Molecular Characteristics of an NDM-4 and OXA-181 Co-Producing K51-ST16 Carbapenem-Resistant Klebsiella pneumoniae: Study of Its Potential Dissemination Mediated by Conjugative Plasmids and Insertion Sequences.

The carbapenem-resistant Klebsiella pneumoniae (CRKP) strain GX34 was recovered from the respiratory tract of an elderly male with severe pneumonia, and only susceptible to amikacin, tigecycline, and colistin. Complete genome suggested that it belonged to K51-ST16 and harbored plasmid-encoded NDM-4 and OXA-181, located on IncFIB plasmid GX34p1_NDM-4 and ColKP3/IncX3 plasmid GX34p4_OXA-181, respectively. A series of transconjugants generated in the plasmid conjugation assays, including Escherichia coli J53-N1 (harboring a self-transmissible and -producing plasmid Eco-N-1-p), J53-N2 (harboring a -producing plasmid and a helper plasmid GX34p5), and J53-O (harboring a -producing plasmid), could be stably inherited after 10 days of serial passage and no significant biological fitness costs were detected. Furthermore, we first reported the gene, derived from mutation (460C>A) under meropenem pressure, could be transferred into a self-conjugative, recombined plasmid Eco-N-1-p of J53-N1. Eco-N-1-p was mainly recombined by GX34p4_OXA-181 (40,449 bp, 75.16%) and GX34p1_NDM-4 (8,553 bp, 15.89%), in which IS and IS probably played a major role. Eco-N-1-p could be transferred into the conjugation recipient K. pneumoniae KP54 and make the latter sacrifice fitness. The retention rates of remained high stability (>80% after 200 generations). The comparative genomic analysis of GX34 and those carrying or genes retrieved from the NCBI RefSeq database showed all (26/26, 100.00%) and (13/13, 100.00%) were surrounded by IS. The immediate environment of and in GX34 and some retrieved strains shared identical features, hinting at their possible dissemination. Effective measures should be taken to monitor the spread of this clone.