A new method for determining the minimum inhibitory concentration of essential oils

A new microdilution method has been developed for determining the minimum inhibitory concentration (MIC) of oil‐based compounds. The redox dye resazurin was used to determine the MIC of a sample of the essential oil of Melaleuca alternifolia (tea tree) for a range of Gram‐positive and ‐negative bact...

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Bibliographic Details
Published inJournal of applied microbiology Vol. 84; no. 4; pp. 538 - 544
Main Authors Mann, C.M., Markham, J.L.
Format Journal Article
LanguageEnglish
Published Oxford, UK Blackwell Science Ltd 01.04.1998
Blackwell Science
Subjects
Biological and medical sciences
General pharmacology
Gram-Negative Bacteria - drug effects
Gram-Positive Bacteria - drug effects
Indicators and Reagents - metabolism
Medical sciences
Melaleuca alternifolia
Microbial Sensitivity Tests
Oils - pharmacology
Oxazines - metabolism
Pharmacognosy. Homeopathy. Health food
Pharmacology. Drug treatments
Xanthenes
Pharmacognosy
Color indicator
Method
Biological activity
Antimicrobial agent
Medicinal plant
Dicotyledones
Angiospermae
Minimum inhibitory concentration
Plant origin
Myrtaceae
Spermatophyta
Essential oil
Antibacterial agent
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Summary:A new microdilution method has been developed for determining the minimum inhibitory concentration (MIC) of oil‐based compounds. The redox dye resazurin was used to determine the MIC of a sample of the essential oil of Melaleuca alternifolia (tea tree) for a range of Gram‐positive and ‐negative bacteria. Use of 0·15% (w/v) agar as a stabilizer overcame the problem of adequate contact between the oil and the test bacteria and obviated the need to employ a chemical emulsifier. A rapid version of the assay was also developed for use as a screening method. A comparison of visual and photometric reading of the microtitre plates showed that results could be assessed without instrumentation; moreover, if the rapid assay format was used, rigorous asepsis was not necessary. Accuracy of the resazurin method was confirmed by plate counting from microwells and MIC values were compared with results obtained using an agar dilution assay. The MIC results obtained by the resazurin method were slightly lower than those obtained by agar dilution.
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ISSN:1364-5072
1365-2672
DOI:10.1046/j.1365-2672.1998.00379.x