Unveiling the mode of action of antibacterial labdane diterpenes from Alpinia nigra (Gaertn.) B. L. Burtt seeds

• Two bactericidal labdane diterpenes were isolated from Alpinia nigra seeds.
• Damage and disintegration of treated bacterial cells were detected.
• Flow cytometry disclosed the compromised state of treated bacterial membrane.
• Compound treatment leads to increased leakage from bacterial cells with time.
• Bactericidal activity of compound B appeared highly promising.

The labdane diterpene, (E)-labda-8(17), 12-diene-15, 16-dial (compound A) and its epoxide analogue, (E)-8β, 17-Epoxylabd-12-ene-15, 16-dial (compound B) were isolated from the seeds of Alpinia nigra for the first time. The antibacterial activities of both compounds were evaluated against three Gram-positive and four Gram-negative bacteria, and flow cytometric analysis revealed that these compounds caused significant damage to the bacterial cell membranes. Further, field emission scanning electron microscope imaging and cell leakage analysis confirmed that the labdane diterpenes were responsible for bacterial cell membrane damage and disintegration. Our findings provide new insight into the broad-spectrum effects of two natural labdane diterpenes that may be useful in the future development of herbal antibiotic products.

Figure optionsDownload as PowerPoint slide