I am using the 96-well MIC method. I diluted my plant extracts using 0.5% DMSO and I used Mueller Hinton broth to prepare the bacteria to achieve the correct log to start with but after that when I am preparing my positive control in the microtiter plate , I don't know what is accurate, putting the bacterial culture that I prepared alone (i.e. the bacteria in the broth that I prepared only) or do I have to dilute it with the same amount of DMSO as I did for my extracts?
I hope I am explaining my question clearly.
Thank you!
The bacteria in the positive control must be in the same environment as in the tested compound well. So the same amount of DMSO must be added to both positive and negative control wells.
I would recommend two control wells - a positive growth control which contains inoculum and growth medium in the same proportions as the test wells, and then a solvent control well which contains growth medium, inoculum and solvent at the same final concentration as is in the test wells. This way you can see whether the solvent alone is having an effect on microbial growth.
i do agree with Katherine A. Hammer . You need to do both. In addition, you can run a known antibiotic and a negative growth control (media with no rganism) to check your aseptic technique.
best wishes
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