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Keywords:

  • antimicrobial activity;
  • Australian medicinal plants;
  • cytotoxicity;
  • Eremophila neglecta;
  • Myoporaceae;
  • serrulatane diterpenoids

Abstract

Aims:  To determine the antibacterial spectrum and cytotoxic activities of serrulatane compounds from the Australian plant Eremophila neglecta.

Methods and Results:  Antimicrobial activities of serrulatane compounds 8,19-dihydroxyserrulat-14-ene (1) and 8-hydroxyserrulat-14-en-19-oic acid (2) were tested against Gram-negative and Gram-positive bacteria including human and veterinary pathogens and some multidrug-resistant isolates. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of the compounds were determined by broth microdilution assay. Both compounds exhibited antibacterial activity against all Gram-positive test strains. They showed antimycobacterial activity against isolates of Mycobacterium fortuitum and Mycobacterium chelonae. Of the five Gram-negative bacteria tested, only Moraxella catarrhalis showed susceptibility to the compounds. Cytotoxic activities were tested in the Vero cell line. Compound 1 showed more activity than 2 in both antibacterial and cytotoxicity assays with cytotoxicity at concentrations similar to the MBC.

Conclusions:  Serrulatane compounds showed significant activity against medically important bacteria, with 1 exhibiting stronger antibacterial activity. However, they also displayed toxicity to mammalian cells.

Significance and Impact of the Study:  Serrulatanes are of interest as novel antibacterial compounds for use in biomedical applications; this study reports data obtained with a range of bacterial strains and mammalian cells, essential for assessing the capabilities and limitations of potential applicability of these compounds.