Assessment of In Vitro antibacterial activity and mic of thyme oil against gram positive and gram negative bacteria

The study was planned to evaluate the in vitro antibacterial activity and minimum inhibitory concentration (MIC) of thyme oil. Screening of thyme oil for antibacterial sensitivity and MIC against Staphylococcus aureus (ATCC 6538), Streptococcus agalactiae (ATCC 13813),Bacillus cereus (ATCC 11778),Listeria monocytogenes (ATCC 19111), Escherichia coli (ATCC 8739)and Pseudomonas aeruginosa (ATCC 9027) was carried out. ABST was performed using an 18 h culture at 37^°C in 10 ml of Muller Hinton Agar (for S. agalactiae 5% defibrinated sheep blood was added) by the disc diffusion method. The test suspension was standardized to match 0.5 McFarland turbidity standards. The thyme oil was suspended in a solution containing 10% dimethyl sulfoxide and0.5% tween 80. Under aseptic condition, empty sterilized discs were impregnated with 50 μl of different concentrations (1:1, 1:2, 1:5, 1:10 and 1:20) of thyme oil and placed on the agar plate surface. Paper disc moistened with vehicle (DMSO plus tween 80) was placed on the seeded petriplate as a vehicle control. Standard disc containing antibacterial drugs (gentamicin, tetracycline, cefpirome and ampicillin) were used as reference control. The petri plates were incubated at 37^°C for 18 h. After the incubation period, the zone of inhibition was measured. Among the tested gram positive and gram negative bacteria,Staphylococcus aureus, Streptococcus agalactiae, Bacillus cereus, Listeria monocytogenes and Escherichia coli showed the remarkable sensitivity at different concentration of thyme oil while Pseudomonas aeruginosa showed resistance. Standard antibiotics (gentamicin, tetracycline, cefpirome and ampicillin) were also found active against tested bacteria. The minimum inhibitory concentration of thyme oil was determined by micro-broth dilution technique. The results of MIC revealed that Staphylococcus aureus, Streptococcus agalactiae, Bacillus cereus, Listeria monocytogenes and Escherichia coli were inhibited with mean value of MIC 0.83±0.17, 0.83±0.17, 1.33±0.33, 0.83±0.17 and 1.17±0.44 μg/ml, respectively. However, Pseudomonas aeruginosa was found resistance.