Studying the Antimicrobial Effects of Oregano and Marjoram Essential Oils Against Escherichia Coli O157:H7 and Staphylococcus Aureus in Raw Minced Beef

Abstract

Increasing consumer awareness of food safety and some of the perceived health risks associated with the use of artificial preservatives as additives in food such as meat have contributed to the increasing trend for the use of natural alternative. One of the known suitable alternatives is the use of essential oils (EOs) which are believed to have antimicrobial properties. Oregano (Origanum vulgare Lamiaceae) essential oil (OEO) and marjoram (Origanum majorana Lamiaceae) essential oil (MEO) were used in this study to determine its antimicrobial effectiveness against Escherichia coli O157: H7 (E. coli O157: H7) and Staphylococcus aureus (S. aureus) in culture and beef samples. Disk diffusion and broth dilution methods were used to determine minimum inhibitory concentration (MIC). Using the disk diffusion method, the MIC of OEO and MEO against E. coli O157: H7 were 0.06 µg/ml and 0.13 µg/ml respectively, while in case of S. aureus the MIC was 0.06 for both EO. For broth dilution, the MIC of OEO and MEO against E. coli O157:H7 was 1 µg/ml and 0.25 µg/ml respectively while for S. aureus it was 0.1 µg/ml and 1µg/ml respectively. Results showed that S. aureus was more sensitive than E. coli O157: H7 and OEO was more effective than MEO against both microbes.

The MIC averages of OEO and MEO for each method were 0.14 µg/ml and 0.55 µg/ml for E. coli and 0.12 µg/ml and 0.57 µg/ml for S. aureus respectively, were added to raw minced beef contaminated with E. coli and S. aureus. Then, also added 2xMIC then 4xMIC to observe incubation growth for a period of 14 days at temperature 37℃.