The goal of this study is to assess microbiome changes associated with omadacycline vs. comparators (moxifloxacin or oral vancomycin). Using a phase I study design, healthy volunteers aged 18-40 years will be given a 10-day course of either omadacycline 450 mg days 1 and 2 followed by 300 mg PO once daily, moxifloxacin 400 mg once daily, or oral vancomycin 125 mg given four times daily. Stool will be collected at baseline, daily during therapy, and at two follow-up time periods (days 13-14 and days 30-32). DNA will be extracted from stool and used for qPCR biomass and microbial metagenomic experiments. Results from the study will provide definitive data on the microbiome effects of omadacycline versus comparator antibiotics.

Inclusion. All volunteers will be considered healthy based on medical history

Exclusion. Patients will be excluded if they report any of the following:

• Cardiovascular disease
• Gastrointestinal disease
• Hepatic or renal disease
• Receipt of an antibiotic for at least three months prior to enrollment.
• Receipt of a probiotic for at least a month prior to enrollment and during the entire study period.

Metagenomic and metadata will be shared by posting to relevant biorepositories or upon reasonable requests from external investigators.