title: The in vitro antimicrobial activity of Cymbopogon essential oil (lemon grass) and its interaction with silver ions.
abstract: BACKGROUND
  It is well known that Cymbopogon (lemon grass) essential oil exhibits antimicrobial activity while the efficacy of silver ions as a disinfectant is equally well reported.
  
  
  OBJECTIVE
  The antimicrobial activity of CEO and Ag(+) and their synergistic combinations will be useful in improving the current treatment strategies for various infections.
  
  
  METHODS
  In the present study, we determined the chemical composition and in vitro antimicrobial activity of six different Cymbopogon essential oils (CEO's) alone and in combination with silver ions (Ag(+)) against two Gram-positive (Staphylococcus aureus and Enterococcus faecalis), two Gram-negative (Escherichia coli and Moraxella catarrhalis) and two yeast species (Candida albicans and Candida tropicalis). The nature of potential interactions was determined by fractional inhibitory concentration indices (FICIs) for CEO's and Ag(+) calculated from microdilution assays and time-kill curves.
  
  
  RESULTS
  Gas chromatography-mass spectrometry results confirmed the presence of nerol, geranial and geraniol as major volatile compounds. Minimum inhibitory concentration (MIC) values confirmed that all the tested pathogens are variably susceptible to both CEO's as well as Ag(+). The MIC of CEO's and Ag(+) against all the tested pathogens ranged from 0.032 mg/ml to 1 mg/ml and 0.004 and 0.064 mg/ml respectively, whereas when assayed in combination the FICI values were drastically reduced to range between 0.258 and 2.186, indicating synergy, additive and indifferent interactions. The most prominent interaction was observed between Cymbopogon flexuosus essential oil and Ag(+) against C. albicans with ∑FIC = 0.254. The synergistic interactions were further confirmed through the construction of isobolograms and time-kill plots. Transmission electron microscopy showed disturbance in the cell envelope upon the concomitant treatment of CEO's and Ag(+), which ultimately leads to cell death.
  
  
  CONCLUSIONS
  Results suggest that CEO's and Ag(+) when used in combination offers an opportunity to the formulation scientist to produce novel combinations acting synergistically in the continued quest to control important infectious pathogens.
authors.affiliation: Department of Pharmaceutical Sciences, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa.
authors.forename: Aijaz
authors.initials: A
authors.lastname: Ahmad
authors.affiliation: Department of Pharmaceutical Sciences, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa; Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, King Abdulaziz University, Jeddah 21589, Saudi Arabia. Electronic address: viljoenam@tut.ac.za.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Viljoen
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D031743:Cymbopogon / Q000737:chemistry*; D004357:Drug Synergism; D008401:Gas Chromatography-Mass Spectrometry; D008826:Microbial Sensitivity Tests; D046529:Microscopy, Electron, Transmission; D009822:Oils, Volatile / Q000494:pharmacology*; D012834:Silver / Q000494:pharmacology*
chemical_list: D000890:Anti-Infective Agents; D009822:Oils, Volatile; D012834:Silver
keywords: Antimicrobial activity; Cymbopogon essential oil; Silver ions; Synergy