Antimicrobial Activity of Selected Essential Oils against Selected Pathogenic Bacteria: In Vitro Study.

Area of Science:

• Phytochemistry
• Microbiology
• Natural Products

Background:

• Emergence of multidrug-resistant (MDR) bacterial strains like Escherichia coli, Staphylococcus aureus, Salmonella Typhi, and Citrobacter koseri presents a global health challenge.
• Antimicrobial agents are vital in controlling infectious diseases, but the rise of MDR strains necessitates the exploration of alternative therapeutic strategies.
• Essential oils, derived from plants, show potential as natural antimicrobial agents against pathogenic bacteria.

Purpose of the Study:

• To evaluate the antimicrobial effectiveness of four essential oils: tea tree (Melaleuca alternifolia), rosemary (Rosmarinus officinalis), eucalyptus (Eucalyptus obliqua), and lavender (Lavandula angustifolia).
• To identify the primary bioactive compounds within these essential oils using Gas Chromatography (GC) and GC-Mass Spectrometric (GC-MSD) analyses.
• To assess the efficacy of these essential oils against specific pathogenic bacterial strains and reference strains.

Main Methods:

• Agar well diffusion method was employed to screen the antimicrobial properties of the essential oils against E. coli, S. aureus, S. Typhi, and C. koseri.
• Gas Chromatography (GC) and GC-Mass Spectrometric (GC-MSD) analyses were conducted to determine the chemical composition of each essential oil.
• Minimum Inhibitory Concentration (MIC) was determined for the essential oils exhibiting antimicrobial activity.

Main Results:

• Melaleuca alternifolia essential oil was richest in terpinen-4-ol; Rosmarinus officinalis and Eucalyptus obliqua oils were rich in 1,8-cineole; Lavandula angustifolia oil contained high levels of α-terpinyl acetate.
• Tea tree oil showed significant antimicrobial activity against S. Typhi (MIC 6.2 mg/mL), C. koseri (MIC 3.4 mg/mL), and E. coli (MIC 3.1 mg/mL and 2.7 mg/mL for reference strain).
• Rosemary, eucalyptus, and lavender oils demonstrated antimicrobial activity primarily against Staphylococcus aureus ATCC 25923 (MICs 1.4 mg/mL, 2.9 mg/mL, and 2.1 mg/mL, respectively).

Conclusions:

• Most of the tested essential oils exhibited notable in vitro antimicrobial properties against the selected pathogenic bacteria.
• Tea tree essential oil demonstrated the strongest overall antimicrobial activity among the tested oils, particularly against E. coli and S. Typhi.
• Tea tree essential oil shows promise as an ecological antimicrobial agent for treating infections caused by the studied pathogens.