Local transmission and global dissemination of New Delhi Metallo-Beta-Lactamase (NDM): a whole genome analysis.
New Delhi metallo-β-lactamase (bla NDM), a plasmid-borne carbapenemase gene associated with significant mortality and severely limited treatment options, is of global public health concern as it is found in extremely diverse Gram-negative bacterial strains. This study thus aims to genetically characterize local and global spread of bla NDM.



To investigate local transmission patterns in the context of a single hospital, whole genome sequencing data of the first 11 bla NDM-positive bacteria isolated in a local hospital were analyzed to: (1) identify and compare bla NDM-positive plasmids; and (2) study the phylogenetic relationship of the bacteria chromosomes. The global analysis was conducted by analyzing 2749 complete plasmid sequences (including 39 bla NDM-positive plasmids) in the NCBI database, where: (1) the plasmids were clustered based on their gene composition similarity; (2) phylogenetic study was conducted for each bla NDM-positive plasmid cluster to infer the phylogenetic relationship within each cluster; (3) gene transposition events introducing bla NDM into different plasmid backbones were identified; and (4) clustering pattern was correlated with the plasmids' incompatibility group and geographical distribution.



Analysis of the first 11 bla NDM-positive isolates from a single hospital revealed very low bla NDM-positive plasmid diversity. Local transmission was characterized by clonal spread of a predominant plasmid with 2 sporadic instances of plasmid introduction. In contrast to the low diversity locally, global bla NDM spread involved marked plasmid diversity with no predominant bacterial clone. Thirty-nine (1.4 %) out of the 2749 complete plasmid sequences were bla NDM-positive, and could be resolved into 7 clusters, which were associated with plasmid incompatibility group and geographical distribution. The bla NDM gene module was witnessed to mobilize between different plasmid backbones on at least 6 independent occasions.



Our analysis revealed the complex genetic pathways of bla NDM spread, with global dissemination characterized mainly by transposition of the bla NDM gene cassette into varied plasmids. Early local transmission following plasmid introduction is characterized by plasmid conjugation and bacterial spread. Our findings emphasize the importance of plasmid molecular epidemiology in understanding bla NDM spread.
Institute of Infectious Disease and Epidemiology, Communicable Disease Centre, Tan Tock Seng Hospital, Singapore, Singapore.
Wei Xin
WX
Khong
NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore, Singapore.
Eryu
E
Xia
Institute of Infectious Disease and Epidemiology, Communicable Disease Centre, Tan Tock Seng Hospital, Singapore, Singapore.|Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
Kalisvar
K
Marimuthu
Saw Swee Hock School of Public Health, National University of Singapore, Singapore, Singapore.
Wenting
W
Xu
NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore, Singapore.|Saw Swee Hock School of Public Health, National University of Singapore, Singapore, Singapore.|Life Sciences Institute, National University of Singapore, Singapore, Singapore.|Department of Statistics and Applied Probability, National University of Singapore, Singapore, Singapore.|Genome Institute of Singapore, Agency for Science, Technology and Research, Singapore, Singapore.
Yik-Ying
YY
Teo
Centre for Biomedical and Life Sciences, Singapore Polytechnic, Singapore, Singapore.|Department of Pediatrics, University Children's Medical Institute, National University of Singapore, Singapore, Singapore.
Eng Lee
EL
Tan
Centre for Biomedical and Life Sciences, Singapore Polytechnic, Singapore, Singapore.
Shiyong
S
Neo
Department of Laboratory Medicine, Tan Tock Seng Hospital, Singapore, Singapore.
Prabha Unny
PU
Krishnan
Institute of Infectious Disease and Epidemiology, Communicable Disease Centre, Tan Tock Seng Hospital, Singapore, Singapore.
Brenda S P
BS
Ang
Institute of Infectious Disease and Epidemiology, Communicable Disease Centre, Tan Tock Seng Hospital, Singapore, Singapore.|Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
David C B
DC
Lye
Institute of Infectious Disease and Epidemiology, Communicable Disease Centre, Tan Tock Seng Hospital, Singapore, Singapore.|Saw Swee Hock School of Public Health, National University of Singapore, Singapore, Singapore.
Angela L P
AL
Chow
Saw Swee Hock School of Public Health, National University of Singapore, Singapore, Singapore.
Rick Twee-Hee
RT
Ong
Institute of Infectious Disease and Epidemiology, Communicable Disease Centre, Tan Tock Seng Hospital, Singapore, Singapore. oon_tek_NG@ttsh.com.sg.|Saw Swee Hock School of Public Health, National University of Singapore, Singapore, Singapore. oon_tek_NG@ttsh.com.sg.|Communicable Disease Centre, Tan Tock Seng Hospital, 11, Jalan Tan Tock Seng, Singapore, 308433, Singapore. oon_tek_NG@ttsh.com.sg.
Oon Tek
OT
Ng
D001424:Bacterial Infections / Q000453:epidemiology / Q000382:microbiology* / Q000635:transmission*; D016000:Cluster Analysis; D003227:Conjugation, Genetic; D003428:Cross Infection; D004251:DNA Transposable Elements; D004755:Enterobacteriaceae / Q000145:classification / Q000187:drug effects / Q000235:genetics; D014644:Genetic Variation; D016680:Genome, Bacterial; D023281:Genomics / Q000379:methods; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D010802:Phylogeny; D010957:Plasmids / Q000235:genetics; D012846:Singapore / Q000453:epidemiology; D018440:beta-Lactam Resistance / Q000235:genetics; D001618:beta-Lactamases / Q000235:genetics*
D004251:DNA Transposable Elements; D001618:beta-Lactamases; C552864:beta-lactamase NDM-1