Abstract

The in vitro antibacterial and cytotoxicity activities of crude methanolic extract of the stem bark of Erythrina caffra Thunb. was investigated. MIC and MBC were used for the antimicrobial assay while the cytotoxic activity of the plants extract was determined using brine shrimp lethality test. In this study, the extract was active against all the Gram-positive and Gram-negative bacteria investigated with Pseudomonas aeruginosa, Proteus vulgaris, Enterococcus faecalis and Micrococcus luteus being the most susceptible. The extract exhibited antibacterial activities with inhibition zones being concentration dependent. At the highest concentration (4500 µg/ml), the extract produced inhibition zones ranging between 18 and 22 ± 1.00 mm. While the agar dilution indicated that the bacteria were susceptible at concentrations ranging between ≤100 and ≤ 1000 µg/ ml, the macrobroth dilution showed that the MICs of the methanolic extract ranged between 20 µg/ml and 2500 µg/ml and the brine shrimp lethality assay indicated that the LC50 and LC90 were 40.22 µg/ml and 56.66 µg/ml respectively. Although the extract was effective against the two groups of bacteria, the Gram-negative bacteria were more susceptible to the extract than the Gram-positive bacteria. The ability of this extract to inhibit bacteria at low concentrations is an indication of its broad spectrum antibacterial potential which may be exploited in the management of microbial infections. The study, therefore, suggests that there are phytochemical constituents in the extract which could serve as a source of chemotherapy drugs useful in the treatment of infections and justifies the use of Erythrina caffra traditionally for the treatment of gastroenteritis in the rural communities.