Seres Health Inc. is administering a range of bacteria to recreate a healthy microbiome in the gut of patients with Clostridium difficile. Rather than replicate the exact flora that existed before infection, the company is trying to restore the microbial protein expression profile, regardless of which bacteria produce the proteins.

C. difficile infection occurs in patients treated with traditional antibiotics. C. difficile often is present in the gut in small amounts. But antibiotics kill not only the target infection but also the desirable bacteria naturally present in the gut that keep C. difficile in check.