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

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-69gene; clone III contained bla_OXA-58 and the intrinsic bla_OXA-69 gene; and clone IV contained only the intrinsic bla_OXA-66 gene. ISAba1 was not associated with the intrinsic bla_OXA-51-like alleles, whereas ISAba3 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.