Hello,

The ampicillin MIC for DH10b is 8ug/ml. ref:

Article Detection and Spread of Escherichia coli Possessing the Plas...

Article A novel large plasmid carrying multiple β-lactam resistance ...

Even 50ug/ml will still have satellite colony in DH10b.. Carbencilin is easier to work with.

Delin Liang satellite colonies are a result of the non-transformed cells growing in the vicinity of transformed cells (as the transformed cells will degrade the ampicillin locally allowing their growth). He specifically asked about the MIC which is used in antibiotic susceptibility testing.

Thank you for correction Hanna Alalam

Hanna is correct, there is a big difference between the MIC and the practical useful concentration for molecular biology applications like plasmid transformation. I would also add that ampicillin in solution does not have a long shelf life, so be sure to use fresh stock solutions if you need to measure MIC's and such with accuracy.

I just want to emphasis sentence said by Michael J. Benedik " I would also add that ampicillin in solution does not have a long shelf life, so be sure to use fresh stock solutions if you need to measure MIC's and such with accuracy. " and apply it is very important to preserve and have proper copy number of plasmid and having optimized expression.

Good luck

Hello, I did several assays with ampicillin sodium salt vs E. Coli DH10B and I Found a lower Minimum Inhibitory concentration, Is it OK? I just Found one article with an 8ug/mL MIC but it says ampicillin only, if I am wrong, do you know some possible causes for the discrepancy?

There is no discrepancy, that is the same value as cited by Hanna Alalam. If you have an E. coli strain that is entirely senstitive to Amp, it would be an inhibitory concentration. However note that the MIC is not the same as the practical useful concentration for doing routine molecular biology experiments where you have plasmid carrying strains expressing enzymes that break down the ampicillin and reduce its concentration (especially locally on a plate). In that case you need to use a much higher concentration.

I got MIC between 6,25 and 3,125ug/mL for ampicillin vs E. Coli DH10B using well plate microdilution, but they got a MIC of 8ug/mL using elipson test, and I don't know why, I don't need it for molecular biology, I'm using it onlyfor microbiology testing.

Yes you might get difference since you did a liquid based test and etest is done in solid plates so it is not surprising that you got this result. I would like to add that a study has been done on factors influencing micro-dilutions test (other than the fact that they are liquid based) find it below:

https://aac.asm.org/content/63/1/e01760-18