Phytochemical Screening and In vitro Antibacterial Evaluation of Plectranthus amboinicus (Lour) Spreng

Plectranthus amboinicus is a medicinal plant widely recognized in Ethiopia but requires scientific validation to support its potential for drug development. This study aimed to evaluate the phytochemical properties and antibacterial activities of P. amboinicus crude extracts against selected pathogenic bacteria. The experiment followed a Completely Randomized Design (CRD) using a laboratory bioassay with three replications. The factorial arrangement included two extract sources (leaf and stem), two solvents (ethanol and distilled water), three concentration levels (100 mg/mL, 120 mg/mL and 150 mg/mL), four bacterial species and three replications, resulting in a 2x2x3x4x3 design. The disc diffusion method was employed to assess bacterial susceptibility, while the Minimum Inhibitory Concentration (MIC) was determined using the broth dilution method and the Minimum Bactericidal Concentration (MBC) was evaluated on nutrient agar. Gram positive bacterial species demonstrated the highest susceptibility, with MIC values ranging from 25 mg/mL to 100 mg/mL and MBC values between 50 mg/mL and 100 mg/mL. The study findings revealed that extracts from the leaves of P. amboinicus were particularly effective against the tested pathogens, highlighting the plant’s antibacterial potential. Furthermore, phytochemical screening confirmed the presence of secondary metabolites and bioactive compounds, supporting the use of P. amboinicus as a medicinal plant. These results provide a scientific basis for its traditional application in treating bacterial infections. However, further research is necessary to investigate its efficacy against a broader range of bacterial and fungal pathogens.