Carbapenemase-producing Enterobacteriaceae, U.S. Rivers

摘要

Our study was initiated by previous isolation of 30imipenem-resistant, gram-negative rods from 7 of 16 U.S.rivers sampled from 1999 to 2001. Imipenem hydrolysiswas detected in 22 of those isolates identified asEnterobacter asburiae. Random amplified polymorphismDNA analysis showed that these E. asburiae isolates weregenetically indistinguishable. An identical clavulanicacid–inhibited β-lactamase IMI-2 was identified from eachisolate that shared 99% and 97% amino acid identity withthe chromosome-encoded β-lactamases IMI-1 and NmcA,respectively, from E. cloacae clinical isolates. The blaIMI-2gene was located on a self-transferable 66-kb plasmid.Sequence analysis of a cloned 5.5-kb DNA fragmentobtained from 1 of the imipenem-resistant E. asburiae iso-lates identified an upstream LysR-type regulator gene thatexplained inducibility of IMI-2 expression. β-Lactamase IMI-2 is the first inducible and plasmid-encoded carbapene-mase. Identification of clonally related E. asburiae isolatesfrom distant rivers indicates an environmental and enter-obacterial reservoir for carbapenemase genes