Science Buddies: "Ask an Expert"

I am currently engaged in a project testing cold plasma's ability to sterilize bacteria. To do this, I decided to culture bacteria on petri dishes, then expose some of the dishes to the plasma, and leave others unexposed as a control. I documented the growth each day (see link below), and the results were definitive, but I am not sure how to quantify my data. There are no definitive colonies, so I can not just do a colony count. Any ideas on how to quantify these results?

I preformed the experiment with ML bacteria in a soy auger, but I plan to try the experiment again with Staph. Epi. and E.coli, and both these bacteria are harder to see, so photographs probably wouldn't work well.

Below is a link with photos of the results I got with ML bacteria after 48 hours (P and Q were exposed to plasma while S and T were not).
http://picasaweb.google.com/ablaty2/Day ... itrcKo_gE#


Thanks in advance,
Alex

Hi Alex,

You will probably want to use a method involving serial dilutions to enumerate your viable bacterial counts (determination of colony forming units per sample). This will allow you to differentiate between your treated and control samples. I have posted a couple of links below that explain this procedure fairly well. Please have a look at them and get back to me with any questions you may have.

http://www2.muw.edu/~lbrandon/Micro/enumeration.doc
http://fire.biol.wwu.edu/brodham/biol34 ... _week4.pdf

Hope this helps.

Mary

Hi Alex,

The first link that Mary posted has an excellent chart for your project. Most researchers do plate serial dilutions like that for counting the number of colonies when they are not sure how many to expect before doing the experiment.

One additional thing though. It seems from your pictures that the bacteria are not being spread evenly across the agar. Next time, make sure to try and spread them evenly over the entire plate, as this will make them easier to count (since it is an even distribution and over a larger surface area). The regular sterile plastic loops normally do the trick, but they also now have these disposable beads that you can put into the petri dish to evenly spread out the bacteria (it's actually quite nice, I've used them a few times). You can find them here: http://www.genlantis.com/objects/catalo ... 400050.pdf. Haha, there's even a youtube video apparently: http://www.youtube.com/watch?v=bp5ORMIHV5o.

Hope this helps!
Aaron Lin