It would be technically possible to culture P. acnes from a friend; however, for purposes of a science fair project, it would make getting approval much more challenging. Culturing unknown bacteria requires preapproval and access to a BSL-2 laboratory. If you want to try this, you should write up your project proposal and submit it for approval right away. There are lots of unknown microorganisms on human skin and you would have a lot of work to do to verify the identity of P. acnes. http://www.sciencebuddies.org/science-f ... ents.shtml
However, it would be easier to obtain a pure culture of an organism so you can work in a BSL-1 laboratory. Carolina Biologicals sells a garden variety E. coli for classroom use that is easy to grow.http://www.carolina.com/product/living+ ... estMatches
Micrococcus luteus is another possible organism, and it is a Gram positive bacterium like P. acnes.http://www.carolina.com/product/living+ ... y=ourPicks
P. acnes is available from the American Type Culture collection, but it prohibitively expensive. It might be possible to obtain a culture from a laboratory that has this organism in their stock culture collection. http://www.atcc.org/ATCCAdvancedCatalog ... e=bacteria
Your idea of making infusions of the herbs is a good idea. Have you tried searching for the chemical composition of the herbs to identify what components might be effective antimicrobial agents? Since acne is an inflammatory response to the presence of the microorganism, some acne medications are anti-inflammatory compounds and you would not expect to see any effect of these compounds on microbial growth. If a compound works against E. coli, you would not be able to say for sure that it would work against P. acnes.
If you are going use a light bulb as a source of heat for your incubator, you need to make sure that the temperature does not exceed the maximum limit for the microorganism that you are using. It is easy to “cook” bacteria and kill them. The optimum temperature for E. coli is about 37 degrees Centigrade, and the maximum is in the low 40’s degrees C. It would be better to have an incubator that is a little cooler to ensure survival. Be sure to test your incubator and verify that it will maintain a temperature between 30 and 37 degrees C.
What are you going to use as a control? How are you going to measure your results?