Hello,
I am having contradicting data from antibacterial activity of plant extracts against selected bacteria.
Under Disc Diffusion Method, at 400mg/ml concentration, there is presence of antibacterial activity meaning apparent zones of inhibitions.
However, under MIC test, at 400 mg/ml, the result is negative meaning absence of antibacterial activity.
What factor cause this or is this simply an error?
Here are few information:
Volume of plant extracts (and its different concentrations)= 50 microliters
Volume of Microbial suspension=50 micrliters
I am looking forward for your reply and greatly appreciated it.
In my opinion, the results from the two methods are not comparable with each other. To make the data roughly comparable, you need calculate the mass of the plant extracts you used in each method. For the disc diffusion method, you added a specific volume of 400 mg/mL plant extract and you need to calculate the mass of the plant extracts. For the MIC test, there is also a mass value of the plant extract in each tube. But all in all, these values are obtained from two different testing systems, i.e. a liquid medium system and a solid agar system, so the results (MIC) are expected to be different.
By the way, other factors should be taken into consideration. First, the inoculation level of the bacteria may be different in the two methods, which may affect the results. Second, the solubility of the plant extracts also contribute to some difference in different testing systems. Also, bacteria in broth and on an agar plate may show different susceptibility to the plant extracts.
Hope this helps you
In my opinion, the results from the two methods are not comparable with each other. To make the data roughly comparable, you need calculate the mass of the plant extracts you used in each method. For the disc diffusion method, you added a specific volume of 400 mg/mL plant extract and you need to calculate the mass of the plant extracts. For the MIC test, there is also a mass value of the plant extract in each tube. But all in all, these values are obtained from two different testing systems, i.e. a liquid medium system and a solid agar system, so the results (MIC) are expected to be different.
By the way, other factors should be taken into consideration. First, the inoculation level of the bacteria may be different in the two methods, which may affect the results. Second, the solubility of the plant extracts also contribute to some difference in different testing systems. Also, bacteria in broth and on an agar plate may show different susceptibility to the plant extracts.
Hope this helps you
Thank you Yezhi Fu for the quick reply,
I just want to add tht in both MIC and Disc Diffusion, I used the same stock solution and its serial dilution. Does this means tht these are comparable?
Hi Zulfadhli Syafiq ,
- 400 mg /ml Means non-active
- Effective plant extract less than 5- 10 mg/ml.
- MIC method The most accurate. Disc Diffusion Method just for scanning
-Can be increase the Volume of plant extracts more than 50
thanks
Issam
There are many factors to take into account here .
Agar and liquid have different diffusion characteristics.
This is a very high concentration of inhibitory substance. Control experiments have to be made to ensure that the extract is not acting as a nutrient source or that it has been concentrated in such a way that the salt concentration inhibits bacteria growth or it is a side effect of the inhibition that can arise from solvents used in the extract.
Also, colonies on agar are not physiologically identical to bacteria in liquid or planktonic growth https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5352697/
Here are a few experiments on different physiologies of test bacteria and their different outcomes in inhibition tests
...https://www.ncbi.nlm.nih.gov/pubmed/23113815
and here https://www.ncbi.nlm.nih.gov/pubmed/23783562
So, the diffusion of your extract will be different in the solid (agar) and liquid MIC tests but also the diffusion of other nutrients will be different in liquid culture. If the liquid growth form is shaken then the availibility of oxygen and other nutrients to the test bacteria will also be different.
Thank you @Gerry A Quinn and @ Issam Jumaa Al-Ani for your replies. I found the attached files are interesting and helpful.
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