 In this prospective multicenter observational study we aim to determine the prevalence of oropharyngeal and rectal Gram-negative bacilli colonization in 4 population of hospitalized subjects, and their susceptibility to chlorehexidine. We plan to recruit 300 subjects in surgical wards 100 in orthopedics, 100 in thoracic and vascular, 100 in abdominal surgery and 100 in the ICU. Each participant will undego a oropharyngeal swab collection at day 0, day 5 and day 10 or discharge, and a rectal swab at day 0 and day 10 or hospital discharge. The Gram-negative bacilli colonization will be identified, E. coli isolates will be studied in terms of phylogeny, antimicrobial and chlorhexidine susceptibility. The primary endpoint is to determine the prevalence of oropharyngeal and rectal Gram-negative bacilli colonization. The secondary endpoints are to determine the incidence of the acquisition of such colonization in a 10 days timeframe; to determine the phylogentic characteristics of E. coli isolates; to compare the phylogentic characteristics of oropharyngeal and rectal E. coli isolates; to compare the phylogentic characteristics of colonization and potential E. coli infection isolates; to compare the rectal and oropharyngeal colonization composition; description of oropharyngeal microbiote. 