Screening essential oils for their antimicrobial activities against the foodborne pathogenic bacteria Escherichia coli and Staphylococcus aureus

The application of essential oils as antimicrobials is a current subject of research and a promising approach in terms of natural food preservation. Due to the diversity of EO producing plant genera and the inconsistent use of susceptibility testing methods, information on the antibacterial potency of many EO varieties is fragmentary. This study was performed to assess the minimal inhibitory concentrations (MIC) of 179 EO samples from 86 plant varieties, using a single method approach, excluding emulsifying agents. MICs were acquired in a broth microdilution assay, using a dispersion based approach to incorporate EOs in a concentration range of 6400 to 50 µg/ml. Staphylococcus aureus and Escherichia coli were used as model bacteria. At concentrations below 400 µg/ml S. aureus was inhibited by 30, E. coli by 12 EO varieties. Azadirachta indica (50 µg/ml vs. S. aureus) and Litsea cubeba (50 µg/ml vs. S. aureus, 200 µg/ml vs. E. coli) essential oils were identified as promising new antimicrobial EO candidates with significant antimicrobial activity against the two foodborne pathogenic bacteria.