Emergence of carbapenem resistance in Enterobacteriaceae strains in Padua (Italy) from January 2008 to July 2012: phenotypic and genotipic assays

Introduction: In the management of nosocomial infections, the emergence of carbapenem-resistance in Enterobacteriaceae strains is a matter of increasing concern. The aim of this study was to detect and actively survey the presence of these strains by using phenotypic and genotypic assays. Methods: The screening of the strains with reduced carbapenem susceptibility was carried out using the automated Vitek®2 System (bioMérieux). Subsequently, we performed both different confirmation phoenotypic assays (Modified Hodge Test, Kirby-Bauer test, Etest® MBL MP/MPI, Etest® AmpC, Mueller-Hinton/cloxacillin test) and molecular identification tests ( PCR assays). Results: All the screened carbapenemase-producing strains (on the bases of the phenotypic tests results) were confirmed to harbour β-lactamase genes (by PCR analysis): 460 strains were positive for the presence of the blaKPC and 6 for the presence of the blaVIM gene. Conclusions: KPC-positive Klebsiella pneumoniae strains caused in our hospital,in the period 2008-2012, an outbreak of infection that was subsequently restricted with effective containment measures. It is mandatory that all carbapenemase-producing species will be closely monitored in hospital setting, to contain the possible rapid spread of strains showing more expansion properties and virulence.