Synergistic inhibition of agr quorum sensing in methicillin-resistant <i>Staphylococcus aureus</i> : a novel approach with natural compound encapsulation

Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) poses a serious threat due to its resistance to common antibiotics. This study investigates the antibacterial and quorum-sensing (QS) inhibitory effects of encapsulated quercetin (QE) and ferulic acid (FA) in chitosan (CS) nanoparticles against MRSA virulence genes. QE and FA were encapsulated into CS nanoparticles and characterized using scanning electron microscope, X-ray diffraction, dynamic light scattering (DLS), thermogravimetric analysis (TGA), and zeta potential analysis. Encapsulation efficiency, antibacterial activity, biofilm inhibition, hemolysis, macrophage intracellular killing, cytotoxicity, and apoptosis induction were assessed for both free and encapsulated forms. Antibacterial activity was evaluated via growth inhibition, biofilm formation assays, and minimum inhibitory concentration (MIC) determination in combination with clindamycin. RT-PCR was used to assess effects on MRSA virulence gene expression. All treatments inhibited MRSA growth, with the CS-QE-FA combination showing the highest inhibition (85%) and biofilm reduction (90%). This combination also synergized with clindamycin, reducing its MIC to 1/64 of the original. RT-PCR revealed significant downregulation of QS-related genes, including <i>RNAIII</i>, <i>agrA</i>, <i>hla</i>, and <i>psmα</i> (<i>P</i> < 0.001). CS nanoparticles encapsulating QE and FA significantly inhibit MRSA growth and QS-related gene expression, especially in combination. Their synergistic action with clindamycin suggests potential for novel therapeutic strategies against antibiotic-resistant infections.IMPORTANCEAntibiotic-resistant infections like those caused by methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) are a growing global health concern, often leading to longer hospital stays, increased costs, and higher mortality. This study presents a novel approach using natural compounds-quercetin and ferulic acid-encapsulated in chitosan nanoparticles to target MRSA. Not only do these nanoparticles inhibit bacterial growth and biofilm formation, but they also disrupt the bacteria's communication system (quorum sensing), which controls the production of toxins. Importantly, these effects are enhanced when combined with clindamycin, a commonly used antibiotic. This combination reduces the amount of antibiotic needed and may help overcome drug resistance. The findings offer a promising strategy for developing safer, more effective treatments against persistent infections while potentially slowing the spread of antibiotic resistance.