Functional and Structural Characterization of the Genetic Environment of an Extended-Spectrum β-Lactamase bla VEB Gene from a Pseudomonas aeruginosa Isolate Obtained in India

Abstract

A Pseudomonas aeruginosa clinical strain isolated from a patient hospitalized in a New Delhi, India, hospital was resistant to expanded-spectrum cephalosporins, imipenem, and aztreonam. A bla _VEB-1 -like gene named bla _VEB-1a , which codes for the extended-spectrum β-lactamase VEB-1a, was identified. The genetic environment of bla _VEB-1a was peculiar: (i) no 5′ conserved sequence (5′-CS) region was present upstream of the β-lactamase gene, whereas bla _VEB-1 -like genes are usually associated with class 1 integrons; (ii) bla _VEB-1a was inserted between two truncated 3′-CS regions in a direct repeat; and (iii) four 135-bp repeated DNA sequences (repeated elements) were located on each side of the bla _VEB-1a gene. Expression of the bla _VEB-1a gene was driven by a strong promoter located in one of these repeated sequences. In addition, cloning of the β-lactamase content of this P. aeruginosa isolate followed by expression in Escherichia coli identified the naturally occurring AmpC β-lactamase and a gene encoding an OXA-2-like β-lactamase located in a class 1 integron, In78, in which an insertion sequence, IS pa7 , was inserted within its 5′-CS region.