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Stupid question about agar... - (Nov/22/2007 )

Hi all,
I always used bacto agar to make LB agar, but this time, by mistake, I used some agar which is not bacto... It's just "plain" agar, whatever that means...
I noticed my mistake because my LB looked cloudy after autoclaving, almost like if there was bacterial growth (but that made no sense as it has just been sterilized). So I was wondering if I could use this LB : I could not find any information about the purity of the different kinds of agar, but I guess people usually use bacto agar for a reason... Thanks for your help!


as long as the medium has gone into the autoclave, it is sterile. I have a medium which is similiar in the sense that in its molten state the medium is cloudy. So don't worry.

I would guess that your LB should be okay. (I too don't know much about agar qualities.) But I believe that agar (no matter the quality) acts as a physical support for the bacteria to grow on. It doesn't really contribute much to e coli's well being.


I use "ordinary" agar for preparaing my LB plates regularly. I the medium is a bit cloudy after sterilization - its ok; just swirl the medium well before pouring the plates


We also use regular agar in LB here in the lab and it works just fine.

Never tried doing it with bacto or micro-agar though. We just use those for yeast-growing media.

I'm not even sure what the difference is between these types of agar in terms of bacterial/yeast growth...