I just did an antibacterial diffusion test of some plant extract. The result shows no inhibition zone at 100% concentration, but there are some inhibition zones at 50%. Is this a credible result? Is there a theory about this? Is the extract too viscous to diffuse? What should I do?
Based on the information provided, it is not possible to answer the question.
Go for well difusion method and also repeat your experiment on disc diffusion.
Well difusion gives better results as some large particles can not diffuse easily in media.
What agar diffusion method did you use (spot-on-lawn, well-assay, disc assay, agar dilution)? That influences both your results and the factors that could explain your observations.
A word of caution: diffusion of complex samples, like a crude plant extract in the agar does not depend exclusively on viscosity. If you're using a relatively crude extract, other factors may be at play, but you need to give us more information in order to obtain an informed, useful contribution.
I would also recommend performing a literature search on the best method for your type of extract. You could start with Article Critical analysis of current methods for assessing the in vi...
. Often, broth microdilution methodologies yield better results, because they circumvent the effect of the diffusion rate of different compounds through the agar.Also, some authors simply start with the 50% solution of their materials because 100% is a) impractical (viscosity, etc.), b) does not represent the reality of the envisaged practical uses.
Overall, I would advise you to base your decision on which will be your next steps on a solid literature review and on the objectives of your work.
Best wishes!
The viscocity is a highly important parameter withinthe cell membrane ,affecting the diffusion of small molecule.more the viscocity of the medium ,more difficult it is for molecule to move, then less is the diffusion rate.
You describe the procedure very generally. What method do you use? What bacteria do you use in test? How do you store and culture them for the test? Also, the sensitivity of bacteria to different substances is not the same. Can you try using a different bacterial representative, gram negative versus gram positive bacteria?
https://www.scielo.br/j/bjm/a/Dh8Ry8WX4vc6QmXBddcwccQ/?format=pdf&lang=en
Do you have the same or similar lab methodology?
Well diffusion method recommended for plant extract antimicrobial testing
The viscosity could be a direct representation of the concentration. If a substance is too concentrated it could affect the results of susceptibility test because of the inability of the active constituents to freely diffuse into the agar thus directly affecting the results for susceptibility test. This is why it is recommended to test at different concentrations. I hope this answer your question. All the best...
Tika Rahmadita I have met similar fact when antibacterials interacted with medium compounds in the narrow pH range. You can repeat the experiment with 2-3 different media suitable for bacterial growth or normalize pH of plant extracts using buffer.
You have to repeat the test. I haven't experienced such before.
You should be able to observe viscosity.
For some antibacterials - e.g. quaternary ammonium compounds and povidone iodine - the concentrated solution has greatly diminshed activity due to its critical micelle formation, the break point being the critical micelle concentration. Not sure that would be expressed in zon eof inhibition testing.
Are ypu seeing any precipitation in the concentrated material?
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