Antimicrobial activity of coronarin D and its synergistic potential with antibiotics

Abstract

Coronarin D is a labdane-type diterpene from the rhizomes of Hedychium coronarium. In the view of our ongoing effort to explore its novel biological activity, antimicrobial activity study of coronarin D was performed. The results showed that coronarin D was active against tested Gram-positive bacteria, inactive for tested Gram-negative bacteria, and weakly active against tested fungi. The antibacterial effect of the combination of coronarin D with nine classical antibiotics against four Gram-positive bacteria was also evaluated. The fractional inhibitory concentration indices (FICI) of coronarin D-antibiotics combinations, calculated from the checkerboard assay, were used as synergism indicator. Out of 36 combinations, 47% showed total synergism, 33% had partial synergistic interaction, 17% showed no effect, and 3% showed antagonism. By combination with coronarin D at concentration of 0.25 minimal inhibitory concentration (MIC), the activities of antibiotics were boosted to 4- to 128-fold. These finding suggested an attractive approach to combat the infectious diseases by using coronarin D-antibiotic drug combination.

Figure 1

Structure of coronarin D (1).

Figure 2

Structures of coronarin D acetate (2), kaurenoic acid (3), (+)-totarol (4), abietic acid (5), (E)-labda-8(17),12-diene-15,16-dial (6), and (E)-8β,17-epoxylabd-12-ene-15,16-dial (7).