Class 1 DISARM system in restriction of conjugative carbapenemase-encoding plasmids in Klebsiella pneumoniae sequence type 23.

BACKGROUND AND

OBJECTIVES

Canonical hypervirulent Klebsiella pneumoniae sequence type 23 (ST23) causes severe infections while it generally maintains susceptibility to a broad spectrum of antimicrobials, yet the molecular basis of this phenotypic characteristic remains poorly understood. The purpose of this study was to investigate whether the presence of the DISARM system prevents antimicrobial-resistant plasmid invasion in K. pneumoniae.

METHODS

Comparative genomic analysis was performed to detect the distribution of DISARM among K. pneumoniae lineages. PacBio single-molecule real-time sequencing was employed to identify DISARM-associated DNA methylation motifs. Transformation and conjugation assays were conducted to evaluate the impact of DISARM on plasmid defence.

RESULTS

Class 1 DISARM system was selectively enriched in ST23 K. pneumoniae strains. The DISARM methylase modified host 5'-GRACRAC-3' motifs, which were distributed in all conjugative plasmids in K. pneumoniae. The transformation efficiency of plasmid pCOLADuet-MTmotif containing the methylation cognate site was reduced 2.9-fold compared with that of the plasmid pCOLADuet-1 in a ST23 DISARM-positive strain KP2613. Conjugation of carbapenemase-encoding plasmids (carrying blaKPC-2, blaNDM-1 and blaNDM-5) decreased 12- to 117-fold in KP2613 and 4.5- to 15.7-fold in Escherichia coli BL21-DISARM(+) compared with DISARM-negative strains KP2613ΔDISARM and BL21-DISARM(-), respectively, indicating that Class 1 DISARM could effectively hinder the antimicrobial resistance plasmid invasion. Systematic deletion of individual DISARM genes revealed that disruption of any single gene did not fully abolish the DISARM-mediated defence or cause substantial growth defects.

CONCLUSIONS

Class 1 DISARM provides robust protection against antimicrobial-resistant plasmids, potentially contributing to the high antimicrobial susceptibility observed in ST23 hypervirulent K. pneumoniae.