Affiliation: Service de Bacteriologie-Virologie, Hopital de Bicetre, 78 rue du General Leclerc, 94275 Le Kremlin-Bicetre, France.
Extended-spectrum AmpC β-lactamases are derived from chromosomal cephalosporinases by amino acid deletion, insertion and replacement. These structural changes are responsible for an increased catalytic efficiency against extended- spectrum cephalosporins, such as ceftazidime, cefotaxime, cefepime, and cefpirome. An overview of the molecular and biochemical characterization of these identified β-lactamases in Enterobacteriaceae is provided. The structural modifications that account for the broadening substrate specificity and the phenotypes of resistance of the clinical isolates are detailed.