Essential Oil Studies Involving Respiratory Tract and Anti-Microbial Action
Editor's note: These two studies show the marked antibactierial effects of essential oils, specifically on microbes that may infect the respiratory tract. While cinnamon oil was noted effective, it is an exceptionally potent oil that may burn mucous membranes. Lemongrass was also noted to have a low minimum inhibitory dose (only a little was needed for the antibacterial effect) and is a much more gentle oil, particularly if used as described in the second study: essential oils are most effective with a high vapor concentration for short periods (short periods are often frequenly repeated in aromatherapy; on the hour or every 90 minutes - this can be done with a professional nebulizing aromatherapy diffuser).
Study: Screening of the antibacterial effects of a variety of essential oils on respiratory tract pathogens, using a modified dilution assay method.
Inouye S, Yamaguchi H, Takizawa T.
Teikyo University Institute of Medical Mycology, 259 Otsuka, Hachioji, Tokyo 192-0395, Japan.
The purpose of this study was to examine the antibacterial effects of a wide variety of essential oils on major respiratory tract pathogens. The antibacterial activity of 14 essential oils and their major components was evaluated by agar-plate dilution assay under sealed conditions, with agar used as a stabilizer for homogeneous dispersion. Of the selected strains of four major bacteria causing respiratory tract infection, Haemophilus influenzae was most susceptible to the essential oils, followed by Streptococcus pneumoniae and Streptococcus pyogenes. Staphylococcus aureus was less susceptible. No cross-resistance was observed between penicillin-sensitive and penicillin-resistant S. pneumoniae. Escherichia coli, used as a control bacterium, showed the lowest susceptibility. Essential oils containing aldehyde or phenol as a major component showed the highest antibacterial activity, followed by the essential oils containing terpene alcohols. Other essential oils, containing terpene ketone, or ether, had much weaker activity, and an oil containing terpene hydrocarbon was inactive. Based on these findings, thyme (wild, red, and geraniol types), cinnamon bark, lemongrass, perilla, and peppermint oils were selected for further evaluation of their effects on respiratory tract infection.
Study:Antibacterial activity of essential oils and their major constituents against respiratory tract pathogens by gaseous contact.
Inouye S, Takizawa T, Yamaguchi H.
Teikyo University Institute of Medical Mycology, Hachioji, Tokyo 192-0395, Japan.
The antibacterial activity of 14 essential oils and their major constituents in the gaseous state was evaluated against Haemophilus influenzae, Streptococcus pneumoniae, Streptococcus pyogenes and Staphylococcus aureus. For most essential oils examined, H. influenzae was most susceptible, followed by S. pneumoniae and S. pyogenes, and then S. aureus. Penicillin-susceptible and -resistant S. pneumoniae were comparable in susceptibility. Escherichia coli, which was used as a control, showed least susceptibility. A minimal inhibitory dose (MID) was introduced as a measure of the vapour activity. Among 14 essential oils, cinnamon bark, lemon-grass and thyme oils showed the lowest MID, followed by essential oils containing terpene alcohols as major constituents. The essential oils containing terpene ketone, ether and, in particular, hydrocarbon had high MIDS.The vapour activity on short exposure was comparable to that following overnight exposure, and rapid evaporation was more effective than slow evaporation of essential oils. The vapour concentration and absorption into agar of essential oils reached a maximum 1 or 2 h after rapid evaporation. These results indicate that the antibacterial action of essential oils was most effective when at high vapour concentration for a short time.
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