Enterobacteria constitute a family of Gram negative bacilli of the gastrointestinal flora. These micro-organisms are frequently responsible for nosocomial or community-acquired infections, for which treatment is essentially based on the use of beta-lactam antibiotics. This class of antibiotics comprises penicillins, cephalosporins, monobactams and carbapenems. Carbapenems have the advantage of possessing a broad antibacterial spectrum and the capacity to resist the hydrolytic action of a large number of beta-lactamases, widespread inactivating enzymes.

However, new enzymes, called carbapenemases, able to confer resistance to carbapenems either alone or in combination with additional resistance mechanisms such as loss of membrane permeability or overexpression of efflux systems, are currently emerging all over the world. Carbapenemases represent a major public health problem because of the risk of therapeutic impasse and their high epidemic potential.

Inclusion Criteria:

• Patients in whom the results of bacteriological examinations reveal the presence of an Enterobacteria strain with reduced susceptibility to carbapenems
• Control : patients ( infected or colonized ) a strain of Enterobacter sensitive to carbapenems immediately isolated after a strain of Enterobacter having decreased susceptibility to carbapenems from the same service and same hospital ( 2 strains susceptible strain with reduced sensitivity).

Exclusion Criteria:

• Duplicate : same strain to a first strain of reduced sensitivity in isolated the same patient during the study period ( same bacterial species , even after characterization resistance mechanism).

patients undergoing bacteriological samples as part of routine clinical practice during their hospital stay in one of the 6 participating centres. Patients in whom the results of bacteriological examinations reveal the presence of an Enterobacteria strain with reduced susceptibility to carbapenems will be included in this project