Characterization of the naturally occurring oxacillinase of Acinetobacter baumannii

Abstract

A chromosomally encoded oxacillinase, OXA-69, was characterized from Acinetobacter baumannii AYE. beta-Lactamase OXA-69 shared 97% amino acid identity with the recently described OXA-51 enzyme of A. baumannii and 62 and 56% amino acid identity with the carbapenem-hydrolyzing oxacillinases OXA-24 and OXA-23, respectively. Biochemical characterization of the purified OXA-69 revealed a narrow-spectrum hydrolysis profile but including, at a low level, imipenem and meropenem. By PCR and sequencing bla(OXA-69)-like genes were identified in all A. baumannii strains tested (n = 12), suggesting that this oxacillinase is naturally occurring in that species.

FIG. 1.

Dendrogram obtained for several oxacillinases by parsimony analysis (35). Branch lengths are drawn to scale and are proportional to the number of amino acid changes. The number of changes is indicated above each branch, and the percent values at branching points (underlined) refer to the number of times that a particular node was found in 100 bootstrap replications. The distance along the vertical axis has no significance. Numbers in parentheses indicate percentages of amino acid identity with the β-lactamase OXA-69. Bacterial species names are for those oxacillinases that are naturally occurring.