New Insight into the Chemical Composition, Antimicrobial and Synergistic Effects of the Moroccan Endemic Thymus atlanticus (Ball) Roussine Essential Oil in Combination with Conventional Antibiotics.

Asad Syed,Ahmed Nafis,Luísa Custódio,Lahcen Hassani,Marcello Iriti,Lahcen Ouchari,Noureddine Mezrioui,Fatima El Otmani,Najat Marraiki,Abdallah M. Elgorban

doi:10.3390/molecules26195850

Abstract

This study reported the volatile profile, the antimicrobial activity and the synergistic potential of essential oil (EO) from the Moroccan endemic Thymus atlanticus (Ball) Roussine, in combination with the antibiotics ciprofloxacin and fluconazole for the first time, to the best of our knowledge. The EO chemical composition was determined by gas chromatography coupled to mass spectrometry (GC-MS) analysis and the antimicrobial activity assessed by the disc diffusion method against three Gram positive (Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus) and three Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli and one clinical isolate, Klebsiella pneumonia). The antifungal activity was evaluated in four pathogenic yeasts (Candida albicans, C. glabrata, C. krusei and C. parapsilosis). The minimum inhibition concentration (MIC) and the synergistic effect with ciprofloxacin and fluconazole were determined by the two-fold dilution technique and checkerboard test, respectively. Twenty-one constituents were identified by GC-MS in the EO, including carvacrol (21.62%) and borneol (21.13%) as the major components. The EO exhibited a significant antimicrobial activity with inhibition zones ranging from 0.7 mm to 22 mm for P. aeruginosa and B. subtilis, respectively, and MIC values varying from 0.56 mg/mL to 4.47 mg/mL. The fractional inhibitory concentration index (FICI) values ranged from 0.25 to 0.50 for bacteria and from 0.25 to 0.28 for yeasts. The maximum synergistic effect was observed for K. pneumonia with a 256-fold gain of antibiotic MIC. Our results have suggested that EO from T. atlanticus may be used alone or in association with antibiotics as a new potential alternative to prevent and control the emergence of resistant microbial strains both in the medical field and in the food industry.

Highlights

Morocco is an important reservoir of biodiversity and Mediterranean speciation with an important flora of around 3913 taxa, including 1298 subspecies in 981 genera and155 families
The essential oil (EO) chemical composition was determined by gas chromatography coupled to mass spectrometry (GC-MS) analysis and the antimicrobial activity assessed by the disc diffusion method against three Gram positive (Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus) and three Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli and one clinical isolate, Klebsiella pneumonia)
The EO exhibited a significant antimicrobial activity with inhibition zones ranging from 0.7 mm to 22 mm for P. aeruginosa and B. subtilis, respectively, and minimum inhibition concentration (MIC) values varying from 0.56 mg/mL to 4.47 mg/mL

Summary

Introduction

Morocco is an important reservoir of biodiversity and Mediterranean speciation with an important flora of around 3913 taxa, including 1298 subspecies in 981 genera and155 families. The genus Thymus, belonging to the Lamiaceae family, is widely distributed in Morocco with 11 endemic species, including Thymus atlanticus (Ball) Roussine, locally known as “Azukni”. This thyme species is characterized by very small white or pale pink flowers with revolute leaves or subplanes, glabrescent and in the form of a condensed carpet. It is the smallest of the Moroccan thymes, and very polymorphic depending on altitude and ecology, growing between 1700 to 3400 m [2]. To the best of our knowledge, the antimicrobial activity of T. atlanticus has never been evaluated

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