Clin Microbiol Infect 2012; 18: 413–431 Abstract Plasmid‐acquired carbapenemases in Enterobacteriaceae, which were first discovered in Europe in the 1990s, are now increasingly being identified at an alarming rate. Although their hydrolysis spectrum may vary, they hydrolyse most β‐lactams, including carbapenems. They are mostly of the KPC, VIM, NDM and OXA‐48 types. Their prevalence in Europe as reported in 2011 varies significantly from high (Greece and Italy) to low (Nordic countries). The types of carbapenemase vary among countries, partially depending on the cultural/population exchange relationship between the European countries and the possible reservoirs of each carbapenemase. Carbapenemase producers are mainly identified among Klebsiella pneumoniae and Escherichia coli, and still mostly in hospital settings and rarely in the community. Although important nosocomial outbreaks with carbapenemase‐producing Enterobacteriaceae have been extensively reported, many new cases are still related to importation from a foreign country. Rapid identification of colonized or infected patients and screening of carriers is possible, and will probably be effective for prevention of a scenario of endemicity, as now reported for extended‐spectrum β‐lactamase (mainly CTX‐M) producers in all European countries.

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Carbapenem-hydrolysing β-lactamases are the most powerful β-lactamases, being able to hydrolyse almost all β-lactams. They are mostly of the KPC, VIM, IMP, NDM and OXA-48 types. Their current extensive spread worldwide in Enterobacteriaceae is an important source of concern, as these carbapenemase producers are multidrug-resistant. Detection of infected patients and of carriers are the two main approaches for prevention of their spread. Phenotypic and molecular-based techniques are able to identify these carbapenemase producers, although with variable efficiencies. The detection of carriers still relies mostly on the use of screening culture media.

Acquired carbapenemases are emerging resistance determinants in Gram-negative pathogens, including Enterobacteriaceae, Pseudomonas aeruginosa and other Gram-negative non-fermenters. A consistent number of acquired carbapenemases have been identified during the past few years, belonging to either molecular class B (metallo-beta-lactamases) or molecular classes A and D (serine carbapenemases), and genes encoding these enzymes are associated with mobile genetic elements that allow their rapid dissemination in the clinical setting. Therefore, detection and surveillance of carbapenemase-producing organisms have become matters of major importance for the selection of appropriate therapeutic schemes and the implementation of infection control measures. As carbapenemase production cannot be simply inferred from the resistance profile, criteria must be established for which isolates should be suspected and screened for carbapenemase production, and for which tests (phenotypic and/or genotypic) should be adopted for confirmation of the resistance mechanism. Moreover, strategies should be devised for surveillance of carbapenemase producers in order to enable the implementation of effective surveillance programmes. The above issues are addressed in this article, as a follow-up to an expert meeting on acquired carbapenemases that was recently organized by the ESCMID Study Group for Antibiotic Resistance Surveillance.

Seventeen Klebsiella pneumoniae clinical isolates carrying the bla VIM-1 metallo-␤-lactamase gene were collected in the intensive care units of three hospitals in Athens, Greece, in 2002. They exhibited various carbapenem resistance levels (Etest MICs of imipenem ranged from 4 to 32 g/ml). All isolates gave positive results by the imipenem-EDTA synergy Etest. The isolates were classified into four main types by pulsed-field gel electrophoresis; the majority of the isolates (5 and 10 isolates) belonged to two types. The bla VIM-1 gene cassette was part of the variable region of a class 1 integron that also included aac6, dhfrI, and aadA. This structure was carried by transferable plasmids.