Abstract
Arabian flora is a rich source of bioactive compounds. In this study, we investigated three aromatic plant species with the aim of finding valuable sources of antimicrobial agents against common pathogenic microorganisms. We focused especially on microorganisms, which cause outbreaks of infectious disease during mass gatherings and pilgrimages season in Saudi Arabia. The essential oils of three aromatic plant species were hydrodistilled from flowering aerial parts of Lavandula pubescens Decne. and Pulicaria incisa subsp. candolleana E.Gamal-Eldin, and from leaves, stems, ripe and unripe fruits of Juniperus procera Hochst. Ex Endl. They were subsequently analyzed by gas chromatography-mass spectrometry (GC-MS). The main constituents of L. pubescens were found to be carvacrol (55.7%), methyl carvacrol (13.4%), and β-bisabolene (9.1%). P. incisa subsp. Candolleana essential oil was rich in linalool (33.0%), chrysanthenone (10.3%), eugenol (8.9%), and cis-chrysanthenol (8.0%); the major components of J. procera essential oil were α-pinene (31.3–62.5%) and δ-3-carene (7.3–30.3%). These essential oils were tested against thirteen American Type Culture Collection (ATCC) strains of Gram-positive and Gram-negative bacteria using the agar diffusion assay. The only effective essential oil was that of L. pubescens and the most sensitive strains were Acinetobacter baumannii, Salmonella typhimurium, Shigella sonnei, Enterococcus faecalis and Staphylococcus epidermidis. Carvacrol, the major constituent of L. pubescens, was tested on these strains and was compared with vancomycin, amikacin, and ciprofloxacin. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) assays of L. pubescens essential oil and carvacrol revealed that Gram-negative strains were more susceptible than the Gram-positive ones.
Highlights
Plants represent valuable sources of bioactive molecules belonging to various classes of secondary metabolites
Due to the increasing presence of multidrug-resistant pathogenic microorganisms, the present study aims to test these three Essential oils (EOs) against three Gram-positive and Gram-negative bacteria to assess their potential use as alternative antimicrobial agents
The predominance of carvacrol and methyl carvacrol as the most abundant compounds in the L. pubescens EO of this study is in accordance with published compositions of the EOs hydrodistilled from several Yemeni specimens [29,30]
Summary
Plants represent valuable sources of bioactive molecules belonging to various classes of secondary metabolites. Among the physiological roles of secondary metabolites in plants, is the resistance to phytopathogens, including bacteria, fungi and viruses [1,2,3] The majority of these metabolites have the ability to interact with cellular enzymes or cell structure, causing irreversible damage to the invasive microorganisms [4,5,6]. For this reason, plant secondary metabolites have become an interesting target for the discovery of new bioactive molecules with antimicrobial effects and variable modes of action, especially after the recent emergence and growth of antibiotic resistance. EOs may represent an open frontier for advances in medicine and pharmaceutical sciences
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