Antibacterial activity of indole alkaloids from Aspidosperma ramiflorum

Abstract

We evaluated the antibacterial activities of the crude methanol extract, fractions (I-V) obtained after acid-base extraction and pure compounds from the stem bark of Aspidosperma ramiflorum. The minimum inhibitory concentration (MIC) was determined by the microdilution technique in Mueller-Hinton broth. Inoculates were prepared in this medium from 24-h broth cultures of bacteria (107 CFU/mL). Microtiter plates were incubated at 37°C and the MICs were recorded after 24 h of incubation. Two susceptibility endpoints were recorded for each isolate. The crude methanol extract presented moderate activity against the Gram-positive bacteria B. subtilis (MIC = 250 μg/mL). Fractions I and II were inactive against standards strains at concentrations of ≤1000 μg/mL and fraction III displayed moderate antibacterial activity against B. subtilis (MIC = 500 μg/mL) and S. aureus (MIC = 250 μg/mL). Fraction IV showed high activity against B. subtilis and S. aureus (MIC = 15.6 μg/mL) and moderate activity against E. coli and P. aeruginosa (MIC = 250 μg/mL). Fraction V presented high activity against B. subtilis (MIC = 15.6 μg/mL) and S. aureus (MIC = 31.3 μg/mL) and was inactive against Gram-negative bacteria (MIC > 1000 μg/mL). Fractions III, IV and V were then submitted to bioassay-guided fractionation by silica gel column chromatography, yielding individual purified ramiflorines A and B. Both ramiflorines showed significant activity against S. aureus (MIC = 25 μg/mL) and E. faecalis (MIC = 50 μg/mL), with EC50 of 8 and 2.5 μg/mL for ramiflorines A and B, respectively, against S. aureus. These results are promising, showing that these compounds are biologically active against Gram-positive bacteria. © 2006 Brazilian Journal of Medical and Biological Research.