Dear Maria,

I have sometimes had a similar problem when I have wanted to test the effect of an insoluble compound on the growth or behaviour of bacteria, and the simplest way is to test whether the solvent by itself has an effect, when compared to a negative control (water) in a preliminary test, or to the antimicrobials in a larger test.

This can be tested using an appropriate statistical design, rather than having to worry about trying to find other solvents or trying to get enough of the insoluble agent dissolved into water to test (ie. a chemical solution to the experimental problem).

You can undertake a post hoc analysis to compare means between the negative control and the antimicrobial treatments using a test such as Dunnett's Method with a Control to see if the effect of the antimicrobials is significantly different from the negative control. Alternatively, you could use a Turkey-Kramer HSD test to see if there is a significant difference between any treatment including the negative control. (Both of these tests assume that data is Normally distributed).

Regards, Andrew.

Thank you Andrew! Do you know any references that you would reccomend ?

Hi Maria,

I agree with Dr. Andrew, focus on the experimental design, on your controls. In any case, I recommend the book below.

Antimicrobial Susceptibility Testing Protocols by Richard Schwalbe

My only concern is that the MIC I get, could be from the active compound or from the combination of the active and the solvent. Actually I need to find a solvent that is synergistic with the active compound. How can I prove synergy between the two? Thanks for your help, guys.