Publications by authors named "Nguyen Dong Tu"

10 Publications

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Phylogenetic Analysis Revealed the Dissemination of Closely Related Epidemic O1 Isolates in Laos, Thailand, and Vietnam.

Open Forum Infect Dis 2020 Nov 16;7(11):ofaa492. Epub 2020 Oct 16.

Department of Bacteriology I, National Institute of Infectious Diseases, Tokyo, Japan.

We performed whole-genome sequencing of O1 isolates from Laos, Thailand, and Vietnam, where cholera outbreaks occurred, to determine their genetic lineages. Core genome phylogenetic analysis revealed that the isolates located in same lineage without regional clusters, which suggests that closely related strains circulated in Southeast Asia.
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http://dx.doi.org/10.1093/ofid/ofaa492DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7679066PMC
November 2020

Whole-genome sequencing and comparative genomic analysis of Shewanella xiamenensis strains carrying bla-like genes isolated from a water environment in Vietnam.

J Glob Antimicrob Resist 2020 06 6;21:272-274. Epub 2020 May 6.

AMR Research Center, National Institute of Infectious Diseases, Tokyo, Japan. Electronic address:

Objectives: The aim of this study was to understand the natural bacterial hosts of antimicrobial resistance genes (ARGs) and their impact on the processes of evolution, spread and positive selection of acquired ARGs.

Methods: Environmental carbapenem-resistant Gram-negative bacteria in Vietnam were screened for based on a One Health approach. Whole-genome sequencing (WGS) and comparative genomic analysis of the isolates were performed. WGS of three carbapenem-resistant Shewanella xiamenensis strains (SxND_W2_2018, SxND_W5_2018 and SxND_W9_2018) isolated from canals in Truc Ninh District and Nghia Hung District, Nam Dinh Province, Vietnam, in 2018 was performed using an Illumina MiniSeq system. ARGs in the draft genome sequences were detected using ResFinder, and comparison of genomic regions was performed using BLASTn and Easyfig.

Results: Thebla-like carbapenem-hydrolysing class D β-lactamase genes bla, bla and bla were detected in chromosomal contigs of SxND_W2_2018, SxND_W5_2018 and SxND_W9_2018, respectively. Comparative analysis of the surrounding regions of the bla-like genes, including both 10 kb upstream and 10 kb downstream of the genes, showed that the genomic regions were highly conserved in all three isolates.

Conclusion: This study analysed the draft genome sequences of carbapenem-resistantS. xiamenensis strains isolated from a water environment in Vietnam. All of the strains carried bla-like gene variants in their chromosomes. This information will contribute to highlight the evolution of bla family carbapenemase genes in nature and the importance of S. xiamenensis as a natural reservoir of important ARGs in the environment in Vietnam.
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http://dx.doi.org/10.1016/j.jgar.2020.04.033DOI Listing
June 2020

Antimicrobial residues, non-typhoidal , spp. and associated microbiological hazards in retail shrimps purchased in Ho Chi Minh city (Vietnam).

Food Control 2020 Jan;107:106756

Oxford University Clinical Research Unit, 764 Vo Van Kiet, Ho Chi Minh City, Viet Nam.

We investigated antimicrobial residues, non-typhoidal (NTS), spp. and their associated antimicrobial resistance (AMR), in shrimps locally purchased in Ho Chi Minh City (Vietnam). In addition, we investigated the relationship between AMR in NTS, spp. and antimicrobial residue in the same sample. A total of 40 samples of shrimp heads/shells from different retail sources was cultured using ISO 6579-1:2017 (NTS) and ISO/TS 21872-1:2007 ( spp.). Phenotypic antimicrobial susceptibility was investigated using Vitek (NTS, 34 antimicrobials) and disk diffusion ( spp., 12 antimicrobials). A total of 9 (22.5%) samples contained antimicrobial residue, including tetracyclines, fluoroquinolones, sulfonamides and macrolides (in 7.5%, 7.5%, 2.5% and 2.5% of samples, respectively). Shrimp samples from supermarkets had a higher prevalence of antimicrobial residue than those purchased in street markets (50% vs. 13.3%) ( = 0.049). A total of 30 (75%) samples were contaminated with NTS. All samples contained spp., with being most common (87.5% samples). A total of 58.9% NTS isolates were multidrug resistant. With regards to the highest priority, critically important antimicrobials, the highest resistance corresponded to quinolones (14.4-47.8%), followed by 3rd and 4th generation cephalosporins (3.3-7.8%). spp. isolates were characterised by their high resistance against ampicillin (82.7%) and 3rd generation cephalosporins (8.3-16.5%). Extended Spectrum Beta-Lactamase (ESBL) activity was detected in 28.1% isolates. Half of ESBL-positive strains harboured . We found an association between the presence of residues and the number of resistances for NTS (p = 0.075) and spp. isolates (p = 0.093) from the same sample. These findings suggest that the presence of residues may contribute to the selection of AMR in foodborne pathogens in shrimps. Authorities should strengthen policies aiming at restricting inappropriate antimicrobial usage in shrimp farming, and step up monitoring of antimicrobial residues and food-borne pathogens at retail in Vietnam.
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http://dx.doi.org/10.1016/j.foodcont.2019.106756DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6894321PMC
January 2020

Development of a loop-mediated isothermal amplification assay for Vibrio cholerae O1 and O139.

Mol Cell Probes 2019 06 10;45:65-67. Epub 2019 May 10.

Department of Bacteriology I, National Institute of Infectious Diseases, Tokyo, Japan.

A loop-mediated isothermal amplification assay was developed. It was designed for recognizing Vibrio cholerae O1/O139, where atpA, rfbN, and wfbR genes were adopted. The assay specifically detected the target with sensitivities of 5-67 copies per reaction in 1 h. The assay will aid rapid detection of the cholera bacterium.
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http://dx.doi.org/10.1016/j.mcp.2019.05.001DOI Listing
June 2019

Cholera prevention and control in Asian countries.

BMC Proc 2018 7;12(Suppl 13):62. Epub 2018 Dec 7.

26World Health Organization, New Delhi, India.

Cholera remains a major public health problem in many countries. Poor sanitation and inappropriate clean water supply, insufficient health literacy and community mobilization, absence of national plans and cross-border collaborations are major factors impeding optimal control of cholera in endemic countries. In March 2017, a group of experts from 10 Asian cholera-prone countries that belong to the Initiative against Diarrheal and Enteric Diseases in Africa and Asia (IDEA), together with representatives from the World Health Organization, the US National Institutes of Health, International Vaccine Institute, Agence de médecine préventive, NGOs (Save the Children) and UNICEF, met in Hanoi (Vietnam) to share progress in terms of prevention and control interventions on water, sanitation and hygiene (WASH), surveillance and oral cholera vaccine use. This paper reports on the country situation, gaps identified in terms of cholera prevention and control and strategic interventions to bridge these gaps.
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http://dx.doi.org/10.1186/s12919-018-0158-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6284268PMC
December 2018

Genetic diversity of environmental Vibrio cholerae O1 strains isolated in Northern Vietnam.

Infect Genet Evol 2017 10 20;54:146-151. Epub 2017 Jun 20.

Vietnam Research Station, Institute of Tropical Medicine, Nagasaki University, Japan; Department of Bacteriology, Graduate School of Medicine, University of the Ryukyus, Japan. Electronic address:

Cholera epidemics have been recorded periodically in Vietnam during the seventh cholera pandemic. Since cholera is a water-borne disease, systematic monitoring of environmental waters for Vibrio cholerae presence is important for predicting and preventing cholera epidemics. We conducted monitoring, isolation, and genetic characterization of V. cholerae strains in Nam Dinh province of Northern Vietnam from Jul 2013 to Feb 2015. In this study, four V. cholerae O1 strains were detected and isolated from 110 analyzed water samples (3.6%); however, none of them carried the cholera toxin gene, ctxA, in their genomes. Whole genome sequencing and phylogenetic analysis revealed that the four O1 isolates were separated into two independent clusters, and one of them diverged from a common ancestor with pandemic strains. The analysis of pathogenicity islands (CTX prophage, VPI-I, VPI-II, VSP-I, and VSP-II) indicated that one strain (VNND_2014Jun_6SS) harbored an unknown prophage-like sequence with high homology to vibriophage KSF-1 phi and VCY phi, identified from Bangladesh and the USA, respectively, while the other three strains carried tcpA gene with a distinct sequence demonstrating a separate clonal lineage. These results suggest that the aquatic environment can harbor highly divergent V. cholera strains and serve as a reservoir for multiple V. cholerae virulence-associated genes which may be exchanged via mobile genetic elements. Therefore, continuous monitoring and genetic characterization of V. cholerae strains in the environment should contribute to the early detection of the sources of infection and prevention of cholera outbreaks as well as to understanding the natural ecology and evolution of V. cholerae.
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http://dx.doi.org/10.1016/j.meegid.2017.06.017DOI Listing
October 2017

Molecular epidemiology of Vibrio cholerae O1 in northern Vietnam (2007-2009), using multilocus variable-number tandem repeat analysis.

J Med Microbiol 2016 Sep 18;65(9):1007-1012. Epub 2016 Jul 18.

Department of Bacteriology I, National Institute of Infectious Diseases, Tokyo 162-8640, Japan.

Cholera is an infectious disease of major concern in Vietnam and other Asian countries. In 2009, there was a large outbreak of cholera in northern Vietnam. To investigate relationships among isolates of the causative pathogen Vibrio cholerae in this region since 2007, we carried out a multilocus variable-number tandem repeat analysis (MLVA) of 170 isolates collected between 2007 and 2009. A total of 24 MLVA types were identified using seven loci. Five clones (1-5) were identified using five loci of the large V. cholerae chromosome; clones 1 and 2 were major, and the others were minor. Clone 1 isolates were responsible for the 2009 outbreak. A shift in the predominant clone occurred between 2007 and 2009, with clone 1 likely derived from clone 2. Moreover, the former was less diverse than the latter, suggesting a single source of cholera dissemination. Epidemiological data indicated a wavelet prior to the large outbreak, suggesting that drinking water source or food chain became contaminated during dissemination. Our results reveal the utility of MLVA for analysis of V. cholerae isolates within a relatively short period and broaden our understanding of its transmission and response to cholera.
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http://dx.doi.org/10.1099/jmm.0.000317DOI Listing
September 2016

Characterization of Vibrio cholerae O139 of an Aquatic Isolate in Northern Vietnam.

Open Microbiol J 2012 10;6:14-21. Epub 2012 Feb 10.

Department of Bacteriology, National Institute of Hygiene and Epidemiology, No.1 Yersin Street, Hanoi, 10, 000, Vietnam.

During the cholera survey in Namdinh province (northern Vietnam) in July, 2010, one strain of Vibrio cholerae O139 was isolated from 7 environmental water samples positive for ctxA, toxR,VCO139 genes and named as V. cholerae O139, ND1 strain. This strain was lysogenic harbouring a genome similar to the filamentous phage fs1. The replicative form DNA of this phage (named as ND1-fs1, 6856 bp) was sequenced and compared with the other filamentous phages. The filamentous phage ND1-fs1 integrates into the region between ctxB and rtxA genes. The genetic organization of the CTXϕ of V. cholerae O139, strain ND1 was determined and the schematic representation of the genetic organization was shown together with the ND1-fs1 prophage.
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http://dx.doi.org/10.2174/1874285801206010014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3282888PMC
August 2012

Two different mechanisms of ampicillin resistance operating in strains of Vibrio cholerae O1 independent of resistance genes.

FEMS Microbiol Lett 2009 Sep 22;298(1):37-43. Epub 2009 Jun 22.

Department of Bacteriology, National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.

Autoagglutinable strains of Vibrio cholerae O1 (seven nonfimbriate strains and one fimbriate strain) were transformed to obtain resistance to ampicillin. Two distinct mechanisms were found in these strains. One was operating in nonfimbriate strains by reducing OmpU protein production and the other was operating in a fimbriate strain (Bgd17) by newly overproducing cpxP protein. The twitching motility in the fimbriate Bgd17 strain disappeared depending on the production of cpxP protein, suggesting that fimbriation of V. cholerae O1 is controlled by a two-component signal transduction system.
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http://dx.doi.org/10.1111/j.1574-6968.2009.01693.xDOI Listing
September 2009

Filamentous vibriophage fs2 encoding the rstC gene integrates into the same chromosomal region as the CTX phage [corrected].

FEMS Microbiol Lett 2008 Jul 23;284(2):225-30. Epub 2008 May 23.

Department of Bacteriology, National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.

The genome of the filamentous phage of Vibrio cholerae fs2 was found to contain rstC and rstB1 (truncated) genes downstream of ORF500. att-fs2-dir and att-fs2-rev sequences homologous to that of att-CTXphi were found between orf500 and rstC of the fs2 genome. This prompted us to search for the integration site of fs2 in the genomes of V. cholerae O1 and O139. The genome of fs2 was found to integrate downstream of attRS of the CTXphi phage, which integrated into chromosome I of V. cholerae O1 and O139. When infected with fs2, a fimbriate strain of V. cholerae O1 appeared to reduce fimbrial production in an adult rabbit ileal loop assay.
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http://dx.doi.org/10.1111/j.1574-6968.2008.01200.xDOI Listing
July 2008