Actually we have 100 micro-liter RPMI, 50 micro-liter oil and 50 micro-liter bacteria. I don't want to have any effect of this solvent on viability of bacteria as well as cells.
I don't think you can use MTT for this experiment considering its a two-step assay: step 1: you have to add MTT to your cells, step 2- dissolve the formazan crystals formed by the reduction of MTT in a suitable solvent such as DMSO. Therefore, I believe that MTT is most appropriate for monolayer cell cultures and not for suspension cultures.
For your assay I would suggest MTS which is based on similar principle, but single step i.e you can directly read your plate in aqueous solution after adding MTS.
First of all, thank you for your suggestion. Actually, I want to know how I can dissolve oil in RPMI. I have googled it and I found some suggested solvents such as DMSO and ethanol. As you know these solvents have detrimental effect on viability of bacteria as well as cells during cell exposure period (treatments) before adding MTT solution.
Additionally, I already added DMSO (5%) to dissolve oil, but it didn’t work properly.
as you mentioned, you can use DMSO and ethanol for solving oil. but not more than 2% of cell culture media, in some case you can use 5% of cell culture media. the amount of DMSO or ethanol is dependent to your cell sensitivity. first of all, you should solve your oil on DMSO and after that you should add cell culture media as much as need