Antibacterial Properties of Methanolic Leaf Extracts of Melia azedarach L. against Gram-Positive and Gram-Negative Pathogenic Bacteria

Melia azedarach L., a Meliaceae family tree, is widely used in traditional folkloric medicine for its pharmaceutical properties. In the present study, we investigated the phytochemical composition of four methanolic leaf extracts of M. azedarach of various origins (Algeria and Tunisia) using high-performance liquid chromatography (HPLC). The antibacterial efficacy and mechanisms of action against Gram-positive and Gram-negative pathogenic microorganisms were then evaluated. Our findings revealed a presence of phenolic acids and flavonoids, such as gallic acid, chlorogenic acid, caffeic acid, hyperoside, isoquercetin, quercetin, and isorhamnetin both in Algerian and Tunisian localities, with an abundance of phenolic acids compared to flavonoids. Additionally, the studied extracts exhibit a broad spectrum of antibacterial activities, with MIC values ranging from 31.25 mg/mL to 125 mg/mL. Methanolic leaf extracts of M. azedarach from Algeria exhibited more potent biofilm eradication, with a percentage of inhibition reaching 72.17% against the S. aureus strain. Furthermore, inhibitory concentrations of tested substances, particularly the extract from the Relizane area, were capable of disrupting the membrane integrity of the treated bacteria as well as producing oxidative stress through ROS generation. Likewise, our results reveal that plant extract induces lipid peroxidation by raising MDA levels in comparison to untreated cells, particularly with the plant extract of Blida. M. azedarach extracts also reduced the synthesis of antioxidant enzymes (CAT and SOD). Our findings illustrate that M. azedarach remains a plant with significant antibacterial potential and distinct mechanisms of action that are closely related to the origins of this specimen.