Shigella: Molecular and Cellular Biology
Caister Academic Press
William D. Picking and Wendy L. Picking
Dept. Pharmaceutical Chemistry, University of Kansas, Lawrence, KS, USA
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Members of the genus Shigella are responsible for bacillary dysentery and are of global public health importance. Shigella is one of the leading bacterial causes of diarrhoea worldwide with greatly elevated morbidity and mortality in developing nations and especially among children.
This book provides a thorough overview of current research on the cellular and molecular biology of Shigella. Expert authors have contributed authoritative and up-to-date reviews of current knowledge and recent advances in the molecular biology of these pathogens. The first section of the book explores aspects of metabolism and gene regulation and examines the molecular and cellular biology of Shigella as a genus diversified from Escherichia. This section also considers often overlooked features of bacterial pathogens and the current understanding of RNA-based regulation of gene expression. The second part of the book focuses on the important area of host-pathogen interplay, the ability of Shigella to subvert host signaling processes, pathways for the destruction of phagocytes, the development of novel methods for assessing host cell targets, an overview of the adaptive immunity elicited by Shigella and current Shigella vaccine candidates. The final section covers the Shigella type III secretion system (T3SS) recognized as a highly evolved nanomachine for promoting cross-species communication between prokaryotes and eukaryotes. Two chapters are dedicated to dynamic aspects of the Shigella T3SS including the needle tip complex and novel methods for the identification of newly recognized effector proteins.
This compendium provides the researcher with a flavour of the molecular and cellular topics that are important in understanding Shigella and the delicate balance it has with its primary host. This is an essential book for Shigella researchers and recommended reading for anyone working in the area of bacterial pathogenesis.
Table of contents
1. Shigella and Shigellosis
Philip R. Adam and William D. Picking
Shigella spp. are Gram-negative, nonmotile bacilli that are important gastrointestinal pathogens responsible for significant morbidity and mortality, especially in developing nations. It is particularly devastating to children ages 2 to 5 who suffer most from the dehydration and complications of shigellosis. The survivors often exhibit impaired growth due to malnutrition and this is exacerbated by repeated diarrheal episodes. The difficulties posed by shigellosis are further complicated by increased antibiotic resistance and the possibility of post-infection sequelae such as episodes of reactive arthritis and inflammatory bowel disease in genetically susceptible individuals. Advances in understanding the pathogenic mechanisms have revealed novel forms of crosstalk between Shigella and its human host. New insights into the type III secretion system of this pathogen, the subversion of normal mammalian cell functions for the benefit of the pathogen, and the use of toxins that enhance infection and cause targeted tissue damage are all part of the Shigella pathogenic arsenal. Nevertheless, shigellosis continues to be a devastating public health problem. This collection of works will illuminate our current understanding of important aspects of Shigella molecular biology and its crosstalk with human cells, and provides the foundation for future research on this important agent of infectious diarrhea.
2. Shigella Iron Transport Systems
A. R. Mey, E. E. Wyckoff and S. M. Payne
Shigella species have several different transport systems for acquisition of the essential element iron. These include both ferric and ferrous iron transporters. These pathogens synthesize and secrete siderophores, high-affinity ferric iron chelators, and both catechol and hydroxamate siderophores have been identified in Shigella. Additionally, the Shigella species have transporters for free ferric (Sit) and ferrous (Feo) iron, and Shigella dysenteriae has an outer membrane receptor and transport system for heme. The expression of genes encoding these transporters is regulated by environmental cues including iron, oxygen and temperature. Iron regulation is accomplished by Fur, a transcriptional regulator that represses these genes in the presence of iron. FNR and ArcAB regulate expression of the genes in response to oxygen levels, while temperature controls expression of the heme transporter ShuA post-transcriptionally through formation of a FourU thermometer structure in the mRNA. Thus, Shigella are able to adapt to a variety of different environments and different iron sources to obtain sufficient iron for growth. In aerobic, iron-limiting conditions in vitro, expression of siderophores allows maximal growth, while the Sit system is crucial to replication in the intracellular environment of the host epithelium.
3. Shigella and Antivirulence: the Dark Side of Bacterial Evolution
Kimberly A. Bliven and Anthony T. Maurelli
The acquisition of novel virulence factors and subsequent remodeling of bacteria systems to incorporate these factors are equally important events in pathogen evolution. Genes that are inactivated or lost from an emerging pathogen's genome due to incompatibility with new virulence factors are known as antivirulence genes (AVGs). AVGs were first described in Shigella, a human-specific gastrointestinal pathogen that evolved from ancestral Escherichia coli. Although AVGs have been described in a variety of bacterial pathogens, including Salmonella, Yersinia, Burkholderia, and Francisella, Shigella remains perhaps the best model organism for the study of antivirulence due to the vast extent of literature on not only Shigella, but also E. coli, which retains the functional AVGs that have been inactivated or lost in Shigella strains. Currently, there are five documented AVGs in Shigella: cadA, nadA/nadB, speG, and ompT. In this chapter, we will discuss the discoveries of these AVGs, their effects on virulence, and the events that led to their inactivation or loss in Shigella. The development of novel therapeutics and vaccines, an improved understanding of virulence mechanisms, and a greater insight into pathogen evolution are just some of the benefits that may arise from exploration of AVGs in bacterial pathogens.
4. The Genetic Organization and Transcriptional Regulation of Shigella Virulence Genes
Natasha Weatherspoon-Griffin, Michael A. Picker and Helen J. Wing
Central to bacterial pathogenicity is the precise and coordinated control of virulence gene expression in response to environmental cues encountered in the human host. This chapter focuses on the transcriptional regulation of Shigella virulence genes encoded by the large virulence plasmid, pINV, found in almost all Shigella species. We describe the silencing of pINV-encoded virulence genes by the chromosomally encoded nucleoid structuring protein H-NS, which serves as the backdrop for all other regulatory events on this plasmid. We then describe the four-tiered virulence regulatory cascade emphasizing the environmental stimuli, transcriptional regulators and mechanisms that govern virulence gene expression at each tier. Finally, we review other regulatory inputs that are received from the Shigella chromosome and their role in the modulation of virulence gene expression. We begin our discussion by describing the genetic organization of Shigella, its relatedness to Escherichia coli and the different forms of pINV carried by Shigella species to highlight how the regulatory cascades controlling Shigella virulence are, in large part, conserved across species. Overall, this chapter reveals that Shigella is a fascinating model for the study of virulence gene regulation, which promotes our understanding of Shigella pathogenesis and mechanisms of virulence gene regulation in other bacterial pathogens.
5. Ribo-regulation in Shigella
Erin R. Murphy, William H. Broach and Andrew B. Kouse
Bacterial ribo-regulators are a diverse collection of molecules defined here as any RNA molecule that functions to specifically control the expression of a target gene(s), or the activity of a target protein. While the role of regulatory proteins in controlling virulence gene expression in Shigella species has long been appreciated, the role of RNA-mediated regulation on this process is just now coming into focus. Recent advances have revealed that ribo-regulators play a central role in modulating Shigella gene expression in response to changes in specific environmental conditions, a process that is essential to the survival and virulence of these important pathogens. This chapter will present a general overview of bacterial ribo-regulators, followed by a detailed discussion of each Shigella ribo-regulator characterized to date. Special emphasis will be placed on the role that each known Shigella ribo-regulator plays in facilitating the survival and/or virulence of these significant pathogens.
6. IpaB Ion Channels Induce Pyroptosis in Macrophages
Lidija Senerovic, Anna Brotcke Zumsteg and Michael Kolbe
The Gram-negative bacterium Shigella flexneri invades the colonic epithelium and causes bacillary dysentery. For successful infection, S. flexneri requires many effector proteins secreted via a Type three secretion system (T3SS). The effector protein IpaB is conserved in many medically important Gram-negative bacteria and is an essential virulence factor with multiple roles in S. flexneri infection. S. flexneri requires IpaB to invade host cells, escape from the phagosome and induce macrophage cell death. The mechanistic details regarding how IpaB functions have recently been elucidated. Secreted IpaB spontaneously oligomerizes and inserts into the plasma membrane of target cells. IpaB oligomers form channels selective for small monovalent cations with optimal activity at an acidic pH. After internalization, IpaB channels permit potassium flux inside macrophage vacuoles causing the disruption of the endolysosomal membranes. Vacuolar leakage is followed by an IPAF-dependent activation of caspase-1 and macrophage death. Mechanistic insights gained from IpaB studies with host cells may be extended to homologues from other medically important enteropathogenic bacteria and could contribute not only to understanding the conserved mechanisms of T3SS dependent infections, but also provide the solutions to fight them.
7. The Cellular Microbiology of Shigella Invasion of Epithelial Cells
Guy Tran Van Nhieu and Philippe Sansonetti
In the most impoverished areas of the planet, bacillary dysentery (i.e. shigellosis) remains a major etiology of enteric infections in infants and children below the age of five and still accounts for significant mortality. The subgroup Shigella flexneri and S. sonnei account for the endemic form of the disease, whereas Shigella dysenteriae serotype 1 accounts for the epidemic form that is currently rarely observed. Following ingestion, the bacteria invade the colonic mucosa where they multiply. Under its most severe forms, shigellosis is associated with an intense inflammation of the colonic mucosa leading to its destruction, thus the dysenteric syndrome. An infectious dose as low as a few thousand bacteria has been estimated to be sufficient to confer the disease in humans, indicative of the high virulence of Shigella. Shigella is a pathogen restricted to humans and higher primates, probably reflecting the specificity of bacterial virulence attributes adapted to cellular invasion and spreading in the colonic mucosa, as well as to the manipulation of host intestinal inflammatory responses. In this chapter, we will focus on our current knowledge of processes involved in the major step of Shigella invasion of epithelial cells.
8. The Molecular Role of the Polar Outer Membrane Protein IcsA (VirG) in Shigella Actin-based Motility
Central to the cytosolic life-cycle of the Gram-negative bacterial pathogen, Shigella, is the ability to polymerize host cell actin at the bacterial pole to generate actin comet tails. The actin tails generate a propulsive force that aid in intracellular and intercellular bacterial motility and is an essential feature of Shigella virulence. The bacterial outer membrane protein, IcsA (VirG), plays a critical role in Shigella actin-based motility. Here we review key findings and discuss recent developments that aid in our understanding of the polar localization of IcsA and IcsA-mediated Shigella actin-tail assembly.
9. Trans-epithelial Communication in the Context of Shigella Infection
Ana Maldonado and Beth A. McCormick
Shigella ssp. are the causative agents of bacillary dysentery, a disease characterized by a severe form of bloody diarrhea. Every year there are about two billion cases of diarrheal disease resulting in millions of deaths. Ninety-nine percent of these cases occur in developing countries, where diarrhea is the second-leading cause of death in children. Shigella is one of the most communicable bacterial agents of diarrheal disease and has evolved to be a highly efficient pathogen, as only humans (and certain higher primates) serve as the only natural host and reservoir. Shigellosis consists of painful abdominal cramps, nausea, fever, tenesmus, and frequently blood and mucus in the stools. These symptoms reflect the invasion of the colonic submucosa by Shigella. Pathogenesis of Shigella ssp. comprise an intricate cross-talk between bacterial factors and host components that leads to the destruction of the epithelium, and the characteristic signs of inflammation exhibited by massive infiltration and exudation of polymorphonuclear cells evidenced in histopathologic analysis of infected patients. At the same time the host activates a sophisticated defense mechanism aimed at clearing the infection. Here we summarized the bacterial-epithelial cell interactions during the course of shigellosis.
10. Imaging Techniques to Track Shigella Infection at the Cellular Level
Nora Mellouk and Jost Enninga
Cellular microbiology has benefitted tremendously from the usage, adaptation, and development of novel imaging tools. This is particularly true for the study of intracellular bacterial pathogens, such as Listeria or Shigella, due to their complex interactions with the host at the tissue and cellular level. In the case of Shigella, microscopy has been instrumental in uncovering a large number of its infection paradigms, for example how it interacts with different host cell types during the infection of the epithelial barrier, how it employs its type III secretion system (T3SS), how it is internalized into host cells and reaches its cytoplasmic niche, and how it moves both intra- and inter-cellularly. More recently, imaging has also been used to monitor the response of individual host cells to the pathogen during infection in a dynamic fashion. Now, dimensions reaching from only a few nanometers to hundreds of micrometers can be bridged correlating different light and electron microscopy approaches. This is important to obtain functional insights into the infection strategy of Shigella. Imaging probes are being continuously improved and developed to uncover functional paradigms of the Shigella infection process. Furthermore, image processing of the experimental data is increasingly done in an automated way to avoid a potential bias of its interpretation. Improving the links between different imaging modalities and their integration for use in dynamic imaging will provide comprehensive information on the Shigella infection process in situ and in vivo, and for the study of other infection processes as well.
11. Immune Responses Against Shigella During Natural Infection and Induced by Vaccination
Shigella is an important gastrointestinal pathogen that affects primarily small children (0-5 years of age) in developing countries. This Gram negative bacterium is a facultative intracellular pathogen that is capable of invading numerous cell types in its human host. Microfold or M cells, macrophages and epithelial cells are the 'main' targets for Shigella invasion during infection, however, dendritic cells and T lymphocytes are also susceptible to bacterial invasion with direct consequences on the resulting the immune response. Many host factors contribute to mounting an immune response against Shigella, but these are not enough to prevent the onset of infection. Furthermore, the host's adaptive immune response tends to be skewed toward LPS recognition which leads to the development of a serotype specific immunity. Therefore, the host is usually not protected against subsequent infections by Shigella bearing different O antigen serotypes. By understanding the immune responses elicited by Shigella, we will more fully appreciate the ways in which Shigella evades the host response and identify the immune mechanisms that provide the most efficient bacterial clearance. This will allow us to identify adequate correlates of protection that could ultimately lead to effective vaccine candidates to prevent shigellosis.
12. Dissecting Shigella flexneri Type III Secretion System Tip Complex Maturation
Olivia Arizmendi and Nicholas E. Dickenson
The type III secretion system (T3SS) is used by many Gram negative bacteria as a means for communicating with target eukaryotic cells. In the most thoroughly characterized systems, the T3SS is used to subvert normal cellular functions as a weapon in the bacterium's virulence arsenal. The T3SS machinery consists of two main structural components. The first is a basal body which is a complex assemblage of proteins that spans the bacterial periplasm and is anchored in the bacterial inner and outer membranes. The second is an exposed needle structure that is involved in sensing host cell contact and delivering the effector proteins responsible for subverting host functions directly into the eukaryotic cell's membrane and cytoplasm. The secreted effector proteins vary greatly with respect to function from one pathogen to another and these effectors ultimately determine the outcome of the pathogen-host interaction. In contrast, there is notable structural and functional homology among the type III secretion apparatuses (T3SAs) studied thus far. Despite such conservation, the mechanisms by which different T3SSs sense the environment and mature is only now being understood. The identification of protein complexes at the tip of the exposed needle that are responsible for secretion control and determination of the structures for some needle and needle tip complex proteins has provided a starting point for dissecting the conserved and divergent aspects of type III secretion induction. This chapter discusses the structures and mechanisms of maturation of the T3SA tip complex, focusing on the model system, Shigella flexneri.
13. Molecular Approaches to Identifying Type 3 Secreted Effectors: a Shigella Case Study
Analise Z. Reeves, Sonia C. Costa and Cammie F. Lesser
Type 3 secretion systems are specialized machines common to plant and animal bacterial pathogens as well as insect endosymbionts that act to deliver tens of proteins directly from bacteria into eukaryotic cells. While protein components of these complex machines are highly conserved, each bacterium delivers its own unique repertoire of proteins, commonly referred to as effectors, into host cells. The function of effectors can be difficult to identify experimentally, as they often act in a functionally redundant manner to mediate specific steps in pathogenesis such that loss of expression of an individual protein does not result in a detectable phenotype. In addition, despite the growing availability of annotated bacterial genome sequences, effectors are challenging to identify via bioinformatic approaches as they have poorly defined secretion sequences and commonly do not share homology with other proteins. Extensive efforts over the past 30-40 years have been extended towards identifying these secreted virulence proteins, and discerning how they act to usurp host cell processes to promote bacterial survival and spread. Here, we provide a historical review of the means by which the currently known ~30 Shigella effectors were discovered to illustrate the variety of experimental approaches including genetic, biochemical, functional and bioinformatic based assays that have been used to identify these important virulence factors.
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(EAN: 9781910190197 9781910190203 Subjects: [microbiology] [bacteriology] [medical microbiology] [molecular microbiology] )