Sub-inhibitory concentration of essential oils induces antibiotic resistance in Staphylococcus aureus

Area of Science:

• Microbiology
• Pharmacology
• Natural Products Chemistry

Background:

• Staphylococcus aureus is a significant human pathogen.
• Antibiotic resistance in S. aureus poses a global health threat.
• Essential oils (EOs) are plant-derived compounds with antimicrobial properties.

Purpose of the Study:

• To investigate the effect of sub-inhibitory concentrations of five essential oils on the antibiotic susceptibility profiles of Staphylococcus aureus.
• To determine if essential oils can induce or modify antibiotic resistance in S. aureus strains.

Main Methods:

• Fourteen wild strains of Staphylococcus aureus were treated with sub-inhibitory concentrations of five essential oils: Leptospermum scoparium (manuka), Origanum majorana (marjoram), Origanum vulgare (oregano), Satureja montana (winter savoury), and Thymus vulgaris (thyme).
• Antibiotic susceptibility was assessed using the agar disk diffusion method before and after essential oil treatment, employing a wide range of antibiotics.
• Changes in susceptibility profiles were analyzed to identify modifications induced by the essential oils.

Main Results:

• Prior to essential oil exposure, S. aureus strains were susceptible to most tested antibiotics, with exceptions for aztreonam and colistin.
• Exposure to sub-inhibitory concentrations of manuka, marjoram, and oregano essential oils resulted in significant modifications to the antibiotic susceptibility profiles.
• Winter savoury and thyme essential oils induced fewer modifications in antibiotic susceptibility compared to manuka, marjoram, and oregano.
• The study observed that essential oil-induced resistance phenomena appeared uncorrelated with specific antibiotic drug classes.

Conclusions:

• Sub-inhibitory concentrations of certain essential oils, particularly manuka, marjoram, and oregano, can alter the antibiotic susceptibility of Staphylococcus aureus.
• These findings suggest that essential oils, even at low concentrations, may contribute to the development of antibiotic resistance phenotypes in bacteria.
• Further research is warranted to understand the mechanisms underlying these phenotypic changes and their clinical implications.