Isolation and identification of antibacterial compounds from Thymus kotschyanus aerial parts and Dianthus caryophyllus flower buds

Abstract 

Aim of the study

The aerial parts of Thymus kotschyanus Boiss. and Hohen. (Lamiaceae) and flower buds of Dianthus caryophyllus L. (Caryophyllaceae) have been traditionally implemented in the treatment of wounds, throat and gum infections and gastro-intestinal disorder by the indigenous people of northern Iraq, although the compounds responsible for the medicinal properties have not been identified. In this study, antibacterial compounds from both plants were isolated and characterized, and the biological activity of each compound was assessed individually and combined.

Materials and methods

Compounds were isolated and characterized from the extracted essential oils of both plants using different spectral techniques: TLC, FTIR spectra and HPLC. The minimum inhibitory concentrations MIC values for the compounds were assessed individually and combined based on a microdilution and the checkerboard method in 96 multi-well microtiter plates.

Results

Two known compounds were isolated from the essential oils of both plants and were identified as thymol and eugenol. The isolated compounds were investigated for their single and combined antibacterial activities against seven selected pathogenic bacteria; Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Proteus mirabilis, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. Thymol MIC values ranged from 15.6 to 250.0μg/ml and B. cereus was found to be the most sensitive pathogen with a MIC value of 15.6μg/ml. Eugenol achieved stronger MIC values against most tested pathogens and the best MIC value (15.6μg/ml) was observed against B. cereus, L. monocytogenes and K. pneumoniae whereas, S. aureus, P. mirabilis and E. coli were inhibited with a MIC value of 31.2μg/ml. Combination results had antibacterial enhancement against most pathogens and the best synergistic result was seen against P. mirabilis and E. coli.

Conclusions

The isolation of two antibacterial compounds from Thymus kotschyanus aerial parts and Dianthus caryophyllus flower buds validates the use of these species in the treatment of throat and gum infections, wound-healing and gastro-intestinal disorder.

Keywords: Thymus kotschyanus, Dianthus caryophyllus, Thymol, Eugenol, HPLC, FTIR, Synergistic antibacterial activity