Time-kill kinetics and antibacterial activity of crude methanolic extract of Thymus daenensis Celak.

Thymus daenensis has been known to possess various medicinal properties, including antibacterial activity. This study was designed to evaluate and quantify killing kinetics and endpoint parameters of antibacterial activity of T. daenensis. A methanolic extract of T. daenensis was prepared and tested against several gram-positive and gram-negative pathogenic bacteria, using a colorimetric microdilution method. The findings revealed that except for Psudomonas aeroginosa, the 50% Minimum Inhibitory Concentrations (MIC50) inhibiting the growth of the gram-negative bacteria were significantly lower as compared to those of the gram-positive bacteria (p<0.05). By contrast, the endpoint MIC values were less different across the bacteria. Overall, the T. daenensis extract was most efficient against Bacillus cereus and Escherichia coli, whilst P. aeroginosa was the least susceptible one. The profiles of killing and re-growth of the bacteria were then assessed as functions of both time and the extract concentration (corresponding to MIC, 1/2 MIC, and 1/4 MIC). E. coli and B. cereus were completely blocked at the concentrations corresponding to MIC at less than two hours after inoculation. This inhibition pattern remained unchanged until the end of the time course. At the concentrations corresponding to 1/2 x MIC, a rapid complete inhibition was observed for E. coli, B. cereus, Staphylococcus aureus, and Enterococcus faecalis. Overall, this quantified information on dose-response rate, endpoint parameters, and kinetic profiles may provide an initial step towards understanding in vitro pharmacodynamics of antibacterial activity of T. daenensis.