Introduction. New Delhi metallo-β-lactamase (NDM)-producing
Klebsiella pneumoniae
has become a serious global health concern.
Hypothesis/Gap Statement. Due to the high genetic diversity among NDM-positive K. pneumoniae, we need further surveillance and studies to better understand the relationships between them. In addition, the coexistence of several plasmid replicon types in NDM-positive
K. pneumoniae
may affect the copy number of bla
NDM, the MIC level to antibiotics, as well as increasing the chance of horizontal gene transfer.
Aim. The aim of this study was to determine incompatible plasmid groups and copy numbers of bla
NDM, and to investigate the genetic relationship of 37 NDM-positive
K. pneumoniae
in Kerman, Iran.
Methodology. The bla
NDM-1 gene was detected and confirmed by PCR-sequencing. The plasmid replicon types were determined by PCR-based replicon typing (PBRT) and the copy number of bla
NDM-1 was determined by quantitaive real time-PCR (qPCR). Random amplified polymorphic DNA (RAPD)-PCR typing was used to detect genetic relationships between the strains.
Results. In this study, 10 different replicon types, including Frep [n=25 (67.5 %)], FIIAs [n=11 (29.7 %)], FIA [n=5 (13.5 %)], FIB [n=3 (8.1 %)], I1-Iγ [n=2 (5.4 %)], L/M [n=7 (18.9 %)], A/C [n=7 (18.9 %)], Y [n=3 (8.1 %)], P [n=1 (2.7 %)] and FIC [n=1 (2.7 %)] were reported. The copy numbers of the bla
NDM-1 gene varied from 30.00 to 5.0×106 and no statistically significant correlation was observed between a rise of the MIC to imipenem and the copy numbers of bla
NDM-1 (P>0.05). According to RAPD typing results, 35 strains were divided into five clusters, while two strains were non-typeable.
Conclusion. The spread of NDM-1-producing
K. pneumoniae
strains that carry several plasmid replicon types increases the chance of horizontal transfer of antibiotic resistance genes in hospital settings. In this study, 10 different replicon types were identified. We could not find any relationship between the increase of MIC levels to imipenem and the copy numbers of bla
NDM-1. Therefore, due to the identification of different replicon types in this study, the type and genetic characteristics of bla
NDM-1-carrying plasmids, and other factors such as antibiotic selective pressure, probably affect the copy number of bla
NDM-1 and change the MIC level to imipenem.