Characterization of DIM1, an integron-encoded metallobeta-lactamase from a Pseudomonas stutzeri clinical isolate in the Netherlands

A carbapenem-resistant Pseudomonas stutzeri strain isolated from a Dutch patient was analyzed in detail. This isolate produced a metallo--lactamase (MBL) whose gene, with 43.5 % GC content, was cloned and expressed in Escherichia coli. -Lactamase DIM-1 (for Dutch imipenemase) was weakly related to other Ambler class B -lactamases, sharing <52 % amino acid identity with the most closely related MBL, GIM-1, and 45% identity with IMP-type MBLs. The -Lactamase DIM-1 significantly hydrolyzed broad-spectrum cephalospo-rins and carbapenems and spared aztreonam. This MBL gene was embedded in a class 1 integron containing two other gene cassettes, encoding resistance to aminoglycosides and disinfectants, that was located on a 70-kb plasmid. Metallo--lactamases (MBLs) are among the most challeng-ing antibiotic resistance threats in Gram-negative organisms (8). These enzymes very efficiently hydrolyze all -lactams, including carbapenems (with the exception of aztreonam), and are located most often on transferable genetic platforms (33). Different MBL-type enzymes have been described, with IMP and VIM derivatives being the most widespread (33). Th