Abstract
A carbapenem-resistant Klebsiella pneumoniae strain 628 was isolated from a human case of intracranial infection in a Chinese teaching hospital. Strain 628 produces KPC-2 and CTX-M-55 encoded by two different conjugative plasmids, i.e., the IncFIIK plasmid p628-KPC and the IncI1 plasmid p628-CTXM respectively. blaKPC−2 is captured by a Tn1722-based unit transposon with a linear structure. ΔTn3-ISKpn27-blaKPC−2-ΔISKpn6-ΔTn1722 and this transposon together with a mercury resistance (mer) gene locus constitutes a 34 kb acquired drug-resistance region. blaKPC−2 has two transcription starts (nucleotides G and C located at 39 and 250 bp upstream of its coding region respectively) which correspond to two promoters, i.e., the intrinsic P1 and the upstream ISKpn27/Tn3-provided P2 with the core −35/−10 elements TAATCC/TTACAT and TTGACA/AATAAT respectively. blaCTX−M−55 is mobilized in an ISEcp1-blaCTX−M−55-Δorf477 transposition unit and appears to be the sole drug-resistant determinant in p628-CTXM. blaCTX−M−55 possesses a single transcription start (nucleotides G located at 116 bp upstream of its coding region) corresponding to the ISEcp1-provided P1 promoter with the core −35/−10 element TTGAAA/TACAAT. All the above detected promoters display a characteristic of constitutive expression. Coexistence of blaKPC and blaCTX−M in K. pneumoniae has been reported many times but this is the first report to gain deep insights into genetic platforms, promoters, and expression of the two coexisting bla genes with determination of entire nucleotide sequences of the two corresponding plasmids.
Highlights
KPC-producing Klebsiella pneumoniae has spread worldwide and became an emerging pathogen with serious clinical and infection control implications (Tzouvelekis et al, 2012; MunozPrice et al, 2013)
All of 628, 628-KPC-EC600 and 628-CTXM-EC600 are resistant to ampicillin, ampicillin/sulbactam, penicillin, monobactam, and cephalosporins tested (Table 1). 628 and 628-KPC-EC600 are resistant to piperacillin/tazobactam. 628 and 628-KPC-EC600 are carbapenem-resistant
KPC-2 and CTX-M-55 enzymes are produced by two different conjugative plasmids, p628-KPC and p628-CTXM respectively, in K. pneumoniae strain 628, and the sequences of these two plasmids are >98% identical to other relevant plasmids carrying the same resistance determinants previously sequenced
Summary
KPC-producing Klebsiella pneumoniae has spread worldwide and became an emerging pathogen with serious clinical and infection control implications (Tzouvelekis et al, 2012; MunozPrice et al, 2013). Coexistence of blaKPC and blaCTX−M in K. pneumoniae has been reported in several countries, such as blaKPC−2/blaCTX−M−1 group, blaKPC−2/blaCTX−M−2 group, and Coexsitence of p628-KPC and p628-CTXM in K. pneumoniae blaKPC−2/blaCTX−M−8 group in Brazil (Peirano et al, 2009), blaKPC−2/blaCTX−M−10, blaKPC−2/blaCTX−M−15, and blaKPC−3/blaCTX−M−2 in Israel (Leavitt et al, 2007, 2010), blaKPC−2/blaCTX−M−14 in China (Cai et al, 2008), and blaKPC−2/blaCTX−M−15 in Greece (Souli et al, 2010) All these studies are confined to PCR detection and sequencing of bla genes, lacking deeper characterization of mechanisms of drug resistance. The promoters and their expression characteristics of these two plasmid-borne bla genes are dissected experimentally
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