Screening for inhibitory activity of essential oils on selected bacteria, fungi and viruses

The purpose of this study was to examine the inhibitory effect of essential oils against a broad spectrum of microorganisms including bacteria, yeast, molds, and two bacteriophage. The inhibitory effects of 45 oils on eight bacteria (four Gram positive and foul Gram negative), two fungi, and one yeast were examined using the disk assay method. Phage inhibition was measured by mixing the oils with a phage suspension, incubating the mixture at 4 degrees C for 24 h, then plating on a lawn of indicator bacteria and assaying for plaque production. Of the oils tested, all oils exhibited inhibition over activity relative to controls. However, a number exhibited only weak inhibition against several gram positive bacteria. Gram negative bacteria were generally more resistant than Gram positive bacteria to oil treatment with Pseudomonas aeruginosa being the most resistant bacteria. Only cinnamon bark (Cinnamomum zeylanicum) and tea tree (Melaleuca alternifolia) oils showed an inhibitor effect against all the test organisms and phage. Coriander oil (Coriandrum sativum) highly inhibited Gram positive bacteria and fungi. Lemongrass (Cymbopogon flexuosus) and Roman chamomile (Chamaemelum nobile) oils showed a high degree of inhibition against both phage types, while 8 oils showed no inhibition against either phage. Angelica (Angelican archangelica) and pine (Pinus sylvestris) oils inhibited the bacteria, but had no effect on any fungi. Oils that exhibited high antimicrobial properties and the broadest range of inhibition included cinnamon bark (Cinnamomum zeylanicum), lemongrass (Cymhogon flexusus), savory (Satureja montana), Roman chamomile (Chamaemelum nobile), rosenwood (Aniba rosaeodora), spearmint (Mentha spicata) and tea tree (Melaleuca alternifolia).