Seres Therapeutics falls despite positive Phase III results with SER-109

US microbiome company Seres Therapeutics (Nasdaq: MCRB) has announced the presentation of data from its Phase III ECOSPOR III study that suggest investigational microbiome-based therapeutic SER-109 prevents recurrent C. difficile infections (rCDI) by rapidly establishing a long-lasting colony of beneficial gut microbes, which can produce fatty acids that disrupt the C. difficile lifecycle. These data were shared in oral and poster presentations at the 2022 Digestive Disease Week (DDW) Annual Meeting.

“These results suggest that our investigational microbiome therapeutic, SER-109, is a potentially fast-acting intervention that can provide durable relief from recurrent C. difficile infections when administered to vulnerable patients,” said Matthew Henn, chief scientific officer at Seres, adding: “Confirming the multiple mechanisms that bacteria in SER-109 utilize to prevent this notoriously challenging infection on the cellular and molecular level not only increases our confidence in this particular therapeutic, but it has the potential to help guide the design of the next generation of microbiome-based therapeutics.”

Investors were not that convinced, with Seres’ shares closing down 7.6% at $3.30 on Monday and a further 8.5% to $3.02 today.