Antimicrobial activity of 5-hydroxy-1,4-naphthoquinone isolated from Caesalpinia sappan toward intestinal bacteria

The methanol extract of Caesalpinia sappan heartwoods was tested for the growth effects toward five intestinal microorganisms. The biologically active constituent of the C. sappan extract was characterized as 5-hydroxy-1,4-naphthoquinone (C10H6O3). The growth responses varied depending on the bacterial species and dose tested. In the test with Clostridium perfringens, 5-hydroxy-1,4-naphthoquinone produced the strong (+++) inhibition at 5 and 2 mg/disk and moderate (++) inhibition at 1, 0.5, and 0.25 mg/disk. Furthermore, this isolate revealed a weak (+) growth inhibition against Lactobacillus casei at 5 and 2 mg/disk. In comparison of naphthoquinone derivatives, 5-hydroxy-2-methyl-1,4-naphthoquinone had moderate growth inhibition against C. perfringens at 5 and 2 mg/disk, whereas 1,4-naphthoquinone at 5 mg/disk significantly inhibited the growth of all bacteria tested. 1,2-Naphthoquinone had growth inhibition against all bacteria tested at 1 mg/disk. The structure-activity relationship revealed that 5-hydroxy-1,4-naphthoquinone had selective growth inhibition against C. perfringens. These results indicate that hydroxyl functional group of naphthoquinone seems to be required for selective growth-inhibiting activity against C. perfringens. Accordingly, as naturally occurring antimicrobial agents, C. sappan heartwood-derived material could be useful as a preventive agent against diseases caused by C. perfringens.