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Basics for preparing bacterial cultures

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

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Basics for preparing bacterial cultures

Postby animus » Sun Nov 25, 2012 10:11 pm

Hello!

I would like to prepare some bacterial cultures in petri dishes to view under the microscope. However, I've never done this before and it looks more complicated than I thought. I'm mostly confused by the different nutrient agars.

I thought you could use one agar (the yellowish one) for all cultures, but I've seen sets with different colored agar gels. What are the different types used for? See here.

How do I heat the agar liquid if I'm buying it in bottles, not prepared in the dish? Is there any way to know when it's done heating?

I'm not really sure what to ask, since I've never done this before. So.. I'll start with that.

Thanks
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Postby JackBean » Sun Nov 25, 2012 11:13 pm

It's hard to say, because I don't see any description what kind of agar should it be. I would guess regular LB and the colorful bottles are there only for advertisement.

You have How-To video even on that page http://www.carolina.com/teacher-resourc ... tr11194.tr
However, I would disagree about the microwave, we use it standardly for melting agarose and agar should work as well. One just has to check that it doesn't boil. It's always good to mix the bottle during heating. By that it melts faster.
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Postby animus » Thu Nov 29, 2012 4:29 am

Ah, good information in that video! Thanks.

I found this: http://faculty.mdc.edu/jmorata/TYPES%20OF%20AGAR.pdf in case you wanted to know which bacteria are used for which type of agar. So.. you do use different agar depending on which bacterium you'd like to culture. What's the standard agar used for, then? Can you use it for all bacteria and fungi?

One more question; sorry: do you know why the bacteria are almost always swabbed on the plates in that zig-zag, overlapped design?
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Postby JackBean » Thu Nov 29, 2012 10:30 am

it's rather which agar is used for which bacteria ;)

Usage of agar really depends on bacteria you're growing, so you have to decide first.

That "design" is used to dilute the bacteria to get single colonies, so that you can see whether you have more than one species.
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Postby animus » Fri Dec 07, 2012 3:03 am

Ha yes that's what I meant. Makes sense. Seems I'm better off getting nutrient agar since there are no bacteria in particular I'd like to observe except maybe E. coli and they grow in nutrient. I thought it'd be cool to see what I can culture in a different type of agar (and, admittedly, I just think the other colors are so pretty!) but nutrient seems to host a broad enough spectrum of bacterial species.

Thanks for your help.
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