OXA-58, a novel class D {beta}-lactamase involved in resistance to carbapenems in Acinetobacter baumannii

Abstract

A carbapenem-resistant Acinetobacter baumannii strain was isolated in Toulouse, France, in 2003. Cloning and expression in Escherichia coli identified the carbapenem-hydrolyzing beta-lactamase OXA-58, which is weakly related (less than 50% amino acid identity) to other oxacillinases. It hydrolyzed penicillins, oxacillin, and imipenem but not expanded-spectrum cephalosporins. The bla(OXA-58) gene was located on a ca. 30-kb non-self-transferable plasmid. After electrotransformation in the A. baumannii CIP7010(T) reference strain, it conferred reduced susceptibility to carbapenems. The bla(OXA-58) gene was bracketed by two novel ISAba3-like insertion elements. This study describes a newly characterized beta-lactamase that may contribute to carbapenem resistance in A. baumannii.

FIG. 1.

Nucleotide sequence of a 1,828-bp fragment of recombinant plasmid pOXA-58 containing the bla_OXA-58 gene. The deduced amino acid sequence is designated in single-letter code below the nucleotide sequence. The start codons of the ORFs are indicated by horizontal arrows. The left inverted repeats (IRL) of ISAba3 are shaded in grey. The tnpA transposase gene of ISAba3 is indicated. Asterisks indicates stop codons.

FIG. 2.

Comparison of the amino acid sequence of OXA-58 with those of OXA-23, -24, -54, and -55, which possess carbapenem-hydrolyzing activity, and with those of reference oxacillinases OXA-1 and OXA-10. The conserved residues for oxacillinases are shaded. Numbering of β-lactamases is according to DBL numbering (13).

FIG. 3.

Dendrogram obtained for representative natural and acquired Ambler class D β-lactamases by parsimony analysis. The origins of the naturally occurring oxacillinases are indicated. The alignment used for tree calculation was performed with ClustalW followed by minor adjustments. Branch lengths are drawn to scale and are proportional to the number of amino acid changes. The distance along the vertical axis has no significance.