title: The agar microdilution method - a new method for antimicrobial susceptibility testing for essential oils and plant extracts.
abstract: OBJECTIVE
  To develop a new agar microdilution technique suitable for the assessment of the antimicrobial activity of natural plant products such as essential oils or plant extracts as well as to evaluate the antimicrobial effect of several essential oils and plant extracts.
  
  
  RESULTS
  The proposed agar microdilution method was evolved on the basis of the CLSI agar dilution method, approved for conventional antimicrobials. However, this new method combines convenience and time/cost effectiveness typical for microtitre methods with the advantages of the agar dilution of hydrophobic or coloured substances. Different concentrations of the tested agents were added to Eppendorf tubes with molten Mueller-Hinton agar, vortexed and dispensed into the 96-well microplate in a small volume of 100 μl per well which allows for rapid, easy and economical preparation of samples as well as providing a uniform and stable dispersion without separation of the oil-water phases which occurs in methods with liquid medium. Next, the agar microdilution plates were inoculated with four reference bacterial strains. The results of our study demonstrated that the minimal inhibitory concentrations (MICs) were successfully determined using the agar microdilution method even with hydrophobic essential oils or strongly coloured plant extracts.
  
  
  CONCLUSIONS
  The new agar microdilution method avoids the problems associated with testing of water insoluble, oily or strongly coloured plant natural products. Moreover, it enables the reliable, cheap and easy MIC determination of such agents.
  
  
  CONCLUSIONS
  In the era of increasing antibiotic resistance high hopes are associated with new drugs of plant origin. However, the lack of standardized and reliable testing methods for assessing antibacterial activity of plant natural products causes impediment to research into this area. This study demonstrated that the agar microdilution method can be used successfully for testing oily and coloured substances.
authors: Department of Biochemistry and Biotechnology, Medical University of Lublin, Lublin, Poland. joanna.golus@umlub.pl.
authors: J
authors: J
authors: Golus
authors: Department of Biochemistry and Biotechnology, Medical University of Lublin, Lublin, Poland.
authors: R
authors: R
authors: Sawicki
authors: Department of Pharmacognosy with Medicinal Plant Unit, Medical University of Lublin, Lublin, Poland.
authors: J
authors: J
authors: Widelski
authors: Department of Biochemistry and Biotechnology, Medical University of Lublin, Lublin, Poland.
authors: G
authors: G
authors: Ginalska
mesh_terms: D000362:Agar; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009822:Oils, Volatile / Q000494:pharmacology*; D010936:Plant Extracts / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D009822:Oils, Volatile; D010936:Plant Extracts; D000362:Agar
keywords: agar microdilution method; antibacterial activity; essential oil; minimal inhibitory concentration; plant extract