Carbapenem-Resistant Pseudomonas aeruginosa with Acquired [bla.sub.VIM] Metallo-[Beta]-Lactamase Determinants, Italy.

To the Editor: Acquired metallo-[Beta]-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-[Beta]-lactamases, as well as their resistance to [Beta]-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-[Beta]-lactamase determinant.

We recently described a new acquired metallo-[Beta]-lactamase determinant, [bla.sub.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.sub.VIM]-positive P. aeruginosa, which was caused both by strains that were clonally related to VR-143/97 and by clonally unrelated strains (4). [bla.sub.VIM] is the second known metallo-[Beta]-lactamase determinant that can spread among P. aeruginosa; the first was [bla.sub.VIM], which was detected in the early 1990s in nosocomial isolates of various Enterobacteriaceae, 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, [bla.sub.VIM] resembles [bla.sub.IMP] 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, [bla.sub.VIM] 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-[Beta]-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 isolates were highly resistant to carbapenems (MICs for imipenem and meropenem were [is greater than] 64 [micro] g/mL) and to carbenicillin, ticarcillin, ticarcillin/clavulanate, piperacillin, piperacillin/ tazobactam, mezlocillin, ciprofloxacin, gentamicin, tobramycin, and netilmicin. All five were also resistant to ceftazidime and cefepime, except for SAP-01/99, which had intermediate resistance to the above drugs. Some isolates retained susceptibility to aztreonam (PPV-97, TS-832035, and SAP-01/99) or amikacin (PPV-108, TS-832035, and TS-832347).

In a colony-blot hybridization assay (3), all the above isolates were recognized by a [bla.sub.VIM]-specific probe consisting of an amplicon that contained the entire [bla.sub.VIM] coding sequence (3). None were recognized by a probe specific for [bla.sub.IMP] and consisting of a 0.5-kb HindIII fragment from the [bla.sub.IMP] gene (8).

Our results indicate that circulation of carbapenem-resistant P. aeruginosa carrying [bla.sub.VIM] metallo-[Beta]-lactamase determinants, originally detected in one Italian hospital (3-4), could soon become widespread. The detection in different hospitals of [bla.sub.VIM]-positive isolates that apparently were epidemiologically unrelated suggests that the environmental reservoir of [bla.sub.VIM]-containing strains is relatively broad and that this novel determinant has potential relevance for the emerging phenomenon of carbapenem resistance in P. aeruginosa. Since we did not sequence the [bla.sub.VIM]-related genes carried by the various isolates, we do not yet know whether they differ from that cloned from P. aeruginosa VR-143/97 (3). The five isolates described in this report are being characterized to ascertain their clonal relatedness and identify the sequences of their [bla.sub.VIM]-related determinants. The recent appearance of this and other acquired metallo-[Beta]-lactamases among P, aeruginosa and other gram-negative pathogens in Europe (810) underlines the need for systematic surveillance to monitor the spread of similar resistance determinants.

This work was supported by grants no. FMRX-CT98-0232 from the European TMR Research Network on metallo-[Beta]-lactamases and no. 9906404271 from MURST ex-40%.

References

(1.) Livermore DM. Acquired carbapenemases. J Antimicrob Chemother 1997;39:673-6.

(2.) Rasmussen BA, Bush K. Carbapenem-hydrolyzing [Beta]-lactamases. Antimicrob Agents Chemother 1997;41:223-32.

(3.) Lauretti L, Riccio ML, Mazzariol A, Cornaglia G, Amicosante G, Fontana R, et al. Cloning and characterization of [bla.sub.VIM], a new integron-borne metallo-[Beta]-lactamase gene from a Pseudomonas aeruginosa clinical isolate. Antimicrob Agents Chemother 1999;43:1584-90.

(4.) Mazzariol A, Cornaglia G, Piccoli P, Lauretti L, Riccio ML, Rossolini GM, et al. Carbapenem-hydrolyzing [Beta]-lactamases in Pseudomonas aeruginosa. Eur J Clin Microbiol Infect Dis 1999;18:455-6.

(5.) Senda K, Arakawa Y, Nakashima K, Ito H, Ichiyama S, Shimokata K, et al. Multifocal outbreaks of metallo-[Beta]-lactamase-producing Pseudomonas aeruginosa resistant to broad-spectrum [Beta]-lactams, including carbapenems. Antimicrob Agents Chemother 1996;40:349-53.

(6.) Lee K, Chong Y, Shin HB, Yong D. Rapid increase of imipenem-hydrolyzing Pseudomonas aeruginosa in a Korean hospital. In: Program and Abstracts of the 38th Interscience Conference on Antimicrobial Agents and Chemotherapy. Washington: American Society for Microbiology; 1998. [Abstract E85].

(7.) Koh TH, Babini GS, Woodford N, Sng LH, Hall LM, Livermore DM. Carbapenem-hydrolysing IMP-1 [Beta]-lactamase in Klebsiella pneumoniae from Singapore. Lancet 1999;353:2162.

(8.) Cornaglia G, Riccio ML, Mazzariol A, Lauretti L, Fontana R, Rossolini GM. Appearance of IMP-1 metallo-[Beta]-lactamase in Europe. Lancet 1999;353:899-900.

(9.) Woodford N, Palepou M-FI, Babini GS, Bates J, Livermore DM. Carbapenemase-producing Pseudomonas aeruginosa in the UK. Lancet 1998;352:546-7.

(10.) Cardoso O, Sousa JC, Leitao R, Peixe L. Carbapenem-hydrolysing [Beta]-lactamase from clinical isolates of Pseudomonas aeruginosa in Portugal. J Antimicrob Chemother 1999;44:135.

Gian Maria Rossolini,(*) Maria Letizia Riccio,(*) Giuseppe Cornaglia,([dagger]) Laura Pagani,([double dagger]) Cristina Lagatolla,([sections] Laura Selan,([paragraph]) and Roberta Fontana([dagger])

(*) Universita di Siena, Siena, Italy; ([dagger]) Universita di Verona, Verona, Italy; ([double dagger]) Universita di Pavia, Pavia, Italy; ([sections]) Universita di Trieste, Trieste, Italy; and ([paragraph]) Universita "La Sapienza," Rome, Italy