Evaluation of reciprocal pharmaceutical effect and antimicrobial activity of Shirazi thyme essential oil against some Gram-positive and Gram-negative bacteria

Shirazi thyme with the scientific name of Zataria multiflora Boiss is an aromatic seasoning shrub related to Lamiaceae family. In traditional medicine, this herbal plant has been used as a flavoring agent, food and beverages preservative, respiratory tract infection treatment, preventing fluctuation and as antispasmodic, disinfectant and anaesthetic drug. The aim of this investigation was to assess the antibacterial activity of Zataria multiflora essential oil (ZMEO) as alone and in combination with gentamicin and chloramphenicol antibiotics against some foodborne pathogenic bacteria. To determine the mutual pharmaceutical effect of ZMEO with the gentamicin and chloramphenicol antibiotics, the sub-minimum inhibitory concentration (sub-MIC) method was used. Disk diffusion agar and well diffusion agar were also used to determine the inhibition zone diameter of ZMEO. Determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were performed using with microdilution broth and pour plate techniques, respectively. Results showed that Gram-negative bacteria had higher inhibition zone diameter as compare with Gram-positive ones. In case of simultaneous application of ZMEO with gentamicin and chloramphenicol antibiotics, the inhibition zone diameter for Listeria innocua was significantly increased. The MIC of ZMEO for Pseudomonas aeruginosa, Salmonella typhimurium, Escherichia coli, Staphylococcus aureus and Listeria innocua were determined as 0.50, 0.25, 0.50, 0.25 and 0.25 mg/mm, respectively. The MBC of ZMEO for all the pathogenic strains was 2 mg/mm. According to the result of this study, Shirazi thyme has a great potential as a preservative in food industry in addition to its application as seasoning agent and herbal-tea production.