Athanasios C. Kimbaris

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

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.

Increased Seizure Latency and Decreased Severity of Pentylenetetrazol-Induced Seizures in Mice after Essential Oil Administration

The effect of pretreatment with essential oils (EOs) from eight aromatic plants on the seizure latency and severity of pentylenetetrazol- (PTZ-) induced seizures in mice was evaluated. Weight-dependent doses of Rosmarinus officinalis, Ocimum basilicum, Mentha spicata, Mentha pulegium, Lavandula angustifolia, Mentha piperita, Origanum dictamnus, and Origanum vulgare, isolated from the respective aromatic plants from NE Greece, were administered 60 minutes prior to intraperitoneal (i.p.) injection of a lethal dose of PTZ to eight respective groups of Balb-c mice. Control group received only one i.p. PTZ injection. Motor and behavioral activity of the animals after EOs administration, development of tonic-clonic seizures, seizure latency and severity, and percentage of survival after PTZ administration were determined for each group. All groups of mice treated with the EOs showed reduced activity and stability after the administration of the oil, except for those treated with O. vulgare (100% mortality after the administration of the oil). After PTZ administration, mice from the different groups showed increased latency and reduced severity of seizures (ranging from simple twitches to complete seizures). Mice who had received M. piperita demonstrated no seizures and 100% survival. The different drastic component and its concentration could account for the diversity of anticonvulsant effects.

Mode of Antimicrobial Action of Origanum Vulgare Essential Oil Against Clinical Pathogens

Oregano essential oil (EO) was extracted via hydro-distillation from Origanum vulgare aromatic plant and tested for its mode of action against 16 clinically isolated strains of Escherichia coli and Staphylococcus aureus (Methicillin resistant and non-methicillin resistant). Initially, Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were estimated by the broth micro-dilution method. Additionally, the extracellular concentrations of total proteins were measured in bacterial suspensions with the presence of EOs near the MIC concentrations and without the presence of EOs by using the Bradford protein assay. Ampicillin was used as a positive control. Most of S. aureus and almost half of E. coli strains exhibited relatively low MIC values when tested with the EO of oregano. Based on the protein assay a 65% of E. coli strains but over 80% of S. aureus strains exhibited a clear dose-response curve indicating that the mode of action was the disruption of the cytoplasmic membrane and cell wall. Differences in sensitivities of Gram(-) and Gram (+) bacteria on the action of EOs are known with the later been more sensitive than Gram (-). However, MRSA strains were proven resistant to the EOs when compared with their non-MRSA counterparts. Current research in nutrition and Food science Journal Website: foodandnutritionjournaal.org ISSN: 2347-467X, Vol. 05, No. (2) 2017, Pg. 109-115 COntACt Athanasios Alexopoulos alexopo@agro.duth.gr Democritus University of Thrace. Department of Agricultural Development, Laboratory of Microbiology, Biotechnology & Hygiene. 193 Pandazidou Str, GR68200, Orestiada, Greece.© 2017 The Author(s). Published by Enviro Research Publishers This is an Open Access article licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License (https://creativecommons.org/licenses/by-nc-sa/4.0/ ), which permits unrestricted NonCommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. To link to this article: http://dx.doi.org/10.12944/CRNFSJ.5.2.07 Article history Received: 14 July 2017 Accepted:19 August 2017