Emergence of a Novel NDM-5-Producing Sequence Type 4523 Klebsiella pneumoniae Strain Causing Bloodstream Infection in China.

Klebsiella pneumoniae is a significant infectious pathogen that causes bloodstream infections. This study aimed to genetically characterize a novel sequence type 4523 (ST4523) multidrug-resistant (MDR) K. pneumoniae strain recovered from the blood of a 79-year-old Chinese female patient with severe pneumonia and chronic obstructive pulmonary disease who ultimately died of the infection. The susceptibility testing results showed that strain 18SHX180 is nonsusceptible to cephalosporin, carbapenems, combinations of β-lactam and β-lactamase inhibitors, levofloxacin, and colistin and is only susceptible to amikacin. The phylogenetic structure showed that strain 18SHX180 belongs to a novel sequence type, ST4523, and capsule serotype K111. ST4523 is closely related to ST11, the most dominant clone of clinical carbapenem-resistant K. pneumoniae in China. ST4523 has 2 single-base variants in mdh and phoE. 18SHX180 showed medium virulence in Galleria mellonella and a mouse intraperitoneal infection model. PacBio Sequel and Illumina sequencing were performed to analyze the genetic characterization of 18SHX180, which contains 2 plasmids (pSHX180-NDM5 and pSHX180-1). pSHX180-NDM5 exhibits 86% coverage and 100% identity with 3 blaNDM-5-carrying plasmids and contains an additional region coding for the frmRAB operon, which permits bacteria to sense and detoxify formaldehyde. pSHX180-1 is responsible for the MDR phenotype: it carries 11 categories of genes for antimicrobial resistance [aadA16, aph(3″)-Ib, aph(6)-Id, blaSHV-182, blaTEM-1A, qacE, aac(6')-Ib-cr, mph(A), floR, qnrB6, arr-3, sul, sul2], all of which are associated with transposons and integrons located in three accessory resistance regions. The novel ST4523 K. pneumoniae strain could threaten the control of antimicrobial resistance, and its discovery calls attention to the genetic evolution of bacteria. IMPORTANCE Klebsiella pneumoniae is a significant infectious pathogen causing bloodstream infections. Due to the dissemination of carbapenemase genes, the incidence of carbapenem-resistant K. pneumoniae (CRKP) has increased, with high morbidity and mortality rates in immunocompromised patients. Here, we reported a novel ST4523 blaNDM-5-bearing CRKP strain initially recovered from a 79-year-old female who died of both a lower respiratory tract infection and bloodstream infection. We also describe the genetic and phenotypic characteristics of this strain. This study provides important insights into the genetic evolution of ST11 K. pneumoniae.