Functional and structural characterization of the genetic environment of an extended-spectrum beta-lactamase blaVEB gene from a Pseudomonas aeruginosa isolate obtained in India.

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 beta-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 beta-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 beta-lactamase content of this P. aeruginosa isolate followed by expression in Escherichia coli identified the naturally occurring AmpC beta-lactamase and a gene encoding an OXA-2-like beta-lactamase located in a class 1 integron, In78, in which an insertion sequence, ISpa7, was inserted within its 5'-CS region.