Cloning and characterization of bla(VIM), a new integron-borne metallo-beta-lactamase gene from a Pseudomonas aeruginosa clinical isolate

Production of a metallo-beta-lactamase activity was detected in a carbapene m-resistant Pseudomonas aeruginosa clinical isolate (isolate VR-143/97) fro m an Italian inpatient at the Verona University Hospital (northern Italy). The metallo-beta-lactamase determinant was isolated from a genomic library of VR-143/97, constructed in an Escherichia coli plasmid vector, by screeni ng for clones with reduced susceptibility to imipenem, Sequencing of the cl oned gene revealed that it encoded a new class B beta-lactamase that was na med VIM-1. At the sequence level VIM-1 was rather divergent from the other class B enzymes (16.4 to 38.7% identity), overall being more similar to mem bers of subclass B1 including the beta-lactamase II of Bacillus cereus (Bc- II), the Bacteroides fragilis CcrA, the Chryseobacterium meningosepticum Bl aB, and the cassette-encoded IMP-1 enzymes. Among these, VIM-1 showed the h ighest degree of similarity to Bc-II. Similarly to bla(IMP), bla(VIM) was a lso found to be carried on a gene cassette inserted into a class 1 integron , The bla(VIM)-containing integron was located on the chromosome of P. aeru ginosa VR-143/97, and the metallo-beta-lactamase-encoding determinant was n ot transferable to E, coli by conjugation, Expression of the integron-borne bla(VIM) gene in E. coli resulted in a significant decrease in susceptibil ity to a broad array of beta-lactams (ampicillin, carbenicillin, piperacill in, mezlocillin, cefotaxime, cefoxitin, ceftazidime, cefoperazone, cefepime , and carbapenems), revealing a very broad substrate specificity of the VIM -1 enzyme.