Enhancing biological activities and phenolic content of wild grapevine roots by severe drought stress

Wild grapevines are a rich source of polyphenolic compounds. Various environmental factors can influence these bioactive metabolites, contributing to stress mitigation and adaptation. The present study aimed to investigate the impact of prolonged drought stress on the accumulation of phytochemicals, antioxidants, and antimicrobial activity in the roots of the endangered Tunisian wild grapevine (Vitis vinifera subsp. sylvestris) "Tebaba" genotype. The results revealed that under prolonged drought stress, there was a significant increase in total phenolic compounds, total flavonoid content, and stilbenes, which showed a positive and significant correlation with the total antioxidant activity. Furthermore, the ethanolic extracts demonstrated an enhanced in vitro antibacterial effect against selected human pathogenic bacterial strains, including Staphylococcus aureus, Methicillin-resistant S. aureus, and Enterococcus faecalis. The minimum inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC) values, relative to prolonged drought stress, ranged from 125 to 250 µg/mL. The values of the ratio between MBC and the MIC showed that the activity of the root extract was bactericidal in all cases (MBC/MIC ≤ 2). This study highlights the potential of wild grapevine roots enriched with drought-inducible phenolic compounds, as a promising source of antimicrobial agents relevant to human health applications.