Hello my dear friend. You must use the disk diffusion as screening test and then according to achievement result (from disk diffusion), setup your MIC test such as agar well.
In the other hand, at the first time, you could select and collect the resistant bacterial isolates and perform the MIC test on these isolates ( NOT ON SENSITIVE ISOLATES)
The advantage of the well diffusion assay is that you can usually load more sample at one time into a well, compared to loading a disc.
Diffusion of the phytocompound through the agar is an important factor while using well diffusion method. However, in disc diffusion, as the compound spreads predominantly on the surface, it is better suited when the diffusion of the compound is not known. Alternatively, tube dilution can be used for large volumes. This way you will also be able to determine MIC of the compound.
you can start with disc diffusion method to detect resistant strains then confirm your result by other tests like e-test ,tube dilution or agar diffusion to detect the MIC for their resistant one.
.Dear, you can start with disc diffusion method to collect all resistant strains and you can do antibiogram for selecting highly resistant rate strains, then confirm your result by agar dilution test. and you can use this equation for selecting the volume of plant extracts C1V1= C2V2. Here is a research about using plant extract
https://drive.google.com/a/koyauniversity.org/file/d/0BwA1C1U1vUb0UWN4TkktS1FRUW8/view
Disc or well diffusion tests are both qualitative assays. Hence, they wont give an accurate estimation of the effect of the antimicrobial activity of plants extracts or any other antimicrobial agent. Minimal Inhibitory Concentration (MIC) and IC50 values must be investigated for quantitative estimation. It all depends on what you are testing e.g. crude extract, protein extract, pure compounds or mixture of phenol-like compounds...doing well diffusion or disc diffusion test of crude or non-purified compound is meaningless... any plant extract would have some inhibitory activity due to the phenolic substances...
Disc diffusion for screening and agar well diffusion for MIC. You may see the link for more details.
Article Evaluation of Antibacterial Activity of Sage (Salvia officin...
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