Lancaster, Chris

ABSTRACT We have previously reported on the susceptibility and epidemiology of Clostridioides difficile isolates from six geographically dispersed medical centers in the United States. This current survey was conducted with isolates collected in 2020–2021 from six geographically dispersed medical centers in the United States, with specific attention to susceptibility to ridinilazole as well as nine comparators. C. difficile isolates or stools from patients with C. difficile antibiotic-associated diarrhea were collected and referred to a central laboratory. After species confirmation of 300 isolates at the central laboratory, antibiotic susceptibilities were determined by the agar dilution method [M11-A9, Clinical and Laboratory Standards Institute (CLSI)] against the 10 agents. Ribotyping was performed by PCR capillary gel electrophoresis on all isolates. Ridinilazole had a minimum inhibitory concentration (MIC) 90 of 0.25 mcg/mL, and no isolate had an MIC greater than 0.5 mcg/mL. In comparison, fidaxomicin had an MIC 90 of 0.5 mcg/mL. The vancomycin MIC 90 was 2 mcg/mL with a 0.7% resistance rate [both CLSI and European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria]. The metronidazole MIC 90 was 1 mcg/mL, with none resistant by CLSI criteria, and a 0.3% resistance rate by EUCAST criteria. Among the 50 different ribotypes isolated in the survey, the most common ribotype was 014–020 (14.0%) followed by 106 (10.3%), 027 (10%), 002 (8%), and 078–126 (4.3%). Ridinilazole maintained activity against all ribotypes and all strains resistant to any other agent tested. Ridinilazole showed excellent in vitro activity against C. difficile isolates collected between 2020 and 2021 in the United States, independent of ribotype.

Abstract Background We have previously reported on a US based national surveillance study from 6 geographically dispersed medical centers for the susceptibility and epidemiology of C. difficile isolates. This current survey was conducted with isolates collected in 2020-21 with specific attention to the susceptibility to ridinilazole as well as nine comparators. A summary of the susceptibilities of 300 isolates of C. difficile tested against 10 antimicrobial agents Methods in 2020-21 C. difficile isolates or stools from patients with C. difficile toxin positive antibiotic associated diarrhea were collected in 6 US medical centers and referred to a central lab. After confirmation of 300 isolates antibiotic susceptibilities were determined by agar dilution method (CLSI M11-A9) against 10 agents listed in Table below. Ribotyping was performed by PCR capillary gel electrophoresis on all isolates. Results A summary of the susceptibilities of the 300 isolates against 10 antimicrobial agents are shown in the Table. The most common ribotype was 014-020 (14.4% compared to 11.8% in 2016), followed by 106 (10%, compared to 15% in 2016), 027 (10% compared to 13.1% in 2016), 002 (8% compared to 8.5% in 2016, 078-126 (4.3% compared to 1.3% in 2016). Ridinilazole was very potent against all isolates collected in the US with an MIC 90 of 0.25 mcg/ml, including against all the hypervirulent ribotypes as well as those isolates with antibiotic resistances to other antibiotics in the test panel. Conclusion Ridinilazole showed excellent in-vitro activity against C. difficile isolates in the US, independent of ribotype. There has been a striking change in ribotype distribution compared to 2016, accompanied by a reduction in C. difficile resistance to moxifloxacin and imipenem. Disclosures Cheleste M. Thorpe, MD, Actelion: Grant/Research Support|Deinove: Advisor/Consultant|General Mills: Grant/Research Support|Merck: Grant/Research Support|Pfizer: Grant/Research Support|Summit: Advisor/Consultant|Summit: Grant/Research Support Stuart Johnson, M.D., Ferring Pharmaceuticals: Membership on Ferring Publication Steering Committee|Ferring Pharmaceuticals: Employee|Summit Plc: Advisor/Consultant Dale N. Gerding, MD, Destiny Pharma plc.: Advisor/Consultant Karen C. Carroll, MD, Abbott Diagnostics: Advisor/Consultant|BD Diagnostics: Advisor/Consultant|BD Diagnostics: Grant/Research Support|BioRad, Inc: Grant/Research Support|Meridian Biosciences: Grant/Research Support|Roche Diagnostics: Advisor/Consultant|Scanogen, Inc: Advisor/Consultant|Scanogen, Inc: Grant/Research Support|Thermo Fisher, Inc: Advisor/Consultant Kevin W. Garey, PharmD, MS, Acurx: Grant/Research Support|cidara: Advisor/Consultant|cidara: Grant/Research Support|Paratek: Grant/Research Support|Seres Health: Grant/Research Support|Summit: Grant/Research Support Esther Duperchy, PhD, Summit Plc: Employee David R. Snydman, MD, Merck: Advisor/Consultant|Merck and Company: Grant/Research Support|Prolacta: Advisor/Consultant|Prolacta: Grant/Research Support|Seres: Advisor/Consultant|Seres Health: Grant/Research Support|Summit Plc: Grant/Research Support|Takeda: Advisor/Consultant|Takeda: Grant/Research Support|Visterra: Advisor/Consultant.