Response to Microbiota-Based Drug RBX2660 is Associated with Reduction in Antimicrobial Resistance Genes in Patients with Recurrent Clostridioides difficile Infections

Julia Garcia-Diaz MD, Courtney Jones, Hiren Karathia PhD, Brian Fanelli, Nur A Hasan PhD, Ken Blount PhD

ASM 2019 Poster: Microbiota-Based Drug Associated with Reduction in Antimicrobial Resistance Genes with Recurrent Clostridiodes difficile Infections

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ASM Microbe 2019
June 20-24, 2019, San Francisco, CA



  • PUNCH Open Label™ (NCT02589847) – prospective, multicenter, open-label Phase 2 study assessing the efficacy and safety of RBX2660 treatment of recurrent CDI.
    • PATIENT POPULATION: multi-recurrent CDI (≥ 2 recurrent episodes at enrollment)
    • TREATMENT: two doses of RBX2660 administered 7 ± 2 days apart
    • EFFICACY: absence of CDI recurrence at 8 weeks after last study treatment
    • FAILURE: documented recurrence, including positive laboratory diagnosis for C. difficile
    • CONTROL GROUP: historical chart review of patients who only received antibiotic therapy for rCDI
  • Analysis included 66 longitudinally matched samples from 22 treatment responsive participants, including before treatment (BL) and 7 ± 3 and 30 ± 10 days after treatment. Sample set represents 17 trial sites from US and Canada.
  • All samples were frozen without stabilizers after collection, extracted, and sequenced using a shallow shotgun method.
  • Sequencing reads were compared to a proprietary database of gene sequences annotated as related to antimicrobial resistance (CosmosID)
  • ≥ 40% sequencing coverage of an AMR gene was considered positive identification in each sample.
  • AMR gene coverage for participant samples were compared to Human Microbiome Project (HMP) data for which comparable sequencing depth was simulated.

RBX2660 is Efficacious & Durable

  • 119 of 149 RBX2660-treated participants (80%) were responders at 8 weeks after treatment
  • 57 of 110 patients (52%) in the historical control group were recurrence free 8 weeks after antibiotic treatment
  • Only 3 of 109 evaluable primary RBX2660 responders reported reinfection at 6 months
  • 97% of RBX2660-treated 8-week responders who were evaluable at 6 months remained recurrence free
  • Follow up ongoing to 24 months

RBX2660 Shifts Microbiome Composition

  • Participants were dysbiotic at study entry, with decreased Bacteroidia and Clostridia and overabundance of Gammaproteobacteria and Bacilli
  • Bacteroidia, Clostridia increased and Gammaproteobacteria, Bacilli decreased after treatment; durable to 6 months after treatment
  • Based on shallow-shotgun sequencing data

Antimicrobial Resistance Genes (AMR) Analysis

  • Prior to treatment (BL) rCDI participants had significantly higher abundance of antimicrobial resistance (AMR) genes than the HMP healthy population
  • After treatment (7 and 30 days), participants’ had decreased AMR gene abundance, not significantly different from HMP


  • In a Phase 2 open label trial, RBX2660 was 80% effective for preventing rCDI, with durable response to at least 6 months.
  • Responding participants’ microbiomes resolved toward a healthier composition after treatment.
  • In a 22-participant subgroup analysis, there was a significant decrease in antimicrobial resistance genes from before to after successful response to RBX2660.