GES-2, a class A beta-lactamase from Pseudomonas aeruginosa with increasedhydrolysis of imipenem

Psendomonas aeruginosa GW-1 was isolated in 2000 in South Africa from blood cultures of a 38-year-old female who developed nosocomial pneumonia. This isolate harbored a self-transferable ca. 100-kb plasmid that conferred an e xpanded-spectrum cephalosporin resistance profile associated with an interm ediate susceptibility to imipenem. A beta -lactamase gene, bla(GES-2), was cloned from whole-cell DNA of P. acruginosa GW-1 and expressed in Escherich ia coli. GES-2, with a pl value of 5.8, hydrolyzed expanded-spectrum cephal osporins, and its substrate profile was extended to include imipenem compar ed to that of GES-1, identified previously in Klebsiella pneumoniae. GES-2 activity was less inhibited by clavulanic acid, tazobactam and imipenem tha n GES-1. The GES-2 amino acid sequence differs from that of GES-1 by a glyc ine-to-asparagine substitution in position 170 located in the omega loop of Ambler class A enzymes. This amino acid change may explain the extension o f the substrate profile of the plasmid-encoded beta -lactamase GES-2.