Characterization of a naturally occurring class D beta-lactamase from Achromobacter xylosoxidans

Abstract

A chromosomally encoded class D beta-lactamase, OXA-114, was characterized from Achromobacter xylosoxidans strain CIP69598. beta-Lactamase OXA-114 shared 56% amino acid identity with the naturally occurring class D beta-lactamase of Burkholderia cenocepacia and 42% identity with the acquired oxacillinases OXA-9 and OXA-18. OXA-114 has a narrow-spectrum hydrolysis profile, although it includes imipenem, at a very low level. PCR and sequencing revealed that bla(OXA-114)-like genes were identified in all A. xylosoxidans strains tested (n = 5), indicating that this beta-lactamase is naturally occurring in that species. Induction experiments with imipenem and cefoxitin did not show inducibility of bla(OXA-114) expression.

FIG. 1.

Dendrogram obtained for representative class D β-lactamases by neighbor-joining analysis. The alignment used for tree calculation was performed with ClustalX. 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. The amino acid identity of each β-lactamase compared to OXA-114a is indicated in parentheses. Acquired β-lactamases in gram-negative organisms are OXA-1, OXA-9, OXA-18, OXA-20, OXA-2, OXA-58, OXA-40, OXA-23, OXA-10, and OXA-48, whereas the others are naturally occurring ones.

FIG. 2.

Amino acid sequence comparison of OXA-114-like determinants. OXA-114a is from A. xylosoxidans isolate CIP69598, OXA-114b is from isolate MER, OXA-114c is from isolate TB1, OXA-114d is from isolate LOL, and OXA-114e is from isolate DUC. Dashes show identical amino acid residues, and the critical motifs for class D β-lactamases are shaded in gray. Numbering is done according to class D nomenclature (2).