Genetic Organization of Transposase Regions Surrounding bla KPC Carbapenemase Genes on Plasmids from Klebsiella Strains Isolated in a New York City Hospital

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Abstract
Carbapenem-resistant Klebsiella strains carrying Klebsiella pneumoniae carbapenemases (KPC) are endemic to New York City and are spreading across the United States and internationally. Recent studies have indicated that the KPC structural gene is located on a 10-kb plasmid-borne element designated Tn 4401 . Fourteen Klebsiella pneumoniae strains and one Klebsiella oxytoca strain isolated at a New York City hospital in 2005 carrying either bla KPC-2 or bla KPC-3 were examined for isoforms of Tn 4401 . Ten of the Klebsiella strains contained a 100-bp deletion in Tn 4401 , corresponding to the Tn 4401 a isoform. The presence of this deletion adjacent to the upstream promoter region of bla KPC in Tn 4401 a resulted in a different −35 promoter sequence of TGGAGA than that of CTGATT present in isoform Tn 4401 b. Complete sequencing of one plasmid carrying bla KPC from each of three nonclonal isolates indicated the presence of genes encoding other types of antibiotic resistance determinants. The 70.6-kb plasmid from K. pneumoniae strain S9 carrying bla KPC-2 revealed two identical copies of Tn 4401 b inserted in an inverse fashion, but in this case, one of the elements disrupted a group II self-splicing intron. In K. pneumoniae strain S15, the Tn 4401 a element carrying bla KPC-2 was found on both a large 120-kb plasmid and a smaller 24-kb plasmid. Pulsed-field gel electrophoresis results indicate that the isolates studied represent a heterogeneous group composed of unrelated as well as closely related Klebsiella strains. Our results suggest that endemic KPC-positive Klebsiella strains constitute a generally nonclonal population comprised of various alleles of bla KPC on several distinct plasmid genetic backgrounds. This study increases our understanding of the genetic composition of the evolving and expanding role of KPC-producing, healthcare-associated, gram-negative pathogens.

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