Hi:

If you have a pure substance, CLSI guidelines say you should apply two-fold agar dilution method for determination of MICs (ranging from 0.008 mgl/l to 128 mg/L).

Regards

Hi, I would suggest you to use crude extract of your plant extract as one of your control and see the antimicrobial activity. Then make a stock solution of 1mg/ml and serially dilute it from a low range to high range and go for antimicrobial activity. In this way you can narrow down the range of your extract and that will help you to find out the exact range of your extract and ultimately you will get to know the Minimum inhibitory Concentration (MIC) of your plant extract. And finally you can compare your result with Commercially available antimicrobial agents.

I hope this will help you out and do let me know whether it worked for you or not.

Dear Abiola,

In my research, I have done antimicrobial susceptibility testings of the fish pathogen F. columnare according to the CLSI-guidelines. Here the Pubmed-link to my article in which you can find the ranges of antimicrobial agents that I have used : http://www.ncbi.nlm.nih.gov/pubmed/22957716

Good luck !

Annelies Declercq

For conventional antimicrobial testing with pure substances, concentrations usually tested are double dilutions from 128 mg/L to 0.008 mg/L (15 concentrations in whole). When testing "atypical" substances, you may be conditioned by its nature(solid or liquid, pure substance or mix of substances...). If your are working with a fern extract, this is probably a mix of substances. You should check the solubility of this extract in different solvents, mainly water and organic solvents.Then, I would use double dilutions of the extract in liquid or solid agar medium.

Yes i agree with Juan you should dissolve the extract in highest concentration that is mixable with your medium. It also depend what solvent you are using. I suggest Tween 80 or DMSO (10%). If your MIC is in range from 100 to 10 microg/ml it is reasonable to search further for any active principles of your fern's.

Consider using an enzyme assay to make a quicker decision on the range of concentration that may work. In this respect a study of inhibition of total dehydrogenases in your test organism will be good. the range of concentration being 0-200mg/L. Make comparison with commercial antimicrobial agents and then take your decisions. see attached

Article Antimicrobial Properties of Euphorbia hyssopifolia and Eupho...

it is easy. just do the serial dilution starting with you plant concoction and make several tenth fold dilution . The dilution of you your concoction to show no visible growth is you MIC. Make your dilution in mg/mls. start with 1/10,1/00,1/1000 etc.

initially you have to describe facultative method like paper desc with a high concentration, according to the zone of inhibition you can guess the best range of inhibition. it almost between 1mg to 32 mg (MIC)

Get the active ingredient of the fern since it may be a mixture of many compounds. Do serial dilution and have a range to work with, then can find the MIC. DMSO 10% will help in dissolving the extract.

Thank you all for the useful answers