143 patients have been recruited instead of 150 but the theoretical date of end of inclusions being reached, we have decided to not prolong again the study.

Patients receiving Ceftriaxone 1 gram or 2 grams per day during their presence in emergency unit of hospital whatever their medical condition, will be included.

Rectal swabs will be collected at inclusion and at days 5 and 30 to perform analysis.

Analysis will be performed to characterize gut microbiome in order to detect intestinal microbiome profiles significantly associated with protection against colonization by third generation cephalosporin resistant Enterobacteriae.

Inclusion Criteria:

• Age 18 years
• Able to comply with study requirement and to provide informed consent
• Outside the context of tutorship and / or guardianship, affiliated to the Social Security Regime and having consented to participate in the ARCMI study.
• Patient receiving ceftriaxone (1 gram or 2 grams per day) in the emergency department

Exclusion Criteria:

• Patients with acute anorectal pathology incompatible with the swabbing strategy or digital rectal examination.
• Prescription of another dosage of ceftriaxone (more than 2 grams per day)
• Patient with inflammatory bowel disease
• Allergy or contraindication to betalactamines and cephalosporins