PHYTOCHEMICAL COMPOUNDS AND ANTIMICROBIAL ACTIVITY OF EXTRACTS OF INDIGOFERA SPICATA (CREEPING INDIGO) AGAINST CANDIDA ALBICANS, STREPTOCOCCUS MUTANS AND E. COLI

Abstract

Indigofera spicata has been used by Kamba community of Kenya as an herbal medicine over a long period to treat coughs and toothaches. There is scanty information on the phytochemical compounds and the antimicrobial activity of Indigofera spicata plant extracts on Candida albicans, Streptococcus mutans and E. coli, which are known to cause many opportunistic infections to humans. This study aimed at investigating the phytochemical compounds and antimicrobial activity of Indigofera spicata leaves, roots and bark extracts against Candida albicans, Streptococcus mutans and E. coli. Plants were collected and plant parts dried separately and crushed to obtain a fine powder which was used to extract the crude extracts using methanol solvent.  Plant samples were subjected to qualitative phytochemical tests for the identification of chemical constituents present using standard qualitative methods.  Phytochemical constituents were analyzed by thin layer chromatography (TLC) in appropriate solvents (n-hexane and methanol, 3:1). The plates were observed under UV lamp at wavelength of 540nm, and Rf values were calculated for each spot. 5mm diameter paper discs were each dipped in a known concentration of the extracts of 0% (distilled water), 25%, 50% and 75% methanol extracts for 2 minutes and placed in either PDA or nutrient agar inoculated with the test organisms. Three discs were placed per petri dish and were incubated at 28 degrees and 48 hours for fungi and 37 degrees for 18-24 hours for bacteria. The experiment was arranged in a completely randomized design in the incubator.  The growth diameter of inhibition was measured with a ruler. Data obtained on zone of inhibition was subjected to analysis of variance (ANOVA) by use of SAS statistical package. The methanolic extracts of the plants revealed the presence of tannins, sterols, alkaloids, saponins and terpenoids. However cardiac glycosides, phenols and flavonoids were absent in all the plant parts. Terpenoids were present in the stems and roots. Elution of the column with the n-hexane and methanol led to isolation of uncharacterized active compounds, three in leaves and stems, and two in roots. There were significant differences (p<0.05) between the extract concentrations, plant parts and the test microorganisms used. The leaves had the highest inhibitory effects at 75% methanol extract, i.e (5.7+0.2 mm, 6.8+0.2 mm and 8.3+0.7 mm growth diameter of Candida albicans, Streptococcus mutans and Escherichia coli respectively) compared to roots (5.7+0.2 mm, 6.0+0.3 mm and 7.0+0.3 mm growth diameter of Candida albicans, Streptococcus mutans and Escherichia coli respectively) and stem (5.8+0.2 mm, 5.3+0.2 mm and 7.7+0.2 mm growth diameter of Candida albicans, Streptococcus mutans and Escherichia coli respectively). The study suggests the potential of the plant as a source of new antimicrobial agents.