IS26 carrying blaKPC-2 mediates carbapenem resistance heterogeneity in extensively drug-resistant Klebsiella pneumoniae isolated from clinical sites.

Background: Due to the widespread and irrational use of antibiotics, the emergence and prevalence of carbapenem-resistant Klebsiella pneumoniae (K. pneumoniae) have become a major challenge in controlling bacterial infections in hospitals. The bla_KPC-2 gene located on mobile genetic elements has further complicated the control of resistant bacteria transmission.

Results: In this study, K. pneumoniae strains were isolated from blood cultures of patients. Using the Kirby-Bauer disk diffusion method, we found carbapenem resistance heterogeneity. The resistant subpopulation KPTA-R1 and the sensitive subpopulation KPTA-S1 were purified. Whole-genome sequencing revealed that the bla_KPC-2 gene in KPTA-R1 was located on an IncFII plasmid (pKPC-R), within a composite transposon (PCTs) formed by two direct repeats of IS26 elements. The structure was identified as IS26-RecA-ISKpn27-bla_KPC-2-ISKpn6-IS26. However, in KPTA-S1, a similar plasmid, pAR-S, lacked this segment. Sequence comparison analysis indicates that the deletion of this bla_KPC-2 encoding sequence in this IncFII plasmid is associated with transposition activity mediated by IS26. Multi-sequence comparison of the plasmids showed that the IS26 transposon facilitated the sequence polymorphism of these plasmids.

Conclusion: This study reveals the key role of IS26-mediated transposition activity, through homologous recombination, in the emergence of carbapenem resistance heterogeneity in clinical K. pneumoniae strains carrying bla_KPC-2. IS26 is able to promote the evolution of resistance in the IncFII plasmid, and through copy-in cointegration or targeted conservative cointegration may result in the acquisition or loss of antibiotic resistance, which may affect clinical care and pose a public health risk.