I just wanted to ask how to conduct a proper disc diffusion assay? Should I impregnate the extract to the disc first before I place it on the agar, or can I just directly pipette the extract to the disc on the agar?
Impregnating your disc with the extract would be my suggestion to you. Directly pipetting to the disc might lead to spilling of extract in the plate and ultimately give you a false result.
Agree with swarnendu..
Disc diffusion method is good when you are looking for qualitative analysis as you are unaware of the concentration/quantity of extract on impregnated disc. For quantitative analysis you can try agar well method where you can add known quantity of extract(10ul-20ul) into agar well and carry out your assay..
Thank you very much for your reply and advices. I tried with well diffusion assay. It seems okay. As for the disc, the inhibition is not there. I'm not sure why
Hi Candace,
What i think, the concentration that you have loaded on the disk must be lower than Minimum inhibitory concentration. you can load four or five or more disc with increasing known concentration of compound (50ug/ml, 100ug/ml, 200ug/ml,300ug/ml,400ug/ml500ug/ml) along with a standard control. than you will be able to check the concentration required for inhibition of growth of test culture. so you can very well quantify.
All the best
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