evaluation of stem bark of Erythrina abysinica for antimicrobial and termiticidal principles.

Abstract

Erythrina species are used as healing agent in traditional medicine in Africa and are prescribed against wide range of diseases including those with microbial and parasitic origin. Erythrina abysinica is a species widely distributed in Southwestern Ethiopia and is well known for its decay/decomposition tolerant bark from matured stem. The main objective of this study was to carry out phytochemical investigation of the stem bark of matured Erythrina abysinica and evaluation of its antimicrobial and termiticidal activities. The bark of Erythrina abysinica was collected from Jimma town, dried and powdered. The powdered sample was extracted with methanol using maceration technique. Phytochemical analysis of the crude extract was carried out using both chemical test and column chromatography. The isolated compounds were characterized using physical and spectral (1H NMR, 13 C NMR, and DEPT) data. The Crude extract and purified compounds were subjected to tests on selected strains of bacteria (S. aureus, E. coli, and B. subtilus) and fungi (Aspargillus spp., Fusariun spp., penicillium spp & Trichophyton spp) using disk diffusion method. Termiticidal activity was also carried out on C. formosans employing No-Choice assay method. The phytochemical screening tests carried on crude methanol extract (53 g, 4.82 %) confirmed the presence of alkaloids, saponins, terpenoids and flavonoids only. Column chromatographic analysis yielded two pure compounds E.A1 and E.A2 which were proposed to be lupinifolin and 9-ethyldodecyl-4-methoxybenzoate respectively by comparison of physical spectral data with those reported in literature. The crude extract was not active against all bacterial trains tested but E.A1 and E.A2 were active both with zone of inhibition 9.0 mm against Bacillus subtilus and E. coli. The crude extract and isolated compounds (E.A1 and E.A2) were active against all fungal stains tested with zone of inhibition 10-18 mm except Aspergillus spp. Activities recorded were highest on Fusariun spp. and lowest on Aspergillus spp. Aspergillus spp was responsive only to E.A 2 and Mancozeb. Killing effects caused by the extracts on termites were both time and concentration dependent. The highest killing effect (100 %) was observed for 5% crude extract solution at 30 minutes which was also the same for 5% Malathion. Other test samples produced < 100 % killing effects even after 5 days. Most results attained in this study were in agreement with earlier reports. The termiticidal and antifungal activities observed here justify decay resistant nature of Erythrina abyssinica stem bark. Isolation of more phytoconstituent and detailed studies on organisms involved in decay process are recommended.