Antibacterial and Antioxidant Activities of Nerium oleander Flower Essential Oil Against Multidrug-Resistant Bacteria.

Abstract

The increasing prevalence of antimicrobial resistance has intensified the search for alternative therapeutic agents derived from natural products. This study aimed to evaluate the antioxidant and antibacterial activities of essential oil extracted from the flowers of Nerium oleander, as well as its combined effect with dimethyl sulfoxide (DMSO) against multidrug-resistant bacteria. The essential oil was tested against Escherichia coli ATCC 700415 and Staphylococcus aureus ST188 using the Kirby–Bauer disc diffusion method, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) assays. The combined activity of the essential oil and DMSO was assessed using inhibition zone diameters. Antioxidant potential was determined using the DPPH free radical-scavenging assay in a 96-well microplate format. The results demonstrated a concentration-dependent antibacterial effect, with maximum inhibition zones of 22.3±1.1 mm and 20.2±0.7 mm against E. coli and S. aureus, respectively, at 300 μg/mL. The MIC and MBC values ranged from 75 to 150 μg/mL and 150 to 300 μg/mL, respectively, indicating high susceptibility in E. coli. A significant combination effect (p < 0.05) was observed when the essential oil was combined with DMSO. Furthermore, the oil exhibited notable antioxidant activity, achieving a maximum DPPH radical-scavenging capacity of 91.4 ± 2.6% at 2.0 mg/mL and an IC50 of 0.51 mg/mL. In conclusion, N. oleander flower essential oil exhibits potent antibacterial activity and moderate antioxidant activity, with enhanced efficacy when combined with DMSO. These findings suggest its potential as a natural source of bioactive compounds for combating multidrug-resistant pathogens and oxidative stress.