Antimicrobial activity of eleagnine isolated from the seed cotyledons of Chrysophyllum albidum
This study evaluated the antimicrobial activity of eleagnine, a β-carboline alkaloid isolated from seed cotyledons of Chrysophyllum albidum G. Don Holl (Sapotaceae), and determined factors affecting it. Antimicrobial activities of eleagnine were determined using the agar diffusion and microdilution methods against selected typed organisms (Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida spp.), clinical isolates (S. aureus, E. coli) and Trichophyton. The effects of inoculum size and pH on the bacteriostatic activity were studied using agar and broth dilution methods. Bactericidal/fungicidal activities were also evaluated using viable count technique. Cytotoxicity was determined using brine shrimp lethality test. Eleagnine showed higher bacteriostatic activity against Gram-positive organisms and Candida spp. than Gram-negative bacteria but showed no activity against Trichophyton. The MIC of eleagnine obtained by microdilution tests ranged from 9.77 μg/mL against S. aureus, 156.25 μg/mL for C. albicans to 312.5 μg/mL for E. coli and P. aeruginosa. Inoculum size (105-107 orgs/mL) did not appreciably affect activity but pH from 5.85 to 8.09 increased the activity against S. aureus and E. coli, suggesting the unionized form as the active compound. Eleagnine (100-400 μg/mL) produced a 4-5 log survivor reduction of S. aureus and E. coli in 30 min. LC50 of eleagnine was 18.8 mg/mL indicating minimal cytotoxicity. This study showed that eleagnine is bactericidal with low cytotoxicity. Factors affecting its activity (pH, solvent) could be optimized in developing effective antimicrobial products alone or in combination with other agents.
Keywords: Eleagnine, Chrysophyllum albidum, antimicrobial, inoculum size, pH