Carbapenem-resistant Pseudomonas aeruginosa with acquired bla(vim) metallo-beta-lactamase determinants, Italy.

To the Editor: Acquired metallo-ß-lactamase determinants in Pseudomonas aeruginosa and other major bacterial pathogens are of concern for development of antimicrobial drug resistance. The carbapenemase and extended-spectrum cephalosporinase activity of metallo-ß-lactamases, as well as their resistance to ß-lactamase inhibitors, may severely limit the antimicrobial agents active against bacterial strains that produce such enzymes (1,2). Antimicrobial chemotherapy may become ineffective against P. aeruginosa strains with a multidrug-resistant phenotype that have acquired a metallo-ß-lactamase determinant. We recently described a new acquired metallo-ß-lactamase determinant, bla VIM , in a carbapenem-resistant P. aeruginosa clinical isolate (VR-143/97) from the University Hospital of Verona, Italy (3). This isolate was the index strain of an outbreak of bla VIM-positive P. aeruginosa, which was caused both by strains that were clonally related to VR-143/97 and by clonally unrelated strains (4). blaVIM is the second known metallo-ß-lactamase determinant that can spread among P. aeruginosa; the first was blaIMP, which was detected in the early 1990s in nosocomial isolates of various Enterobacteri-aceae, P. aeruginosa, and other nonfastidious gram-negative nonfermenters from the Far East (1,2,5-7) and, recently, in an Acinetobacter baumannii clinical isolate from Italy (8). Although completely unrelated at the sequence level, blaVIM resembles blaIMP in being carried on an integron-borne mobile gene cassette and in encoding an enzyme (VIM-1) with broad substrate specificity (3). Because of these properties, blaVIM has the potential to become a dangerous resistance determinant. An analysis of carbapenem-resistant P. aeruginosa from Italian hospitals since 1998 showed production of metallo-ß-lactamase, assayed as described (3), in five isolates from three hospitals in Italy. Two isolates (PPV-97 and PPV-108) were from the University Hospital of Pavia (PPV-97 was isolated in September 1998 from the urine of an inpatient in the neurosurgery department, and PPV-108 was isolated in November 1998 from a decubitus ulcer of an inpatient in the vascular surgery department); two (TS-832035 and TS-832347) were isolated in February 1999 from the University Hospital of Trieste (both from the blood of inpatients, in the intensive care unit and in the internal medicine department, respectively); and one (SAP-01/99) was isolated in September 1999 from the Rome University Hospital " Policlinico Umberto I " (from the blood of an inpatient in the vascular surgery department). Except for those from Pavia Hospital, where the two departments share the same surgical unit, no epidemiologic relationship could be established among any of them or with those previously isolated in Verona (3,4). The five …