Antistaphylococcal activity of Thymus vulgaris and Origanum vulgare essential oils: time-lapse kinetics, antibiofilm activity and synergistic potential

Staphylococcus aureus is one of the most frequent human pathogens, whose high virulence and severity of chronic infections are related to their ability to produce biofilms. In the present study, antimicrobial potential of oregano and thyme essential oils on the planktonic growth of S. aureus clinical strains (isolated from nose, throat and wound), as well as the effect of the oils on the biofilm production, compared with conventional antibiotic streptomycin were investigated. In addition, time-lapse kinetics and combinations of individual oils with streptomycin were investigated for synergism against the selected staphylococcal strains. The results showed high potential of both oils where minimal inhibitory values ranged between 0.078 and 2.50 mg/ml, while biofilms were reduced up to 96%. In the case of biofilms, the reverse concentration dependency has been observed. Time-lapse kinetics showed recovery of some strains after 4 h of contact with the oils, but these strains demonstrated significantly reduced growth in comparison to the control. All mentioned assays showed slightly higher efficacy of oregano essential oil. Calculated FICs showed either synergistic or additive effect of all tested combinations (thyme-oregano, thyme-streptomycin, oregano-streptomycin), with the thyme-streptomycin as the most efficient one. All mentioned results point to a very high potential of both oils to be used as an adjuvant agent for control of human staphylococcal infections.