In recent years, there have been a number of studies looking at inhibition of microorganisms by spices, herbs or their extracts.  Many of these products have been shown to have antimicrobial activity against foodborne pathogens.  The purpose of this research was to evaluate the antimicrobial activity of three essential oil (EO) compounds (thymol, eugenol, and trans-cinnamaldehyde) alone and in combination with three naturally-occurring apple aroma (AA) compounds (hexanal, trans-2-hexenal and 1-hexanol) to identify the minimum inhibitory concentrations necessary to inhibit E. coli O157:H7.  Three commercial apple juice flavoring mixtures (natural apple cinnamon, natural apple spice and natural red apple) were additionally tested alone for antimicrobial activity against E. coli O157:H7. The standard agar dilution method (SAD) and checkerboard assay were used to evaluate the efficacy of the nine compounds, alone and in combination against E. coli O157:H7.  In general, the EO compounds were significantly more effective against E. coli O157:H7 than the AA compounds (P<0.05).  Cinnamaldehye, with an MIC of 0.2 mg/mL, exhibited the highest degree of activity, followed by thymol, eugenol and trans-2-hexenal, which each had individual MIC values of 1.6 mg/mL.  No synergism was found in the combinations of EO compounds with AA compounds. / Master of Science in Life Sciences