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BackgroundBacterial multidrug resistance currently poses an increasingly serious threat, with important clinical consequences regarding treatment options. In 2017, the WHO released a global list of resistant bacteria, identifying multidrug-resistant (MDR) Gram-negative bacteria such as carbapenem-resistant Enterobacteriaceae, Pseudomonas aeruginosa or Acinetobacter baumannii, extended-spectrum cephalosporin-resistant Enterobacteriaceae as critical priorities for developing new strategies of treatment.PurposeThe novelty presented in this study refers to the evaluation of the volatile oil obtained from the leaves of Mentha×piperita L., on MDR strains from hospitalized patients.Material and methodsThe essential oil was extracted by steam distillation and tested on six reference bacterial strains and also on the MDR strains collected from patients of the “Pius Brînzeu” Emergency Clinical County Hospital Timișoara. The in vitro antibacterial activity was evaluated by agar disk diffusion method and microdilution method.ResultsTesting the antibacterial activity of peppermint oil on both reference strains and isolated MDR strains from hospitalized patients demonstrated its bactericidal effect. Minimum inhibitory concentration (MIC) was lower (20 mg/mL) for Staphylococcus aureus, Escherichia coli and Proteus mirabilis and higher (40 mg/mL) for Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii strains. Minimum bactericidal concentration (MBC) was equal to MIC, with the exception of Pseudomonas aeruginosa strains, where MBC was the double of MIC.ConclusionThe present study highlights the bactericidal activity of Mentha×piperita L. essential oil on all tested MDR or extensively drug-resistant Gram-positive and Gram-negative strains of Staphylococcus aureus, Escherichia coli, Klebsiellapneumoniae, Proteus mirabilis, Pseudomonas aeruginosa and Acinetobacter baumannii. This oil may be a therapeutic option in the near future for many infectious diseases produced by MDR bacteria.

This study was conducted to identify the volatile compounds of Mentha × smithiana essential oil (MSEO) and evaluate its antioxidant and antibacterial potential. The essential oil (EO) content was assessed by gas chromatography–mass spectrometry (GC-MS). Carvone (55.71%), limonene (18.83%), trans-carveol (3.54%), cis-carveol (2.72%), beta-bourbonene (1.94%), and caryophyllene oxide (1.59%) were the main identified compounds. The MSEO displayed broad-spectrum antibacterial effects and was also found to be the most effective antifungal agent against Candida albicans and Candida parapsilosis. The antioxidant activity of MSEO was tested against cold-pressed sunflower oil by peroxide, thiobarbituric acid, 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), and β-carotene/linoleic acid bleaching methods. The EO showed strong antioxidant effects as reflected by IC50 values of 0.83 ± 0.01 mg/mL and relative antioxidative activity of 87.32 ± 0.03% in DPPH and β-carotene/linoleic acid bleaching assays, respectively. Moreover, in the first 8 days of the incubation period, the inhibition of primary and secondary oxidation compounds induced by the MSEO (0.3 mg/mL) was significantly stronger (p < 0.05) than that of butylated hydroxyanisole. In silico molecular docking studies were conducted to highlight the underlying antimicrobial mechanism as well as the in vitro antioxidant potential. Recorded data showed that the antimicrobial activity of MSEO compounds could be exerted through the D-Alanine-d-alanine ligase (DDl) inhibition and may be attributed to a cumulative effect. The most active compounds are minor components of the MSEO. Docking results also revealed that several mint EO components could exert their in vitro antioxidant activity by employing xanthine oxidase inhibition. Consequently, MSEO could be a new natural source of antioxidants and antiseptics, with potential applications in the food and pharmaceutical industries as an alternative to the utilization of synthetic additives.

The origin of the steadily increasing interest that has fascinated for over a century the scientific effort of many researchers, laboratories and concerns for polyethylene glycols (PEG n) and polyoxyethylene chains (PEO), is largely due to the specific structure and properties of ethylene oxide [3,4]. A slightly colored gas at 25°C, with a sweetish odor and taste characteristic of ethers particularly at concentrations above 500 ppm in air, it is readily soluble in water, ethanol and other organic solvents. It is relatively thermally stable. In the absence of catalysts up to 300°C it does not dissociate, but above 570°C the major exothermic decomposition is recorded. Union Carbide at the beginning of the 20th century inaugurated the first production plant of EO by the air oxidation of ethylene in the presence of catalytic metallic silver. Later Shell Oil Co. replaced air with high-purity oxygen and processed EO at 200-300°C and 1-3 MPa, respectively, with an oxidation yield between 63-75% and 75-82%. The reactivity of the three-atom (two carbon, one oxygen) ether heterocycle (oxirane) (Figure 2a), also founded on the "ring tension theory", favors the nucleophilic attack of organic compounds with hydroxyl, thiol, primary and/or secondary amine, etc., function with breaking of the CO bond of the oxirane ring. Its typical reactions are with nucleophiles, which proceed via the SN2 mechanism, both in acidic (weak nucleophiles: water, alcohols) and alkaline media (strong nucleophiles: OH¯, RO¯, NH 3 , RNH 2 , RR'NH, etc.). The general reaction scheme is presented in Figure 2b. Reactions of ethylene oxide with fatty alcohols proceed in the presence of sodium metal, sodium hydroxide or boron trifluoride and are used for the synthesis of surfactants.