Omadacycline gut microbiome exposure does not induce Clostridium difficile proliferation or toxin production in a model that simulates the proximal, medial and distal human colon [Clinical Therapeutics]

A clinically reflective model of the human colon was used to investigate the effects of the broad-spectrum antibiotic omadacycline on the gut microbiome, and subsequent potential to induce simulated Clostridium difficile infection (CDI). Triple stage chemostat gut models were inoculated with pooled human faecal slurry from healthy volunteers (age ≥60 years). Models were challenged twice with 107 cfu C. difficile spores (PCR ribotype 027). Omadacycline effects were assessed in a single gut model. Observations were confirmed in a parallel study with omadacycline and moxifloxacin. Antibiotic instillation was performed once daily for 7 days. The models were observed for 3 weeks post-antibiotic challenge. Gut microbiota populations and C. difficile total viable and spore counts were enumerated daily by culture. Cytotoxin titres and antibiotic concentrations were also measured. Gut microbiota populations were stable before antibiotic challenge. Moxifloxacin instillation caused a ~4 log₁₀ cfu/mL decline in enterococci and Bacteroides fragilis group populations, and a ~3 log₁₀ cfu/mL decline in bifidobacteria and lactobacilli, followed by simulated CDI (vegetative cell proliferation and detectable toxin). In both models, omadacycline instillation decreased populations of bifidobacteria (~8 log₁₀ cfu/mL), B. fragilis group populations (7-8 log₁₀ cfu/mL), lactobacilli (2-6 log₁₀ cfu/mL), and enterococci (4-6 log₁₀ cfu/mL). Despite these microbial shifts, there was no evidence of C. difficile germination or toxin production. In contrast to moxifloxacin, omadacycline exposure did not facilitate simulated CDI, suggesting this antibiotic may have a low propensity to induce CDI in the clinical setting.

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