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 microg/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 ( approximately 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.