Antimicrobial and Antioxidant Activities of Ethanol Extracts from Red Guava Leaves (Psidium Guajava L.) Against Staphylococcus Aureus, Escherichia Coli, and Candida Albicans Using the Disk Diffusion Method

Abstract

Red guava leaves (Psidium guajava L.), a member of the Myrtaceae family, contain secondary metabolites such as flavonoids, alkaloids, and tannins that exhibit potential antibacterial, antifungal, and antioxidant activities. This experimental study employed the maceration method using 96% ethanol as the extraction solvent. Antimicrobial activity was evaluated using the disk diffusion method against Staphylococcus aureus, Escherichia coli, and Candida albicans at concentrations of 20%, 40%, and 60%. Antioxidant activity was assessed using the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay at concentrations of 10, 20, 40, and 80 µg/mL, with vitamin C used as a comparator. The results showed that the ethanol extract inhibited the growth of all tested microorganisms, with each treatment repeated three times. For S. aureus, the largest inhibition zone was observed at the 60% concentration (16.75 mm on average), whereas the smallest inhibition zone was observed at the 20% concentration (7.53 mm). For E. coli, the largest inhibition zone was also observed at the 60% concentration (8.44 mm on average), while the smallest was recorded at the 20% concentration (6.38 mm). For C. albicans, the largest inhibition zone occurred at the 60% concentration (10.46 mm on average), whereas the smallest was observed at the 20% concentration (8.81 mm). Regarding antioxidant activity, an increase in extract concentration was associated with decreased absorbance and increased free-radical scavenging activity. The ethanol extract exhibited an IC₅₀ value of 13.40 µg/mL, indicating very strong antioxidant activity, compared with vitamin C, which showed an IC₅₀ value of 2.36 µg/mL.