Characteristics of NDM-1-producing Klebsiella pneumoniae ST234 and ST1412 isolates spread in a neonatal unit

Abstract Background The emergence of carbapenem-resistant Klebsiella pneumoniae (CR-KP) has become a significant problem worldwide and also being a major threat to children and newborns. Here we report an outbreak of NDM-1-producing K. pneumoniae in a neonatal unit. Results Six CR-KP strains, isolated from neonates with symptoms of infection, were identified using a VITEK-2 compact system, and the clinical data were retrieved from the electronic case records. In vitro susceptibility testing with broth dilution method showed that all six K. pneumoniae isolates were resistant to carbapenems and susceptible to colistin, aminoglycosides, fluoroquinolones and tigecycline. Based on the polymerase chain reaction results, each isolate was found to be bla NDM-1 gene positive. Clonal relationships were analysed using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) and showed that two different PFGE patterns were formed, which belonged to sequence types ST234 and ST1412. Plasmids carrying bla NDM-1 were successfully transferred from four of the six isolates to an Escherichia coli recipient through conjugative assays. S1-PFGE and Southern blot hybridization showed that four NDM-1-producing K. pneumoniae were clonal and carried bla NDM-1 on the same plasmid. The outbreak was effectively controlled by reducing the potential infection sources. All the patients were successfully treated and recovered after receiving an increased dose of carbapenems. Although the source of this outbreak was not clear, comprehensive measures were carried out and the outbreak was effectively controlled. Conclusions ST234 and ST1412 of NDM-1-producing Klebsiella pneumoniae are the resistant clone spread in the neonatal unit, comprehensive infection control measures and optimized carbapenem therapy played an important role in controlling this NDM-1-producing K. pneumoniae outbreak