Dissemination of a blaNDM − 1-harboring IncH plasmid associated with concurrent ST30 Klebsiella pneumoniae and ST2 Klebsiella oxytoca outbreaks in a Chinese neonatal unit

Objectives Carbapenem-resistant Klebsiella pneumoniae (CRKP) and Klebsiella oxytoca (CRKO) strains threaten neonatal health. This study investigates concurrent outbreaks in a Chinese neonatal intensive care unit (NICU). Methods We characterized 13 clinical isolates (10 CRKP TJ01–TJ10 and 3 CRKO TJ11–TJ13) recovered from preterm infants between September 2013 and January 2014. The whole genome sequencing of strains (CRKP TJ03 and CRKO TJ11) was performed using MiSeq and MinION platforms, while the plasmids pNDM-TJ03 and pNDM-TJ11 were derived from the above-mentioned strains. Antimicrobial susceptibility testing, plasmid conjugal transfer, and other experiments were conducted. Results PFGE revealed clonal dissemination of CRKP ST30 and CRKO ST2 strains. This represents both the first documented neonatal outbreak caused by CRKP ST30 globally and the first report of CRKO ST2 in China, demonstrating novel transmission patterns of these high-risk clones in neonatal settings. All isolates carried bla NDM − 1 , bla OXA − 1 , bla DHA − 1 , qnrB4 , and aac(6 ′ )-Ib-cr genes. Plasmid analysis identified both as IncH-type, showing high homology with pNDM-MAR. Their structure included contained a conserved IncH backbone region and separate accessory modules that contained five insertion sequences, transposon Tn 6344 , and a multidrug-resistant (MDR) region. The MDR region contained four mobile elements (ΔTn 125 , ΔInRBDHA, ΔTn 1548 , and ΔTn 5393c ) carrying a complement of 10 resistance genes. Conjugation experiments confirmed successful transfer of both plasmids to Escherichia coli J53Azi R . Conclusions This study demonstrates that there may have been intra-strain and inter-species spread of a bla NDM − 1 -harboring IncH plasmid in the NICU. Our findings provide new insights into horizontal transfer of resistance genes mediated by IncH-type plasmids.