Comparison of Inhibitory Effect of Thyme Alcoholic Extract on Verotoxin Production by Entrohemorrhagic Escherichia Coli through Reverse Agglutination and Vero Cell Culture

Introduction: The Escherichia coli O157:H7 is considered an agent responsible for the outbreak of hemorrhagic colitis and the hemolytic uremic Syndrome (HUS). This serotype belongs to the subspecies of enterohemorrhagic E. coli (EHEC). The EHEC O157:H7 produces intimin, Shiga toxins (Stx1, Stx2 or both). This study investigates the effect of thyme alcoholic extract on the growth and production of verotoxin of Escherichia coli o157:h7. We also examine cytotoxicity on the vero cell line

Materials and Methods: Extraction was performed using ethanol 85° the extract was then concentrated. For initial screening agar well diffusion assay was used. Dried extract powder was used for determination of Minimal Inhibitory Concentration (MIC) & Minimal Bactericidal Concentration (MBC) through tube dilution method in broth media. Verotoxin was produced in inhibitory concentration using VTEC-RPLA kit (Reverse Passive latex Agglutination) .Cytotoxicity on the vero cell line was performed and the result was examined using a converted microscope and was compared to the result of VTEC-RPLA kit. The procedure was repeated three times.

Results: The dried herb mean weight was 50 mg/ml and MIC&MBC was 1/64= 780µg/ml and SIC: 1/128=390µg/ml and SIC: 1/256=195µg/ml.Inhibitory zone of MIC was 13 mm. Verotoxin production in inhibitory concentration of less than 390µg/ml was totally controlled. The results of VTEC-RPLA kit and Vero cell Cytotoxicity were similar.

Conclusion: Our result indicates that thyme, as an ingredient added to the food, can affect the growth of Entrohemorrhagic Escherichia coli. This means that it could be used as a natural preservative replacing the chemical ones. Although some of the concentrations of the thyme alcoholic extract showed pronounced antibacterial activity, the introduction of it as an antibacterial compound requires further investigation.