Abstract
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.
Highlights
Investigating the antimicrobial activities of plant essential oils (EO) has concerned many scientific studies within the last two decades
The findings published to date, are still very fragmentary regarding a wide variety of essential oils [10]
Inhibition was generally stronger against the Gram-positive bacterium S. aureus than against Gram-negative E. coli
Summary
Investigating the antimicrobial activities of plant essential oils (EO) has concerned many scientific studies within the last two decades. Besides a few general screenings [1, 2, 3], most studies were focused on one type of essential oil only, mainly Thymus vulgaris, Origanum vulgare or Cinnamomum species. Significant activities of these and other EOs against certain foodborne pathogenic bacteria such as Escherichia coli, Listeria monocytogenes, and Salmonella typhimurium have been demonstrated [4, 5, 6]. It is difficult to reliably compare results from literature data, due to the strong variance of the used antimicrobial susceptibility testing methods This complicates the selection of the most suitable EO candidates for further antimicrobial research and applications. For this study we defined a critical minimal inhibitory concentration (MIC) of 400 μg/ml in vitro, to select EOs with the most promising suitability for future application trials
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