Oak-fruit-extract-mediated synthesis of silver and copper quantum dots reduces biofilm gene expression in clinical isolates of Staphylococcus aureus and Acinetobacter baumannii

Background: The emergence of multidrug-resistant (MDR) bacteria, particularly Staphylococcus (S.) aureus and Acinetobacter (A.) baumannii, poses a critical global health challenge due to their strong ability to form biofilms. Alternative strategies targeting biofilm formation are urgently needed. Methods: Silver (Ag) and copper (Cu) quantum dots (QDs) were synthesized via a green hydrothermal method using oak fruit extract. Their antimicrobial and antibiofilm activities were tested against strong biofilm-producing clinical isolates of S. aureus (n=5) and A. baumannii (n=5) using broth microdilution and biofilm inhibition assays. The effect of sub-MIC concentrations of QDs on biofilm-associated genes (icaA, icaD, icaR in S. aureus; bap, ompA in A. baumannii) was evaluated by RT-qPCR. Results: The MIC values of Ag-QDs and Cu-QDs were 300 µg/mL and 400 µg/mL, respectively. Both QDs significantly inhibited biofilm formation at sub-MIC levels. RT-qPCR analysis showed marked downregulation of all tested genes following QD treatment, with Ag-QDs exhibiting a stronger inhibitory effect than Cu-QDs. Conclusion: Green-synthesized Ag-QDs and Cu-QDs demonstrate significant antibiofilm activity by suppressing key biofilm-related genes in S. aureus and A. baumannii. These findings highlight their potential as eco-friendly nano-antibiofilm agents for infection control.