Background/Aims: The nano-method has been used as a technique for creating novel, non-traditional antimicrobial agents. This effective method for treating infectious diseases has many advantages over conventional antibiotics, including increased efficacy against species that have developed drug resistance, and the ability to circumvent the development of resistance that disrupts a number of biological pathways. As a result, the objective of this study was to synthesize and characterize silver nanoparticles using phenolic compounds obtained from Camellia sinensis. The nanoparticles were then used as antibacterial agents on the multidrug resistant Staphylococcus aureus, as well as, biofilm formation mechanism were also investigated. Methods: Ten isolates of Staphylococcus aureus were acquired from the labs of the University of Baghdad's Genetic Engineering and Biotechnology Institute. The VITEK-2 system was used to confirm the diagnosis. Aqueous and methanolic extracts of Camellia sinensis leaves were used to create silver nanoparticles and obtain CAgNPs, which were then characterized using Atomic Fluorescence Microscopy (AFM), X-ray diffractometer (XRD), and Zeta potential analyzers. The extracts were put through a series of assays, including High-performance liquid chromatography (HPLC), antibacterial activity assessments, and the microtiter plate method to determine the lowest inhibitory concentration (MIC) and antibiofilm formation. Results: Both aqueous and methanolic extracts containing silver nanoparticles included spherical nanoparticles that may be single or combined. The HPLC results showed the presence of two phenolic compounds (gallic acid and caffeine) by comparing their retention durations to those of the reference compounds. The results of the antibacterial activity of (CAgNPs) showed that the methanolic (CAgNPs) extract was more effective than the aqueous (CAgNPs) extract, producing inhibitory zones of 15.67 ± 0.58 and 20.33 ± 0.58 mm, at 375 and 750 ppm respectively, when compared to the aqueous (CAgNPs) extract, which produced inhibitory zones of 12.33 ± 0.58 and 15.67 ± 0.58 mm, respectively. The MIC result also showed that the CAgNPs methanolic extract was more effective than the CAgNPs aqueous extract. The MIC of the CAgNPs methanolic extract on S. aureus isolates were 11.718 and 23.43 µg/ml, while the MIC of the CAgNPs aqueous extract on all S. aureus isolates were 46.87 µg/ml except isolate No. 3 and 6 which was 11.718 and 93.75 µg/ml respectively. Additionally, The anti-biofilm in S. aureus was increased when CAgNPs methanolic extract were used compared with the CAgNPs aqueous extract, the CAgNPs methanolic extract inhibited 80%, 90% and 100% of the biofilm formation of S. aureus in 23.43, 46.87 and 93.75 µg/ml respectively, while the anti-biofilm activity of the CAgNPs aqueous extract on S. aureus isolates was 80% and 100% of the biofilm formation in 46.87 and 93.75 µg/ml respectively. Conclusion: The methanolic and aqueous leaves extracts from Camellia sinensis are a successful method for producing CAgNPs. The synthesized CAgNPs also have significant antibacterial activity against S. aureus, depending on the concentrations, and inhibit S. aureus biofilm formation.
