Enhanced Klebsiella pneumoniae Carbapenemase Expression from a Novel Tn 4401 Deletion

The Klebsiella pneumoniae carbapenemase gene ( bla KPC ) is typically located within mobile transposon Tn 4401 Enhanced KPC expression has been associated with deletions in the putative promoter region upstream of bla KPC Illumina sequences from bla KPC -positive clinical isolates from a single institution were mapped to a Tn 4401 b reference sequence, which carries no deletions. The novel isoform Tn 4401 h (188-bp deletion [between istB and bla KPC ]) was present in 14% (39/281) of clinical isolates. MICs showed that Escherichia coli strains containing plasmids with Tn 4401 a and Tn 4401 h were more resistant to meropenem (≥16 and ≥16, respectively), ertapenem (≥8 and 4, respectively), and cefepime (≥64 and 4, respectively) than E. coli strains with Tn 4401 b (0.5, ≤0.5, and ≤1, respectively). Quantitative real-time PCR (qRT-PCR) demonstrated that Tn 4401 a had a 16-fold increase and Tn 4401 h a 4-fold increase in bla KPC mRNA levels compared to the reference Tn 4401 b. A lacZ reporter plasmid was used to test the activity of the promoter regions from the different variants, and the results showed that the Tn 4401 a and Tn 4401 h promoter sequences generated higher β-galactosidase activity than the corresponding Tn 4401 b sequence. Further dissection of the promoter region demonstrated that putative promoter P1 was not functional. The activity of the isolated P2 promoter was greatly enhanced by inclusion of the P1-P2 intervening sequence. These studies indicated that gene expression could be an important consideration in understanding resistance phenotypes predicted by genetic signatures in the context of sequencing-based rapid diagnostics.