The Gut Microbiome - Source of Sepsis and Novel Target in Intensive Care Units?

Inclusion Criteria: * Age ≥ 18 years * One of the following criteria 1. Critically ill patients treated with meropenem or piperacillin/tazobactam started within the last 72 h 2. Critically ill patients without systemic antimicrobial therapy within the last 72 hours and an expected ICU length of stay of more than 3 days 3. Long-term survivors of sepsis, e.g. from pre-existing sepsis cohorts Exclusion Criteria: * Inflammatory bowel disease * Major bowel resection * Selective decontamination of the oral and digestive tract * Oral vancomycin therapy * Immunocompromised patients * History of chemotherapy during the last 6 months. * Known travel history to countries to areas of high antimicrobial resistance (\>5% according to the report of the European Centre for Disease Prevention and Control and all countries except USA and Canada) within the last 4 weeks * Acute neurological diseases (e.g., brain ischemia, hemorrhage, meningoencephalitis, tumor) * Manifest dementia, pre-existing psychiatric diseases (schizophrenia, psychosis) * Acute brain surgery * MRI contraindications: pacemakers, hearing aids, neurostimulation, insulin pumps, other potentially ferromagnetic implants, screws, clips, prostheses, metal splinters, etc., pregnancy, claustrophobia, extensive tattoos.