Chemical Composition and Biological Activities of Tunisian Wild Rosemary (Rosmarinus officinalis L.) Essential Oils

This study was undertaken with the aim to characterize the phytochemical composition and to evaluate the antioxidant, the antibacterial and the anti-biofilm activities of Tunisian wild rosemary essential oils (REOs). The chemical composition of REOs was analyzed by GC-MS and its antioxidant activity was determined using 2, 2- diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging method. The antibacterial activity, evaluated by disc diffusion and micro-dilution method, and the anti-biofilm activity, assessed using a crystal violet test, were tested against two Gram-positive bacteria (Staphylococcus aureus and Staphylococcus epidermidis) and two Gram-negative strains (Escherichia coli and Salmonella typhimurium). Thirty-one compounds were identified in REOs which represent 95.64-97.43% of the oil. The main components of the REOs that define the chemotype were eucalyptol (40.77-55.47%), camphor (5.42-18.65%) and α-pinene (9.88- 13.83%). REOs showed antiradical activity by inhibiting DPPH radical with IC50 values ranging from 397.51 to 792.53 L/mL. The inhibition zone diameter values were determined and the results showed that all the tested REOs showed a strong activity against all bacterial strains. The minimum inhibitory concentration (MIC) varied between <0.97 and 1.95 except MIC of S. typhimurium that reached 3.9μL/mL and the minimum bactericidal concentration (MBC) ranged from 0.97 to 15.62 L/mL. Furthermore, the studied REOs showed potential anti-biofilm activities. The percentages of inhibition varied from >50% to more than 90% except for KS and KMS against Salmonella typhimurium, where the inhibition rates did not surpass the 37%. Similarly, in the eradication activity, the majority of the tested REOs were able to eradicate the bacterial preinstalled biofilms with rates attending the 92%. Rosemary EOs exhibited interesting biological activities that explain the traditional uses of bioactive molecules of this plant that could be further explored for food and pharmaceutical industries as a potential source of natural antioxidant and antibacterial bioactive compounds.