New project aims to develop a liquid oral formulation of SER-155 to prevent gut-derived antimicrobial-resistant infections in ICU settings

(BOSTON: December 2, 2025) – Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator (CARB-X) has awarded Seres Therapeutics, Inc. up to US$3.6M in funding to support the development of a novel live biotherapeutic, SER-155-LF, formulated for oral liquid delivery to prevent gut-seeded antimicrobial-resistant (AMR) infections in patients in the medical intensive care unit (ICU).

SER-155-LF is designed to target specific microbial functions to improve gastrointestinal epithelial barrier integrity and reduce pathogen colonization to prevent bacterial translocation of gastrointestinal pathogens such as Escherichia coli into the bloodstream without increasing AMR organism carriage.

In 2017, CARB-X welcomed SER-155 into the portfolio and supported the development of this FDA Breakthrough Therapy Designated biotherapeutic to prevent life-threatening bacterial infections and graft versus host disease in patients following solid organ and allogeneic stem cell transplantation. This new award will advance the development of an oral, liquid formulation broadening the potential use of this drug in medically compromised patients at high-risk of AMR infections. In addition, the new funding and support will position the program for clinical evaluation in ICU patients through a Phase 1b clinical trial designed to evaluate safety, engraftment, and exploratory endpoints related to E. coli colonization and antimicrobial resistance.

“We are pleased to support Seres Therapeutics in advancing the development of a novel live biotherapeutic designed to prevent infections in critically ill patients,” said Richard Alm, PhD, Interim Chief of R&D at CARB-X. “Preventing infections without contributing to antimicrobial resistance represents an important goal, and this project should help expand our understanding of how microbiome-based approaches may play a role in achieving that.”

“We are proud to partner with CARB-X to advance live biotherapeutic medicines designed to target microbe-host functional interactions that can protect medically vulnerable patient populations from bloodstream and AMR infections,” said Marella Thorell and Tom Derosier, Co-Chief Executive Officers of Seres Therapeutics. “Support from CARB-X will support development of a novel oral, liquid formulation of SER-155 for use in intensive care and other settings serving patients unable to swallow a capsule, where preventing infections without driving antimicrobial resistance could have transformative benefits for both patient outcomes and the healthcare systems.”

In March 2024, CARB-X launched a new funding solicitation designed to fill major R&D gaps in the global antibacterial development pipeline. More than 300 initial applications were accepted in four distinct product themes: therapeutics for infections caused by Gram-negative pathogens, novel approaches to the prevention of invasive disease caused by Staphylococcus aureus or E. coli, diagnostics for neonatal sepsis, proof-of-concept for novel sample types for diagnosing lower-respiratory tract infections. Ten awards were announced from the first cycle of the 2024 funding round. Additional projects from the second cycle will be announced this year. CARB-X will begin accepting applications for the second cycle of the 2025 funding round from December 1 to December 12.  Register for the CARB-X newsletter to receive updates.

When CARB-X was founded in 2016, the early-stage antibacterial pipeline was stalled. Since its inception, CARB-X has supported 119 R&D projects in 15 countries, and CARB-X product developers have made significant progress: 22 projects have advanced into or completed clinical trials; 14 remain active in clinical development, including late-stage clinical trials; and 3 products have reached the market. Additionally, more than 10 product developers with active R&D projects have already secured advanced development partnerships to support their clinical development after leaving the CARB-X portfolio. All CARB-X-funded product developers are contractually obligated to develop a Stewardship and Access Plan for their product, outlining strategies to ensure responsible stewardship and appropriate access in low- and middle-income countries.

CARB-X is funded in part with federal funds from the U.S. Department of Health and Human Services (HHS); Administration for Strategic Preparedness and Response; Biomedical Advanced Research and Development Authority (BARDA) under agreement number 75A50122C00028 and by awards from Wellcome (WT224842), the UK Department of Health and Social Care’s Global Antimicrobial Resistance Innovation Fund (GAMRIF), the Gates Foundation, Germany’s Federal Ministry of Research, Technology and Space (BMFTR), the Public Health Agency of Canada (PHAC), the Novo Nordisk Foundation, Italy’s Ministry of Economy and Finance (MEF), and Japan’s Ministry of Health. The U.S. National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH) in HHS, provides support in the form of in-kind services through access to a suite of preclinical services for product development. The content of this publication is solely the responsibility of the authors and does not necessarily represent the official views of any CARB-X funders.

CARB-X Contact: Marissa Novel, carbxpr@bu.edu

Seres Contact: IR@serestherapeutics.com

About CARB-X

CARB-X (Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator) is a global non-profit partnership dedicated to supporting early-stage antibacterial research and development to address the rising threat of drug-resistant bacteria. CARB-X supports innovative therapeutics, preventatives and rapid diagnostics. CARB-X is led by Boston University and funded by a consortium of governments and foundations. CARB-X funds only projects that target the most serious, resistant bacteria identified on global priority lists, syndromes with the greatest global morbidity and mortality, and performance characteristics necessary for patients. https://carb-x.org/ | X (formerly Twitter) @CARB_X

About Seres Therapeutics, Inc.

Seres Therapeutics, Inc. (Nasdaq: MCRB) is a clinical-stage company focused on improving patient outcomes in medically vulnerable populations through novel live biotherapeutics. Seres led the successful development and approval of VOWST™, the first FDA-approved orally administered microbiome therapeutic, which was sold to Nestlé Health Science in September 2024. The Company is developing SER-155, which has received Breakthrough Therapy designation for the reduction of bloodstream infections in adults undergoing allo-HSCT and Fast Track designation for reducing the risk of infection and graft-versus-host disease in adults undergoing allo-HSCT, and which has demonstrated a significant reduction in bloodstream infections and related complications (as compared to placebo) in a Phase 1b clinical study in patients undergoing allo-HSCT. SER-155 and the Company’s other pipeline programs are designed to target multiple disease-relevant pathways and are manufactured from standard clonal cell banks via cultivation, rather than from the donor-sourced production process used for VOWST. In addition to allo-HSCT, the Company intends to evaluate SER-155 and other cultivated live biotherapeutic candidates in other medically vulnerable patient populations including autologous-HSCT patients, cancer patients with neutropenia, CAR-T recipients, individuals with chronic liver disease, solid organ transplant recipients, as well as patients in the intensive care unit and long-term acute care facilities. For more information, please visit www.serestherapeutics.com.

About BARDA and NIAID

The U.S. Department of Health and Human Services (HHS) works to enhance and protect the health and well-being of all Americans, providing for effective health and human services and fostering advances in medicine, public health, and social services. The Administration for Strategic Preparedness and Response (ASPR) leads the nation’s medical and public health preparedness for, response to and recovery from disaster and other public health emergencies. Within ASPR, the Biomedical Advanced Research and Development Authority (BARDA) invests in innovation, advanced research and development, acquisition, and manufacturing of medical countermeasures needed to combat health security threats. BARDA is one of the leading public sector funders of advanced development of antimicrobial therapeutics and diagnostics worldwide, having invested more than $2.4 billion in antimicrobial products since 2010. This investment has supported the development of over 160 antimicrobial products and led to the U.S. Food and Drug Administration (FDA) approval of four new antibiotics and FDA 510(k) clearance of eight diagnostics.

As part of HHS, NIH is the primary U.S. federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. NIAID conducts and supports research — at NIH, throughout the United States, and worldwide — to study the causes of infectious and immune-mediated diseases, and to develop better means of preventing, diagnosing and treating these illnesses.

About Wellcome

Wellcome supports science to solve the urgent health challenges facing everyone. We support discovery research into life, health and wellbeing, and we’re taking on three worldwide health challenges: mental health, infectious disease and climate and health.

About the German Federal Ministry of Research, Technology, and Space and Research (BMFTR)

Research and innovation are the foundations for our future. The promotion of science and research by BMFTR represents an important contribution to securing Germany’s prosperity. Research is a German Federal Government policy priority, which is reflected in the development of the funding it is making available to these fields.

About the Global AMR Innovation Fund (GAMRIF)

The Global AMR Innovation Fund (GAMRIF) is a One Health aid fund that supports research and development around the world to reduce the threat of antimicrobial resistance (AMR) in humans, animals and the environment for the benefit of people in low- and middle-income countries (LMICs). GAMRIF core objectives are to develop innovative One Health solutions to tackle AMR; increase availability of context-specific, accessible, and affordable innovations for LMICs; establish international research partnerships with industry, academia, and governments; and collaborate with and leverage additional funding from other global donors.

About the Public Health Agency of Canada

The Public Health Agency of Canada (PHAC), established in 2004, is responsible for public health, emergency preparedness and response, and infectious and chronic disease control and prevention.  Its mission is to improve the health of all people and communities in Canada by addressing public health priorities through science, innovation, service delivery, and collaborative action. The Agency collaborates closely with all levels of government, non-government organizations, and international partners to build an effective public health system. PHAC has a strong history of addressing health threats, including collaboration on a One Health approach to antimicrobial resistance (AMR). As part of the Pan-Canadian Action Plan on AMR 2023-2027, PHAC is developing an economic pull-incentive pilot project which aims to increase access to essential antimicrobial drugs not yet market-authorized in Canada to address priority unmet public health needs.

About the Novo Nordisk Foundation

Established in Denmark in 1924, the Novo Nordisk Foundation is an enterprise foundation with philanthropic objectives. The vision of the Foundation is to improve people’s health and the sustainability of society and the planet. The Foundation’s mission is to progress research and innovation in the prevention and treatment of cardiometabolic and infectious diseases as well as to advance knowledge and solutions to support a green transformation of society. www.novonordiskfonden.dk/en

About Ministry of Economy and Finance of Italy

The Italian Ministry of Economy and Finance (MEF) performs the functions and tasks incumbent on the State in matters of economic and financial policy, budgeting, public investment planning and public debt management. The Ministry’s activities include coordinating and monitoring public spending and its trends, tax policies and the tax system and state assets. Moreover, the Ministry represents the Italian Government in the main European and international economic and financial fora, performs functions related to global governance and international financial cooperation, maintains relations with international economic, monetary, and financial institutions (such as the IMF, OECD, and Multilateral Development Banks), and negotiates and concludes international agreements and treaties with economic and financial content.

About Japan’s Ministry of Health, Labour and Welfare (MHLW)

MHLW is a ministry of the Government of Japan whose missions are to improve and promote social welfare, social security, and public health in order to secure and improve the livelihoods of the people and contribute to economic development. Recognizing the urgent global public health threat posed by AMR, MHLW has been supporting various domestic and international efforts to advance research and development of antimicrobials. MHLW has committed to providing contributions to CARB-X from 2024 to 2026.

About Boston University

Founded in 1839, Boston University is an internationally recognized institution of higher education and research. With nearly 37,000 students, it is one of the largest private residential universities in the United States. BU consists of 17 schools and colleges, along with the Faculty of Computing & Data Sciences and a number of multi-disciplinary centers and institutes integral to the University’s research and teaching mission. In 2012, BU joined the Association of American Universities (AAU), a consortium of leading research universities in the United States and Canada. For further information, please contact Kim Miragliuolo at kmira@bu.edu. www.bu.edu