Rationale: Postantibiotic diarrhoea in critically ill patients is common, often prolonged and currently there is no effective treatment of it.

Aim: To test safety and feasibility of faecal microbial transplantation in critically ill patients with postantibiotic diarhoea.

Design: Prospective, single center, parallel group randomised controlled trial. Subjects: ICU patients (both general and burn ICU) who developed diarhea after a course of antibiotic therapy that is persistent for 24 hours and is not due to other causes. Patients with septic shock or approaching death will be excluded.

Treatment in the intervention group: Faecal bacteriotherapy (FBT) delivered as enema (and repeated once in the subgroup of patients with C. dif. infection) of 350 ml of standardised mixed transplantate prepared from faeces of 7 healthy donors.

Control group: Standard-of-care protocolised treatment of postantibiotic diarhea (which includes vancomycine 250 mg p.o. 6 hourly in the subgroup with C. dif. infection).

Primary outcome: Percentage of patients with treatment failure at day 7 after randomisation, which is defined as treatment either not being delivered or not being effective.

Secondary and exploratory outcomes: Influence of the intervention on colonic microbiome and metabolome, small bowel and colonic permeability, bacterial translocation and systemic inflammation response to procedure.

Inclusion Criteria:

• signing of informed consent (see below)
• age > 18 yrs.
• in-patient in ICU or HDU (incl. burn unit) and expected to stay for >7 days
• diarrhea following antibiotic treatment defined as 3 or more stools per day or Bristol type 7 stool in the volume >300 ml/day if stool derivative device is in place, persisting for 24 hours despite enteral feeding formula has been stopped.

Exclusion Criteria:

• death appears imminent or ceilings of care put in place
• presence of new-onset sepsis defined as per 2016 definition
• lactate >2.0 mM, colon diameter > 9 cm on plain AXR
• the necessity of ongoing antibiotic treatment for another reasons
• unable to tolerate enema for any reason (e.g. surgery of the GI tract in the past year)
• pregnant and lactating woman
• patients with a history of severe anaphylactic food allergy, any other reason which - as per judgement of the treating clinician - makes faecal transplantation unsafe or not feasible (Note: All screening failures based on this criterion will be reported separately, inc. the reason why it was considered unsafe or not feasible to proceed).