Detection of VIM-5 metallo- -lactamase in a Pseudomonas aeruginosa clinical isolate from Turkey

Sir, The acquisition of metallo-β-lactamases is one of the most important emerging mechanisms of carbapenem resistance in Pseudomonas aeruginosa. Once thought to be a problem limited to Japan, this is now acknowledged to be a global problem, as documented by reports from various continents.1 Four families of acquired metallo-β-lactamases, namely IMP, VIM, SPM (GenBank accession no. AJ492820.1) and GIM (GenBank accession no. AJ620678.1), have been thus far identified in P. aeruginosa isolates.1–4 The VIM-type enzymes appear to be the most prevalent in Europe and in Korea, and at least 10 different variants have been described.1 VIM-5, a variant closely related to VIM-1, was originally reported in an imipenem-resistant Klebsiella pneumoniae isolate from Turkey.5 Compared with VIM-1, VIM-5 differs by five amino acid substitutions: A130K, H224L, E225A, S228R, K291T (numbering is according to the BBL scheme). In this paper, we report the detection of a carbapenem-resistant P. aeruginosa isolate that produced VIM-5 enzyme. P. aeruginosa GB-K5 was isolated in January 2003 from the respiratory tract of a 53-year-old patient undergoing cardiovascular surgery at the SSK Training Hospital, Ankara, Turkey. The patient had heart and renal failure, but no overt signs of lower respiratory tract infection, suggesting that the isolate was a colonizer. GB-K5 was resistant to imipenem, meropenem, aztreonam, ceftazidime, piperacillin, piperacillin–tazobactam, cefepime, ciprofloxacin, tobramycin, amikacin and gentamicin, based on the results of broth-microdilution susceptibility testing and NCCLS interpretive guidelines. MICs of imipenem and meropenem were >128 mg/L. MBL Etest (AB Biodisk, Solna, Sweden) revealed a decrease in imipenem MIC in the presence of EDTA (from >256 mg/L to <1 mg/L), suggesting the production of a metallo-β-lactamase. However, a double-disc test with 2-mercaptopropionic acid (MPA) as a metallo-β-lactamase inhibitor did not show any synergic activity between ceftazidime and MPA; synergy was clearly detected with control strain VR-143/97, which produces VIM-1.2 Testing a crude extract of GB-K5 for the presence of EDTA-inhibitable carbapenemase activity2 revealed the presence of imipenemase activity (specific activity, 1.8 × 10−7 mol/min/mg), which was inhibited by >80% in the presence of 2 mM EDTA. PCR for detection of blaIMP and blaVIM genes yielded a 523 bp amplification product with blaVIM-specific primers. Amplification of the entire blaVIM determinant using primers VIM-CF (5′-GCACCCACCCTCATGGAG) and VIM-CR (5′-ATGCCGCATCTGCTACTC) yielded an amplicon of 836 bp. Direct sequencing of both strands confirmed the presence of blaVIM-5 (GenBank accession no. AY456196), which was previously reported in a K. pneumoniae isolate from a different city of the same country (GenBank accession no. AY144612). To our knowledge, this is the first report of a metallo-β-lactamase-producing P. aeruginosa isolate from Turkey. The presence of VIM-5 enzyme, which was detected in a K. pneumoniae isolated from a different Turkish area, suggests regional spread of this resistance determinant. These findings underscore the dissemination potential of metallo-β-lactamases as emerging resistance determinants in Gram-negative pathogens, and the need for their systematic surveillance. 1Clinical Microbiology, SSK Training Hospital, Ankara, Turkey 2Department of Pathology, University of Verona, Strada Le Grazie, 8, 37134 Verona 3Department of Molecular Biology, University of Siena, Siena, Italy