Acquired metallo-␤-lactamases (MBLs) are resistance determinants of increasing clinical importance in Gram-negative bacterial pathogens, which confer a broad-spectrum ␤-lactam resistance, including carbapenems. Several such enzymes have been described since the 1990s. In the present study, a novel acquired MBL, named FIM-1, was identified and characterized. The bla FIM-1 gene was cloned from a multidrug-resistant Pseudomonas aeruginosa clinical isolate (FI-14/157) cultured from a patient with a vascular graft infection in Florence, Italy. The isolate belonged in the sequence type 235 epidemic clonal lineage. The FIM-1 enzyme is a member of subclass B1 and, among acquired MBLs, exhibited the highest similarity (ca. 40% amino acid identity) with NDM-type enzymes. In P. aeruginosa FI-14/157, the bla FIM-1 gene was apparently inserted into the chromosome and associated with ISCR19-like elements that were likely involved in the capture and mobilization of this MBL gene. Transfer experiments of the bla FIM-1 gene to an Escherichia coli strain or another P. aeruginosa strain by conjugation or electrotransformation were not successful. The FIM-1 protein was produced in E. coli and purified by two chromatography steps. Analysis of the kinetic parameters, carried out with the purified enzyme, revealed that FIM-1 has a broad substrate specificity, with a preference for penicillins (except the 6␣-methoxy derivative temocillin) and carbapenems. Aztreonam was not hydrolyzed. Detection of this novel type of acquired MBL in a P. aeruginosa clinical isolate underscores the increasing diversity of such enzymes that can be encountered in the clinical setting.A cquired metallo-␤-lactamases (MBLs) are resistance determinants of increasing clinical importance in Gram-negative bacterial pathogens, including Pseudomonas aeruginosa, Enterobacteriaceae, and other Gram-negative nonfermenters. These enzymes can degrade most ␤-lactams, including carbapenems, and escape inhibition by the conventional ␤-lactamase inhibitors or avibactam. Thus, they are able to confer an extended ␤-lactam resistance profile to the bacterial host that is not reversible by ␤-lactamase inhibitors (1).Acquired MBLs were detected since the early 1990s, the first representatives being IMP-and VIM-type enzymes (2-4). Thereafter, a number of additional lineages of acquired MBLs have been described, including the SPM-, GIM-, SIM-, KHM-, NDM-, AIM-, DIM-, SMB-, and TMB-type enzymes (5, 6; see also reference 1 and references therein). By convention, different MBL types diverge from each other at by least 30% at the amino acid sequence level (7). Enzymes of different types may differ in functional properties, and the corresponding genes may be associated with different types of mobile genetic elements responsible for their dissemination, such as mobile gene cassettes inserted into integrons, ISCR elements, or composite transposons (8, 9).We report here on the identification and characterization of a new type of acquired MBL, named FIM-1, in a multidrug-resistant clinical ...

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