analyses, and reactive oxygen species generation, revealing structural modifications of the biofilm matrix and a remarkable decrease in viable bacterial cell population. In addition to this, significant siderophore (81.38%) and exoprotease (81.57%) content reductions indicated a minimized bacterial virulence. The absence of hemolysis further signified quorum sensing inhibition and reduced virulence. Time-correlated single photon count and inductively coupled plasma-mass spectrometry depicted the interaction of the AgNPs with the bacterial cells (with a fluorescence lifetime of 2.75 ns) and validated the cellular uptake of AgNPs (84.70 ng/ml), respectively. This work highlights the mechanistic insights about how the L.sibiricus -mediated green AgNPs could attenuate the virulence due to activities of exoprotease, siderophore, haemolysin production and also the biophysical interaction between the bacterial cells and the AgNPs alongside antibiofilm activities and oxidative stress generation.