Science Buddies: "Ask an Expert"

My daughter (7th grade) is doing a science fair project in which she will swab surfaces of public areas (such as drinking fountain handles, elevator buttons, etc.) and plates them to see how "dirty" our world might be. How do you suggest that she quantify her results? Her teacher has said she will loan her a microscope for home use. Thanks for your time!

You may want to check out sites like the following by googling 'bacterial growth measurement' for information and instruction to help with your project:
http://textbookofbacteriology.net/growth.html
http://www.pubmedcentral.nih.gov/articl ... tid=170070

tnshutterbug-
I hope your daughter's project is going well. If you haven't seen these already, there are several exellent projects ideas described in the "microbiology" section of the Science Buddies web page. You certainly don't have to do the projects as listed, but I'd encourage your daughter to check out the methodology for ideas on how to carefully analyze and quantify her results. Especially useful might be the projects called "How well do disenfectants work" and "Germ invasion".

Another student examining a similar problem asked us about quantifying results. The questions and answers are posted in this forum under "Tea Tree Oil vs. Chemical Disinfectants" (Dec. 29, 2006) and "Mouth Microbes Science Project" (Jan 22, 2007). The posts may also give your daughter an idea of the kinds of problems she may run into while performing her experiment.

If it is possible to distinguish individual bacterial colonies on the plates, an easy method of quantification is to count them. The back of the plate is divided into quarters and eighths with a permanent marker. If the sections seem to contain few colonies, all colonies can be counted. Otherwise the number of colonies in one or two sections is counted, and from them the number of colonies in the other sections can be estimated.

I hope your daughter's project goes well!
Sonia