Recurrent C difficile Infection Risk in Patients Treated With the Investigational Oral Microbiome Therapeutic SER-109

c difficile
Clostridium bacteria, computer illustration. Clostridia are spore-forming bacteria that include several human pathogenic species, C. difficile, C. tetani, C. botulinum, C. perfringens, and others. C. difficile is a normal inhabitant of the human intestine, but it can become a pathogen when antibiotics disrupt the normal intestinal flora and allow C. difficile to become established in the colon. A toxin produced by the bacteria can cause diarrhoea, abdominal pain, fever, inflammation of the colon, vomiting and dehydration. C. tetani is the causative agent of tetanus, C. botulinum causes food poisoning botulism, C. perfringens causes gas gangrene and also food poisoning. Clostridium novyi (oedematiens) causes gas gangrene and infectious necrotic hepatitis. The toxins produced by C. tetani (tetanospasmin) and C. botulinum are among the most dangerous known. Some of the clostridia species are involved in the development of bacterial vaginosis.
Researchers conducted a study to determine whether the investigational oral microbiome therapeutic SER-109 decreases the risk for recurrent Clostridioides difficile infection.

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Compared with placebo, patients treated with the investigational oral microbiome therapeutic SER-109 were found be at decreased risk for recurrent Clostridioides difficile infection (CDI) regardless of individual risk factors, according to research presented at IDWeek, held virtually from September 29 to October 3, 2021.

Researchers enrolled a subgroup of patients from the ECOSPOR III double-blind, placebo-controlled trial. The researchers sought to assess the superiority of SER-109 vs placebo in decreasing recurrent CDI up to 8 weeks after treatment. A total of 182 patients with 3 or more previous episodes of CDI were included in the final analysis. Patients were randomly assigned to receive either standard care followed by 4 capsules of SER-109 daily for 3 days or placebo.

To analyze the rate of recurrent CDI, the researchers divided patients into subgroups according to baseline risk factors, including, proton-pump inhibitor use, number of CDI recurrences, prior fecal microbiome transplantation, presence of comorbid conditions, and exposure to non-CDI indicated antibiotics after dosing.

Of 182 patients included in the analysis, the overall rates of recurrent CDI were significantly decreased in those who received treatment with SER-109 (12.4%) compared with those who received placebo (39.8%). The relative risk for recurrent CDI was 0.32 (95% CI, 0.18-0.58; P <.001 for RR< 1.0: P <.001 for RR< 0.833). In regard to comorbid conditions, 32.4% of patients had 1 and 34.1% had 2 or more. Regardless of subgroup and presence or absence of recurrent CDI risk factors, patients treated with SER-109 consistently showed a greater decreased risk for recurrent CDI compared with those treated with placebo.

According to the researchers, “despite a high proportion of patients with comorbidities in ECOSPORIII, SER-109 significantly [decreased] the risk for [recurrent CDI] compared with placebo.”

Disclosure: Some author(s) declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.


Cohen SH, Louie TJ, Sims M, et al. Investigational microbiome therapeutic SER-109 reduces recurrence of Clostridioides difficile infection (CDI) compared to placebo, regardless of risk factors for recurrence. Presented at: IDWeek 2020; September 29 to October 3, 2021. Poster 634.

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