---
schema_version: "secwatch.filing_event.v1"
accession: "0001193125-24-217627"
form_type: "8-K"
ticker: "MCRB"
cik: "0001609809"
company_name: "Seres Therapeutics, Inc."
filed_at: "2024-09-12T23:59:59+00:00"
generated_at: "2026-05-31T05:14:16.257468+00:00"
event_type: "other_material"
sentiment: "positive"
materiality_score: 0.75
calibrated_materiality_score: 0.75
confidence: "high"
source: SEC EDGAR
---

# Seres' SER-155 reduces BSIs 10% vs 42.9% in allo-HSCT Phase 1b; seeks Breakthrough Therapy

## Summary
- SER-155 cut bloodstream infections to 10% vs 42.9% placebo (p=0.0423) in 34 evaluable patients.
- Antibiotic exposure duration significantly shorter: 9.2 days vs 21.1 days (p=0.0494).
- Febrile neutropenia incidence 65% vs 78.6% (not statistically significant).
- No treatment-related serious adverse events; drug strains engrafted in GI tract.
- Plans to seek FDA Breakthrough Therapy designation and discuss next steps for allo-HSCT.

## SEC filing metadata
- accession: 0001193125-24-217627
- form_type: 8-K
- ticker: MCRB
- cik: 0001609809
- company_name: Seres Therapeutics, Inc.
- filed_at: 2024-09-12T23:59:59+00:00
- event_type: other_material
- sentiment: positive
- materiality_score: 0.75
- calibrated_materiality_score: 0.75
- confidence: high
- sec_items: 7.01, 8.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1609809/000119312524217627/0001193125-24-217627-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1609809/000119312524217627/d887152d8k.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001193125-24-217627
- JSON: https://secwatch.observer/filing/0001193125-24-217627.json
- Plain text: https://secwatch.observer/filing/0001193125-24-217627.txt

This AI-assisted summary is a reading aid. Review the linked SEC EDGAR filing before relying on any specific claim.