Antimicrobial activity of Origanum ehrenbergii extracts on resistant bacterial strains -

Abstract

The aim of this thesis was to explore the antimicrobial activity of Origanum ehrenbergii essential oils and extracts on selected heat resistant bacterial strains of Escherichia coli, Staphylococcus spp. and Salmonella spp., isolated from foods in the Lebanese market. These bacterial strains were tested at 55, 60, 65, 70 and 75°C, to determine their heat resistance. E. coli strains isolated from two different sources of raw meat recorded D₆₀ of 7.32 and 28.80 minutes; D₆₅ of 0.65 and 1.02 minutes; D₇₀ of 0.50 and 0.11 minutes; and D₇₅ of 0.38 and 0.11 minutes; respectively. The Salmonella strain isolated from Tahini had D₆₀, D₆₅, D₇₀ and D₇₅ of 9.45, 0.49, 0.19 and 0.19 minutes; respectively. Two other Salmonella strains isolated from poultry samples had D₆₀ of 3.64 and 3.00 minutes; D₆₅ of 0.47 and 0.69 minutes; D₇₀ of 0.19 and 0.54 minutes and D₇₅ of 0.13 and 0.46 minutes; respectively. The Staphylococcus spp. isolated from a chicken sandwich and parmesan cheese had D₆₀ of 10.10 and 11.38 minutes, D₆₅ of 1.78 and 1.47 minutes, D₇₀ of 1.91 and 0.45 minutes and D₇₅ of 0.44 and 0.19 minutes. These results, which are higher than what is present in the literature, show that Salmonella, E. coli and Staphylococcus spp. are resistant to thermal processing. Origanum ehrenbergii was extracted using water and methanol. The extracted compounds were tested against the isolated bacterial strains to determine the inhibition zone diameter, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Essential oils obtained by hydrodistillation were more effective than methanol extracts. MICs of the former were effective at 0.1percent, 0.5percent and 1percent, compared to 1percent, 5percent and 10percent of the latter. This thesis highlights emerging concerns regarding the safety of certain food products in the Lebanese market. Subseq