title: Antimicrobial and antioxidant activity and chemical characterisation of Erythrina stricta Roxb. (Fabaceae).
abstract: BACKGROUND
  The bark of Erythrina stricta Roxb. (Fabaceae) has been used in Indian indigenous systems as a remedy for rheumatism, stomach-ache, asthma, dysentery, contact dermatitis, eczema and skin infections. However, there have been limited phytochemical or biological studies on the bark of E. stricta and there are no studies that align with its traditional medicinal uses.
  
  
  OBJECTIVE
  The aim of this study was to assess the antimicrobial and antioxidant activity of the stem bark of E. stricta to support its topical use in the treatment of contact dermatitis, eczema and skin infections and to isolate and identify any bioactive compounds.
  
  
  METHODS
  MTT microdilution and disc diffusion assays were used to determine the antimicrobial activities of n-hexane, dichloromethane, ethyl acetate, methanol and water extracts of the bark of E. stricta. Column and preparative thin layer chromatography were used for the purification of the dichloromethane extract. The structures of the compounds isolated were elucidated by extensive 1D and 2D NMR spectroscopic techniques and comparison with published data. The antioxidant activities of the extracts were determined by DPPH free radical scavenging and FRAP assays and the antioxidant activity of the pure compounds by dot-blot and DPPH staining methods.
  
  
  RESULTS
  The dichloromethane, ethyl acetate, and n-hexane extracts showed the most significant activity with MIC values of 7.8µg/mL, 125µg/mL, and 125µg/mL against a sensitive strain of Staphylococcus aureus. The dichloromethane and ethyl acetate extracts also showed significant activity against Candida albicans with MIC values of 125µg/mL and 1mg/mL respectively. GC-MS analysis of the n-hexane extract showed the presence of the antibacterial and antifungal compounds β-caryophyllene, caryophyllene oxide, α-selinene, β-selinene, selin-11-en-4-α-ol, α-copaene and δ-cadenine. Phytochemical studies of the dichloromethane extract led to the isolation of the novel compound erynone (1), together with six known compounds; wighteone (2), alpinum isoflavone (3), luteone (4), obovatin (5), erythrinassinate B (6) and isovanillin (7). Luteone (4) exhibited the most significant antibacterial activity with minimum inhibitory quantity (MIQ) values of 1.88µg, 1.88µg and 3.75µg, respectively, against sensitive (MSSA) and resistant strains (MRSA and MDRSA) of S. aureus using a TLC bioautography assay. Erynone (1) exhibited the greatest DPPH free radical scavenging activity.
  
  
  CONCLUSIONS
  Seven compounds, including a new chromanone, were isolated from the antimicrobial dichloromethane extract of the stem bark of E. stricta. Six of the seven compounds showed antibacterial and/or antioxidant activities. These findings provide support for the customary (traditional and contemporary) use of E. stricta bark for the treatment of skin and wound infections.
authors.affiliation: Indigenous Bioresources Research Group, Faculty of Science and Engineering, Macquarie University, North Ryde, Sydney 2109, Australia.
authors.forename: Kaisarun
authors.initials: K
authors.lastname: Akter
authors.affiliation: Indigenous Bioresources Research Group, Faculty of Science and Engineering, Macquarie University, North Ryde, Sydney 2109, Australia.
authors.forename: Emma C
authors.initials: EC
authors.lastname: Barnes
authors.affiliation: Indigenous Bioresources Research Group, Faculty of Science and Engineering, Macquarie University, North Ryde, Sydney 2109, Australia.
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Loa-Kum-Cheung
authors.affiliation: Indigenous Bioresources Research Group, Faculty of Science and Engineering, Macquarie University, North Ryde, Sydney 2109, Australia.
authors.forename: Ping
authors.initials: P
authors.lastname: Yin
authors.affiliation: Indigenous Bioresources Research Group, Faculty of Science and Engineering, Macquarie University, North Ryde, Sydney 2109, Australia.
authors.forename: Meyanungsang
authors.initials: M
authors.lastname: Kichu
authors.affiliation: School of Chemistry, Faculty of Science, University of New South Wales, Sydney 2052, Australia.
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Brophy
authors.affiliation: Research School of Chemistry, Faculty of Science, Australian National University, Acton, ACT 2601, Australia.
authors.forename: Russell A
authors.initials: RA
authors.lastname: Barrow
authors.affiliation: Chungtia Senso Mokokchung Town, Mokokchung, Nagaland 798601, India.
authors.forename: Imchawati
authors.initials: I
authors.lastname: Imchen
authors.affiliation: Indigenous Bioresources Research Group, Faculty of Science and Engineering, Macquarie University, North Ryde, Sydney 2109, Australia.
authors.forename: Subramanyam R
authors.initials: SR
authors.lastname: Vemulpad
authors.affiliation: Indigenous Bioresources Research Group, Faculty of Science and Engineering, Macquarie University, North Ryde, Sydney 2109, Australia. Electronic address: joanne.jamie@mq.edu.au.
authors.forename: Joanne F
authors.initials: JF
authors.lastname: Jamie
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D000935:Antifungal Agents / Q000737:chemistry / Q000494:pharmacology*; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects; D002176:Candida albicans / Q000187:drug effects; D004895:Erythrina / Q000737:chemistry*; D015394:Molecular Structure; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D000935:Antifungal Agents; D000975:Antioxidants; D010936:Plant Extracts
keywords: Alpinum Isoflavone (PubChem CID: 54901393), Isovanillin (PubChem ID: 12127); Antimicrobial; Antioxidant; Chemical constituents; Erythrina stricta; Isoflavanone; Luteone (PubChem CID: 5281797); Obovatin (PubChem CID: 13940733); Wighteone (PubChem ID: 5281814)