Carbapenem-hydrolyzing GES-type extended-spectrum beta-lactamase in Acinetobacter baumannii

Abstract

Acinetobacter baumannii isolate AP was recovered from a bronchial lavage of a patient hospitalized in Paris, France. A. baumannii AP was resistant to all β-lactams, including carbapenems, and produced the extended-spectrum β-lactamase (ESBL) GES-14, which differs from GES-1 by two substitutions, Gly170Ser and Gly243Ala. Cloning of the bla(GES-14) gene followed by its expression in Escherichia coli showed that GES-14 compromised significantly the efficacy of all β-lactams, including cephalosporins, aztreonam, and carbapenems. The carbapenemase activity of purified GES-14 was confirmed by kinetic studies. The bla(GES-14) gene was located into a class 1 integron structure and located onto a ca. 95-kb self-transferable plasmid. This study identified a very broad-spectrum β-lactamase in A. baumannii.

FIG. 1.

Alignment of the amino acid sequences of β-lactamases GES-1, GES-2, GES-5, GES-6, GES-7 (IBC-1), GES-9, GES-11, GES-13, and GES-14. Boldface amino acids are conserved residues among Ambler class A β-lactamases. The amino acids of the omega loop are underlined.

FIG. 2.

Schematic map representing integron structures harboring the bla_GES-14 (A) and bla_GES-11 (B) genes. The genes and their corresponding transcriptional orientations are indicated by horizontal arrows. The 59-base elements are indicated by black circles.

FIG. 3.

Comparative structures of the sequences located upstream of the bla_GES-14 and bla_GES-1 genes. The 238-bp nucleotide sequence that is deleted in In125 containing bla_GES-14 (A) but present in In52 containing bla_GES-1 (B) is represented. The sequences of the promoters are underlined, and the attI1 recombination site is italicized. The −35 and −10 sequences of the P_c and P₂ promoters are underlined, and the start codons of the bla_GES genes are in bold. The core site sequence of the bla_GES-1 gene cassette is boxed.