Chemical Composition of <i>Plectranthus amboinicus</i> Leaf Essential Oil from Phetchabun, Thailand, and Its Potential to Combat Enteropathogenic Bacteria and Regulate Blood Pressure

The increasing demand for natural therapeutics has driven interest in plant-derived essential oils as potential alternatives to synthetic drugs for managing infectious and chronic diseases. Plectranthus amboinicus is a traditional medicinal plant known for its diverse therapeutic uses, particularly in Asian and African folk medicine. In this study, the chemical composition and biological activities of P. amboinicus essential oil (PAEO), derived from plants grown in Phetchabun, Thailand, were investigated. Gas chromatography–mass spectrometry (GC–MS) analysis identified 142 volatile compounds, with shyobunol (9.1%), germacrene D (8.3%), α-cadinol (7.7%), and carvacrol (7.5%) being the predominant constituents. Antibacterial testing revealed that PAEO exhibited moderate to strong bactericidal activity against Escherichia coli, Salmonella Typhimurium, and Shigella flexneri, with minimum inhibitory concentrations (MIC) ranging from 1 to 2 mg/mL. Time-kill kinetics assays demonstrated a rapid bactericidal effect, whereas post-antibiotic effect (PAE) analysis showed prolonged suppression of bacterial regrowth compared with standard antibiotics. Scanning electron microscopy (SEM) and biochemical studies confirmed that PAEO disrupts bacterial cell membranes, leading to the leakage of nucleic acids and proteins. In addition, PAEO significantly inhibited the activity of angiotensin-converting enzyme 1 (ACE1) in vitro in a dose-dependent manner, achieving over 70% inhibition at 1 mg/mL, with a median inhibitory concentration (IC₅₀) of approximately 0.51 mg/mL. These results highlight the potential of PAEO as a multifunctional agent for the treatment of microbial infections and hypertension warranting further preclinical and clinical investigation.