Detection of Colistin-resistant Isolates From Patients of Intensive Care Units and Oncohaematology Wards.

From rectal swabs of patients admitted in ICU and oncohaematology ward, investigators will use first a new culture medium (SuperPolymyxin) for screening the colistin resistant Gram negative and then a new rapid test (Rapid Polymyxin NP test) to confirm this resistance. These tests will be compared to the reference test of MIC (Minimal Inhibitory Concentration) determined by the broth micro-dilution (BMD) method.