Carbapenem-resistant Enterobacter cloacae and the emergence of metallo-β-lactamase-producing strains in a third-level hospital (Santiago de Compostela, NW Spain)

Abstract

The purpose of this paper was to investigate the occurrence of carbapenem-resistant Enterobacter cloacae in our institution, to detect the carbapenemase-associated resistance and to determine the genetic relatedness of the isolates. Species identification and antimicrobial susceptibility testing were performed using the Vitek 2 system and Etest. Multiplex polymerase chain reaction–enzyme linked immunosorbent assay (PCR-ELISA) was used for the detection of extended-spectrum β-lactamase (ESBL)-producers. The bla _IMP and bla _VIM genes were amplified by PCR and sequenced. The DiversiLab System was used for strain-typing. During the period 2006–2008, 12 different isolates of carbapenem-resistant E. cloacae (2.3 %) were recovered in our laboratory. Only two positive isolates for the bla _VIM gene were detected. The minimum inhibitory concentration (MIC) values were higher for all carbapenems in the group of non-metallo-β-lactamase (MBL)-producers. All isolates showed MIC values ≤2 against this tigecycline. The two bla _VIM-1-carrying isolates showed different genotypes. For non-MBL-producers, two clonally related clusters were observed. Different mechanisms can be associated with carbapenem-resistance in E. cloacae. MBL-producing strains are less prevalent than those with other mechanisms of resistance. The clonal relationship confirms the risk of spread of these organisms with the transfer of patients to different wards and the persistence of these clones over time or the ‘de novo’ acquisition of the resistance caused by the selective pressure exerted by antibiotics treatments.