In Vitro Antibacterial and Antioxidant Activities of Ethyl Acetate Extracts of Xerophyta Spekei (Baker), Senna Singueana (Delile) and Grewia Tembensis (Fresen)

Abstract

Bacterial infections are a leading cause of mortality and morbidity worldwide. During bacterial diseases, the elevation of host immune response occurs, which involves production of free radicals in response to the bacterial infection. Overproduction of free radicals in excess of the antioxidants leads to oxidative stress. To combat the bacterial diseases, conventional antibiotics are normally used. Conventional antibiotics are associated with side-effects such as hypersensitivity reactions, toxicity, and bacterial pathogens developing resistance against them. Artificial antioxidants are said to be carcinogenic. This study sought to confirm folklore use and validate the antibacterial and antioxidant activities of Grewia tembensis, Senna singueana, and Xerophyta spekei, which have been widely used in the Mbeere community in Kenya. The in vitro antibacterial activities of the plant extracts were investigated on Gram positive bacteria (Bacillus subtilis ATCC 21332 and Staphylococcus aureus ATCC 25923) and Gram negative bacteria (Escherichia coli ATCC 25922 and Salmonella typhi ATCC 1408). Ciprofloxacin (100 μg/ml) drug was used as a standard reference, whereas 5% DMSO was used as a negative reference. The antibacterial tests included disc diffusion, minimum inhibitory and bactericidal concentrations. Antioxidant properties of the extracts were determined through scavenging effects of DPPH, H2O2 (hydrogen peroxide), and hydroxyl radicals and iron chelating effects, as well as FRAP assay. S. singueana extract showed broad-spectrum activity against tested bacterial microbes producing mean zones of inhibition (MZI) from 07.67±0.33 to 17.67±0.33 mm. Ethyl acetate stem bark extract of G. tembensis showed a notable antibacterial effect on S.aureus only with MZI ranging from 07.07±0.07 to 12.33±0.33 mm. Likewise, ethyl acetate leaf extract of G. tembensis also exhibited an antibacterial effect against only S. aureus with MZI ranges of 08.33±0.33 to 11.67±0.33 mm, while the ethyl acetate extract of X. spekei revealed notable antibacterial effects on studied Gram positive bacteria only with inhibition zones ranging from 07.67±0.33 to 14.67±0.33 mm. S. singueana extract exhibited significantly higher antibacterial effects than all the other plant extracts (p<0.05). X. spekei extract had significantly higher in vitro antioxidant activity than all the other extracts (p<0.05). The quantitative phytocompounds screening demonstrated the availability of compounds with known antibacterial and antioxidant effects. Therefore, the current study recommends ethnomedicinal and therapeutic use of S. singueana as antibacterial agent against S. aureus, B. subtilis, S. typhi and E. coli while X. spekei as antibacterial agent against S. aureus, B. subtilis and finally G. tembensis as antibacterial agent against S. aureus. They can also be used as antioxidant agents after a comprehensive study of their toxicity and safety profiles.