ANTIMICROBIAL ACTIVITY OF THE DITERPENES FLEXIBILIDE AND SINULARIOLIDE DERIVED FROM SINULARIA-FLEXIBILIS QUOY AND GAIMARD 1833 (COELENTERATA, ALCYONACEA, OCTOCORALLIA)

The soft coral Simularia flexibilis is rarely overgrown by bacteria an d algae. Various studies have shown that it contains diterpenes that p rotect it from competitors and predators. However, of the many diterpe noids isolated from S. flexibilis, only sinulariolide has been studied for antibiotic properties. Samples of soft corals were collected from Orpheus Island and freeze-dried for chemical extraction and isolation of pure diterpenes. Antimicrobial activity of the diterpenes was dete rmined using the disc assay method with antibiotics as controls and th e minimum inhibitory concentrations of the diterpenes were determined using the Tube Dilution Technique. Two out of the five diterpenes test ed (sinulariolide and flexibilide), showed marked antimicrobial activi ty and inhibited growth of Gram-positive bacteria. Flexibilide was eff ective even at concentrations as low as 5 ppm, whereas sinulariolide w as effective at concentrations of 10 ppm. These compounds show potenti al as antibiotics. (C) 1998 Elsevier Science Inc. All rights reserved.