In this prospective observational study we aim to determine the prevalence of oropharyngeal and rectal Gram-negative bacilli colonization in healthy subjects, and their susceptibility to chlorehexidine. We plan to recruit 100 healthy volunteers secondary endpoints are to determine the phylogentic characteristics of E. coli isolates; to compare the phylogentic characteristics of oropharyngeal and rectal of predominant GNB colonization.

In this prospective observational study we aim to determine the prevalence of oropharyngeal and rectal Gram-negative bacilli colonization in 100 healthy subjects, and their susceptibility to chlorehexidine. Each participant will undego a oropharyngeal swab collection and a rectal swab at day 0. The Gram-negative bacilli colonization will be identified, E. coli isolates will be studied in terms of phylogeny; gram-negative isolates will be studied in terms of antimicrobial and chlorhexidine susceptibility. The primary objective is to determine the prevalence of oropharyngeal Gram-negative bacilli colonization. The secondary objectives are to determine the chlorhexidine and antimicrobial susceptibility of such colonization; to determine the phylogentic characteristics of oropharyngeal and rectal predominant E. coli isolates; to compare the phylogentic characteristics of oropharyngeal and rectal E. coli isolates.

Inclusion Criteria:

• age > 18 yo
• personal history of neck or face irradiation
• no history of gastrointestinal disease
• no symptoms of immunosuppression
• no antibiotic therapy in the previous month
• no hospitalization in the 3 months preceding inclusion
• medical exmination prior to inclusion

Exclusion Criteria:

• affiliated to the social security
• The refusal of a patient to participate in a study

healthy volonteers