Effects of wild Thymus vulgaris essential oil on clinical isolates biofilm-forming bacteria

Abstract

Background: A biofilm is group of bacteria embedded in a self-produced matrix made of polysaccharide and protein. Bacterial biofilms cause chronic infections because they show increased tolerance to antibiotics and disinfectant chemicals as well as resisting phagocytosis. Biofilm bacteria show much greater resistance to antibiotics than their free-living counterparts. Essential oils are a cheap and effective alternative to antibiotics that could be used to combat antibiotics resistant microorganisms. The aim of the present study was to determine the effects of essential oil of wild Thymus vulgaris grown in Jordan on biofilm-forming clinical bacterial isolates. Results: All of the isolates included in this study were able to produce a stable biofilm that adhered to polystyrene microwells. Thymus vulgaris essential oil produced inhibitory effects against all isolates with considerable variation in susceptibility. The minimum inhibitory concentration (MIC) and biofilm inhibitory concentration (BIC) values varied between 0.0625 to 2% v/v. Isolate 6 (Pseudomonas aeruginosa) was the most resistant for both planktonic and biofilm growth while isolate 4 Escherichia coli was the most sensitive. Isolate 6 was the only isolate to exhibit a specific biofilm-related response to Thymus vulgaris essential oil i.e. the minimum Thymus vulgaris essential oil concentration needed to inhibit biofilm adherence was much lower than that required to inhibit planktonic growth. For the remaining isolates, BIC for the biofilm did not differ from the MIC for planktonic. Thymus vulgaris essential oil was able to inhibit Pseudomonas aeruginosa adherence to polystyrene. Conclusions The MIC and BIC values of Thymus vulgaris essential oil show that the essential oil has strong antibacterial and antibiofilm activity. Thymus vulgaris was able to inhibit biofilm formation in the most tolerant isolate at sub-inhibitory concentrations.