Antimicrobial activity of aqueous and ethanolic leaf extracts of Psidium guajava against Staphylococcus aureus and Bacillus cereus

Abstract

Current strategies to overcome the global problem of antimicrobial resistance include research in finding new antimicrobials from plants. This study screened for the phytochemical profile and determined the antibacterial activity of the aqueous and ethanolic extracts of Psidium guajava leaves from the College of Veterinary medicine, Animal resources and Biosecurity at Makerere University Kampala, Uganda. The phytochemical screening of the plant leaf extracts was done through various tests which included the frothing test for saponins, Dragendoff's test and Mayer's test for tannins, lead acetate test for phenolic compounds, alkaline reagent test for flavanoids, Benedict's test and Fehlings test for reducing sugars, Salkowski's test for terpenoids as well as the Liebermann-Burchard test for steroids. The antimicrobial susceptibility testing was done using the agar well diffusion method against Staphylococcus aureus ATCC 25923 (a standard), wild Staphylococcus aureus and Bacillus cereus. This study revealed that both the extracts contained saponins, alkaloids, tannins, phenolic compounds, flavanoids, terpenoids, reducing sugars at similar intensities. Steroids were contained only in the ethanolic extract. The aqueous extract exhibited better activity with mean zone of inhibition (20.33±2.08 mm) greater than the ethanolic extract (18.67±3.22 mm) for S. aureus ATCC 25923. Similarly, the aqueous extract had a higher mean zone of inhibition (18.00±8.72 mm) than the ethanolic extract (17.67±2.89 mm) for wild S. aureus. For B. cereus, the ethanolic extract had mean zone of inhibition (15.00±1.00 mm) while the aqueous extract had (14.67±3.51 mm). The Minimum Inhibitory Concentration (MIC) for the ethanolic extract was 7.81 mg/ml on S. aureus ATCC 25923 and 3.91 mg/ml on both wild S. aureus and B. cereus. The MIC for the aqueous extract was 15.63 mg/ml, 7.81 mg/ml and 1.95 mg/ml on S. aureus ATCC 25923, wild S. aureus and B. cereus respectively. The Minimum Bactericidal Concentration (MBC) of the ethanolic extract was 7.81 mg/ml, 62.5 mg/ml and 3.91 md/ml for S. aureus ATCC 25923, wild S. aureus and B. cereus respectively. The MBC of the aqueous extract was 15.63 mg/ml, 250 mg/ml and 3.91 md/ml for S. aureus ATCC 25923, wild S. aureus and B. cereus respectively. This study has demonstrated that the P. guajava plant in our geographical setting can be a potential candidate in search for alternative therapeutics. Thus, a comprehensive study should be conducted to quantify the phytochemical composition of the various parts of the P. guajava plant and evaluate the safety of the aqueous and ethanolic extracts of the plant.