Mic
 

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 !!

Re: Mic
 

Not sure why you're using DMEM (assume Dulbecco's modified) as it's a cell culture medium but interesting observation. what were the MIC's?

Re: Mic
 

Jorge1907 : Thank you for your interest.

I wanted to be sure that these are the correct MIC values. I infect the cells with these bacteria in DMEM containing 0.5% FCS, so I tested the MIC values again in DMEM cntaining 0.5% FCS. The MIC values were:

Listeria monocytogenes wild type (TSB) : 0.125-0.5 µg/ml
L.m. wild type (DMEM) : 0.004-0.002 µg/ml

Re: Mic
 

That's pretty profound a difference. Have you repeated?

Re: Mic
 

Yes, I did this in duplicates and repeated thrice.

Re: Mic
 

In your knowledge, does media affect MIC values ? Or should they be the same irrespective of the media used ?

Re: Mic
 

Not to the extent you;ve reported.

Re: Mic
 

What do you suggest I should do ?

Re: Mic
 

Have you made growth curves in both media. It is possible that your growth is reduced in your DMEM as this is not the suitable media for Listeria. If you evaluate your mic at the same time point for both media, you will get a lower value. It is also possible that this growth reduction is strain specific due to different metabolic pathways being present. So before drawing any conclusions, make some growth curves of both strains in both media and compare those.