Plasmid pKP12226 was extracted and analyzed from a CTX-M-15-producing Klebsiella pneumoniae sequence type 11 (ST11) isolate collected in South Korea. The plasmid represents chimeric characteristics consisting of a pIP1206-like backbone and lysogenized phage P1-like sequences. It bears a resistance region that includes resistance genes to several antibiotics and is different from previously characterized plasmids from South Korea bearing bla CTX-M-15 . It may have resulted from recombination between an Escherichia coli plasmid backbone, a bla CTX-M-15 -bearing resistance region, and lysogenized phage P1-like sequences.A lthough the spread of CTX-M-15 has mainly been associated with a high-risk clone of Escherichia coli sequence type 131 (ST131), Klebsiella pneumoniae isolates that produce CTX-M-15 are also disseminated worldwide (1, 2). In particular, the K. pneumoniae ST11 clone has been reported to be the most predominant CTX-M-15-producing clone in many countries, including South Korea (3-5). Similar to E. coli ST131, it has been observed that bla CTX-M-15 is usually located on IncF-type plasmids in K. pneumoniae isolates that produce CTX-M-15. Our previous studies have shown somewhat contradictory results on the evolution of the plasmid bearing bla CTX-M-15 in K. pneumoniae: while replicon typing of IncFII-type plasmids indicated that bla CTX-M-15 might not have been transferred directly from E. coli to K. pneumoniae, whole-plasmid analysis showed that bla CTX-M-15 -bearing plasmids from three different K. pneumoniae clones might result from recombination between a common plasmid backbone in K. pneumoniae and the resistance regions from plasmids of E. coli ST131 (6, 7). However, previous studies did not analyze the plasmids of CTX-M-15-producing K. pneumoniae ST11, a disseminating clone present worldwide, including in South Korea.In the present study, we determined the complete sequence of a plasmid carrying bla CTX-M-15 from a South Korean K. pneumoniae ST11 isolate, because the IncF-type plasmid of ST11 is the most prevalent in South Korea. We identified that the backbone of the plasmid is very similar to a plasmid of E. coli, and phage-like sequences were identified.pKP12226 is a plasmid carrying bla CTX-M-15 from K. pneumoniae strain K01-12226 isolated from a patient with bacteremia in South Korea. The isolate was determined to produce CTX-M-15-type extended-spectrum -lactamases (ESBLs) and was found in our previous study (2) to belong to ST11. Conjugation of the plasmid carrying the bla CTX-M-15 gene was accomplished by using E. coli strain J53 as a recipient, which is sodium azide resistant and plasmid free, as shown in previous studies (7,8). A Roche 454 genome sequencer FLX system (version 2.6) was used for wholeplasmid sequencing of plasmid pKP12226. A total of 51,656 sequence reads were generated, yielding a mean sequence coverage of 15ϫ. The sequencing reads were assembled into consensus de novo assembly contigs using the Roche 454 genome sequencer FLX software GSA assembler (version 2.6), yieldin...