Seres Therapeutics Unveils Preclinical Data for SER-428 at IDWeek…

Event summary

Seres Therapeutics will present preclinical data for SER-428, an investigational live biotherapeutic, at IDWeek 2026 on October 22.
SER-428 demonstrated up to a 1,000-fold reduction in Enterococcus faecium and Klebsiella pneumoniae in preclinical models.
The liquid formulation of SER-428 is designed for critically ill patients who cannot take oral capsules.
Seres is planning a Phase 1b trial for SER-428 in Medical Intensive Care Unit (MICU) patients, pending funding.

The big picture

Seres Therapeutics is leveraging its experience with SER-155 to develop SER-428, targeting a high-risk patient population prone to bloodstream infections. The company's focus on live biotherapeutics aligns with broader industry trends toward microbiome-based therapies, particularly in infectious disease prevention. The success of SER-428 could expand Seres' portfolio beyond oncology into critical care, a market with significant unmet needs.

What we're watching

Clinical Development: Whether Seres can secure funding to advance SER-428 into Phase 1b trials and demonstrate efficacy in critically ill patients.
Market Positioning: How SER-428's liquid formulation differentiates it from SER-155 and addresses unmet needs in the critically ill population.
Regulatory Pathway: The pace at which Seres can navigate regulatory hurdles for SER-428, given its novel formulation and target population.