Clinical experience of serious infections caused by Enterobacteriaceae producing VIM-1 metallo-β-lactamase in a Greek university hospital

Background. The dissemination of acquired metallo-beta-lactamases (MBLs) in members of the family Enterobacteriaceae is regarded as an emerging clinical threat. The clinical characteristics and outcomes of 17 cases of infection due to MBL-producing isolates were analyzed. Methods. During a 3-year period, medical records for all patients with confirmed infection due to an MBL-producing strain belonging to the Enterobacteriaceae family were retrospectively analyzed. We screened for MBL production with the imipenem-ethylenediaminetetraacetic acid disk synergy test, and results were confirmed by polymerase chain reaction. Genetic relatedness between isolates was evaluated by repetitive extragenic palindromic polymerase chain reaction. Results. Fourteen cases of bacteremia and 3 cases of ventilator-associated pneumonia due to an MBL-producing isolate were studied. Most of the patients had previously been colonized with an MBL-producing organism, and almost 60% had been exposed to carbapenems before infection. The isolated pathogens (Klebsiella pneumoniae, 14 cases; and Klebsiella oxytoca, Enterobacter cloacae, and Enterobacter aerogenes, 1 case each) exhibited variable minimum inhibitor concentrations of carbapenems (1 to > 32 mu g/mL) and resistance to most other beta-lactams. Tigecycline was active against all isolates, whereas colistin and gentamicin were active against 88% of them. Molecular studies confirmed the presence of a gene belonging to bla(VIM-1) cluster in all isolates. Among the 12 K. pneumoniae isolates, which were subjected to molecular typing, 11 distinct clones were identified. Five cases (similar to 30%) occurred in patients who were already receiving carbapenem-containing treatment, and carbapenem treatment was considered to have failed. Twelve cases were treated with a colistin-containing regimen. The attributable mortality rate was 18.8%. Conclusions. MBL-producing Enterobacteriaceae can cause severe, often fatal infection in severely ill patients, irrespective of the MIC of carbapenems. Colonization with an MBL-producer is a preceding event, highlighting the importance of surveillance. Both infection control practices and antibiotic policies should be intensified to contain the spread of these problematic bacteria.