Patient description: The patient is a 17-year-old boy complaining of severe migratory pain in the right lower quadrant of his abdomen that started four days ago. The pain is accompanied by nausea and vomiting. He was febrile with tenderness, rebound tenderness and guarding on palpation. His WBC was elevated with dominant neutrophils. CT scan showed evidence of acute perforated appendicitis with free fluid in the pelvis. Diagnostic laparoscopy revealed phlegmon with no other abdominal abnormalities. He is now a candidate for emergent laparoscopic appendectomy under general anesthesia.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Appendicitis Adult ≥18 years; 2. Clinical diagnosis of acute uncomplicated appendicitis (AUA) established by clinical care team, supported by any of the following usual care radiological tests (computed tomography (CT), ultrasound (US), and/or magnetic resonance imaging (MRI)). AUA is defined by the usual signs, symptoms, and imaging finding of appendicitis without: 1. Diffuse peritonitis on clinical exam (i.e., rigid abdomen / four quadrant peritonitis); 2. Radiologic findings of : i. Free air; ii. Walled off fluid collection concerning for an abscess; iii. Significant amounts of intra-abdominal fluid throughout abdomen (i.e., more than trace fluid); or iv. Extent of inflammation or adjacent organ involvement on radiologic imaging such that appendectomy is relatively contraindicated. 3. Ability to provide written or electronic informed consent in English or Spanish  1. Unable or unwilling to return or be contacted for clinical follow-up visits and/or research surveys; 2. Currently incarcerated in a detention facility or in police custody (patients wearing a monitoring device can be enrolled) at baseline/screening; 3. Evidence of severe sepsis or septic shock (e.g., new presumed sepsis-related organ dysfunction, elevated lactate, and/or fluid unresponsive hypotension); 4. Conditions with altered immune response or at risk for bacterial seeding; 5. Immunodeficiency (e.g., absolute neutrophil count <500/mm3, chronic immunosuppressive drugs, active chemotherapy or plans for chemotherapy in the following 30 days, or known acquired immune deficiency syndrome (AIDS) [cluster of differentiation 4 (CD4) count <200 or AIDS-defining illness within the last year] assessed by patient history); 6. Uncompensated liver failure; 7. Taking medication to treat active inflammatory bowel disease (e.g., Crohn's, ulcerative colitis); 8. Malignancy, not in remission (ongoing chemotherapy patients excluded); 9. Pregnant or expectation of becoming pregnant in the 30 days following baseline/screening; 10. Expected concurrent hemodialysis, peritoneal dialysis, or treatments using indwelling venous catheters; 11. Recent (within 90 days) placement of surgical implant (e.g., pacemaker, joint prosthesis, mechanical valve); 12. Indwelling Left Ventricular Assist Device (LVAD); 13. Patients with another infection (e.g., pneumonia, urinary tract infection) that requires treatment with another antibiotic at baseline/screening; 14. Concurrent illness that would otherwise mandate hospitalization outside of appendicitis and associated symptoms at baseline/screening; 15. Imaging findings of any of the following: 1. Appendiceal soft-tissue mass; 2. Imaging features of mucocele or tumor (e.g., appendix measuring ≥ 15mm in diameter and no other CT evidence of appendicitis); 3. Concern for carcinomatosis on imaging; or 16. Severe allergy or reaction (e.g., immediate urticaria or anaphylaxis) to all of the proposed antibiotics; 17. Prior enrollment in the study or other investigational drug or vaccine while on study treatment; 18. Abdominal/pelvic surgery in the past month; or 19. More than seven hours have transpired since the patient received the first parenteral dose of antibiotics