molecular epidemiology of clonally related metallo-β-lactamase-producing klebsiella pneumoniae isolated from newborns in a hospital in shandong, china

Background: the infection caused by metallo-β-lactamase (mbl)-producing klebsiella pneumoniae has become a challenge to anti- infection treatments for newborns. objectives: 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. methods: 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). results: 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. conclusions: 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 preven- tion and control of the infection of k. pneumonia.