Genetic and Functional Variability of AmpC-Type β-Lactamases from Acinetobacter baumannii

The incidence of naturally occurring AmpC beta-lactamases with extended activities toward several cephalosporins was evaluated among 17 ceftazidime (CAZ)-resistant Acinetobacter baumannii isolates. Five AmpC beta-lactamases (named ADC beta-lactamases) were identified, among which those possessing the Val208Ala (inside the omega-loop) or Asn283Ser (helix H-10) substitution conferred higher levels of resistance (4- to 64-fold higher) to CAZ and to cefotaxime in Escherichia coli. This study demonstrates that peculiar AmpCs playing a role in resistance to broad-spectrum cephalosporins in A. baumannii may be identified.