Effect of Essential Oils on Growth Inhibition, Biofilm Formation and Membrane Integrity of Escherichia coli and Staphylococcus aureus

Abstract

Biofilm as a cellular conformation confers survival properties to microbial populations and favors microbial resistance. Here, we investigated the antimicrobial, antibiofilm, antimotility, antihemolytic activity, and the interaction with synthetic membranes of 15 essential oils (EOs) on <i>E. coli</i> ATCC 25922 and <i>S. aureus</i> ATCC 29213. Antimicrobial activity of EOs was determined through microdilution method; development of the biofilm was assessed using the crystal violet assay and SEM microscopy. Results indicate that <i>Lippia origanoides</i> thymol-carvacrol II chemotype (LTC II) and <i>Thymus vulgaris</i> (TV) exhibited a significant antibacterial activity, with MIC values of 0.45 and 0.75 mg/mL, respectively. The percentage of biofilm formation inhibition was greater than 70% at subinhibitory concentrations (MIC₅₀) for LTC II EO. The results demonstrate that these two oils had significantly reduced the hemolytic effect of <i>S. aureus</i> by 54% and 32%, respectively, and the mobility capacity by swimming in <i>E. coli</i> with percentages of decrease of 55% and 47%, respectively. The results show that LTC II and TV EOs can interact with the hydrophobic core of lipid bilayers and alter the physicochemical properties of membranes. The findings suggest that LTC II and TV oils may potentially be used to aid in the treatment of <i>S. aureus</i> and <i>E. coli</i> infections.