What have you tried thus far? Have you tried using cycloserine-cefoxitin-fructose agar?

There is also a cheaper version CCFA-

http://jcm.asm.org/content/47/2/397.full

Tray Kannmaycine

If you are starting with a mixed culture (such as a patient sample) and really want to use antibiotics rather than enriched media, you can try to inhibit other flora by using clindamycin or cephalosporins, but this is not easy as many bacteria are resistant to these. It would be better to grow on enriched media instead, like the CCFA agar where C. diff grows as yellow "crushed glass" colonies (as Brandon Henry suggested).

We do not having any idea which clostridia it is. When we did gram staining we observed tennis rackets or drumsticks kind of structure . But when we are streaking it on columbia agar we are finding cocci pure culture, currently we are adding gentamicin at conc. Of 4mg. Do i need to change any thing in it?

What kind of sample are you using?

Industrial gel

Hi Rahoo. Why don't you try ethanol shock treatment instead? It is a standard method for recovery of Clostridium species from faeces. Add about 1 gram of your specimen to 3 mLs of 100% ethanol and vortex mix. Sit at room temperature for five minutes, then plate out onto non-selective agar. The ethanol kills everything except for Clostridium and Bacillus spores, which then grow after about two to three days incubation. Adding taurocholate to the agar you plate the ethanol/specimen solution onto will promote bacterial growth from the spores and improve yield. Avoids the issues of missing rare strains of Clostridium spp. which are sensitive to the antibiotics in your selective agar too.

Hi rahoo can you try this protocol

synthetic medium+0.2% of resazurin

link http://jb.asm.org/content/181/10/3262.full.pdf+html

Hi, it depend on your sample, but chocolate agar and brilliant green bile broth can be of a great assistant to your work..