Ultraviolet-A-Enhanced Antibacterial Activities on Gentamicin-ResistantEscherichia coli by Silver Nanorods Synthesized from Callistemonviminalis Leaf Extract

Introduction: The rise of antibiotic-resistant bacteria poses a significant threat to healthcare systems, warranting the development of novel antibiotics with enhanced efficacy. Methodology: In this study, silver nanorods (AgNR) were synthesized for the first time using a Callistemon viminalis leaf extract and evaluated for their DPPH antioxidant property and antibacterial properties against gentamicin-resistant Escherichia coli. Results: The synthesis success of AgNR was confirmed by UV-Vis spectroscopy, as evidenced by a clear LSPR peak at 466 nm. X-ray diffraction analysis validated the crystalline form of metallic AgNR. Meanwhile, TEM analysis revealed that the silver nanomaterials were rectangular nanorods with an average size of 85 nm. Fourier transform infrared analysis confirmed the presence of carboxylic acids, alkanes, alkenes, aromatic compounds, alkyl and aryl functional groups on the surface of silver nanorods (AgNR) with efficient antioxidant property. The bandgap energy calculated from the Tauc plot was 2.0 eV. Antimicrobial analysis revealed that E. coli demonstrated resistance to gentamicin, even at concentrations 125 and 1250 times those recommended by the Swedish Reference Group on Antibiotics (SRGA) and Clinical Laboratory Standards Institute (CLSI), respectively. Similarly, 0.1% m/V AgNR exhibited zones of inhibition measuring 17 mm and 18 mm, respectively, at 125 and 1250 times higher than the standard concentration, confirming E. coli is susceptible but exhibiting resistance behaviour. Under Ultraviolet-A (UVA) irradiation, the photocatalytic antibacterial activity of AgNR was substantially higher than the standard value of 2, demonstrating ≥99% reduction in bacterial viability. Discussions: Biogenic AgNR is suitable for antibacterial activities and photocatalysis activities, which are important in the future to combat bacterial resistant problems. Conclusion: This indicates that UVA irradiation significantly enhanced the antibacterial properties of AgNR. The external UVA irradiation promotes electron excitation and transfer from the valence to the conduction band, leading to the inactivation of E. coli. Therefore, the antimicrobial activity of biogenic AgNR amplified by UVA irradiation presents a potent and sustainable approach for combating gentamicin-resistant E. coli.