Caister Academic Press

Pathogenic Treponema: Molecular and Cellular Biology | Book

Publisher: Caister Academic Press
Edited by: Justin D. Radolf and Sheila A. Lukehart
University of Connecticut Health Center, Farmington, CO 06030-3715, USA and University of Washington School of Medicine, Seattle, WA 98104, USA respectively
Pages: x + 466
Hardback:
Publication date: July 2006Buy book
ISBN: 978-1-904455-10-3
Price: GB £159 or US $319
Pathogenic <i>Treponema</i> book
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In the past Treponema research was severely handicapped because the organisms were notoriously difficult to work with and were unculturable in the laboratory. Powerful molecular and genetic tools developed in recent years have been successfully used to dramatically expand our understanding of treponemal diversity, genomics, and cellular and molecular biology. Major breakthroughs include sequencing of Treponema genomes and the development of modern molecular methods.

This volume is the first comprehensive review of treponemal research to be published in more than twenty years. Written by leading experts in the field, this book presents the current state of research on these organisms that affect the health of millions of people worldwide. The structure and metabolism of the treponemes are explored in light of the comparative genomics data now available. The newest information concerning their pathogenic mechanisms, as well as the complex innate and adaptive immune responses they elicit, are detailed. A number of chapters illustrate how our knowledge of syphilis has grown in the molecular era despite the continuing inability to propagate its elusive etiologic agent. The book also provides an historical perspective on treponemal research that will be of considerable interest. This compilation will serve as an essential reference for microbiologists, immunologists, and physicians who deal with these organisms on a day-by-day basis or who wish to understand them better in the context of contemporary microbiology.

Topics covered include the phylogenic diversity, comparative genomics, metabolism and cultivation, motility, antigenic variation, immunology of syphilis, the use cultivatable treponemes as surrogates for T. pallidum, oral treponemes, and much much more.

Essential reading for all scientists and researchers working on trepenomes and other spirochetes and a recommended reference book for all microbiology laboratories.

Reviews

"This is a very comprehensive work by multiple authors on the current state of the research being conducted on the treponemal pathogens. There are few books that specifically cover this area of microbiology." from CAB Abstracts (2006)

"this comprehensive review reveals the main breakthroughs of research on pathogenic Treponema" from Microbiology Today (2007)

"an essential reference for students and scientists in microbiology and immunology" from Microbiology Today (2007)

"extremely comprehensive and well-referenced ... The editors should be congratulated on assembling a number of scholarly contributions from international scientific experts in the field." from J. Microbiological Methods (2007)

"especially recommended for advanced students in the field, senior researchers, physicians, and dentists; but all microbiologists will find in the book an exceptional opportunity for extending their understanding of an unusual and unique microbial group." from Int. Microbiol. Vol. 10 (2007)

"a comprehensive treatise of articles by some of the leading experts in the field ... a wealth of information about these fascinating microorganisms. This is not only a book for those working in the area, but also a wonderful text for any microbiologist's reference library" from Soc. Ind. Microbiol. News 56: 230

"a comprehensive update of the current state of knowledge of the Treponemes and other spirochaetes ... sturdily bound and beautifully printed on very high quality paper. It will make a welcome and useful addition to the libraries of any microbiological research laboratory and pathology establishment." from Aus. J. Med. Sci. (2008) 29: 63-64

Table of contents
1. The Phylogenetic Diversity of the Genus Treponema
Bruce J. Paster and Floyd E. Dewhirst
Species of Treponema are generally considered as anaerobic, host-associated spirochetes that represent one of nine spirochetal genera of the phylum Spirochaetes as based on 16S rRNA sequence analysis. Traditionally, treponemal species have been characterized using conventional phenotypic and genotypic traits. More recently, comparative whole genomic analysis has been useful to provide insight on the evolutionary aspects of treponemes. Clonal analysis of 16S rRNA genes amplified from clinical and environmental samples has revealed hundreds of not-yet-cultivated treponemal species in the human oral cavity, the termite gut, the bovine rumen, other host-associated sources, and environmental sources, such as waste treatment plants. It is likely that there remains a considerable number of unrecognized species of Treponema.
2. Comparative Genomics of Spirochetes
Steven J. Norris and George M. Weinstock
The recent sequencing of the genomes of several spirochetes permits a thorough analysis of the similarities and differences within this bacterial phylum. Treponema pallidum subsp. pallidum has one of the smallest bacterial genomes at 1.14 million base pairs (Mb) and has limited metabolic capabilities, reflecting its adaptation through genome reduction to the rich environment of mammalian tissue. Comparison with the genome of Treponema denticola reveals that, despite its larger genome size (2.84 Mb), it also has limited biosynthetic activities and is highly dependent on the gingival crevice microenvironment to provide required nutrients. The two Borrelia species sequenced to date also have limited 'core' metabolic functions encoded on a 0.91 Mb linear chromosome, but have acquired multiple plasmids that are important in their survival in the tick midgut and mammalian or avian species and in transmission between these two environments. The larger genomes of the two Leptospira interrogans strains sequenced (4.6 Mb) are highly similar and reflect extensive biosynthetic ATP production mechanisms consistent with its ability to live free in the environment as well as infect and cause disease in mammals. Information to date indicates that the genus Treponema evolved from a common ancestor early in bacterial evolution (perhaps hundreds of millions of years ago), whereas the T. pallidum subspecies are closely related and may have diverged within tens of thousands of years.
3. Structural and Genomic Features of Treponemal Architecture
Jacques Izard and Ronald J. Limberger
Treponema denticola and Treponema phagedenis are important models for deciphering the unique architectural and genetic features of treponemes. Darkfield and electron microscopy have delineated the general structure of treponemes as deduced from these two dimensional techniques. Advances in genetic tools and three dimensional visualization techniques are now linking cell architecture, cell ultrastructures, and genetic data. Ultrastructures are multi-component assemblies within the cell that drive specific functions critical to the cell such as cell division, cell shape and motility. A key treponemal ultrastructure is the cytoplasmic filament ribbon which is involved in the cell division process. Recently, application of new methods to the structural analysis of T. phagedenis has revealed novel features of the cytoplasmic filament ribbon. The observed cytoplasmic filament ribbon actually consists of independent filaments connected to each other via bridging components and anchored to the inner membrane. The nature and components of this macromolecular complex are discussed as well as the novelty of the filamentous ribbon structure. The availability of whole genome sequences from two treponemal species also allows the comparative study with other bacterial cytoskeleton-associated structures towards achieving a global picture of spirochetal cell biology.
4. Metabolism of the Treponema
David L. Cox and Justin D. Radolf
The metabolism of the three most extensively studied treponemal species, Treponema pallidum, T. denticola, and T. phagedenis, is presented and discussed. The genomes of T. pallidum and T. denticola have been sequenced and annotated, while that that of T. phagedenis has not. The availability of these two genomic sequences allows us not only to explore potential metabolic pathways within the respective organisms but also to assess the accuracy of pre-genomic studies. In the case of T. pallidum, performance and interpretation of pre-genomic metabolic investigations were greatly complicated by the unavoidable presence of rabbit testicular contaminants in treponemal suspensions. A tabular comparison of key metabolic pathways and enzymes of T. pallidum and T. denticola (with the gene and Enzyme Commission {EC} numbers) also is presented as a reference tool. The cultivation methods for all three treponemes are discussed with emphasis on the numerous, but unsuccessful, attempts to propagate T. pallidum continuously in vitro. Finally, discoveries from genomic studies will be addressed in the context of solving the cultivation problem of T. pallidum. Although metabolically T. pallidum and T. denticola share many common pathways, they are still quite diverse in their genomic makeup. T. denticola has almost 2000 genes that are absent in T. pallidum; many of these are predicted to encode proteins with physiological functions. Three areas where the latter appears to be lacking when compared to T. denticola are (1) DNA repair and housekeeping, (2) oxygen metabolism and stress, and (3) transport capabilities.
5. Metal Utilization and Oxidative Stress
Frank Gherardini, Julie Boylan and Paul Brett
Spirochetes living in oxygen-rich environments or when challenged by host immune cells are exposed to reactive oxygen (ROS) and reactive nitrogen (RNS) species. These can harm polyunsaturated lipids, cysteinyl residues, iron-sulfur clusters and DNA (Fenton Reaction) leading to inhibition of growth and, if the damage is too extensive, cell death. As is the case with other bacteria, spirochetes harbor genes encoding proteins such as superoxide dismutases (SOD), superoxide reductase (SOR), alkylhydroperoxide reductases (AhpR), peroxidases and small molecular weight thiols (i.e., thioredoxin, glutathione, CoA) to protect cellular components and maintain intracellular oxidation/reduction potential (redox). While defending against an oxidative challenge, cells must also maintain sufficient, biochemically relevant intercellular concentrations of the metals which constitute a major ROS/RNS target. To maintain this balance, bacterial cells coordinately regulate metal transport and defense enzymes using oxidative stress response regulators and metal-dependent repressors. Within the Spirochetales, different systems have evolved to deal with the interplay between the requirements for metals and oxidative challenge. In this chapter, we compare the more "conventional" mechanisms seen in Treponema denticola and Leptospira interrogans with the more limited systems seen in Treponema pallidum and Borrelia burgdorferi.
6. The Beguiling Motility of the Genus Treponema
Nyles W. Charon, Chunhao Li and Stuart F. Goldstein
Understanding the motility of Treponema species is still at its infancy. An analysis of motility mutants indicate that the periplasmic flagella, which are situated between the outer membrane sheath and cell cylinder, are directly involved in the motility in both Treponema denticola and Treponema phagedenis. Furthermore, not only do these organelles rotate in a manner similar to the flagella of rod-shaped bacteria, but they also have a skeletal function, i.e., they influence the shape of the cell of both species. A model of how these two species swim states the following: During cell displacement, the periplasmic flagella rotate in one direction (counter-clockwise) as viewed from behind the cell, and the right-handed cell cylinder rolls in the opposite direction (clockwise). Because a gel-like medium is essential for translocation of both these spirochetes, this rolling of the cell cylinder is essential for cell displacement. In contrast, almost nothing is known about the dynamics of motility of Treponema pallidum.

The organelle for motility, the periplasmic flagellum, has been studied in some detail in these three species. Its structure is unique, as a protein sheath composed of FlaA surrounds a core of three different FlaB proteins, FlaB1, FlaB3, and FlaB3. Although the function of each protein is unclear, recent results with a related spirochete species suggest that some of these proteins have an overlap in function. Specifically, in Brachyspira hyodysenteriae, mutants that lack FlaB1 or FlaB2 are still motile, but mutants that lack both are completely non-motile.

Genomic analysis of T. denticola and T. pallidum reveal that both species have all the necessary genes for flagella based motility. Although sequence analysis indicates that their motility genes are well conserved between these species, their gene order is quite different. Furthermore, several lines of evidence indicate that motility gene regulation is controlled at both the transcriptional and translational levels. Finally, because a large number of genes in both species are dedicated to motility, this cell function likely plays an important role in its survival and disease progression in the host. However, there is no experimental evidence as yet to support this contention.

7. Chemotaxis Signaling Systems in Spirochetes: Their Role in Directed Cell Movement and Pathogenesis
Renate Lux and Wenyuan Shi
Chemotaxis enables motile bacteria including spirochetes to monitor their environment and change their motility according to the stimuli perceived. In pathogenic species, chemotaxis and motility have emerged as important virulence factors. Host invasion appears to be greatly affected when these features are missing. The general mechanism of the basic chemotaxis pathway and the proteins involved are highly conserved throughout motile bacteria and archaea. Spirochetes, such as Treponema ssp., however, appear to contain a few interesting variations in form of novel fusion proteins and specific signal co-ordination problems related to their unique morphology. In addition to the chemotaxis pathway and the role of chemotaxis in spirochete pathogenesis, with a special focus on treponemes, phylogenetic aspects of the individual chemotaxis proteins are examined.
8. Genetic Manipulation of Cultivable Treponemes
Howard K. Kuramitsu
Until relatively recently, genetic characterization of treponemes was limited to cloning genes from these organisms into nonspirochete hosts such as Escherichia coli. However, the recent development of transformation systems for a few cultivable spirochetes, particularly the oral spirochete Treponema denticola, has now enabled the construction of monospecific mutants in these organisms. In addition, construction of novel shuttle plasmids has resulted in the expression of heterologous genes in these transformable strains. This will now allow for the expression and characterization of genes from noncultivable treponemes in selected cultivable treponemes. Thus, the development of these genetic tools should lead to more detailed characterization of virulence factors in both cultivable and noncultivable treponemes.
9. Historical Evidence of Syphilis and Other Treponemes
By Laura J. McGough and Emily Erbelding
This chapter explains the methodological and theoretical issues that historians face in researching the history of syphilis and other treponemes. Differences in disease definitions make simple comparisons between past and present difficult. On the other hand, a wealth of newly tapped historical material regarding mortality, demography, and population movements makes it possible to reach some conclusions about the early history of the late fifteenth century epidemic. Wartime played a critical role in producing the syphilis-or French disease-epidemic in the Italian peninsula, which apparently was recognized as a new disease, not just a clinical misdiagnosis of leprosy. Evidence does not support the claim that the disease was unusually virulent during this period. The disease's association with sexuality, later understood as sexual transmission as contagion theory became accepted, complicated descriptions of the disease. Prejudices about the sexual behaviors of different races, ethnic groups, or social classes often contributed to the confusion between venereal syphilis and other treponemal diseases. A collaborative research project between scientists and historians focusing on an ecological history of disease could yield more definitive conclusions about the history of treponemal transmission.
10. Pathogenesis of Syphilis
Justin D. Radolf, Karsten R. O. Hazlett, and Sheila A. Lukehart
Venereal syphilis is caused by Treponema pallidum, a noncultivatable, microaerophilic spirochete and obligate human pathogen. T. pallidum utilizes glycolysis for energy production, has extremely limited biosynthetic capacity, and possesses limited tolerance for environmental stress. Transmission of T. pallidum occurs in a high percentage of individuals exposed to primary or secondary syphilitic lesions. T. pallidum is extremely invasive. Invasion at the local site occurs shortly after inoculation, while hematogenous dissemination occurs well before the appearance of the primary lesion (chancre). Penetration of the blood-brain barrier by T. pallidum, a distinctive aspect of human disease, is common during early syphilis and, in untreated individuals, sets the stage for the subsequent development of neurological complications (neurosyphilis). Clinical manifestations result from the inflammatory responses elicited by spirochetes and spirochetal constituent (e.g., lipoproteins) locally and systemically. Clearance of spirochetes from sites of infection is accomplished by activated macrophages most likely in concert with opsonic antibodies. The limited surface antigenicity of T. pallidum is thought to be a major factor in the spirochete's ability to establish persistent infection; selection of tprK sequence variants also may contribute to immune evasion. As with other spirochetal pathogens, motility is thought to be critical for treponemal invasiveness. The lack of orthologs for well characterized virulence determinants in the T. pallidum genome emphasizes the uniqueness of the bacterium's parasitic strategies. Genetic approaches for identifying treponemal virulence determinants are beginning to emerge.
11. The T. pallidum Outer Membrane and Outer Membrane Proteins
Caroline E. Cameron
The spirochetal bacterium that causes syphilis, Treponema pallidum subsp.pallidum, has been termed the "stealth pathogen" due to its remarkable ability to evade the host immune response and remain quiescent for extended periods of time. This capability is due, at least in part, to the unusual outer membrane that surrounds the bacterium and interfaces with the host. This chapter correlates the pathogenic potential of T. pallidum with the cellular morphology of the outer membrane, and details the current state of knowledge of the composition of the T. pallidum outer membrane and its constituent proteins. Within this chapter the treponemal outer membrane ultrastructure, antigenicity, lipid composition, and permeability are described; in silico and experimental techniques that have been used to identify outer membrane proteins are reviewed; and current outer membrane protein candidates that have been identified via these methods are outlined.
12. Antigenic Variation in Treponema pallidum
Arturo Centurion-Lara
The pathogenic treponemes include three subspecies of Treponema pallidum (T. pallidum), T. carateum, T. paraluiscuniculi, and the unclassified Fribourg-Blanc (simian) isolate. These treponemes are antigenically highly related, cause persistent infections in their respective hosts, and induce similar histopathological changes and immune responses. The host immune response is able clear the great majority of spirochetes from early active lesions, however, some organisms escape immune clearance and cause chronic infections. Several mechanisms, including antigenic variation, have been proposed to explain the ability of T. pallidum to disseminate and evade the immune response of the host. One member of the tpr gene family, tprK, undergoes extensive sequence diversification during infection, and its encoded protein induces an active immune response. The variable portions of the protein are antibody epitopes, and variation of these epitope sequences would potentially allow T. pallidum to avoid the immune response or, alternatively, to adapt to the changing micro-environments posed by dissemination to different tissue sites. We describe in this chapter a non-reciprocal gene conversion-like mechanism for the generation of tprK diversity in Treponema pallidum subsp pallidum, in which new variants are created by unidirectional exchange between donor sites and the tprK expression site. This mechanism of antigenic variation is likely to be shared by all members of this group of pathogenic treponemes and is likely to contribute to the persistence of treponemal infections.
13. Immunology of Syphilis
Justin D. Radolf and Sheila A. Lukehart
Though venereal syphilis is infectious in origin, there is now a clear consensus among syphilologists that tissue damage and the clinical manifestations of the disease result from the host immune response elicited by the spirochete and its constituents. Whereas acute syphilitic infection was once regarded as being immunosuppressive, there is now abundant evidence that Treponema pallidum evokes a robust humoral and cellular response soon after inoculation. It also has become evident that a cooperative interaction between the humoral and cellular arms of the immune response is required to clear treponemes from sites of infection as well as to establish long lasting protective immunity. Antibodies that promote uptake and killing of spirochetes by activated macrophages are believed to play an essential role in bacterial clearance, while their role in neutralization and immobilization in vivo appears to be limited. The mechanisms that enable a small number of spirochetes to establish persistent infection are poorly understood, although recent evidence indicates that the poor antigenicity of the spirochetal outer membrane, coupled with an ability to generate TprK antigenic variants, may be important for the organism's ability to evade the host's immune response. Efforts to develop a safe and effective syphilis vaccine have been hindered by uncertainty about the relative importance of humoral and cellular mechanisms to protective immunity and the fact that T. pallidum outer membrane proteins have not been unambiguously identified.
14. The Oral Spirochetes: Their Ecology and Role in the Pathogenesis of Periodontal Disease
Stanley C. Holt and Jeffrey L. Ebersole
Nearly 350 years ago Antoni van Leeuwenhoek described "living animalcules aswimming... The biggest sort bent their body into curves going forward...". Thus, the first written descriptions of what we now know to be spirochetes. These prokaryons are found both free-living in nature, and associated with a variety of animals, and humans. Both nonpathogenic and pathogenic species of spirochetes have been identified. Their participation as etiologic agents in human oral disease has been debated for many years. Numerous investigations have reported low numbers of spirochetes in the gingival sulcus at health sites, while disease progression with gingival inflammation, increased pocket depth, and a more anaerobic microenvironment correlated with an increase in the numbers and variety (small, medium, large) of spirochetes. Additionally, return to oral health resulted in the decease in the number of spirochetes to levels consistent with gingival health. Seminal contributions of Socransky and colleagues demonstrated that the microbial ecology in oral health and periodontitis was comprised of many individual genera and species; however, several specific microbial complexes or consortia appeared to reflect alterations in the clinical state of the site. In particular, one prominent consortium consists of P. gingivalis, T. forsythensis, and T. denticola. This chapter provides an overview of the characteristics of oral spirochetes, and particularly T. denticola as important members of oral biofilms and their relationship to periodontal disease. The content of the chapter also focuses on attempting to summarize the literature with regard to the numerous potential "virulence molecules" expressed by the spirochetes that might be essential for their in vivo survival and contribution to the progression of oral disease in susceptible hosts.
15. Virulence Determinants of Oral Treponemes
Richard P. Ellen
Oral treponemes are indigenous bacteria that become opportunistic pathogens in the mixed microflora that colonizes the space between the teeth and inflamed gingival tissues (periodontal pocket). The extensively studied Treponema denticola binds to and degrades extracellular matrix and thereby probably contributes to the disruption of the gingival epithelial barrier and bacterial penetration of the underlying connective tissue. Well-conserved motility and chemotactic properties also promote local tissue invasion. The major outer sheath protein (Msp) of T. denticola is differentially toxic to a variety of host cells. It also perturbs cytoskeletal and calcium dynamics in host cells that retain viability (e.g. fibroblasts). The generation of volatile sulphur containing compounds from amino acid metabolism by the enzyme cystalysin is also cytotoxic. Some lipoproteins and outer sheath glycolipids trigger proinflammatory pathways of tissue damage. T. denticola may degrade chemokines of innate immunity pathways and activate host matrix metalloproteinases; yet, it is relatively resistant to b-defensins. Since 80% of the phylotypes of oral treponemes have yet to be cultivated in vitro, their potential pathogenicity has probably been underestimated.
16. Innate and Adaptive Immune Responses to Oral Treponemes
Nicolas W.J. Schröder, Ralf R. Schumann, and Ulf B. Göbel
Innate immunity plays an important role in the pathogenesis of periodontitis. Toll-like recep-tors, a family of pattern recognition receptors recognizing a wide array of microbial ligands, are widely expressed on cells within the oral cavity. Oral treponemes exhibit at least two dif-ferent types of molecules within their outer membranes interacting with TLRs: lipoproteins, exhibiting a common triacylated lipid motif, as well as glycolipids, sharing structural simi-larities with lipoteichoic acid (LTA) of Gram-positive bacteria. Both compounds have been found to interact with TLR-2, inducing cytokine release. Since pro-inflammatory cytokines have been shown to exhibit worsening effects within the course of periodontitis, the interac-tion of TLR-2 ligands with the host may be regarded as an event triggering disease. Next to innate immune responses, oral treponemes are also known to initiate adaptive immune re-sponses though the production of antibodies. Since adaptive immune responses are initiated at least in part by dendritic cells also expressing TLR-2, the interaction of the host with TLR-2 ligands may be an important event for the induction of immunity.
17. Treponema and Bovine Skin Disease: Papillomatous Digital Dermatitis and Ulcerative Mammary Dermatitis
Lola V. Stamm and Darren J. Trott
Papillomatous digital dermatitis (PDD) is an infectious, superficial dermatitis that primarily affects the feet of dairy cattle. PDD is associated with intensive housing of cattle and prolonged exposure of bovine feet to moist, unhygienic conditions. Experimental transmission of PDD has been achieved by inoculating the feet of cattle with lesion material. Treatment of the lesions with antibiotics results in rapid resolution, consistent with the bacterial etiology of the disease. PDD lesions contain a mixed population of predominantly anaerobic bacteria. A pathognomonic feature of PDD lesions is the presence of large numbers of spirochetes invading deep into the epidermis, whereas other bacteria are located more superficially. It is currently unclear whether the PDD-associated spirochetes are primary pathogens or secondary opportunists. A number of Treponema phylogenetic groups have been demonstrated in PDD lesions. Of the spirochetes that are cultivable, only Treponema brennaborense has been classified as a new species. The remaining cultivable Treponema are closely related to human-associated T. denticola, T. medium/vincentii, and T. phagedenis. Cattle affected by PDD develop an immune response to Treponema antigens. A bacterin incorporating cultivable PDD-associated Treponema has been shown to be effective at reducing lesion development. PDD-associated Treponema have been recently demonstrated in cases of bovine ulcerative mammary dermatitis and contagious ovine digital dermatitis. Little is known concerning the origin and pathogenic mechanisms of the PDD-associated Treponema. Further research is required to clarify the taxonomic position and basic biology of these spirochetes.
18. Termite Gut Spirochetes
John A. Breznak
Spirochetes comprise an unusually abundant component of the hindgut microbiota of termites, accounting for as many as one-half of all prokaryotic cells. However, for many years our understanding of termite gut spirochetes was meager owing, in part, to a lack of pure culture representatives. In recent years this situation has changed dramatically. Cultivation-independent (molecular biological) approaches have shown that termite gut spirochetes constitute a rich diversity of novel species of Treponema. Moreover, studies of the first pure cultures have revealed physiological capabilities (H2/CO2-acetogenesis and dinitrogen fixation) previously unknown in spirochetes which contribute to the nutrition and vitality of their host. This chapter will summarize our current understanding of termite gut treponemes and the extent to which they have already expanded our appreciation of spirochetal phylogenetic and physiological diversity.
19. Afterword
Daniel M. Musher and Ronald F. Schell
If our book, Pathogenesis and Immunology of Treponemal Infections, brought to mind the medieval metaphor of dwarfs standing on the shoulders of giants, the current work, Pathogenic Treponema: Molecular and Cellular Biology, makes us think that a new generation of giants has arisen. In our work of 1983, we tried to bring together what was known about treponemes - their biology and immunology, the pathogenesis of diseases that they cause, and the host response to them - all the time painfully aware that Hollander and Turner, in 1957, had stated, or at least hinted at, many of the same conclusions. It is exciting now to see what a new generation of scientists has done for the challenging, and now enlarged, field of treponemal research.

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(EAN: 9781904455103 Subjects: [bacteriology] [microbiology] [medical microbiology] [molecular microbiology] )