Genetic structures at the origin of acquisition of the β-lactamase blaKPC gene

Genetic structures surrounding the carbapenem-hydrolyzing Ambler class A bla(KPC) gene were characterized in several KPC-positive Klebsiella pneumoniae and Pseudomonas aeruginosa strains isolated from the United States, Colombia, and Greece. The bla(KPC) genes were associated in all cases with transposon-related structures. In the K. pneumoniae YC isolate from the United States, the beta-lactamase bla(KPC-2) gene was located on a novel Tn3-based transposon, Tn4401. Tn4401 was 10 kb in size, was delimited by two 39-bp imperfect inverted repeat sequences, and harbored, in addition to the beta-lactamase bla(KPC-2) gene, a transposase gene, a resolvase gene, and two novel insertion sequences, ISKpn6 and ISKpn7. Tn4401 has been identified in all isolates. However, two isoforms of this transposon were found: Tn4401a was found in K. pneumoniae YC and K. neumoniae GR from the United States and Greece, resectively, and differed by a 100-bp deletion, located just upstream of the bla(KPC-2) gene, compared to the sequence of Tn4401b, which was found in the Colombian isolates. In all isolates tested, Tn4401 was flanked by a 5-bp target site duplication, the signature of a recent transposition event, and was inserted in different open reading frames located on plasmids that varied in size and nature. Tn4401 is likely at the origin of carbapenem-hydrolyzing beta-lactamase KPC mobilization to plasmids and its further insertion into various-sized plasmids identified in nonclonally related K. pneumoniae and P. aeruginosa isolates.