Phenotypic and genotypic characterization of Klebsiella pneumoniae strains with reduced susceptibiliy to carbapenems

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Simone Ambretti
Paolo Gaibani
Federica Caroli
Luisa Miragliotta
Gloria Bua
Vittorio Sambri *
(*) Corresponding Author:
Vittorio Sambri | vittorio.sambri@unibo.it

Abstract

Reduced susceptibility to carbapenems in Gram-negative pathogens is an emerging feature of the antibiotic-resistance phenomenom Reports about strains resistant to this class of antibiotics among Enterobacteriaceae, particularly in Klebsiella pneumoniae, are increasing.The aims of this study were to assess the incidence of Klebsiella pneumoniae with reduced susceptibility to carbapenems in Bologna area and to carry out the characterization of these strains.The study included isolates of K. pneumoniae that showed reduced susceptibility to carbapenems, as detected by an automated system (Vitek2, bioMérieux). Between January and May 2009, 26 strains were collected (mainly isolated from urinary samples).These isolates were tested for susceptibility to carbapenems by E-test, to define MIC values for meropenem and ertapenem. Moreover, to detect the production of metallo-beta lactamases (MBL) and carbapenemases (KPC) were respectively performed the Etest with imipenem and imipenem/EDTA (IPM-IPM/EDTA) and the modified Hodge test. Susceptibility assays performed by E-test showed that 25/26 strains were susceptible to meropenem, while for ertapenem 20/26 strains resulted resistant.The modified Hodge test was positive for 1 strain, while all the isolates were negative to the IPM-IPM/EDTA E-test.These results show that, as recently reported, the majority of strains of K. pneumoniae exhibiting reduced susceptibility to carbapenems, especially to ertapenem, are characterized by the production of ESBLs, which likely is associated with the loss of porins. On the other side, one strain was found to produce KPC and this finding confirms that the diffusion of carbapenemases producing K. pneumoniae has also to be considered in this geographic area.

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