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Agar Plates

Posted: Mon Feb 03, 2014 10:42 am
by leighannlamb
My daughter is doing the experiment about which disinfectant works best. She has swabbed the test areas and we currently have the agar plates upside down in an incubator. Our problem is there is a lot of condensation on the agar plates. We need to log her results tonight. When we turn the agar plates right side up, is the water that has formed inside the plates going to interfere with the results? Is there anything I can do today to get rid of the condensation. Do I open the lid to the agar plates or is that not a good idea since there is bacteria growing. I was hoping to leave the lid on, but she may not be able to see the colonies as well with the lid on. What is the best practice when using agar plates. Thanks!

Re: Agar Plates

Posted: Wed Feb 05, 2014 5:45 pm
by khufker
You are probably beyond this, but there is some information on working with agar plates here http://www.sciencebuddies.org/science-fair-projects/project_ideas/MicroBio_Agar.shtml.
Condensation is definitely a common problem. Please don't open them as that is a safety concern. It may be a little harder to count the colonies, but it is not worth the risk (and possible violation of your fair's safety rules) to open the plates. Is tonight the only time you are counting the colonies or are you doing it everyday for a week or so? If today is the only day, the condensation shouldn't influence the results, especially since it should influence all of your plates the same. It may, however, make the colonies merge together faster if you are counting them over several days.
Sorry, but I don't think there is an easy fix for this one. My other piece of advice is to mark the colonies with a marker as you count them, especially since the condensation will make them more difficult to see. Just let me know if you have any other questions.
Katie

Re: Agar Plates

Posted: Thu Feb 06, 2014 7:38 am
by leighannlamb
Thank you for your reply. I only counted them on the one night so I should be ok. I do however have another question. Most colonies we observed were very faint. There were some that had truly formed and were a milky white in color. There were a couple that were yellow and one that was brown. In analyzing my cleaners how should I judge this. Do I strictly count colonies or do the ones that had truly formed a completed circle that had color to them count differently than the ones that were very faint? I was actually pleased that not much showed up. It made me feel better about the cleaners, but I feel we don't have a lot to show as results. They mostly had the faint colonies that were hard to see. Thanks for any help you can give me.

Re: Agar Plates

Posted: Thu Feb 06, 2014 5:53 pm
by khufker
The fact that there weren't many is definitely an interesting result by itself! Did you run a control by seeing how many colonies grew with no disinfectant?
Strictly counting colonies would probably be the easiest way. Most of the colonies would probably become fully developed if given more time. I would recommend pointing out how some of the colonies differed in color or how well formed they were, but I wouldn't count them separately.
You don't need to worry about having tons of results for an elementary school project. I would say that a simple table, a bar graph, and pictures of all of the plates would be great. I would also include some simple observations like the differences between the colonies and the condensation on the plates.
Good Luck!

Re: Agar Plates

Posted: Fri Feb 07, 2014 8:16 am
by leighannlamb
OK. Thank you so much. We did run a control with distilled water. It of course had the most, but I was confused that it only had one that had truly formed but several that were faint. I would have expected it to have the most that had formed with color. One of my plates only had 1, but it it was very well formed, while there was one that had 2 faint and another that only had 3 faint. So would you say that the one that only had one did the best even though it had a true colony growing where the others were just starting to form. I had another that had 3 that had true colonies with all three colors, pale white, yellow and brown, but I saw no other evidence of other beginning to grow. I felt like this one did not do good since the colonies were so distinct and full of color, but should I list this better than ones that had more faint colonies beginning to grow? If I do just count the colonies, it would make more sense due to the control having several even though only one had truly formed. I was just getting confused by the size and colors of some of them. I guess since it was just 3 days, they just had not had time to fully develop.

Thanks for all your help.

Re: Agar Plates

Posted: Fri Feb 07, 2014 3:59 pm
by khufker
What you are doing is great! Graph the results using only the number of colonies, but also include all of the details you just gave me in the report and through photos of the plates.