Clusters of imipenem-resistant Acinetobacter baumannii clones producing different carbapenemases in an intensive care unit

ABSTRACT During a 2-year period (April 2005–March 2007), 31 intensive care unit (ICU) patients in a Greek hospital were infected or colonised with imipenem-resistant isolates of Acinetobacter baumannii. Twelve patients died, with imipenem-resistant A. baumannii infection contributing to the death of seven patients. The 31 representative A. baumannii isolates were multidrug-resistant and clustered in four distinct clones, each of which contained different carbapenemase genes: clone I was predominant and contained bla VIM-1 , bla OXA-58 and the intrinsic bla OXA-66 gene; clone II contained bla VIM-4 , bla OXA-58 and the intrinsic bla OXA-69 gene; clone III contained bla OXA-58 and the intrinsic bla OXA-69 gene; and clone IV contained only the intrinsic bla OXA-66 gene. I SAba1 was not associated with the intrinsic bla OXA-51-like alleles, whereas I SAba3 was found upstream and downstream of bla OXA-58 in isolates of clone I, and upstream of bla OXA-58 in isolates of clone III, but was not detected in isolates of clone II. PCR, curing and hybridisation experiments indicated that the bla VIM alleles were chromosomally located, whereas the bla OXA-58 alleles were plasmid-located. This study provides the first description of the clonal spread of multidrug-resistant A. baumannii isolates carrying bla VIM-1 and bla VIM-4 metallo-β-lactamase genes, and revealed that distinct carbapenem-resistant A. baumannii clusters bearing different carbapenemase genes may emerge and cause severe infections, even in a well-defined regional hospital setting.