Abstract
Carbapenem-resistant Enterobacterales (CRE) pose a serious threat to clinical management and public health. We investigated the molecular characteristics of 12 IMP-4 metallo-β-lactamase-producing strains, namely, 5 Enterobacter cloacae, 3 Escherichia coli, 2 Klebsiella pneumoniae, and 2 Citrobacter freundii. These strains were collected from a tertiary teaching hospital in Zhengzhou from 2013 to 2015. The minimum inhibitory concentration (MIC) results showed that each blaIMP–4-positive isolate was multidrug-resistant (MDR) but susceptible to colistin. All of the E. coli belonged to ST167, two C. freundii isolates belonged to ST396, and diverse ST types were identified in E. cloacae and K. pneumoniae. S1-PFGE, Southern blotting, and PCR-based replicon typing assays showed that the blaIMP–4-carrying plasmids ranged from ∼52 to ∼360 kb and belonged to FII, FIB, HI2/HI2A, and N types. N plasmids were the predominant type (8/12, 66.7%). Plasmid stability testing indicated that the blaIMP–4-carrying N-type plasmid is more stable than the other types of plasmids. Conjugative assays revealed that three of the blaIMP–4-carrying N plasmids were transferrable. Complete sequence analysis of a representative N type (pIMP-ECL14–57) revealed that it was nearly identical to pIMP-FJ1503 (KU051710) (99% nucleotide identity and query coverage), an N-type blaIMP–4-carrying epidemic plasmid in a C. freundii strain. PCR mapping indicated that a transposon-like structure [IS6100-mobC-intron (K1.pn.I3)-blaIMP–4-IntI1-IS26] was highly conserved in all of the N plasmids. IS26 involved recombination events that resulted in variable structures of this transposon-like module in FII and FIB plasmids. The blaIMP–4 gene was captured by a sul1-type integron In1589 on HI2/HI2A plasmid pIMP-ECL-13–46.
Highlights
The Zn(II)-containing metallo-β-lactamases (MBLs) comprise Imipenemase (IMP), New Delhi metallo-β-lactamase (NDM), and Verona Integron-encoded Metallo-βlactamase (VIM) types that belong to class B β-lactamase according to the Ambler classification
Multilocus sequence typing (MLST) was performed for all the IMP-4-positive E. cloacae, E. coli, C. freundii, and K. pneumoniae isolates
Drastic loss of the F-type plasmid pIMP-CF-15-127 and HI2-type plasmid pIMPECL-13-46 in transformants from CF-15-127 and ECL-13-46 was observed after 50 generations of multiplication, with 35 and 3%, respectively, retaining the blaIMP−4-harboring plasmid after 150 generations. These results revealed that, among the plasmids carrying blaIMP−4, the N type is more stable than the F type and HI2 type
Summary
The Zn(II)-containing metallo-β-lactamases (MBLs) comprise Imipenemase (IMP), New Delhi metallo-β-lactamase (NDM), and Verona Integron-encoded Metallo-βlactamase (VIM) types that belong to class B β-lactamase according to the Ambler classification. The most commonly encountered blaIMP−4 gene has been found captured by class 1 integrons and carried by plasmids belonging to multiple replicon types including HI2, L/M, A/C, and N for dissemination (Lai et al, 2017; Matsumura et al, 2017). An epidemic N plasmid in Enterobacterales isolates was recently recovered from Shanghai, Guangdong, and Fujian provinces of China and was responsible for the dissemination of blaIMP−4 gene (Wang et al, 2017). It is not known if this type of plasmid is prevalent in other regions of China and if it is involved in the spread of blaIMP genes.
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