I have a rather strange problem. I tested wild type Listeria monocytogenes strain EGDe and 3 mutant strains (out of which 2 strains are erythromycin resistant for Azithromycin resistance test by broth tube dilution method in DMEM media containing 0.5% FCS. The MIC values of the erythromycin resistant strains were the same when they were grown in DMEM containing 0.5% FCS and in TSB. However, the MIC values of the wild type starin and the other mutant strain were lower in case of DMEM as compared to TSB. Can someone plz explain the reason for this difference in MIC values between DMEM and TSB ?? Plz help ASAP !!