Re: Why does eucalyptus have antibacterial properties?

Hi Natasha,
Thanks for your questions. This would make a very interesting investigation, the plant world is a great source of undiscovered compounds with medical uses and there are lots of opportunities to work in that area.

There are 2 ways to answer your first question: what are the compounds in eucalyptus that are antibacterial and how do they work? It's been known for some time that extracts of eucalyptus oil inhibit the growth of some bacteria. The simplest way to test this is to soak small paper disks in the oil and lay them on a petri plate containing a "lawn" of bacteria (spread all over the surface). Compounds in the oil diffuse out into the plate and if growth is inhibited, there will be a clear ring around each disk. You could even get some idea of how strong the inhibition is by the size of the ring.

The next step is to try and isolate some chemicals from the oil and see if they have the same effect. At http://ci.mond.org/9619/961915.h tml you can read about work done by Japanese researchers in this area. The chemicals that they isolated were called macrocarpals. Like a lot of names in organic chemistry this doesn't mean very much! It means that they are big molecules and they are named after a eucalyptus species called Eucalyptus macrocarpa. (By the way there are over 700 species of eucalypt and most of them are right here in Australia. If you get the chance to see a eucalypt forest, it's a beautiful sight). You can read some more information about chemical compounds from eucalyptus at http://onhealthnetworkcompany.com/alternative/resource/herbs/index.asp (click on E).

So, we know some of the compounds in the oil and we know that they have an effect. As to why they are antibacterial, that is still a mystery to be solved! Antibacterial compounds can work in many ways-they might interfere with building the cell walls and membranes, or inhibit protein synthesis, or inhibit some vital enzyme in the cells. The Japanese team suggest that an enzyme called glucosyltransferase is affected by some of the macrocarpals. You might like to do some web searching for this enzyme name, see what comes up!

If you'd like to do some experiments, they're quite easy provided that you can get hold of some materials. You'll need some petri dishes, some chemicals to make growth media for the bacteria and some agar to make solid plates. Then you need a source of bacteria-you'll have to decide if you want to use a single type or a mixed culture, the second is easier to grow yourself, and finally an incubator or a warm place (37 degrees is best) to grow them. You'll also need to know how to work under aseptic conditions. I guess this depends how your school is set up. If you need to know any details, you can contact me again too.

Hope this helps,
Neil Saunders