Evaluation of Antioxidant, Antibacterial, and Anti-hemolytic Properties of Ethanol Extract from Plectranthus barbatus Andrews (Lamiaceae) Leaves

Polyphenols can act as antioxidants, antibacterial, antifungal, or insecticidal agents. Given that microbial infections and arboviruses transmitted by Aedes aegypti significantly contribute to global morbidity and mortality, there is an urgent need to discover new antimicrobials and insecticides. This study investigated the ethanol extract (PbLE) of Plectranthus barbatus Andrews (Lamiaceae) leaves for its chemical constituents, antioxidant, antimicrobial, anti-hemolytic, and larvicidal activities. Qualitative analysis by Thin Layer Chromatography revealed cinnamic derivatives, flavonoids, terpenes, and steroids in PbLE. Quantitative analysis showed that PbLE contained 98.64 ± 0.87 mg EAG/g of total phenols, with flavonoids comprising 21.84 ± 0.34 mg EQ/g (c.a. 22%). PbLE demonstrated scavenging activity against ABTS+ (IC50 = 3246.00 ± 0.97 µg/mL) and DPPH (IC50 = 1371.75 ± 0.94 µg/mL) free radicals and exhibited reducing ability in the phosphomolybdenum method (IC50 = 899.33 ± 0.73 µg/mL). Although PbLE did not affect the growth or survival of pathogenic microorganisms, it significantly reduced (c.a. 80% for the extract at 256 mg/mL) the hemolysis caused by Staphylococcus aureus in human erythrocytes. Furthermore, PbLE (7 mg/mL) caused 40% mortality of A. aegypti third-instar larvae after 48-h exposure. In conclusion, PbLE, rich in phenolic compounds, acts as an antioxidant that mitigates S. aureus virulence to human erythrocytes and reduces the viability of A. aegypti larvae. The data reported herein contribute to the science by exploring P. barbatus, a medicinal plant with a long history of traditional use, as source of bioactive compounds with pharmacological and insecticidal properties. The determination of LC50 and mechanisms of PbLE larvicidal activity are underway.