title: Antibacterial constituents of Eremophila alternifolia: An Australian aboriginal traditional medicinal plant.
abstract: BACKGROUND
  For traditional medicinal purposes Aboriginal Australians have utilised numerous plant species, Eremophila alternifolia is among the most prominent. Traditionally, fresh leaves, leaf-infusions and handmade leaf-pastes have been used as both external and internal preparations to provide relief from a variety of conditions. Preparations of the species have been used to treat various infections of skin, eyes and throat including the treatment of septic wounds. These usages suggest that the plant contains antibacterial compounds; however, to date they have not been isolated and identified.
  
  
  OBJECTIVE
  The present study aimed to identify antibacterial compounds from this important traditionally recorded medicinal species.
  
  
  METHODS
  Bioassay-guided fractionation was used to isolate compounds from the crude leaf-extract. Antibacterial activity of pure compounds was assessed through broth microdilution method by determining both minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs). Structure elucidation was performed using spectroscopic techniques such as 1D and 2D nuclear magnetic resonance spectroscopy and high resolution mass spectrometry.
  
  
  RESULTS
  Four compounds have been isolated from the leaf-extract; they include previously known flavanones [pinobanksin (1), pinobanksin-3-acetate (2) and pinobanksin-3-cinnamate (3)] and a serrulatane diterpene, 8-hydroxyserrulat-14-en-19-oic acid (4). While compound 4 had been found in other Eremophilas, flavanones 2 and 3 are identified for the first time from the genus Eremophila. The flavanone 3 is the most promising antibacterial compound with significant activity (10-20µM) against strains of the Gram-positive bacterium Staphylococcus aureus including methicillin resistant and biofilm forming strains. No activity was observed for any isolated compounds against the Gram-negative bacterium Escherichia coli.
  
  
  CONCLUSIONS
  The antibacterial activity of the crude extract of E. alternifolia and of the isolated compounds against Gram-positive bacteria provides a Western scientific explanation of the therapeutic modality of this plant species in traditional Aboriginal medicinal practice.
authors.affiliation: Future Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia; Wound Management Innovation Cooperative Research Centre, Toowong, QLD 4066, Australia. Electronic address: Israt.Biva@mymail.unisa.edu.au.
authors.forename: Israt J
authors.initials: IJ
authors.lastname: Biva
authors.affiliation: Quality Use of Medicines and Pharmacy Research Centre, Sansom Institute for Health Research, School of Pharmacy and Medical Sciences, University of South Australia, Frome Road, Adelaide, SA 5000, Australia. Electronic address: Chi.Ndi@unisa.edu.au.
authors.forename: Chi P
authors.initials: CP
authors.lastname: Ndi
authors.affiliation: Future Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia; Wound Management Innovation Cooperative Research Centre, Toowong, QLD 4066, Australia. Electronic address: Hans.Griesser@unisa.edu.au.
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Griesser
authors.affiliation: Quality Use of Medicines and Pharmacy Research Centre, Sansom Institute for Health Research, School of Pharmacy and Medical Sciences, University of South Australia, Frome Road, Adelaide, SA 5000, Australia. Electronic address: Susan.Semple@unisa.edu.au.
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Semple
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001315:Australia; D004926:Escherichia coli / Q000187:drug effects* / Q000254:growth & development; D044950:Flavanones / Q000032:analysis / Q000494:pharmacology*; D006801:Humans; D010936:Plant Extracts / Q000032:analysis / Q000494:pharmacology*; D018515:Plant Leaves; D010946:Plants, Medicinal; D028083:Scrophulariaceae; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development
chemical_list: D000900:Anti-Bacterial Agents; D044950:Flavanones; D010936:Plant Extracts
keywords: Antibacterial; Australian aboriginal; Eremophila; Flavonoids; Scrophulariaceae