Bioassay directed fractionation of antibacterial compounds from traveller’s tree (ravenala Madagascariensis sonnerat) and its phytochemical constituents

Investigations were conducted to determine the antibacterial and phytochemical activities of extracts from the leaves of traveller’s tree ( Ravenala madagascariensis ). Different concentrations (i.e. 25 - 200 mg/ml) of the extracts prepared using ethanol; n-Hexane, hot water and cold water were tested against some selected human pathogenic bacteria using agar well diffusion method. Clinical isolates and typed cultures of the organisms were screened with the plant extracts. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the extracts to susceptible organisms were determined. The rate of inhibition of bacterial growth was also investigated using turbidometry method. Crude extracts were screened for the type and amounts of phytochemicals, while the biologically active fractions of the extracts were structurally elucidated using Infra-Red spectroscopy. Ethanol extract induced the highest zone of inhibition (10.80 ± 0.04mm) on Proteus mirabilis (ATCC 25933) and the lowest zone of inhibition (4.6 ± 0.01mm) on Proteus vulgaris when exposed to crude ethanol extract. Ethanol extract remarkably suppressed the growth of Proteus vulgaris, Serratia marcescens, Klebsiella pneumoniae, Citrobacter freundii, Proteus mirabilis (ATCC 25933) , Serratia marcescens (ATCC 39006) , Klebsiella pneumoniae (ATCC 13883) , Citrobacter freundii and Shigella flexneri (ATCC 12022). N-Hexane extract was only effective against Serratia marcescens and Klebsiella pneumoniae with 24% inhibition respectively. However, cold and hot water extracts had no effect on any of the test organisms, irrespective of the concentration. The clinical isolates were more susceptible to the extracts than the typed cultures in ratio 4:3. Phytochemical screening revealed the presence of tannins (0.31%), flavonoids (16.32%), phlobatannins (0.36%), cardiac glycosides (0.08%), cyanogenic glycosides (47%) and anthraquinones (16.20%) in the plant extracts.