Phytochemical Analysis and Antibacterial Activity of Trunk Bark of Erythrina excelsa Baker

Pseudomonas agarici is a bacterial strain responsible for at least three diseases affecting cultivated mushrooms: drippy gill, brown discoloration and yellow blotch. The present study aimed to investigate the trunk barks extract of Erythrina excelsa Baker, to find bioactive constituents against Pseudomonas agarici. The bioactivity guided fractionation of the methanolic extract yielded ten known compounds: neorautenol (1), calopocarpin (2), abyssinone-IV-4′-O-methyl ether (3), abyssinone-V-24′-O-methyl ether (4), abyssinone V (5), (-)-sigmoidin E (6), 4′-O-methylderrone (7), erycaffra A (8), genistein (9) and 5,4′-dihydroxy-2″-hydroxyisopropyldihydrofurano[4,5:7,8]isoflavone (10). Their structures have been established using one-dimensional (1D) and two-dimensional (2D) Nuclear Magnetic Resonance (NMR) experiments in combination with Infared (IR) and Mass Spectrometry (MS). The broth microdilution method was used to assess the antibacterial activity of the crude extract against Pseudomonas agarici and three others strains namely Escherichia coli, Bacillus subtilis and Staphylococcus warneri. The crude extract and n-Hexane/ethyl acetate (7:3) fraction exhibited significant activity against P. agarici, with Minimum Inhibitory Concentration (MIC) values of 36.9 and 27.1 μg/mL, respectively. From the isolates, only calopocarpin (2) showed significant activity against P. agarici, with MIC value of 12.8 μg/mL, comparable to gentamycin as reference.