Extended-spectrum cephalosporinases in Pseudomonas aeruginosa.

Antimicrobial agents and chemotherapy (2009-03-05)
José-Manuel Rodríguez-Martínez, Laurent Poirel, Patrice Nordmann

The characterization of AmpC-type beta-lactamases was performed in a collection of 32 clinical Pseudomonas aeruginosa isolates with intermediate susceptibility or resistance to imipenem and ceftazidime. Twenty-one out of those 32 isolates overexpressed AmpC beta-lactamase, and the MICs of ceftazidime and imipenem were reduced after cloxacillin addition. Cloning and sequencing identified 10 AmpC beta-lactamase variants. Reduced susceptibility to imipenem, ceftazidime, and cefepime was observed only with recombinant P. aeruginosa strains expressing an AmpC beta-lactamase that had an alanine residue at position 105. The catalytic efficiencies (k(cat)/K(m)) of the AmpC variants possessing this residue were increased against oxyiminocephalosporins and imipenem. In addition, we show here that those AmpC variants constitute a favorable background for the in vitro selection of imipenem-resistant strains. This report identified a novel resistance mechanism that may contribute to imipenem resistance in P. aeruginosa.

Product Number
Product Description

Amoxicillin, 95.0-102.0% anhydrous basis