Molecular Epidemiology of Clonally Related Metallo-β-Lactamase-Producing Klebsiella pneumoniae Isolated from Newborns in a Hospital in Shandong, China

The infection caused by metallo-β-lactamase (MBL)-producing Klebsiella pneumoniae has become a challenge to anti-infection treatments for newborns.
The aim of this study is to investigate the molecular epidemiological characteristics of clonally related MBL-producing K. pneumoniae isolated from newborns in a hospital in Northern China.
A total of 16 isolates of carbapenem-resistant K. pneumonia were obtained from newborns between September 2011 and June 2014. Resistance genes were identified by PCR and sequencing. The isolates were classified by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST).
Our results show that the most prevalent genotypes of carbapenem-resistant K. pneumonia were ST54 and ST705. There were respectively 6 strains and 9 strains of K. pneumonia ST54 harboring the blaNDM-1 and blaIMP-4 genes, while the K. pneumoniae ST705 harbored the blaIMP-4 gene. Other resistance genes included extended-spectrum β-lactamases, plasmid-mediated AmpC enzymes and a class 1 gene cassette. The transferability of metallo-β-lactamase was determined by conjugation experiments, which showed that the blaNDM-1 and blaIMP-4 genes were transferable and likely through a plasmid-mediated event.
Our results showed that New Delhi metallo-beta-lactamase-1 (NDM-1) and imipenemase-4 (IMP-4) carbapenemases were the major players responsible for the carbapenem-resistance. Co-production of NDM-1 with CTX-M-15 in K. pneumoniae isolates was detected for the first time in our neonatal intensive care unit. Early detection of these drug resistance genes will help in prevention and control of the infection of K. pneumonia.