Essential oils and their antimicrobial activity

Among new therapeutic approaches based on medicinal plants and their extracts, the use of essential oils is attractive and increasingly under investigation. The essential oils, odorous and volatile products of plant secondary metabolism, have had a wide application in folk medicine, fragrance industries, as well as food flavoring and preservation, but only in recent years they have started to be recognized for their potential antimicrobial role. The essential oils therapeutic use must be accompanied by a valid scientific investigation with results that confirm the suggested therapeutic activity. We have to remember that essential oils, while giving fewer side effects, are not harmless if used incorrectly. To make a valid assessment of antimicrobial activity of essential oils and an effective comparison with conventional drugs, it is important to analyze classic microbiological parameters, such as the minimal inhibitory concentration (MIC), the bactericide/fungicide concentration (MBC/MFC), the post-antibiotic effect (PAE), the antibiogram/aromatogram, etc. Lastly, clinical experience showed that the therapeutic efficacy of conventional antimicrobial agents depends both on their direct effect on a given microorganism and on the activity of the host immune system. To eradicate the infectious agent it is important to evaluate even for essential oils their possible influence on host defense mechanisms to find compounds that are able to stimulate and not to interfere negatively with them.