The study is the WP4 of the EU-funded (7th FW) project SATURN (Impact of Specific Antibiotic Therapies on the prevalence of hUman host ResistaNt bacteria). A total of 6 surgical and 6 medical wards will participate in the study. Sites of the study are located in 3 countries (Italy, Serbia, Romania). This WP will compare nosocomial acquisition rates of methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum beta-lactamase (ESBL)-producing gram-negative bacteria (E.coli, Klebsiella spp. and Proteus spp.) among different treatment groups and define the temporal relationship between the start of antibiotic therapy, the acquisition of new colonisation in patients previously not colonised, and the development of a bacterial infection caused by the same strain isolated in a screening sample. This goal will be achieved by completing the following primary objectives: