Green-Synthesized Rheum cordatum Root-Based Carbon Nanosphere-Based ZIF-8 Nanocomposite Against MRSA: In Vitro Antioxidant, Antibacterial Activity and Gene Expression Profiling

Background & Aim: The emergence of multidrug-resistant pathogens, particularly methicillin-resistant Staphylococcus aureus (MRSA), necessitates the development of novel antimicrobial strategies. Green synthesis approaches and composite nanomaterials have attracted considerable attention as promising alternatives to conventional antimicrobial agents. Therefore, this study aimed to synthesize a carbon nanosphere/zeolitic imidazolate framework-8 (CNS@ZIF-8) nanocomposite using Rheum cordatum Losinsk. root-derived carbon nanospheres and to evaluate its antioxidant, antibacterial, antibiofilm, and anti-virulence properties against MRSA and methicillin-sensitive S. aureus (MSSA). Methods: Carbon nanospheres (CNS) were green-synthesized from the roots of Rheum cordatum Losinsk. and subsequently integrated with ZIF-8 to fabricate the CNS@ZIF-8 nanocomposite. The synthesized materials were characterized using UV–Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Antioxidant activity was assessed using DPPH and ABTS radical scavenging assays. Antibacterial activity was evaluated by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Antibiofilm activity, SEM-based bacterial morphology analysis, and quantitative real-time PCR of virulence- and resistance-associated genes (icaA, dltA, dltB, mepA, and norA) were also performed. Results: Characterization analyses confirmed the successful synthesis of the CNS@ZIF-8 nanocomposite. CNS@ZIF-8 exhibited antibacterial activity against both MRSA and MSSA, with MIC and MBC values of 128 and 256 µg/mL, respectively. SEM analysis revealed severe membrane disruption and morphological damage in treated bacterial cells. Gene expression analysis demonstrated significant downregulation of biofilm formation-, cell wall modification-, and efflux pump-associated genes. CNS@ZIF-8 also showed enhanced antioxidant activity compared with pristine ZIF-8, with IC50 values of 45.1 ± 0.55 µg/mL (DPPH) and 9.1 ± 0.44 µg/mL (ABTS), whereas ZIF-8 exhibited IC50 values of 149.2 ± 0.32 and 22.3 ± 0.31 µg/mL, respectively. However, CNS alone displayed the strongest radical scavenging activity. The antioxidant standard butylated hydroxytoluene (BHT) exhibited IC50 values of 23.4 ± 0.42 µg/mL (DPPH) and 26.3 ± 0.63 µg/mL (ABTS). Conclusion: The CNS@ZIF-8 nanocomposite demonstrated promising antioxidant, antibacterial, antibiofilm, and anti-virulence activities against S. aureus, particularly MRSA. These findings suggest that CNS@ZIF-8 represents a multifunctional nanomaterial with potential for the development of alternative therapeutic strategies against multidrug-resistant bacterial infections.