Chromosomal Integration of the Klebsiella pneumoniae Carbapenemase Gene, bla KPC , in Klebsiella Species Is Elusive but Not Rare.

Carbapenemase genes in Enterobacteriaceae are mostly described as being plasmid associated. However, the genetic context of carbapenemase genes is not always confirmed in epidemiological surveys, and the frequency of their chromosomal integration therefore is unknown. A previously sequenced collection of bla KPC -positive Enterobacteriaceae from a single U.S. institution (2007 to 2012; n = 281 isolates from 182 patients) was analyzed to identify chromosomal insertions of Tn 4401 , the transposon most frequently harboring bla KPC Using a combination of short- and long-read sequencing, we confirmed five independent chromosomal integration events from 6/182 (3%) patients, corresponding to 15/281 (5%) isolates. Three patients had isolates identified by perirectal screening, and three had infections which were all successfully treated. When a single copy of bla KPC was in the chromosome, one or both of the phenotypic carbapenemase tests were negative. All chromosomally integrated bla KPC genes were from Klebsiella spp., predominantly K. pneumoniae clonal group 258 (CG258), even though these represented only a small proportion of the isolates. Integration occurred via IS 15 -ΔI-mediated transposition of a larger, composite region encompassing Tn 4401 at one locus of chromosomal integration, seen in the same strain ( K. pneumoniae ST340) in two patients. In summary, we identified five independent chromosomal integrations of bla KPC in a large outbreak, demonstrating that this is not a rare event. bla KPC was more frequently integrated into the chromosome of epidemic CG258 K. pneumoniae lineages (ST11, ST258, and ST340) and was more difficult to detect by routine phenotypic methods in this context. The presence of chromosomally integrated bla KPC within successful, globally disseminated K. pneumoniae strains therefore is likely underestimated.