Sequence analysis of ARI-1, a novel OXA beta-lactamase, responsible for imipenem resistance in Acinetobacter baumannii 6B92

Abstract

The sequence of the bla(ARI-1) gene from imipenem-resistant Acinetobacter baumannii 6B92 has been determined. The structural gene encodes a 273-amino-acid protein which is most related to the OXA class D beta-lactamases. The conserved S-T-F-K and K-T-G motifs were identified in the ARI-1 protein sequence, also named OXA-23, but significantly, a point mutation (Y-->F) was identified in the Y-G-N conserved motif, also known to function in the active site.

FIG. 1

Nucleotide and deduced amino acid sequences of the ARI-1 gene and the ARI-1 protein from A. baumannii 6B92. The boldface ATG and TAA represent the initiation and termination codons, respectively. The β-lactamase active site S-T-F-K and the conserved motifs F-G-N and K-T-G are shown in boldface type. A proposed cleavage site generating a possible signal sequence is indicated with a vertical arrow. Nucleotide sequence in italics shows >90% homology with the phaB_Ac upstream region (19). ⧫ indicates the transcription start site identified by Schembri et al. (20). An imperfect inverted repeat sequence at the 3′ end of the gene is shown by a broken line, and possible cassette junctions are shown boxed.

FIG. 2

Cladogram relating ARI-1 to 18 other class D β-lactamases. Analysis was done with the CLUSTAL W Multiple Sequence Alignment Program (22), based on a progressive alignment using the minimum mutation matrix of Dayhoff for scoring (9). A gap penalty of 3 was applied, and 100 bootstrap replications gave node values.