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Interference of selective medium

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#1 mjones



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Posted 22 October 2014 - 08:54 AM



I have some questions related to classical microbiology.

Can I prepare a bacterial suspension for a disk diffusion susceptibility testing from a blood agar plate? Is there any inconvenient? All guidelines say that I should use "non-selective medium" but that is how far they go. Is there any official document stating what kinds of mediums can be used?


In a related matter, is there any problem on extracting DNA from a selective medium plate? Can that interfere with PCR reactions somehow? Again, do you know about any document that state that?


Thanks a lot.



#2 bob1


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Posted 22 October 2014 - 11:58 AM

Non-selective means a medium that doesn't contain selective agents such as antibiotics, especially the ones you would be testing, or related ones (e.g. don't take from a penicillin plate if testing ampicillin), blood agar is a non-selective medium.


There shouldn't be a problem with DNA extraction from a selective plate, but you will find that you get better yields from broth cultures. If extracting from colonies on a plate you have to be very careful not to take any of the agar as this will often contain things that can inhibit PCR.

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