Inclusion Criteria:

• 1. Children and adolescents between 7 and 21 years of age.
• 2. A history at least one infection due to ESC-R Enterobacteriaceae. ESC-R isolates will be defined as those non-susceptible to ceftriaxone, cefotaxime, or ceftazidime.
• 3. Parent/guardian and participant must be able to attend baseline and follow-up study visits.
• 4. Subject must be willing and able to provide written informed consent or assent (as appropriate by age).

Exclusion Criteria:

• 1. Patients with any history of malignancy or any immunocompromised state (e.g. absolute neutrophil count outside the normal range) induced by disease or therapy will be excluded.
• 2. Patients with past or current use of systemic immunosuppressive agents will be excluded. Receipt of non-systemic agents such as inhaled, nasal, or topical steroids or immune-modulating agents are allowed.
• 3. Lack of intestinal carriage of ESC-R Enterobacteriaceae (negative selective stool culture for ESC-R Enterobacteriaceae).
• 4. Allergy or hypersensitivity to omeprazole and polyethylene glycol.
• 5. Pregnancy.
• 6. Current history of frequent (\>1 per week) vomiting.
• 7. Active inflammatory gastrointestinal disease, such as inflammatory bowel disease
• 8. Active mucositis or acute graft versus host disease of the gastrointestinal tract
• 9. Concurrent abdominal radiation therapy.
• 10. Inability to tolerate nasogastric tube placement or contraindication to having an NG tube placed.
• 11. Presence of a ventriculoperitoneal shunt or other intrabdominal device, receipt of renal dialysis, presence of ascites, or other conditions/devices that would increase the risk of peritonitis.
• 12. Bleeding diatheses
• 13. Patients with current active ESC-R Enterobacteriaceae infection who have not yet completed antibiotic treatment will be excluded until their treatment is completed
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