ORCID Profile
0000-0002-7006-622X
Current Organisation
Independent University Bangladesh (IUB)
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Informa UK Limited
Date: 21-01-2017
Publisher: American Society for Microbiology
Date: 06-2003
DOI: 10.1128/IAI.71.6.2993-2999.2003
Abstract: The major virulence factors of toxigenic Vibrio cholerae are cholera toxin, which is encoded by a lysogenic filamentous bacteriophage (CTXΦ), and toxin-coregulated pilus (TCP), an essential colonization factor that is also the receptor for CTXΦ. The genes involved in the biosynthesis of TCP reside in a pathogenicity island, which has been reported to correspond to the genome of another filamentous phage (designated VPIΦ) and to encode functions necessary for the production of infectious VPIΦ particles. We examined 46 V. cholerae strains having erse origins and carrying different genetic variants of the TCP island for the production of the VPIΦ and CTXΦ in different culture conditions, including induction of prophages with mitomycin C and UV irradiation. Although 9 of 10 V. cholerae O139 strains and 12 of 15 toxigenic El Tor strains tested produced extracellular CTXΦ, none of the 46 TCP-positive strains produced detectable VPIΦ in repeated assays, which detected as few as 10 particles of a control CTX phage per ml. These results contradict the previous report regarding VPIΦ-mediated horizontal transfer of the TCP genes and suggest that the TCP island is unable to support the production of phage particles. Further studies are necessary to understand the mechanism of horizontal transfer of the TCP island.
Publisher: Medknow
Date: 05-2013
Publisher: American Society for Microbiology
Date: 08-2002
DOI: 10.1128/AEM.68.8.3908-3913.2002
Abstract: Bacillary dysentery caused by Shigella species is a public health problem in developing countries including Bangladesh. Although, shigellae-contaminated food and drinks are often the source of the epidemic's spread, the possible presence of the pathogen and transmission of it through environmental waters have not been adequately examined. We analyzed surface waters collected in Dhaka, Bangladesh, for the presence of shigellae by a combination of PCR assays followed by concentration and culturing of PCR-positive s les. Analysis of 128 water s les by PCR assays for Shigella -specific virulence genes including ipaBCD , ipaH , and stx1 identified 14 (10.9%) s les which were positive for one or more of these virulence genes. Concentration of the PCR-positive s les by filtration followed by culturing identified live Shigella species in 11 of the 14 PCR-positive s les. Analysis of rRNA gene restriction patterns (ribotype) showed that the environmental isolates shared ribotypes with a collection of clinical isolates, but in contrast to the clinical isolates, 10 of the 11 environmental isolates were either negative or carried deletions in the plasmid-encoded invasion-associated genes ipaB , ipaC , and ipaD . However, all environmental Shigella isolates were positive for the chromosomal multicopy invasion-associated gene ipaH and all Shigella dysenteriae type 1 isolates were positive for the stx1 gene in addition to ipaH . This study demonstrated the presence of Shigella in the aquatic environment and dispersion of different virulence genes among these isolates which appear to constitute an environmental reservoir of Shigella -specific virulence genes. Since critical virulence genes in Shigella are carried by plasmids or mobile genetic elements, the environmental gene pool may contribute to an optimum combination of genes, causing the emergence of virulent Shigella strains which is facilitated in particular by close contact of the population with surface waters in Bangladesh.
Publisher: American Society for Microbiology
Date: 15-06-2005
DOI: 10.1128/JB.187.12.4095-4103.2005
Abstract: KSF-1Φ, a novel filamentous phage of Vibrio cholerae , supports morphogenesis of the RS1 satellite phage by heterologous DNA packaging and facilitates horizontal gene transfer. We analyzed the genomic sequence, morphology, and receptor for KSF-1Φ infection, as well as its phylogenetic relationships with other filamentous vibriophages. While strains carrying the mshA gene encoding mannose-sensitive hemagglutinin (MSHA) type IV pilus were susceptible to KSF-1Φ infection, naturally occurring MSHA-negative strains and an mshA deletion mutant were resistant. Furthermore, d -mannose as well as a monoclonal antibody against MSHA inhibited infection of MSHA-positive strains by the phage, suggesting that MSHA is the receptor for KSF-1Φ. The phage genome comprises 7,107 nucleotides, containing 14 open reading frames, 4 of which have predicted protein products homologous to those of other filamentous phages. Although the overall genetic organization of filamentous phages appears to be preserved in KSF-1Φ, the genomic sequence of the phage does not have a high level of identity with that of other filamentous phages and reveals a highly mosaic structure. Separate phylogenetic analysis of genomic sequences encoding putative replication proteins, receptor-binding proteins, and Zot-like proteins of 10 different filamentous vibriophages showed different results, suggesting that the evolution of these phages involved extensive horizontal exchange of genetic material. Filamentous phages which use type IV pili as receptors were found to belong to different branches. While one of these branches is represented by CTXΦ, which uses the toxin-coregulated pilus as its receptor, at least four evolutionarily erged phages share a common receptor MSHA, and most of these phages mediate horizontal gene transfer. Since MSHA is present in a wide variety of V. cholerae strains and is presumed to express in the environment, erse filamentous phages using this receptor are likely to contribute significantly to V. cholerae evolution.
Publisher: American Society for Microbiology
Date: 07-2006
DOI: 10.1128/JB.00141-06
Publisher: American Society for Microbiology
Date: 02-2003
DOI: 10.1128/IAI.71.2.1020-1025.2003
Abstract: The major virulence factors of toxigenic Vibrio cholerae are cholera toxin (CT), which is encoded by a lysogenic bacteriophage (CTXΦ), and toxin-coregulated pilus (TCP), an essential colonization factor which is also the receptor for CTXΦ. The genes for the biosynthesis of TCP are part of a larger genetic element known as the TCP pathogenicity island. To assess their pathogenic potential, we analyzed environmental strains of V. cholerae carrying genetic variants of the TCP pathogenicity island for colonization of infant mice, susceptibility to CTXΦ, and diarrheagenicity in adult rabbits. Analysis of 14 environmental strains, including 3 strains carrying a new allele of the tcpA gene, 9 strains carrying a new allele of the toxT gene, and 2 strains carrying conventional tcpA and toxT genes, showed that all strains colonized infant mice with various efficiencies in competition with a control El Tor biotype strain of V. cholerae O1. Five of the 14 strains were susceptible to CTXΦ, and these transductants produced CT and caused diarrhea in adult rabbits. These results suggested that the new alleles of the tcpA and toxT genes found in environmental strains of V. cholerae encode biologically active gene products. Detection of functional homologs of the TCP island genes in environmental strains may have implications for understanding the origin and evolution of virulence genes of V. cholerae .
Publisher: Springer Science and Business Media LLC
Date: 28-11-2016
DOI: 10.1038/SREP37956
Abstract: Predation by bacteriophages can significantly influence the population structure of bacterial communities. Vibrio cholerae the causative agent of cholera epidemics interacts with numerous phages in the aquatic ecosystem, and in the intestine of cholera patients. Seasonal epidemics of cholera reportedly collapse due to predation of the pathogen by phages. However, it is not clear how sufficient number of the bacteria survive to seed the environment in the subsequent epidemic season. We found that bacterial cell density-dependent gene expression termed “quorum sensing” which is regulated by signal molecules called autoinducers (AIs) can protect V. cholerae against predatory phages. V. cholerae mutant strains carrying inactivated AI synthase genes were significantly more susceptible to multiple phages compared to the parent bacteria. Likewise when mixed cultures of phage and bacteria were supplemented with exogenous autoinducers CAI-1 or AI-2 produced by recombinant strains carrying cloned AI synthase genes, increased survival of V. cholerae and a decrease in phage titer was observed. Mutational analyses suggested that the observed effects of autoinducers are mediated in part through the quorum sensing-dependent production of haemaglutinin protease, and partly through downregulation of phage receptors. These results have implication in developing strategies for phage mediated control of cholera.
Publisher: Public Library of Science (PLoS)
Date: 02-07-2021
DOI: 10.1371/JOURNAL.PONE.0254068
Abstract: Prevalence of toxigenic Vibrio cholerae O1 in aquatic reservoirs in Bangladesh apparently increases coinciding with the occurrence of seasonal cholera epidemics. In between epidemics, these bacteria persist in water mostly as dormant cells, known as viable but non-culturable cells (VBNC), or conditionally viable environmental cells (CVEC), that fail to grow in routine culture. CVEC resuscitate to active cells when enriched in culture medium supplemented with quorum sensing autoinducers CAI-1 or AI-2 which are signal molecules that regulate gene expression dependent on cell density. V . cholerae O1 mutant strains with inactivated cqsS gene encoding the CAI-1 receptor has been shown to overproduce AI-2 that enhance CVEC resuscitation in water s les. Since V . cholerae non-O1 non-O139 (non-cholera-vibrios) are abundant in aquatic ecosystems, we identified and characterized naturally occurring variant strains of V . cholerae non-O1 non-O139 which overproduce AI-2, and monitored their co-occurrence with V . cholerae O1 in water s les. The nucleotide sequence and predicted protein products of the cqsS gene carried by AI-2 overproducing variant strains showed ergence from that of typical V . cholerae O1 or non-O1 strains, and their culture supernatants enhanced resuscitation of CVEC in water s les. Furthermore, prevalence of V . cholerae O1 in the aquatic environment was found to coincide with an increase in AI-2 overproducing non-O1 non-O139 strains. These results suggest a possible role of non-cholera vibrios in the environmental biology of the cholera pathogen, in which non-O1 non-O139 variant strains overproducing AI-2 presumably contribute in resuscitation of the latent pathogen, leading to seasonal cholera epidemics. Importance . Toxigenic Vibrio cholerae which causes seasonal epidemics of cholera persists in aquatic reservoirs in endemic areas. The bacteria mostly exist in a dormant state during inter-epidemic periods, but periodically resuscitate to the active form. The resuscitation is enhanced by signal molecules called autoinducers (AIs). Toxigenic V . cholerae can be recovered from water s les that normally test negative for the organism in conventional culture, by supplementing the culture medium with exogenous AIs. V . cholerae belonging to the non-O1 non-O139 serogroups which do not cause cholera are also abundant in natural waters, and they are capable of producing AIs. In this study we characterized V . cholerae non-O1 non-O139 variant strains which overproduce an autoinducer called AI-2, and found that the abundance of the cholera pathogen in aquatic reservoirs correlates with an increase in the AI-2 overproducing strains. Our results suggest a probable role of these variant strains in the environmental biology and epidemiology of toxigenic V . cholerae , and may lead to novel means for surveillance, prevention and control of cholera.
Publisher: Elsevier BV
Date: 08-2015
Publisher: Oxford University Press (OUP)
Date: 09-2001
DOI: 10.1086/322807
Abstract: To investigate whether intestinal presentation of an antigen by Vibrio cholerae, a noninvasive organism, could induce an anatomically distant mucosal immune response in reproductive tract tissues, the endocervical immune responses of women in Bangladesh were evaluated after cholera. Endocervical secretions were analyzed for secretory IgA (sIgA) antibody against the B subunit of cholera toxin (CtxB) in 9 women with cholera and 8 women with diarrhea caused by neither V. cholerae nor heat labile enterotoxin-producing Escherichia coli. Women infected with V. cholerae developed significant sIgA anti-CtxB responses in endocervical s les (P< or =.02). Antibody subtype analysis of endocervical IgA was consistent with local mucosal production (P< or =.001). Women with cholera did not develop sIgA anti-CtxB responses in serum. The ability to generate specific mucosal immune responses in reproductive tract tissues after intestinal presentation of antigen could facilitate development of vaccines effective against reproductive tract pathogens.
Publisher: Elsevier BV
Date: 06-2013
DOI: 10.1016/J.DIAGMICROBIO.2013.02.016
Abstract: The extended-spectrum β-lactamase gene bla(CTX-M-15) was almost ubiquitous in erse antibiotic-resistant Escherichia coli isolated from surface water around Dhaka City, Bangladesh. Forty-eight isolates represented 34 multi-locus sequence types and a variety of plasmid replicons were identified in association with bla(CTX-M-15) and other resistance genes. This water is likely to be an important source of transmissible antibiotic resistance in Bangladesh.
Publisher: American Society for Microbiology
Date: 07-2010
DOI: 10.1128/AEM.00008-10
Abstract: Toxigenic Vibrio cholerae , the causative agent of the epidemic diarrheal disease cholera, interacts with erse environmental bacteriophages. These interactions promote genetic ersity or cause selective enrichment of phage-resistant bacterial clones. To identify bacterial genes involved in mediating the phage-resistant phenotype, we screened a transposon insertion library of V. cholerae O1 El Tor biotype strain C6706 to identify mutants showing altered susceptibility to a panel of phages isolated from surface waters in Bangladesh. Mutants with insertion in cyaA or crp genes encoding adenylate cyclase or cyclic AMP (cAMP) receptor protein (CRP), respectively, were susceptible to a phage designated JSF9 to which the parent strain was completely resistant. Application of the cyaA mutant as an indicator strain in environmental phage monitoring enhanced phage detection, and we identified 3 additional phages to which the parent strain was resistant. Incorporation of the cyaA or crp mutations into other V. cholerae O1 strains caused similar alterations in their phage susceptibility patterns, and the susceptibility correlated with the ability of the bacteria to adsorb these phages. Our results suggest that cAMP-CRP-mediated downregulation of phage adsorption may contribute to a mechanism for the V. cholerae O1 strains to survive predation by multiple environmental phages. Furthermore, the cyaA or crp mutant strains may be used as suitable indicators in monitoring cholera phages in the water.
Publisher: Springer Science and Business Media LLC
Date: 11-2017
DOI: 10.1038/S41598-017-14839-2
Abstract: CRISPR-Cas (clustered regularly interspersed short palindromic repeats-CRISPR-associated proteins) are microbial nuclease systems involved in defense against phages. Bacteria also resist phages by hosting phage-inducible chromosomal islands (PICI) which prevent phage reproduction. Vibrio cholerae which causes cholera epidemics, interacts with numerous phages in the environment and in cholera patients. Although CRISPR-Cas systems are usually carried by bacteria and archea, recently V . cholerae specific ICP1 phages were found to host a CRISPR-Cas system that inactivates PICI-like elements (PLE) in V . cholerae . We analyzed a collection of phages and V . cholerae isolated during seasonal cholera epidemics in Bangladesh, to study the distribution, and recent evolution of the phage-encoded CRISPR-Cas system. Five distinct but related phages carrying the CRISPR-Cas system, and possible CRISPR-Cas negative progenitor phages were identified. Furthermore, CRISPR arrays in the phages were found to have evolved by acquisition of new spacers targeting erse regions of PLEs carried by the V . cholerae strains, enabling the phages to efficiently grow on PLE positive strains. Our results demonstrate a continuing arms-race involving genetic determinants of phage-resistance in V . cholerae , and the phage-encoded CRISPR-Cas system in the co-evolution of V . cholerae and its phages, presumably fostered by their enhanced interactions during seasonal epidemics of cholera.
Publisher: Public Library of Science (PLoS)
Date: 10-07-2017
Publisher: Springer Science and Business Media LLC
Date: 10-2010
DOI: 10.1038/NATURE09469
Publisher: American Society for Microbiology
Date: 2002
DOI: 10.1128/IAI.70.1.163-170.2002
Abstract: In toxigenic Vibrio cholerae , cholera toxin is encoded by the CTX prophage, which consists of a core region carrying ctxAB genes and genes required for CTXΦ morphogenesis, and an RS2 region encoding regulation, replication, and integration functions. Integrated CTXΦ is often flanked by another genetic element known as RS1 which carries all open reading frames (ORFs) found in RS2 and an additional ORF designated rstC . We identified a single-stranded circularized form of the RS1 element, in addition to the CTXΦ genome, in nucleic acids extracted from phage preparations of 32 out of 83 (38.5%) RS1-positive toxigenic V. cholerae strains analyzed. Subsequently, the corresponding double-stranded replicative form (RF) of the RS1 element was isolated from a representative strain and marked with a kanamycin resistance (Km r ) marker in an intergenic site to construct pRS1-Km. Restriction and PCR analysis of pRS1-Km and sequencing of a 300-bp region confirmed that this RF DNA was the excised RS1 element which formed a novel junction between ig1 and rstC . Introduction of pRS1-Km into a V. cholerae O1 classical biotype strain, O395, led to the production of extracellular Km r transducing particles, which carried a single-stranded form of pRS1-Km, thus resembling the genome of a filamentous phage (RS1-KmΦ). Analysis of V. cholerae strains for susceptibility to RS1-KmΦ showed that classical biotype strains were more susceptible to the phage compared to El Tor and O139 strains. Nontoxigenic (CTX − ) O1 and O139 strains which carried genes encoding the CTXΦ receptor toxin-coregulated pilus (TCP) were also more susceptible ( ,000-fold) to the phage compared to toxigenic El Tor or O139 strains. Like CTXΦ, the RS1Φ genome also integrated into the host chromosomes by using the att RS sequence. However, only transductants of RS1-KmΦ which also harbored the CTXΦ genome produced a detectable level of extracellular RS1-KmΦ. This suggested that the core genes of CTXΦ are also required for the morphogenesis of RS1Φ. The results of this study showed for the first time that RS1 element, which encodes a site-specific recombination system in V. cholerae , can propagate horizontally as a filamentous phage, exploiting the morphogenesis genes of CTXΦ.
Publisher: Wiley
Date: 25-08-2010
DOI: 10.1111/J.1365-2958.2010.07286.X
Abstract: Vibrio2009, the third international conference on the biology of Vibrios, was held in Rio de Janeiro, Brazil, in November 2009. This conference united researchers studying various aspects of pathogenesis, symbiosis and environmental persistence of this erse group of marine bacteria. Through many of the presentations, it became apparent how horizontal gene transfer and genetic flexibility has driven the incredible ersity of these microbes. Interestingly, unifying themes of behaviour could be seen in the interaction(s) of Vibrios with other organisms, such as with other bacteria, corals, invertebrates and humans. Presentations illuminated the idea that the path towards symbiosis is not that different from the path towards disease, and that alterations in environmental conditions, such as climate change, can tip the balance and change the Vibrio interactions from benign to pathogenic.
Publisher: Elsevier BV
Date: 2007
DOI: 10.1016/J.VACCINE.2006.08.031
Abstract: A live oral Vibrio cholerae O1 El Tor vaccine, Peru-15 was tested in a double-blind, randomized placebo controlled study for safety and immunogenicity in Phase I and Phase II studies in 240 Bangladeshi children aged 9 months-5 years of age. Two different doses (2x10(7) and 2x10(8)cfu) were tested. Vaccination did not elicit adverse events and the strain was genetically stable. Vibriocidal antibody responses developed in 42/50 (84%) toddlers (2-5 years) and 35/50 (70%) of younger children (9-23 months) and overall 77/100 (77%) who received the high dose. LPS-IgA-antibody responses were seen in 60% of toddlers and 34% of infants 40% responded with IgA antibodies to cholera toxin. The responses to the reduced dose was lower. These studies demonstrate that Peru-15 at a dose of 2x10(8)cfu is safe and immunogenic in children in Bangladesh.
Publisher: American Society for Microbiology
Date: 2002
DOI: 10.1128/JCM.40.1.284-286.2002
Abstract: Sixty-six strains of Vibrio parahaemolyticus belonging to 14 serotypes were isolated from hospitalized patients in Dhaka, Bangladesh, from January 1998 to December 2000. Among these, 48 strains belonging to four serotypes had the pandemic genotype and possessed the tdh gene. A marker (open reading frame ORF8) for a filamentous phage previously thought to correspond to the pandemic genotype was found to have a poor correlation with the pandemic genotype.
Publisher: Public Library of Science (PLoS)
Date: 10-2019
Publisher: American Society for Microbiology
Date: 09-2014
DOI: 10.1128/IAI.01699-14
Abstract: In El Tor biotype strains of toxigenic Vibrio cholerae , the CTXϕ prophage often resides adjacent to a chromosomally integrated satellite phage genome, RS1, which produces RS1ϕ particles by using CTX prophage-encoded morphogenesis proteins. RS1 encodes RstC, an antirepressor against the CTXϕ repressor RstR, which cooperates with the host-encoded LexA protein to maintain CTXϕ lysogeny. We found that superinfection of toxigenic El Tor strains with RS1ϕ, followed by inoculation of the transductants into the adult rabbit intestine, caused elimination of the resident CTX prophage-producing nontoxigenic derivatives at a high frequency. Further studies using recA deletion mutants and a cloned rstC gene showed that the excision event was recA dependent and that introduction of additional copies of the cloned rstC gene instead of infection with RS1ϕ was sufficient to enhance CTXϕ elimination. Our data suggest that once it is excised from the chromosome, the elimination of CTX prophage from host cells is driven by the inability to reestablish CTXϕ lysogeny while RstC is overexpressed. However, with eventual loss of the additional copies of rstC , the nontoxigenic derivatives can act as precursors of new toxigenic strains by acquiring the CTX prophage either through reinfection with CTXϕ or by chitin-induced transformation. These results provide new insights into the role of RS1ϕ in V. cholerae evolution and the emergence of highly pathogenic clones, such as the variant strains associated with recent devastating epidemics of cholera in Asia, sub-Saharan Africa, and Haiti.
Publisher: Proceedings of the National Academy of Sciences
Date: 28-05-2013
Abstract: Cholera epidemics have long been known to spread through water contaminated with human fecal material containing the toxigenic bacterium Vibrio cholerae . However, detection of V. cholerae in water is complicated by the existence of a dormant state in which the organism remains viable, but resists cultivation on routine bacteriological media. Growth in the mammalian intestine has been reported to trigger “resuscitation” of such dormant cells, and these studies have prompted the search for resuscitation factors. Although some positive reports have emerged from these investigations, the precise molecular signals that activate dormant V. cholerae have remained elusive. Quorum-sensing autoinducers are small molecules that ordinarily regulate bacterial gene expression in response to cell density or interspecies bacterial interactions. We have found that isolation of pathogenic clones of V. cholerae from surface waters in Bangladesh is dramatically improved by using enrichment media containing autoinducers either expressed from cloned synthase genes or prepared by chemical synthesis. These results may contribute to averting future disasters by providing a strategy for early detection of V. cholerae in surface waters that have been contaminated with the stools of cholera patients or asymptomatic infected human carriers.
Publisher: Proceedings of the National Academy of Sciences
Date: 14-01-2003
Abstract: The cholera toxin genes of Vibrio cholerae are encoded by the filamentous phage, CTXΦ. Chromosomal CTXΦ prophage DNA is often found flanked by copies of a related genetic element designated RS1, and RS1 DNA can be packaged into filamentous phage particles (designated RS1Φ) by using the CTXΦ morphogenesis genes. RS1Φ is a satellite phage that further controls expression and dissemination of CTXΦ. Here we describe a CTXΦ-independent mechanism for production of RS1Φ. A nontoxigenic environmental V. cholerae strain (55V71) was identified that supports production of RS1Φ. However, newly infected CTX-negative strains did not produce RS1Φ, indicating that additional 55V71 genes were involved in production of RS1Φ. Analysis of nucleic acids from phage preparations of 55V71 revealed a 7.5-kb single-stranded DNA, whose corresponding replicative form was found in plasmid preparations. This DNA likely corresponds to the genome of a new filamentous phage, which we have designated KSF-1Φ. The replicative form DNA of KSF-1Φ was cloned into pUC18, and the resulting construct pKSF-1.1 supported the production of RS1Φ particles by CTX-negative V. cholerae strains. RS1Φ particles produced in this way infect recipient V. cholerae strains by a mechanism that is independent of the CTXΦ receptor, the toxin-coregulated pilus. Thus, KSF-1Φ is capable of facilitating the transfer of the RS1 element to strains that do not express toxin coregulated pilus. Given that RS1Φ can enhance coproduction of CTXΦ particles, KSF-1Φ-mediated dissemination of RS1 may indirectly promote the spread of toxin genes among V. cholerae strains. This study also shows that filamentous phages can package erse DNA elements and thus may play a role in horizontal transfer of more genes than previously appreciated.
Publisher: Proceedings of the National Academy of Sciences
Date: 06-02-2004
Abstract: To understand the evolutionary events and possible selection mechanisms involved in the emergence of pathogenic Vibrio cholerae , we analyzed erse strains of V. cholerae isolated from environmental waters in Bangladesh by direct enrichment in the intestines of adult rabbits and by conventional laboratory culture. Strains isolated by conventional culture were mostly (99.2%) negative for the major virulence gene clusters encoding toxin-coregulated pilus (TCP) and cholera toxin (CT) and were nonpathogenic in animal models. In contrast, all strains selected in rabbits were competent for colonizing infant mice, and 56.8% of these strains carried genes encoding TCP alone or both TCP and CT. Ribotypes of toxigenic O1 and O139 strains from the environment were similar to pandemic strains, whereas ribotypes of non-O1 non-O139 strains and TCP - nontoxigenic O1 strains erged widely from the seventh pandemic O1 and the O139 strains. Results of this study suggest that ( i ) the environmental V. cholerae population in a cholera-endemic area is highly heterogeneous, ( ii ) selection in the mammalian intestine can cause enrichment of environmental strains with virulence potential, ( iii ) pathogenicity of V. cholerae involves more virulence genes than currently appreciated, and ( iv ) most environmental V. cholerae strains are unlikely to attain a pandemic potential by acquisition of TCP and CT genes alone. Because most of the recorded cholera pandemics originated in the Ganges Delta region, this ecological setting presumably favors extensive genetic exchange among V. cholerae strains and thus promotes the rare, multiple-gene transfer events needed to assemble the critical combination of genes required for pandemic spread.
Publisher: Proceedings of the National Academy of Sciences
Date: 04-01-2010
Abstract: The factors that enhance the waterborne spread of bacterial epidemics and sustain the pathogens in nature are unclear. The epidemic diarrheal disease cholera caused by Vibrio cholerae spreads through water contaminated with the pathogen. However, the bacteria exist in water mostly as clumps of cells, which resist cultivation by standard techniques but revive into fully virulent form in the intestinal milieu. These conditionally viable environmental cells (CVEC), alternatively called viable but nonculturable cells, presumably play a crucial role in cholera epidemiology. However, the precise mechanism causing the transition of V. cholerae to the CVEC form and this form's significance in the biology of the pathogen are unknown. Here we show that this process involves biofilm formation that is dependent on quorum sensing, a regulatory response that is controlled by cell density. V. cholerae strains carrying mutations in genes required for quorum sensing and biofilm formation displayed altered CVEC formation in environmental water following intestinal infections. Analysis of naturally occurring V. cholerae CVEC showed that organisms that adopt this quiescent physiological state typically exist as clumps of cells that comprise a single clone closely related to isolates causing the most recent local cholera epidemic. These results support a model of cholera transmission in which in vivo-formed biofilms convert to CVEC upon the introduction of cholera stools into environmental water. Our data further suggest that a temporary loss of quorum sensing due to dilution of extracellular autoinducers confers a selective advantage to communities of V. cholerae by blocking quorum-mediated regulatory responses that would break down biofilms and thus interfere with CVEC formation.
Publisher: American Society for Microbiology
Date: 09-2002
DOI: 10.1128/JCM.40.9.3296-3299.2002
Abstract: The sixth pandemic of cholera and, presumably, the earlier pandemics were caused by the classical biotype of Vibrio cholerae O1, which was progressively replaced by the El Tor biotype representing the seventh cholera pandemic. Although the classical biotype of V. cholerae O1 is extinct, even in southern Bangladesh, the last of the niches where this biotype prevailed, we have identified new varieties of V. cholerae O1, of the El Tor biotype with attributes of the classical biotype, from hospitalized patients with acute diarrhea in Bangladesh. Twenty-four strains of V. cholerae O1 isolated between 1991 and 1994 from hospitalized patients with acute diarrhea in Matlab, a rural area of Bangladesh, were examined for the phenotypic and genotypic traits that distinguish the two biotypes of V. cholerae O1. Standard reference strains of V. cholerae O1 belonging to the classical and El Tor biotypes were used as controls in all of the tests. The phenotypic traits commonly used to distinguish between the El Tor and classical biotypes, including polymyxin B sensitivity, chicken cell agglutination, type of tcpA and rstR genes, and restriction patterns of conserved rRNA genes (ribotypes), differentiated the 24 strains of toxigenic V. cholerae O1 into three types designated the Matlab types. Although all of the strains belonged to ribotypes that have been previously found among El Tor vibrios, type I strains had more traits of the classical biotype while type II and III strains appeared to be more like the El Tor biotype but had some classical biotype properties. These results suggest that, although the classical and El Tor biotypes have different lineages, there are possible naturally occurring genetic hybrids between the classical and El Tor biotypes that can cause cholera and thus provide new insight into the epidemiology of cholera in Bangladesh. Furthermore, the existence of such novel strains may have implications for the development of a cholera vaccine.
Publisher: Centers for Disease Control and Prevention (CDC)
Date: 09-2003
Abstract: During March and April 2002, a resurgence of Vibrio cholerae O139 occurred in Dhaka and adjoining areas of Bangladesh with an estimated 30,000 cases of cholera. Patients infected with O139 strains were much older than those infected with O1 strains (p<0.001). The reemerged O139 strains belong to a single ribotype corresponding to one of two ribotypes that caused the initial O139 outbreak in 1993. Unlike the strains of 1993, the recent strains are susceptible to trimethoprim, sulphamethoxazole, and streptomycin but resistant to nalidixic acid. The new O139 strains carry a copy of the Calcutta type CTX(Calc) prophage in addition to the CTX(ET) prophage carried by the previous strains. Thus, the O139 strains continue to evolve, and the adult population continues to be more susceptible to O139 cholera, which suggests a lack of adequate immunity against this serogroup. These findings emphasize the need for continuous monitoring of the new epidemic strains.
Location: Bangladesh
No related grants have been discovered for Shah Faruque.