I want to screen antimicrobial activity of certain extracts, and i choose to do agar well diffusion method. For positive control, can I used the standard antibiotic and placed it on the agar, instead of using antibiotic solutions in the respective wells? thanks in advanced! =)
There is a compromise solution, you can make a hole with the same size of the disk for all assays. Then you can place a disk in the hole and add the same vehicle solvent or buffer that you use for your extract. The antibiotic will diffuse out from the disk to the solvent and to the agar. It should work. I hope this helps.
You can refer to the following links to get certain valuable informations:-
1. www.ijmm.org/documents/Antimicrobial.doc
2. https://books.google.co.in/books?isbn=9814354864
3. http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1517-83822007000200034
dissolved the commercial disk in 100ml solvent that you used for extraction and use as control.
Yes you can use the commercial disc as you control but it is advisable to use the same experimental method for your control so that you can monitor and draw your inference if same procedure is used for both the control and the experiment. In as much you can use the commercial disc method for your control, it is not advisable for this experiment but the agar well diffusion method will be better for easy comparison of parameters in the experiment. Hope this help.
As to using antibiotic discs and placing it on the agar as a control for your analysis. The answer is No. Experimental conditions for test and control should be as close as possible so that the conclusion of your results can be valid. You have to use a solution in a well, either of the powder or disc of the standard antibiotic as already suggested for you. I will suggest you check and follow the current CLSI guidelines.
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