Antimicrobial activity of carbazole alkaloids from Murraya koenigii (L) Spreng leave

Murraya koenigii (L) Spreng, commonly known as curry leaf, is used in traditional and folk medicine for treatment of various ailments. Three carbazole alkaloids namely, mohanimbine, koenimbine & koenidine and a flavonoid, quercetin (+)-D-glucoside were isolated from dichloromethane and methanol extract by silica gel column chromatography and HPLC, respectively and their structures were elucidated by spectroscopic methods including 1D & 2D NMR. The antimicrobial properties of mohanimbine and koenimbine were investigated in vitro against a good number of pathogenic microorganisms including Bacillus cereus, Staphylococcus aureus, Escherichia coli, E. coli 0157:H7, Salmonella enteritidis, Vibrio cholerae, Shigella flexnari, Klebsiella spp, Pseudomonas aeruginosa, Aspergillus niger and Saccharomyces cerevisiae. Mohanimbine exhibited strong antimicrobial activity, but only to S. aureus, and the activity was found heat sensitive. Cytotoxic activity in fresh sheep erythrocytes revealed that mohanimbine does not possess cellular toxicity. Koenimbine could not produce either antibacterial or antifungal activities.