Antimicrobial Activities of the Crude Extract and Fractions of Erythrina abyssinica Stem Bark




Erythrina abyssinica commonly known as “the red hot poker tree” from the brilliance and shape of the bloom, is a medium-sized tree, usually 5-15 m in height. It belongs to the family Leguminosae consisting of 730 genera and over 19,400 species distributed all over the world. Erythrina abyssinica is the most widespread species in Africa.


Traditionally, different parts of this plant are used by many communities to treat a number of ailments. In Kenya the Maasai boil the stem bark with meat to treat gonnorrhoea. The stem bark stem is pounded and tied into a fine piece of cloth and the liquid from it squeezed into the eyes to cure inflammation of the lids (trachoma). A decoction is taken orally as an anthelmintic and to relive abdominal pains. The roots are used to treat syphilis, and the leaves to cure skin diseases in cattle.


In this study, the antimicrobial activity of the extract of the stem bark of this plant was ascertained to validate its traditional use in treating infectious diseases. The extract was purified by fractionation depending on polarity with the aim of comparing the antimicrobial activity of the fractions with respect to the total extract to establish whether or not the extracts constituents act synergistically or not. Fractionation increases the concentration of a particular class of compounds but reduces the synergistic interaction with other classes of compounds.


To achieve this dried and ground stem bark of Erythrina abyssinica was subjected to cold extraction using CH2Cl2:MeOH (1:1). The solvent was removed by using a rotary evaporator.  The extract was subjected to gravity column chromatography on silica gel eluting with mixtures of n-hexane/dichloromethane/methanol with increasing polarity. Further purification of the fractions using chromatography on silica gel and analytical Thin Layer Chromatography (TLC) and crystallization led to the isolation of one compound from this extract. The structure of this compound was elucidated using 1D and 2D NMR.


The crude extract and the nine fractions (IO-11A-11G) obtained from the major column were tested for their antimicrobial activity against three strains of bacteria: Staphyloccocus aureus (ATCC259213), Escherichia coli (NC35218) and a local strain of fungus, Candida albicans SC5314 and Aspergillus niger ATCC 16404 using the disc diffusion method. Fractions IO-11A-11G showed good activity against two bacteria; Staphylococcus aureus and Escherichia coli among others.


Key Words: Erythrina abyssinica, Stem bark, Phytochemistry, Antimicrobial activity

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