Morphological Changes Induced by Thymus vulgaris Essential Oil on Staphylococcus aureus Cells

Introduction: Microbial resistance to antibiotics, especially among staphylococcal strains, is a major threat to public health. Since resistance by certain strains of Staphylococcus to multiple antibiotics like methicillin emerged in the past decades, many strategies to control antibiotic resistance have been proposed. However, some staphylococcal strains have become resistant, at least to some extent, even to vancomycin – indicating a dire need for new alternative therapeutic approaches.

Purpose: To investigate the action of Thymus vulgaris essential oil on Staphylococcus aureus cell morphology.

Methods: The effect of thyme essential oil on S. aureus was evaluated by bio-assay preparation and minimal inhibitory concentrations (MICs). Morphological changes were assessed using gram staining, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 

Results: Exposure to thyme oil induced alterations in the bacterial membrane of S. aureus, which led to loss of cell wall integrity, as demonstrated by gram staining, SEM and TEM. In addition, loss of cellular contents, irregular cytoplasmic membrane, swollen cells; shrinkage of the cell, incomplete cell division and the presence coagulated material, as indicated by SEM and TEM were observed. Therefore, thyme oil when compared to antibiotics, damages the cellular membrane of S. aureus, which eventually leads to cell death. 

Significance: Thyme essential oil shows effective antimicrobial activity and is therefore considered a potential antimicrobial agent. Moreover, evidence provided in this study indicates that thyme essential oil might enhance the chances of developing new conventional and natural antimicrobial agents (drugs as well as food preservatives) and be good alternatives to synthetic chemicals.