title: Antimicrobial activity of essential oils of cultivated oregano (Origanum vulgare), sage (Salvia officinalis), and thyme (Thymus vulgaris) against clinical isolates of Escherichia coli, Klebsiella oxytoca, and Klebsiella pneumoniae.
abstract: BACKGROUND
  Oregano (Origanum vulgare), sage (Salvia officinalis), and thyme (Thymus vulgaris) are aromatic plants with ornamental, culinary, and phytotherapeutic use all over the world. In Europe, they are traditionally used in the southern countries, particularly in the Mediterranean region. The antimicrobial activities of the essential oils (EOs) derived from those plants have captured the attention of scientists as they could be used as alternatives to the increasing resistance of traditional antibiotics against pathogen infections. Therefore, significant interest in the cultivation of various aromatic and medicinal plants is recorded during the last years. However, to gain a proper and marketable chemotype various factors during the cultivation should be considered as the geographical morphology, climatic, and farming conditions. In this frame, we have studied the antimicrobial efficiency of the EOs from oregano, sage, and thyme cultivated under different conditions in a region of NE Greece in comparison to the data available in literature.
  
  
  METHODS
  Plants were purchased from a certified supplier, planted, and cultivated in an experimental field under different conditions and harvested after 9 months. EOs were extracted by using a Clevenger apparatus and tested for their antibacterial properties (Minimum inhibitory concentration - MIC) against clinical isolates of multidrug resistant Escherichia coli (n=27), Klebsiella oxytoca (n=7), and Klebsiella pneumoniae (n=16) strains by using the broth microdilution assay.
  
  
  RESULTS
  Our results showed that the most sensitive organism was K. oxytoca with a mean value of MIC of 0.9 µg/mL for oregano EOs and 8.1 µg/mL for thyme. The second most sensitive strain was K. pneumoniae with mean MIC values of 9.5 µg/mL for thyme and 73.5 µg/mL for oregano EOs. E. coli strains were among the most resistant to EOs antimicrobial action as the observed MICs were 24.8-28.6 µg/mL for thyme and above 125 µg/mL for thyme and sage. Most efficient were the EOs from thyme followed by those of oregano.
  
  
  CONCLUSIONS
  With MIC values above 150 µg/mL, sage EOs did not show any antibacterial efficiency against the majority of the strains. However, no significant differences were observed concerning the antimicrobial action of all EOs originating from irrigated versus non-irrigated cultivated aromatic plants.
authors.affiliation: Laboratory of Microbiology, Biotechnology & Hygiene, Faculty of Agricultural Development, Democritus University of Thrace, Orestiada, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Fournomiti
authors.affiliation: Laboratory of Chemistry & Biochemistry, Faculty of Agricultural Development, Democritus University of Thrace, Orestiada, Greece.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Kimbaris
authors.affiliation: Laboratory of Microbiology, Biotechnology & Hygiene, Faculty of Agricultural Development, Democritus University of Thrace, Orestiada, Greece.
authors.forename: Ioanna
authors.initials: I
authors.lastname: Mantzourani
authors.affiliation: Laboratory of Microbiology, Biotechnology & Hygiene, Faculty of Agricultural Development, Democritus University of Thrace, Orestiada, Greece.
authors.forename: Stavros
authors.initials: S
authors.lastname: Plessas
authors.affiliation: Laboratory of Microbiology, Biotechnology & Hygiene, Faculty of Agricultural Development, Democritus University of Thrace, Orestiada, Greece.
authors.forename: Irene
authors.initials: I
authors.lastname: Theodoridou
authors.affiliation: Anticancer Hospital of Piraeus "METAXA", Piraeus, Greece.
authors.forename: Virginia
authors.initials: V
authors.lastname: Papaemmanouil
authors.affiliation: Anticancer Hospital of Piraeus "METAXA", Piraeus, Greece.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Kapsiotis
authors.affiliation: Laboratory of Microbiology, Medical School, Democritus University of Thrace, Alexandroupolis, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Panopoulou
authors.affiliation: Medical School, Democritus University of Thrace, Alexandroupolis, Greece.
authors.forename: Elisavet
authors.initials: E
authors.lastname: Stavropoulou
authors.affiliation: Laboratory of Microbiology, Biotechnology & Hygiene, Faculty of Agricultural Development, Democritus University of Thrace, Orestiada, Greece; empezirt@agro.duth.gr.
authors.forename: Eugenia E
authors.initials: EE
authors.lastname: Bezirtzoglou
authors.affiliation: Laboratory of Microbiology, Biotechnology & Hygiene, Faculty of Agricultural Development, Democritus University of Thrace, Orestiada, Greece.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Alexopoulos
keywords: E. coli; K. oxytoca; K. pneumoniae; essential oils; oregano; sage; thyme