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Byrne AS, Bissonnette N, Tahlan K. Mechanisms and implications of phenotypic switching in bacterial pathogens. Can J Microbiol 2025; 71:1-19. [PMID: 39361974 DOI: 10.1139/cjm-2024-0116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/05/2024]
Abstract
Bacteria encounter various stressful conditions within a variety of dynamic environments, which they must overcome for survival. One way they achieve this is by developing phenotypic heterogeneity to introduce diversity within their population. Such distinct subpopulations can arise through endogenous fluctuations in regulatory components, wherein bacteria can express diverse phenotypes and switch between them, sometimes in a heritable and reversible manner. This switching may also lead to antigenic variation, enabling pathogenic bacteria to evade the host immune response. Therefore, phenotypic heterogeneity plays a significant role in microbial pathogenesis, immune evasion, antibiotic resistance, host niche tissue establishment, and environmental persistence. This heterogeneity can result from stochastic and responsive switches, as well as various genetic and epigenetic mechanisms. The development of phenotypic heterogeneity may create clonal populations that differ in their level of virulence, contribute to the formation of biofilms, and allow for antibiotic persistence within select morphological variants. This review delves into the current understanding of the molecular switching mechanisms underlying phenotypic heterogeneity, highlighting their roles in establishing infections caused by select bacterial pathogens.
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Affiliation(s)
| | - Nathalie Bissonnette
- Sherbrooke Research and Development Center, Agriculture and Agri-Food Canada, Sherbrooke, QC, Canada
| | - Kapil Tahlan
- Department of Biology, Memorial University of Newfoundland, St. John's, NL, Canada
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2
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Qin J, Wilson KA, Sarkar S, Heras B, O'Mara ML, Totsika M. Conserved FimH mutations in the global Escherichia coli ST131 multi-drug resistant lineage weaken interdomain interactions and alter adhesin function. Comput Struct Biotechnol J 2022; 20:4532-4541. [PMID: 36090810 PMCID: PMC9428848 DOI: 10.1016/j.csbj.2022.08.040] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Revised: 08/16/2022] [Accepted: 08/16/2022] [Indexed: 11/27/2022] Open
Abstract
The binding of the type 1 fimbrial adhesin FimH to mannosylated receptors is allosterically regulated to enhance the fitness of uropathogenic Escherichia coli (UPEC) during urinary tract infection (UTI). Mutations in the two FimH domains (pilin and lectin) located outside the mannose binding pocket have been shown to influence mannose binding affinity, yet the details of the allostery mechanism are not fully elucidated. Here we characterised different FimH conformational states (termed low-affinity tense and high-affinity relaxed conformations) of natural FimH variants using molecular dynamics (MD) simulation techniques and report key structural dynamics differences between them. The clinically dominant FimH30 variant from the pandemic multidrug resistant E. coli ST131 lineage contains an R166H mutation that weakens FimH interdomain interactions and allows enhanced mannose interactions with pre-existing high-affinity relaxed conformations. When expressed in an isogenic ST131 strain background, FimH30 mediated high human cell adhesion and invasion, and enhanced biofilm formation over other variants. Collectively, our computational and experimental findings support a model of FimH protein allostery that is mediated by shifts in the pre-existing conformational equilibrium of FimH, additional to the sequential step-wise process of structural perturbations transmitted from one site to another within the protein. Importantly, it is the first study to shed light into how natural mutations in a clinically dominant FimH variant influence the protein’s conformational landscape optimising its function for ST131 fitness at intestinal and extraintestinal niches.
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Sarkar S, Roberts LW, Phan MD, Tan L, Lo AW, Peters KM, Paterson DL, Upton M, Ulett GC, Beatson SA, Totsika M, Schembri MA. Comprehensive analysis of type 1 fimbriae regulation in fimB-null strains from the multidrug resistant Escherichia coli ST131 clone. Mol Microbiol 2016; 101:1069-87. [PMID: 27309594 DOI: 10.1111/mmi.13442] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/13/2016] [Indexed: 12/17/2022]
Abstract
Uropathogenic Escherichia coli (UPEC) of sequence type 131 (ST131) are a pandemic multidrug resistant clone associated with urinary tract and bloodstream infections. Type 1 fimbriae, a major UPEC virulence factor, are essential for ST131 bladder colonization. The globally dominant sub-lineage of ST131 strains, clade C/H30-R, possess an ISEc55 insertion in the fimB gene that controls phase-variable type 1 fimbriae expression via the invertible fimS promoter. We report that inactivation of fimB in these strains causes altered regulation of type 1 fimbriae expression. Using a novel read-mapping approach based on Illumina sequencing, we demonstrate that 'off' to 'on' fimS inversion is reduced in these strains and controlled by recombinases encoded by the fimE and fimX genes. Unlike typical UPEC strains, the nucleoid-associated H-NS protein does not strongly repress fimE transcription in clade C ST131 strains. Using a genetic screen to identify novel regulators of fimE and fimX in the clade C ST131 strain EC958, we defined a new role for the guaB gene in the regulation of type 1 fimbriae and in colonisation of the mouse bladder. Our results provide a comprehensive analysis of type 1 fimbriae regulation in ST131, and highlight important differences in its control compared to non-ST131 UPEC.
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Affiliation(s)
- Sohinee Sarkar
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072, Australia.,Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland, 4072, Australia.,Institute of Health and Biomedical Innovation, School of Biomedical Sciences, Queensland University of Technology, Brisbane, Queensland, 4059, Australia
| | - Leah W Roberts
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072, Australia.,Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland, 4072, Australia
| | - Minh-Duy Phan
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072, Australia.,Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland, 4072, Australia
| | - Lendl Tan
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072, Australia.,Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland, 4072, Australia
| | - Alvin W Lo
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072, Australia.,Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland, 4072, Australia
| | - Kate M Peters
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072, Australia.,Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland, 4072, Australia
| | - David L Paterson
- Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland, 4072, Australia.,Royal Brisbane and Women's Hospital, University of Queensland Centre for Clinical Research, Brisbane, Queensland, 4029, Australia
| | - Mathew Upton
- Plymouth University Peninsula Schools of Medicine and Dentistry, Plymouth, PL4 8AA, UK
| | - Glen C Ulett
- School of Medical Science, Menzies Health Institute Queensland, Griffith University, Gold Coast, Queensland, 4222, Australia
| | - Scott A Beatson
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072, Australia. .,Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland, 4072, Australia.
| | - Makrina Totsika
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072, Australia. .,Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland, 4072, Australia. .,Institute of Health and Biomedical Innovation, School of Biomedical Sciences, Queensland University of Technology, Brisbane, Queensland, 4059, Australia.
| | - Mark A Schembri
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072, Australia. .,Australian Infectious Disease Research Centre, The University of Queensland, Brisbane, Queensland, 4072, Australia.
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4
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Ares MA, Fernández-Vázquez JL, Rosales-Reyes R, Jarillo-Quijada MD, von Bargen K, Torres J, González-y-Merchand JA, Alcántar-Curiel MD, De la Cruz MA. H-NS Nucleoid Protein Controls Virulence Features of Klebsiella pneumoniae by Regulating the Expression of Type 3 Pili and the Capsule Polysaccharide. Front Cell Infect Microbiol 2016; 6:13. [PMID: 26904512 PMCID: PMC4746245 DOI: 10.3389/fcimb.2016.00013] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Accepted: 01/22/2016] [Indexed: 12/14/2022] Open
Abstract
Klebsiella pneumoniae is an opportunistic pathogen causing nosocomial infections. Main virulence determinants of K. pneumoniae are pili, capsular polysaccharide, lipopolysaccharide, and siderophores. The histone-like nucleoid-structuring protein (H-NS) is a pleiotropic regulator found in several gram-negative pathogens. It has functions both as an architectural component of the nucleoid and as a global regulator of gene expression. We generated a Δhns mutant and evaluated the role of the H-NS nucleoid protein on the virulence features of K. pneumoniae. A Δhns mutant down-regulated the mrkA pilin gene and biofilm formation was affected. In contrast, capsule expression was derepressed in the absence of H-NS conferring a hypermucoviscous phenotype. Moreover, H-NS deficiency affected the K. pneumoniae adherence to epithelial cells such as A549 and HeLa cells. In infection experiments using RAW264.7 and THP-1 differentiated macrophages, the Δhns mutant was less phagocytized than the wild-type strain. This phenotype was likely due to the low adherence to these phagocytic cells. Taken together, our data indicate that H-NS nucleoid protein is a crucial regulator of both T3P and CPS of K. pneumoniae.
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Affiliation(s)
- Miguel A Ares
- Unidad de Investigación Médica en Enfermedades Infecciosas y Parasitarias, Hospital de Pediatría, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, Hospital de PediatríaMexico City, Mexico; Departamento de Microbiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico NacionalMexico City, Mexico
| | - José L Fernández-Vázquez
- Unidad de Investigación en Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México Mexico City, Mexico
| | - Roberto Rosales-Reyes
- Unidad de Investigación en Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México Mexico City, Mexico
| | - Ma Dolores Jarillo-Quijada
- Unidad de Investigación en Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México Mexico City, Mexico
| | | | - Javier Torres
- Unidad de Investigación Médica en Enfermedades Infecciosas y Parasitarias, Hospital de Pediatría, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, Hospital de Pediatría Mexico City, Mexico
| | - Jorge A González-y-Merchand
- Departamento de Microbiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional Mexico City, Mexico
| | - María D Alcántar-Curiel
- Unidad de Investigación en Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México Mexico City, Mexico
| | - Miguel A De la Cruz
- Unidad de Investigación Médica en Enfermedades Infecciosas y Parasitarias, Hospital de Pediatría, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, Hospital de Pediatría Mexico City, Mexico
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5
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Bateman SL, Seed PC. Epigenetic regulation of the nitrosative stress response and intracellular macrophage survival by extraintestinal pathogenic Escherichia coli. Mol Microbiol 2012; 83:908-25. [PMID: 22221182 DOI: 10.1111/j.1365-2958.2012.07977.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Extraintestinal pathogenic Escherichia coli (ExPEC) reside in the enteric tract as a commensal reservoir, but can transition to a pathogenic state by invading normally sterile niches, establishing infection and disseminating to invasive sites like the bloodstream. Macrophages are required for ExPEC dissemination, suggesting the pathogen has developed mechanisms to persist within professional phagocytes. Here, we report that FimX, an ExPEC-associated DNA invertase that regulates the major virulence factor type 1 pili (T1P), is also an epigenetic regulator of a LuxR-like response regulator HyxR. FimX regulated hyxR expression through bidirectional phase inversion of its promoter region at sites different from the type 1 pili promoter and independent of integration host factor (IHF). In vitro, transition from high to low HyxR expression produced enhanced tolerance of reactive nitrogen intermediates (RNIs), primarily through de-repression of hmpA, encoding a nitric oxide-detoxifying flavohaemoglobin. However, in the macrophage, HyxR produced large effects on intracellular survival in the presence and absence of RNI and independent of Hmp. Collectively, we have shown that the ability of ExPEC to survive in macrophages is contingent upon the proper transition from high to low HyxR expression through epigenetic regulatory control by FimX.
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Affiliation(s)
- Stacey L Bateman
- Department of Molecular Genetics and Microbiology Center for Microbial Pathogenesis Department of Pediatrics, Duke University School of Medicine, Durham, NC 27710, USA
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6
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Abstract
Uropathogenic Escherichia coli (UPEC) is the leading cause of urinary tract infections in women, causing significant morbidity and mortality in this population. Adherence to host epithelial cells is a pivotal step in the pathogenesis of UPEC. One of the most important virulence factors involved in mediating this attachment is the type 1 pilus (type 1 fimbria) encoded by a set of fim genes arranged in an operon. The expression of type 1 pili is controlled by a phenomenon known as phase variation, which reversibly switches between the expression of type 1 pili (Phase-ON) and loss of expression (Phase-OFF). Phase-ON cells have the promoter for the fimA structural gene on an invertible DNA element called fimS, which lines up to allow transcription, whereas transcription of the structural gene is silenced in Phase-OFF cells. The orientation of the fimS invertible element is controlled by two site-specific recombinases, FimB and FimE. Environmental conditions cause transcriptional and post-transcriptional changes in UPEC cells that affect the level of regulatory proteins, which in turn play vital roles in modulating this phase switching ability. The role of fim gene regulation in UPEC pathogenesis will be discussed.
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7
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Shimada T, Bridier A, Briandet R, Ishihama A. Novel roles of LeuO in transcription regulation of E. coli genome: antagonistic interplay with the universal silencer H-NS. Mol Microbiol 2011; 82:378-97. [DOI: 10.1111/j.1365-2958.2011.07818.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Klemm P, Hancock V, Schembri MA. Fimbrial adhesins from extraintestinal Escherichia coli. ENVIRONMENTAL MICROBIOLOGY REPORTS 2010; 2:628-640. [PMID: 23766248 DOI: 10.1111/j.1758-2229.2010.00166.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Extraintestinal pathogenic Escherichia coli (ExPEC) represent an important subclass of E. coli that cause a wide spectrum of diseases in human and animal hosts. Fimbriae are key virulence factors of ExPEC strains. These long surface located rod-shaped organelles mediate receptor-specific attachment to host tissue surfaces (tissue tropism). Some ExPEC fimbriae have additional functions such as the promotion of biofilm formation, cell aggregation and adherence to abiotic surfaces. Here we review the structure, function and contribution to virulence of fimbriae associated with ExPEC strains.
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Affiliation(s)
- Per Klemm
- Microbial Adhesion Group, DTU Food, Technical University of Denmark, Lyngby, Denmark. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia
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9
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Timmermans J, Van Melderen L. Post-transcriptional global regulation by CsrA in bacteria. Cell Mol Life Sci 2010; 67:2897-908. [PMID: 20446015 PMCID: PMC11115721 DOI: 10.1007/s00018-010-0381-z] [Citation(s) in RCA: 138] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2010] [Revised: 04/14/2010] [Accepted: 04/20/2010] [Indexed: 12/16/2022]
Abstract
Global regulation allows bacteria to rapidly modulate the expression of a large variety of unrelated genes in response to environmental changes. Global regulators act at different levels of gene expression. This review focuses on CsrA, a post-transcriptional regulator that affects translation of its gene targets by binding mRNAs. CsrA controls a large variety of physiological processes such as central carbon metabolism, motility and biofilm formation. The activity of CsrA is itself tightly regulated by the CsrB and CsrC small RNAs and the BarA-UvrY two-component system.
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Affiliation(s)
- Johan Timmermans
- Laboratoire de Génétique et Physiologie Bactérienne, Institut de Biologie et de Médecine Moléculaires, Faculté des Sciences, Université Libre de Bruxelles, 12 rue des Professeurs Jeener et Brachet, 6041 Gosselies, Belgium
| | - Laurence Van Melderen
- Laboratoire de Génétique et Physiologie Bactérienne, Institut de Biologie et de Médecine Moléculaires, Faculté des Sciences, Université Libre de Bruxelles, 12 rue des Professeurs Jeener et Brachet, 6041 Gosselies, Belgium
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10
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Trade-off between iron uptake and protection against oxidative stress: deletion of cueO promotes uropathogenic Escherichia coli virulence in a mouse model of urinary tract infection. J Bacteriol 2008; 190:6909-12. [PMID: 18723628 DOI: 10.1128/jb.00451-08] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The periplasmic multicopper oxidase (CueO) is involved in copper homeostasis and protection against oxidative stress. Here, we show that the deletion of cueO in uropathogenic Escherichia coli increases its colonization of the urinary tract despite its increased sensitivity to hydrogen peroxide. The cueO deletion mutant accumulated iron with increased efficiency compared to its parent strain; this may account for its advantage in the iron-limited environment of the urinary tract.
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11
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Protein translation and cell death: the role of rare tRNAs in biofilm formation and in activating dormant phage killer genes. PLoS One 2008; 3:e2394. [PMID: 18545668 PMCID: PMC2408971 DOI: 10.1371/journal.pone.0002394] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Accepted: 04/28/2008] [Indexed: 01/25/2023] Open
Abstract
We discovered previously that the small Escherichia coli proteins Hha (hemolysin expression modulating protein) and the adjacent, poorly-characterized YbaJ are important for biofilm formation; however, their roles have been nebulous. Biofilms are intricate communities in which cell signaling often converts single cells into primitive tissues. Here we show that Hha decreases biofilm formation dramatically by repressing the transcription of rare codon tRNAs which serves to inhibit fimbriae production and by repressing to some extent transcription of fimbrial genes fimA and ihfA. In vivo binding studies show Hha binds to the rare codon tRNAs argU, ileX, ileY, and proL and to two prophage clusters D1P12 and CP4-57. Real-time PCR corroborated that Hha represses argU and proL, and Hha type I fimbriae repression is abolished by the addition of extra copies of argU, ileY, and proL. The repression of transcription of rare codon tRNAs by Hha also leads to cell lysis and biofilm dispersal due to activation of prophage lytic genes rzpD, yfjZ, appY, and alpA and due to induction of ClpP/ClpX proteases which activate toxins by degrading antitoxins. YbaJ serves to mediate the toxicity of Hha. Hence, we have identified that a single protein (Hha) can control biofilm formation by limiting fimbriae production as well as by controlling cell death. The mechanism used by Hha is the control of translation via the availability of rare codon tRNAs which reduces fimbriae production and activates prophage lytic genes. Therefore, Hha acts as a toxin in conjunction with co-transcribed YbaJ (TomB) that attenuates Hha toxicity.
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Abstract
Fimbria-mediated interaction with the host elicits both innate and adaptive immune responses, and thus their expression may not always be beneficial in vivo. Furthermore, the metabolic drain of producing fimbriae is significant. It is not surprising, therefore, to find that fimbrial production in Escherichia coli and Salmonella enterica is under extensive environmental regulation. In many instances, fimbrial expression is regulated by phase variation, in which individual cells are capable of switching between fimbriate and afimbriate states to produce a mixed population. Mechanisms of phase variation vary considerably between different fimbriae and involve both genetic and epigenetic processes. Notwithstanding this, fimbrial expression is also sometimes controlled at the posttranscriptional level. In this chapter, we review key features of the regulation of fimbrial gene expression in E. coli and Salmonella. The occurrence and distribution of fimbrial operons vary significantly among E. coli pathovars and even among the many Salmonella serovars. Therefore, general principles are presented on the basis of detailed discussion of paradigms that have been extensively studied, including Pap, type 1 fimbriae, and curli. The roles of operon specific regulators like FimB or CsgD and of global regulatory proteins like Lrp, CpxR, and the histone-like proteins H-NS and IHF are reviewed as are the roles of sRNAs and of signalling nucleotide cyclic-di-GMP. Individual examples are discussed in detail to illustrate how the regulatory factors cooperate to allow tight control of expression of single operons. Molecular networks that allow coordinated expression between multiple fimbrial operons and with flagella in a single isolate are also presented. This chapter illustrates how adhesin expression is controlled, and the model systems also illustrate general regulatory principles germane to our overall understanding of bacterial gene regulation.
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Bergsten G, Wullt B, Svanborg C. Escherichia coli, fimbriae, bacterial persistence and host response induction in the human urinary tract. Int J Med Microbiol 2005; 295:487-502. [PMID: 16238023 DOI: 10.1016/j.ijmm.2005.07.008] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Urinary tract infections (UTI) are among the most common bacterial infections in humans. Symptomatic UTIs may be acute, recurrent or chronic but the most frequent form of UTI is asymptomatic bacteruria (ABU). In ABU, the mucosa remains inert, despite the presence of large bacterial numbers in urine. The difference in disease severity reflects the virulence of the infecting strain and the propensity of the host to respond to infection. It is essential to understand the molecular basis of disease diversity and the molecular interactions between bacteria and host that determine asymptomatic carriage and the transition to disease. We discuss the initial interactions between bacteria and the mucosal surfaces in the human urinary tract, and the bacterial factors involved in the breach of mucosal inertia. Specifically, the contribution of P and type 1 fimbriae to bacterial establishment and host response induction are investigated. The results show that P fimbriae serve as independent virulence factors when expressed by an ABU strain, by promoting the establishment of bacteriuria and the innate host response, which is the cause of symptoms and tissue damage. P fimbriae thus fulfil the molecular Koch postulates as independent virulence factors in the human urinary tract. Type 1 fimbriae, in contrast, did not act as virulence factors in this model, and thus appear to serve a different function in man than in the murine model.
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Affiliation(s)
- Göran Bergsten
- Department of Microbiology, Immunology and Glycobiology, Institute of Laboratory Medicine, Lund University, Lund, Sweden
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Klemm P, Schembri M. Type 1 Fimbriae, Curli, and Antigen 43: Adhesion, Colonization, and Biofilm Formation. EcoSal Plus 2004; 1. [PMID: 26443347 DOI: 10.1128/ecosalplus.8.3.2.6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2004] [Indexed: 06/05/2023]
Abstract
This review is primarily concerned with the first step in biofilm formation, namely, bacterial attachment to surfaces. It describes three examples of bacterial adhesins, each of which belongs to a different subgroup and follows different strategies for surface presentation and adhesin exposure. These are type 1 fimbriae, very long stiff rodlike organelles; curli, amorphous fluffy coat structures; and finally antigen 43, short outer membrane structures with a simple assembly system. Their role as adhesins, their structure and biosynthesis, and their role in biofilm formation are described in detail in the review. The FimH protein presented by type 1 fimbriae seems to be a highly versatile adhesin fulfilling a diverse spectrum of roles ranging from pellicle and biofilm formation to being a bona fide virulence factor in uropathogenic E. coli (UPEC) strains, where it plays important roles in the manifestation of cystitis. Curli formation promotes two fundamental processes associated with biofilm formation: initial adhesion and cell-to-cell aggregation. A role for curli in the colonization of inert surfaces has been demonstrated. Severe sepsis and septic shock are frequently caused by gram-negative bacteria, and several factors suggest a significant role for curli during E. coli sepsis. The protection provided by Ag43-mediated aggregation was underlined in a series of experiments addressing the role of Ag43 in protection against oxidizing agents. Type 1 fimbriae, curli, and Ag43 are structurally different bacterial surface structures and follow completely different strategies for surface display and assembly.
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15
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Gunther NW, Snyder JA, Lockatell V, Blomfield I, Johnson DE, Mobley HLT. Assessment of virulence of uropathogenic Escherichia coli type 1 fimbrial mutants in which the invertible element is phase-locked on or off. Infect Immun 2002; 70:3344-54. [PMID: 12065472 PMCID: PMC128061 DOI: 10.1128/iai.70.7.3344-3354.2002] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Type 1 fimbria is a proven virulence factor of uropathogenic Escherichia coli (UPEC), causing urinary tract infections. Expression of the fimbria is regulated at the transcriptional level by a promoter situated on an invertible element, which can exist in one of two different orientations. The orientation of the invertible element that allows the expression of type 1 fimbriae is defined as "on," and the opposite orientation, in which no transcription occurs, is defined as "off." During the course of a urinary tract infection, we have observed that the infecting E. coli population alternates between fimbriated and nonfimbriated states, with the fimbriated on orientation peaking at 24 h. We propose that the ability of the invertible element to switch orientations during infection is itself a virulence trait. To test this hypothesis, nucleotide sequence changes were introduced in the left inverted repeat of the invertible element of UPEC pyelonephritis strain CFT073 that locked the invertible elements permanently in either the on or the off orientation. The virulence of these mutants was assessed in the CBA mouse model of ascending urinary tract infection at 4, 24, 48, and 72 h postinoculation (hpi). We conducted independent challenges, in which bladders of mice were inoculated with either a single mutant or the wild type, and cochallenges, in which a mutant and the wild type were inoculated together to allow direct competition in the urinary tract. In both sets of experimental infections, the locked-off mutant was recovered from the urine, bladder, and kidneys in significantly lower numbers than the wild type at 24 hpi (P < or = 0.05), demonstrating its attenuation. Conversely, the locked-on mutant was recovered in higher numbers than the wild type at 24 hpi (P < or = 0.05), showing enhanced virulence of this mutant. No significant differences were seen between the mutants and wild type in the urine or the bladder at 48 or 72 hpi. However, the wild type outcompeted the locked-off mutant in the kidneys during the cochallenge experiment at 72 hpi (P = 0.009). Overall, these data suggest that the ability of the invertible element controlling type 1 fimbria expression to phase vary contributes significantly to virulence early (24 hpi) in the course of a urinary tract infection by UPEC and most profoundly influences colonization of the bladder.
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Affiliation(s)
- Nereus W Gunther
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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16
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Geerlings SE, Meiland R, Hoepelman AIM. Pathogenesis of bacteriuria in women with diabetes mellitus. Int J Antimicrob Agents 2002; 19:539-45. [PMID: 12135845 DOI: 10.1016/s0924-8579(02)00090-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Women with diabetes mellitus (DM) have asymptomatic bacteriuria (ASB) and symptomatic urinary tract infections (UTIs) more often than women without DM. The increased prevalence of bacteriuria in diabetic patients can be the result of differences in the host responses between diabetic and nondiabetic patients, or a difference in the infecting bacterium itself. We have shown that the increased prevalence of ASB in diabetic women is not the result of a difference in bacteria, because the same number of virulence factors was found in the infecting Escherichia coli (most common causative microorganism of ASB) in our diabetic women with ASB, as listed in the literature for nondiabetic patients with ASB. We found that bacterial growth in vitro was increased after the addition of different glucose concentrations, as found in urine of poorly controlled patients. However, we could not confirm that glucosuria was a risk factor for ASB in vivo. In addition, we demonstrated that women with both DM and ASB have lower urinary cytokine and leukocyte concentrations than women without DM but with ASB. Finally, we found that E. coli expressing type 1 fimbriae (the virulence factor that plays an important role in the pathogenesis of UTIs) adhere better to uroepithelial cells of women with DM compared with the cells of women without DM.
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Affiliation(s)
- Suzanne E Geerlings
- Department of Internal Medicine, Free University Medical Center, Amsterdam, The Netherlands
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18
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Schembri MA, Givskov M, Klemm P. An attractive surface: gram-negative bacterial biofilms. SCIENCE'S STKE : SIGNAL TRANSDUCTION KNOWLEDGE ENVIRONMENT 2002; 2002:re6. [PMID: 12011496 DOI: 10.1126/stke.2002.132.re6] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
In nature, most bacteria live in close association with surfaces as complex communities referred to as biofilms. Community members within these compact microbial consortia show extraordinary resistance to conventional antibiotics, biocides, and hydrodynamic shear forces when compared to their planktonic counterparts. The buildup of these surface-associated bacterial communities is a highly organized and complex process that requires many signal transduction mechanisms to orchestrate the different stages of development. In this review, we describe several types of signal transduction that Gram-negative bacteria employ during the adhesion and expansion stages of biofilm formation, as well as discuss quorum-sensing in relation to the production of virulence factors.
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Affiliation(s)
- Mark A Schembri
- Center for Microbial Interactions, BioCentrum-DTU, Bldg. 301, Technical University of Denmark, DK-2800 Lyngby, Denmark
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19
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Abstract
The ability of bacterial pathogens to bind to the host mucosa is a critical step in the pathogenesis of many bacterial infections and, for Escherichia coli, a large number of different fimbrial adhesins have been implicated as virulence factors. In this chapter, our current understanding of the regulatory mechanisms that control the expression of two of the best characterized fimbrial adhesins, pyelonephritis-associated pilus (encoded by pap) and the type 1 fimbria (encoded by fim), will be described. The expression of both fimbrial adhesins is controlled by phase variation (the reversible and apparently random switching between expressing ('on') and non-expressing ('off') states), and is regulated in response to environmental conditions. The phase variation of pap (and of some other fimbriae in Escherichia coli) is determined by the formation of alternative nucleoprotein complexes that either activate (phase 'on') or suppress (phase 'off') transcription of the fimbria genes. Formation of each complex protects a single Dam methylation site (5' GATC) from modification (GATCdist in phase 'on' cells and GATCprox in phase 'off' cells). Furthermore, complex formation is inhibited by methylation of the two 5' GATC sites. Both the phase variation of pap and the transcription of the pap genes in phase 'on' cells, are regulated and expression is subject to both positive and negative feedback control. In contrast to pap, the phase variation of fim is determined by the site-specific inversion of a short element of DNA (the fim switch). In phase 'on' cells, a promoter within the invertible element directs the transcription of the fim structural genes, whereas in phase 'off' cells transcription of the fimbrial genes is silenced. Despite the very different molecular mechanisms controlling the expression of pap and fim, the two systems share many features in common and have probably evolved to fulfill the same function. In addition to details about the molecular mechanisms that control pap and fim, the possible physiological significance of the observed regulation will be discussed.
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Affiliation(s)
- I C Blomfield
- Research School of Biosciences, University of Kent at Canterbury, Canterbury, Kent, CT2 7NJ, UK.
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20
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Abstract
Fimbriae are thread-like polymers displayed in large amounts on the bacterial surface and used by many pathogens to attach to receptors on host tissue surfaces. Fimbriae contain disulfide bridges, contrary to many Escherichia coli surface proteins produced in bulk amounts. Here we investigate whether fimbriae expression can affect expression of other genes. Analysis of gene expression in two E.coli strains, differing in the fim locus, indicated the flu gene to be affected. The flu gene encodes the antigen 43 (Ag43) surface protein, specifically involved in bacterial aggregation, and microcolony and biofilm formation. Ag43 production is repressed by the global regulator OxyR, which monitors the cell's thiol-disulfide status. Only the thiol form of OxyR represses Ag43 production. We demonstrate that production of several different disulfide-containing fimbriae results in the abolition of Ag43 production. No effect was observed in an oxyR mutant. We conclude that fimbriae expression per se constitutes a signal transduction mechanism that affects a number of unrelated genes via the thiol-disulfide status of OxyR. Thus, phase variation in fimbrial expression is coordinated with the expression of other disease- and colonization-related genes.
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Affiliation(s)
| | - Per Klemm
- Microbial Adhesin Group, Section of Molecular Microbiology, BioCentrum-DTU, Technical University of Denmark, Bldg 301, DK-2800 Lyngby, Denmark
Corresponding author e-mail:
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Tinker JK, Hancox LS, Clegg S. FimW is a negative regulator affecting type 1 fimbrial expression in Salmonella enterica serovar typhimurium. J Bacteriol 2001; 183:435-42. [PMID: 11133935 PMCID: PMC94897 DOI: 10.1128/jb.183.2.435-442.2001] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Type 1 fimbriae are proteinaceous surface appendages that carry adhesins specific for mannosylated glycoproteins. These fimbriae are found on most members of the family Enterobacteriaceae and are known to facilitate binding to a variety of eukaryotic cells, including those found on the mucosal surfaces of the alimentary tract. We have shown that the regulation of type 1 fimbrial expression in Salmonella enterica serovar Typhimurium is controlled, in part, by the products of four genes found within the fim gene cluster: fimZ, fimY, fimW, and fimU. To better understand the specific role of FimW in fimbrial expression, a mutation was constructed in this gene by the insertion of a kanamycin resistance DNA cassette into the chromosome. The resulting fimW mutation was characterized by mannose-sensitive hemagglutination and agglutination with fimbria-specific antiserum. Assays suggested that this mutant was more strongly fimbriate than the parental strain, exhibiting a four- to eightfold increase in fimbrial production. The fimW mutation was introduced into a second strain of Salmonella enterica serovar Typhimurium, and this mutant was also found to be strongly fimbriate compared to the parental strain. Consistent with the role of this protein as a negative regulator, fimA-lacZ expression in serovar Typhimurium, as well as in Escherichia coli, was increased twofold in the absence of functional FimW. Primer extension analysis determined that fimW transcription is initiated from its own promoter 31 bp upstream of the translation start site. Analysis using a fimW-lacZ reporter indicated that fimW expression in serovar Typhimurium was increased under conditions that select for poorly fimbriate bacteria and low fimA expression. FimW also appears to act as an autoregulator, since expression from the fimW-lacZ reporter was increased in a fimW mutant. FimW was partially purified by fusion with the E. coli maltose-binding protein. Use of this FimW protein extract, as well as others, in DNA-binding assays was unable to identify a specific binding site for FimW in the fimA, fimZ, fimY, or fimW promoter regions. To analyze protein-protein interactions, FimW was expressed in a LexA-based two-hybrid system in E. coli. A significant interaction between FimW and the DNA-binding activator protein, FimZ, was detected using this system. These results indicate that FimW is a negative regulator of serovar Typhimurium type 1 fimbrial expression and may function by interfering with FimZ-mediated activation of fimA expression.
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Affiliation(s)
- J K Tinker
- Department of Microbiology, College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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Tinker JK, Clegg S. Characterization of FimY as a coactivator of type 1 fimbrial expression in Salmonella enterica serovar Typhimurium. Infect Immun 2000; 68:3305-13. [PMID: 10816478 PMCID: PMC97587 DOI: 10.1128/iai.68.6.3305-3313.2000] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Type 1 fimbriae of Salmonella enterica serovar Typhimurium are surface appendages that carry adhesins specific for mannosylated host glycoconjugates. Regulation of the major fimbrial subunit is thought to be controlled by a number of ancillary fim genes, including fimZ, fimY, fimW, and fimU. Previous studies using a FimZ mutant have indicated that this protein is necessary for fimA expression, and in vitro DNA binding assays determined that FimZ is a transcriptional activator that binds directly to the fimA promoter. To determine the role of FimY as a potential regulator of fimbrial expression, a fimY mutant of serovar Typhimurium was generated by allelic exchange. This mutant was found to be phenotypically nonfimbriate. No transcription from the fimA promoter was detected in a fimY mutant containing a fimA-lacZ reporter construct located on the chromosome. In addition, transcription from the cloned fimY promoter was not detected in Escherichia coli unless both FimZ and FimY were present, indicating that these proteins also act as coactivators of fimY expression. Consistent with these results, there is no transcription from a fimY-lacZ reporter construct within a serovar Typhimurium fimY or fimZ mutant. Studies using the fimY-lacZ construct reveal that expression of this gene varies with environmental conditions in a manner similar to fimA expression. Extensive in vitro DNA binding assays using extracts from E. coli that overexpress FimY, as well as partially purified FimY, were unable to identify a specific interaction between FimY and the fimA or fimY promoter. The results indicate that FimY is a positive regulator of fimbrial expression and that this protein acts in cooperation with FimZ to regulate the expression of Salmonella type 1 fimbrial appendages.
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Affiliation(s)
- J K Tinker
- Department of Microbiology, College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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Burns LS, Smith SG, Dorman CJ. Interaction of the FimB integrase with the fimS invertible DNA element in Escherichia coli in vivo and in vitro. J Bacteriol 2000; 182:2953-9. [PMID: 10781567 PMCID: PMC102007 DOI: 10.1128/jb.182.10.2953-2959.2000] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The FimB protein is a site-specific recombinase that inverts the fimS genetic switch in Escherichia coli. Based on amino acid sequence analysis alone, FimB has been assigned to the integrase family of tyrosine recombinases. We show that amino acid substitutions at positions R47, H141, R144, and Y176, corresponding to highly conserved members of the catalytic motif of integrase proteins, render FimB incapable of inverting the fimS element in vivo. The arginine substitutions reduced the ability of FimB to bind to fimS in vivo or in vitro, while the substitution R144Q resulted in a protein unable to bind independently to the half sites located at the left end of fimS in phase-on bacteria. These data confirm that FimB is an integrase and suggest that residue R144 has a role in binding to a specific component of the fim switch.
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Affiliation(s)
- L S Burns
- Department of Microbiology, Moyne Institute of Preventive Medicine, University of Dublin, Trinity College, Dublin 2, Republic of Ireland
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O'Gara JP, Dorman CJ. Effects of local transcription and H-NS on inversion of the fim switch of Escherichia coli. Mol Microbiol 2000; 36:457-66. [PMID: 10792731 DOI: 10.1046/j.1365-2958.2000.01864.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The fim switch of Escherichia coli is responsible for phase-variable expression of type 1 fimbriae. Switching in the ON-to-OFF and OFF-to-ON directions is promoted by the FimB recombinase, while the FimE recombinase directs switching predominantly in the ON-to-OFF direction. The effects of local promoter activity and the H-NS nucleoid-associated protein on inversion of the switch were assessed. In contrast to FimB-mediated inversion, inversion of the switch by the FimE recombinase was unaffected by the H-NS status of the cell. Transcription towards the switch from within a translationally inactivated fimE gene was found to bias the switch strongly in the OFF direction, creating a FimE+-like phenotype in the absence of the FimE protein. This biasing was H-NS dependent and was also contingent on transcription from within the switch. These data show that local transcription and a nucleoid-associated protein both contribute to the modulation of a site-specific recombination event on the bacterial chromosome.
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Affiliation(s)
- J P O'Gara
- Department of Microbiology, Moyne Institute of Preventive Medicine, University of Dublin, Trinity College, Dublin 2, Republic of Ireland
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25
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Abstract
The expression of most bacterial genes is controlled at the level of transcription via promoter control mechanisms that permit a graded response. However, an increasing number of bacterial genes are found to exhibit an 'all-or-none' control mechanism that adapts the bacterium to more than one environment. One such mechanism is phase variation, traditionally defined as the high-frequency ON<-->OFF switching of phenotype expression. Phase variation events are usually random, but may be modulated by environmental conditions. The mechanisms of phase variation events and their significance within the microbial community are discussed here.
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Affiliation(s)
- I R Henderson
- Center for Vaccine Development, Department of Pediatrics, University of Maryland School of Medicine, 685 West Baltimore Street, Baltimore, MD 21201, USA.
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