Antibacterial, antibiofilm and antiquorum sensing effects of Thymus daenensis and Satureja hortensis essential oils against Staphylococcus aureus isolates

Aims The present study was conducted to investigate the effects of Thymus daenensis and Satureja hortensis essential oils ( EO s) on the planktonic growth, biofilm formation and quorum sensing ( QS ) of some Staphylococcus aureus isolates (strong biofilm producers). Methods and Results Minimum inhibitory concentration ( MIC ) of the EO s, inhibition of biofilm formation as well as disruption of preformed Staph. aureus biofilms were assessed. The antibiofilm activity of the EO s was determined using microtitre plate test (MtP) and scanning electron microscope ( SEM ). The QS inhibitory activity was also examined on the pregrown biofilms by gene expression analysis using quantitative real‐time RT ‐polymerase chain reaction ( PCR ) of hld gene ( RNAIII transcript). Moreover, tetrazolium‐based colorimetric assay ( MTT ) was performed to detect cytotoxic effects of these EO s on the Vero cell line. Finally, the major components of the tested EO s were determined using Gas Chromatography‐Mass Spectrometry ( GC ‐ MS ). The MIC s of T. daenensis and S. hortensis EOs against planktonic cells of the isolates were 0·0625 and 0·125  μ l ml −1 respectively. The minimum bactericidal concentrations for both of the EO s was 0·125  μ l ml −1 . The MtP test showed a significant inhibitory effect of the EO s on the biofilm formation and disruption at sub‐ MIC concentrations. These results were confirmed by SEM . Real‐time PCR revealed a significant down‐regulation of hld gene following treatment with MIC /2 concentration of S. hortensis EO . GC ‐ MS analysis showed that carvacrol, terpinene and thymol were the major components of the applied EO s. Conclusions As selected EO s did not show significant cytotoxic effects even up to tenfold of MIC concentration, the applied EO s seem to be good candidates for preventing of biofilm formation of Staph. aureus cells. Significance and Impact of the Study The present study introduced T. daenensis and S. hortensis EO s as new antibiofilm, and S. hortensis EO as anti‐QS herbal agents with natural origin against Staph. aureus .