Comparative Analysis of bla_KPC Expression in Tn4401 Transposons and the Tn3-Tn4401 Chimera

Two basic structures that carry the bla_KPC gene, the Tn4401 transposon and the Tn3-Tn4401 chimera, have been identified within and outside China. However, the different bla_KPC expression levels and promoter activities of these two structures are not completely understood. We constructed Tn4401a, Tn4401b, and Tn3-Tn4401 chimera recombinants and found that the imipenem (IPM) and meropenem (MEM) MICs for the Escherichia coli transformants carrying the chimera were 2-fold higher than for those carrying Tn4401b but 2-fold lower than for those carrying Tn4401a In addition to the promoter P1, we characterized a novel potential promoter sequence (PX) in the chimera using 5' rapid amplification of cDNA ends (5' RACE), of which the -35 and -10 sequences were TTCAAA and TGAGACAAT, respectively. Although mutation of P1, P2, or PX significantly downregulated bla_KPC mRNA expression in each structure (P < 0.05), the P2 mutation resulted in 2- and 3-fold greater decreases than the P1 mutation in Tn4401a and Tn4401b, respectively. Similarly, despite no significant difference in the PX and P1 mutations in the chimera, the carbapenem MIC and Klebsiella pneumoniae carbapenemase (KPC) production resulting from P2 mutations were significantly lower than those of P1 (P < 0.01) in the Tn4401 transposons. These studies indicate that the Tn3-Tn4401 chimera contains a novel potential bla_KPC promoter, PX, and that its carbapenem resistance falls in between those of Tn4401a and Tn4401b.