The increased care toward substituting chemical antimicrobials with natural preparations has led to increased studies. To demonstrate the antimicrobial physiognomies of plant extracts, their consequence on infectious pathogenic microorganisms has to be studied in laboratory. In this study, aqueous, ethanol and n-hexane leaf extracts of Plectranthus lanuginosus were tested for their antibacterial activity against Staphylococcus aureus (ATCC 25923), Escherchia coli (ATCC 25922), and Pseudomonas aeruginosa (ATCC 27853) using the disk diffusion assay. The minimum inhibitory and bactericidal concentrations of the extracts (MIC and MBC) were also determined. All the leaf extracts, except the n-hexane extract showed antibacterial activity on tested bacteria. The ethanol extract inhibited bacteria with inhibition zones higher than that of the aqueous extract. The inhibition zones of the ethanol extract ranged from 7.83±0.17 mm (P. aeruginosa) to 10.67±0.33 mm (S. aureus and E. coli) while that of the aqueous extract ranged from 7.17±0.17 mm (P. aeruginosa) to 9.27±0.03 mm (S. aureus). The MIC/MBC values for ethanol extract were 75/150, 75/150, 150/300 mg/ml against S. aureus, E. coli, and P. aeruginosa, respectively. The corresponding aqueous extract MIC/MBC values were 150/300, 150/300, 300/300 mg/ml. In conclusion, the plant has shown antibacterial inhibition in the tested pathogenic bacteria. Further work is recommended to warrant use of the plant as a source of antibacterial agent.

Keywords: Antibacterial Activity, Disc Diffusion, Plectranthus lanuginosus