Phytochemical and antimicrobial studies on Detarium microcarpum Guill and Sperr (Caesalpinioceae) seeds coat
Ninety percent aqueous methanol extract of the seeds coat (32.324%, w/w) of Detarium microcarpum was screened against clinical isolates of Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomona aeruginosa, Klebsiella pneumonia, Salmonella paratyphi and Candida albicans. A broad spectrum antimicrobial activity at the test concentration of 10 mg/ml comparable with the control drugs chloramphenicol and penicillin G for bacteria and nystatin for the mould C. albicans was observed. On bio-guided fractionation, the ethyl acetate soluble fraction (ES) retains the observed spectrum of antimicrobial activity. Preparative thin layer chromatographic separation of the active ESF on silica gel 60G using butan-2-one : chloroform : acetic acid : water (40:40:2:1 v/v/v/v) gave eight constituent bands: B1 (Rf = 0.000), B2 (Rf = 0.079), B3 (Rf = 0.250), B4 (Rf = 0.286), B5 (Rf = 0.500), B6 (Rf = 0.686), B7(Rf = 0.814), and B8 (Rf = 1.000). B1 retained the observed antimicrobial activity spectrum, B2 and B3 showed residual inhibition against B. subtilis and B4 - B8 were inactive. Phytochemical screening indicated the presence steroidal saponins and flavonoids in B1, and flavonoids in B2 and B3. The UV visible
spectrum of B2 and B3 revealed the characteristic benzopyrone maxima (236 – 300 nm). Against the selected bacteria, MIC range of B1 of 1.0488 -2.8887 mg/ml was observed comparable to those of standard control (1.2357 - 3.3420 mg/ml) and chloramphenicol (2.0840 -3.9630 mg/ml) which is suggestive of resistant strains. This study revealed the antimicrobial principles in the seed coat of D. microcarpum to be steroidal saponins and flavonoids with the possibility of synergistic action.
Key words: Detarium microcarpum, seed coat, antimicrobial activity, benzopyrone, flavonoids, steroidal saponins, phytoalexins.