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Abstract
Quorum sensing (QS) controls the production of virulence factors in many pathogenic bacterial species, making QS inhibition a potential strategy for preventing antibiotic resistance. This study aimed to investigate the effect of different extraction methods including conventional solvent (CS), microwave-assisted (MA), and ultrasound-assisted (UA) extraction of olive leaf on QS inhibition. Olive leaf was extracted using methanol:water (MW) (50/50, v/v), ethanol:water (EW) (50/50, v/v), and water (W). The extracts were also analyzed for their total phenolic content, with the microwave-assisted water extract (MAW) showing the highest amount (113.33 ± 0.94 mg GAE/g), while the classical solvent water extract (CSW) had the lowest content (24.46 ± 0.97 mg GAE/g). The MAW demonstrated better antioxidant capacity with a values of 316.62 ± 7.82 µmol Trolox/g (DPPH method) and 314.45 ± 1.12 TEAC/mg (ABTS method). Moreover, CSEW, CSMW, UAEW, MAW, and MAEW extracts exhibited antibacterial activity against all test bacteria except Escherichia coli by agar well diffusion method. The extracts were also evaluated for their QS inhibition effects on model bacteria, including Chromobacterium violaceum (C. violaceum) CV026, C. violaceum CECT 494, and Pseudomonas aeruginosa PA01. The microwave-assisted water extract exhibited QS inhibition without affecting bacterial growth, as confirmed by qRT-PCR analysis at minimum inhibition concentration (MIC)/2 (1.875 mg/mL), MIC/4 (0.938 mg/mL), and MIC/8 (0.469 mg/mL). Additionally, the SEM images provided evidence of extract homogeneity. The present study demonstrates the potential of a microwave-assisted water extract of olive leaf, obtained through green technology and using a non-toxic solvent, as a natural antibacterial agent.