bluuebunny/crossref_metadata_2025 huggingface dataset:
Expression of Neuronal CXCL10 Induced by Rabies Virus Infection Initiates Infiltration of Inflammatory Cells, Production of Chemokines and Cytokines, and Enhancement of Blood-Brain Barrier Permeability
Authors: Chai Qingqing , She Ruiping , Huang Ying , Fu Zhen F.
Published: October 2014

It has been shown that enhancement of blood-brain barrier (BBB) permeability is modulated by the expression of chemokines/cytokines and reduction of tight junction (TJ) proteins in the brains of mice infected with rabies virus (RABV). Since CXCL10 was found to be the most highly expressed chemokine, its temporal and spatial expression were determined in the present study. The expression of the chemokine CXCL10 was initially detected in neurons as early as 3 days postinfection (p.i.) in the brains of RABV-infected mice, after which it was detected in microglia (6 days p.i.) and astrocytes (9 days p.i.). Neutralization of CXCL10 by treatment with anti-CXCL10 antibodies reduced gamma interferon (IFN-γ) production and Th17 cell infiltration, as well as restoring TJ protein expression and BBB integrity. Together, these data suggest that it is the neuronal CXCL10 that initiates the cascade that leads to the activation of microglia/astrocytes, infiltration of inflammatory cells, expression of chemokines/cytokines, reduction of TJ protein expression, and enhancement of the BBB permeability.
Autophagy Restricts HIV-1 Infection by Selectively Degrading Tat in CD4
+
T Lymphocytes
Authors: Sagnier Sophie , Daussy Coralie F. , Borel Sophie , Robert-Hebmann Véronique , Faure Mathias , Blanchet Fabien P. , Beaumelle Bruno , Biard-Piechaczyk Martine , Espert Lucile
Published: October 2014

Autophagy is a ubiquitous mechanism involved in the lysosomal-mediated degradation of cellular components when they are engulfed in vacuoles called autophagosomes. Autophagy is also recognized as an important regulator of the innate and adaptive immune responses against numerous pathogens, which have, therefore, developed strategies to block or use the autophagy machinery to their own benefit. Upon human immunodeficiency virus type 1 (HIV-1) infection, viral envelope (Env) glycoproteins induce autophagy-dependent apoptosis of uninfected bystander CD4
+
T lymphocytes, a mechanism likely contributing to the loss of CD4
+
T cells. In contrast, in productively infected CD4
+
T cells, HIV-1 is able to block Env-induced autophagy in order to avoid its antiviral effect. To date, nothing is known about how autophagy restricts HIV-1 infection in CD4
+
T lymphocytes. Here, we report that autophagy selectively degrades the HIV-1 transactivator Tat, a protein essential for viral transcription and virion production. We demonstrated that this selective autophagy-mediated degradation of Tat relies on its ubiquitin-independent interaction with the p62/SQSTM1 adaptor. Taken together, our results provide evidence that the anti-HIV effect of autophagy is specifically due to the degradation of the viral transactivator Tat but that this process is rapidly counteracted by the virus to favor its replication and spread.

IMPORTANCE
Autophagy is recognized as one of the most ancient and conserved mechanisms of cellular defense against invading pathogens. Cross talk between HIV-1 and autophagy has been demonstrated depending on the virally challenged cell type, and HIV-1 has evolved strategies to block this process to replicate efficiently. However, the mechanisms by which autophagy restricts HIV-1 infection remain to be elucidated. Here, we report that the HIV-1 transactivator Tat, a protein essential for viral replication, is specifically degraded by autophagy in CD4
+
T lymphocytes. Both Tat present in infected cells and incoming Tat secreted from infected cells are targeted for autophagy degradation through a ubiquitin-independent interaction with the autophagy receptor p62/SQSTM1. This study is the first to demonstrate that selective autophagy can be an antiviral process by degrading a viral transactivator. In addition, the results could help in the design of new therapies against HIV-1 by specifically targeting this mechanism.
Uneven Genetic Robustness of HIV-1 Integrase
Authors: Rihn Suzannah J. , Hughes Joseph , Wilson Sam J. , Bieniasz Paul D.
Published: October 2014

Genetic robustness (tolerance of mutation) may be a naturally selected property in some viruses, because it should enhance adaptability. Robustness should be especially beneficial to viruses like HIV-1 that exhibit high mutation rates and exist in immunologically hostile environments. Surprisingly, however, the HIV-1 capsid protein (CA) exhibits extreme fragility. To determine whether fragility is a general property of HIV-1 proteins, we created a large library of random, single-amino-acid mutants in HIV-1 integrase (IN), covering >40% of amino acid positions. Despite similar degrees of sequence variation in naturally occurring IN and CA sequences, we found that HIV-1 IN was significantly more robust than CA, with random nonsilent IN mutations only half as likely to cause lethal defects. Interestingly, IN and CA were similar in that a subset of mutations with high
in vitro
fitness were rare in natural populations. IN mutations of this type were more likely to occur in the buried interior of the modeled HIV-1 intasome, suggesting that even very subtle fitness effects suppress variation in natural HIV-1 populations. Lethal mutations, in particular those that perturbed particle production, proteolytic processing, and particle-associated IN levels, were strikingly localized at specific IN subunit interfaces. This observation strongly suggests that binding interactions between particular IN subunits regulate proteolysis during HIV-1 virion morphogenesis. Overall, use of the IN mutant library in conjunction with structural models demonstrates the overall robustness of IN and highlights particular regions of vulnerability that may be targeted in therapeutic interventions.

IMPORTANCE
The HIV-1 integrase (IN) protein is responsible for the integration of the viral genome into the host cell chromosome. To measure the capacity of IN to maintain function in the face of mutation, and to probe structure/function relationships, we created a library of random single-amino-acid IN mutations that could mimic the types of mutations that naturally occur during HIV-1 infection. Previously, we measured the robustness of HIV-1 capsid in this manner and determined that it is extremely intolerant of mutation. In contrast to CA, HIV-1 IN proved relatively robust, with far fewer mutations causing lethal defects. However, when we subsequently mapped the lethal mutations onto a model of the structure of the multisubunit IN-viral DNA complex, we found the lethal mutations that caused virus morphogenesis defects tended to be highly localized at subunit interfaces. This discovery of vulnerable regions of HIV-1 IN could inform development of novel therapeutics.
Identification of Residues in the Human Respiratory Syncytial Virus Fusion Protein That Modulate Fusion Activity and Pathogenesis
Authors: Hotard Anne L. , Lee Sujin , Currier Michael G. , Crowe James E. , Sakamoto Kaori , Newcomb Dawn C. , Peebles R. Stokes , Plemper Richard K. , Moore Martin L.
Published: October 2014

Human respiratory syncytial virus (RSV) lower respiratory tract infection can result in inflammation and mucus plugging of airways. RSV strain A2-line19F induces relatively high viral load and mucus in mice. The line 19 fusion (F) protein harbors five unique residues compared to the non-mucus-inducing strains A2 and Long, at positions 79, 191, 357, 371, and 557. We hypothesized that differential fusion activity is a determinant of pathogenesis. In a cell-cell fusion assay, line 19 F was more fusogenic than Long F. We changed the residues unique to line 19 F to the corresponding residues in Long F and identified residues 79 and 191 together as responsible for high fusion activity. Surprisingly, mutation of residues 357 or 357 with 371 resulted in gain of fusion activity. Thus, we generated RSV F mutants with a range of defined fusion activity and engineered these into recombinant viruses. We found a clear, positive correlation between fusion activity and early viral load in mice; however, we did not detect a correlation between viral loads and levels of airway mucin expression. The F mutant with the highest fusion activity, A2-line19F-K357T/Y371N, induced high viral loads, severe lung histopathology, and weight loss but did not induce high levels of airway mucin expression. We defined residues 79/191 as critical for line 19 F fusion activity and 357/371 as playing a role in A2-line19F mucus induction. Defining the molecular basis of the role of RSV F in pathogenesis may aid vaccine and therapeutic strategies aimed at this protein.

IMPORTANCE
Human respiratory syncytial virus (RSV) is the most important lower respiratory tract pathogen of infants for which there is no vaccine. Elucidating mechanisms of RSV pathogenesis is important for rational vaccine and drug design. We defined specific amino acids in the fusion (F) protein of RSV strain line 19 critical for fusion activity and elucidated a correlation between fusion activity and viral load in mice. Further, we identified two distinct amino acids in F as contributing to the mucogenic phenotype of the A2-line19F virus. Taken together, these results illustrate a role for RSV F in virulence.
Separate Cellular Localizations of Human T-Lymphotropic Virus 1 (HTLV-1) Env and Glucose Transporter Type 1 (GLUT1) Are Required for HTLV-1 Env-Mediated Fusion and Infection
Authors: Maeda Yosuke , Terasawa Hiromi , Tanaka Yuetsu , Mitsuura Chisho , Nakashima Kaori , Yusa Keisuke , Harada Shinji
Published: October 2014

Interaction of the envelope glycoprotein (Env) of human T-lymphotropic virus 1 (HTLV-1) with the glucose transporter type 1 (GLUT1) expressed in target cells is essential for viral entry. This study found that the expression level of GLUT1 in virus-producing 293T cells was inversely correlated with HTLV-1 Env-mediated fusion activity and infectivity. Chimeric studies between GLUT1 and GLUT3 indicated that the extracellular loop 6 (ECL6) of GLUT1 is important for the inhibition of cell-cell fusion mediated by Env. When GLUT1 was translocated into the plasma membrane from intracellular storage sites by bafilomycin A1 (BFLA1) treatment in 293T cells, HTLV-1 Env-mediated cell fusion and infection also were inhibited without the overexpression of GLUT1, indicating that the localization of GLUT1 in intracellular compartments rather than in the plasma membrane is crucial for the fusion activity of HTLV-1 Env. Immunoprecipitation and laser scanning confocal microscopic analyses indicated that under normal conditions, HTLV-1 Env and GLUT1 do not colocalize or interact. BFLA1 treatment induced this colocalization and interaction, indicating that GLUT1 normally accumulates in intracellular compartments separate from that of Env. Western blot analyses of FLAG-tagged HTLV-1 Env in virus-producing cells and the incorporation of HTLV-1 Env in virus-like particles (VLPs) indicate that the processing of Env is inhibited by either overexpression of GLUT1 or BFLA1 treatment in virus-producing 293T cells. This inhibition probably is due to the interaction of the Env with GLUT1 in intracellular compartments. Taken together, separate intracellular localizations of GLUT1 and HTLV-1 Env are required for the fusion activity and infectivity of HTLV-1 Env.

IMPORTANCEThe deltaretrovirus HTLV-1 is a causative agent of adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Although HTLV-1 is a complex retrovirus that has accessory genes, no HTLV-1 gene product has yet been shown to regulate its receptor GLUT1 in virus-producing cells. In this study, we found that a large amount of GLUT1 or translocation of GLUT1 to the plasma membrane from intracellular compartments in virus-producing cells enhances the colocalization and interaction of GLUT1 with HTLV-1 Env, leading to the inhibition of cell fusion activity and infectivity. The results of our study suggest that GLUT1 normally accumulates in separate intracellular compartments from Env, which is indeed required for the proper processing of Env.
Coxsackievirus B3 Engineered To Contain MicroRNA Targets for Muscle-Specific MicroRNAs Displays Attenuated Cardiotropic Virulence in Mice
Authors: He Feng , Yao Hailan , Wang Jianmin , Xiao Zonghui , Xin Le , Liu Zhuo , Ma Xiaolin , Sun Juan , Jin Qi , Liu Zhewei
Published: October 2014

Coxsackievirus B3 (CVB3) is trophic for cardiac tissue and is a major causative agent for viral myocarditis, where local viral replication in the heart may lead to heart failure or even death. Recent studies show that inserting microRNA target sequences into the genomes of certain viruses can eradicate these viruses within local host tissues that specifically express the cognate microRNA. Here, we demonstrated both
in vitro
and
in vivo
that incorporating target sequences for miRNA-133 and -206 into the 5′ untranslated region of the CVB3 genome ameliorated CVB3 virulence in skeletal muscle and myocardial cells that specifically expressed the cognate cellular microRNAs. Compared to wild-type CVB3, viral replication of the engineered CVB3 was attenuated in human TE671 (rhabdomyosarcoma) and L6 (skeletal muscle) cell lines
in vitro
that expressed high levels of miRNA-206. In the
in vivo
murine CVB3-infection model, viral replication of the engineered CVB3 was attenuated specifically in the heart that expressed high levels of both miRNAs, but not in certain tissues, which allowed the host to retain the ability to induce a strong and protective humoral immune response against CVB3. The results of this study suggest that a microRNA-targeting strategy to control CVB3 tissue tropism and pathogenesis may be useful for viral attenuation and vaccine development.

IMPORTANCE
Coxsackievirus B3 (CVB3) is a major causative agent for viral myocarditis, and viral replication in the heart may lead to heart failure or even death. Limiting CVB3 replication within the heart may be a promising strategy to decrease CVB3 pathogenicity. miRNAs are ∼21-nucleotide-long, tissue-specific endogenous small RNA molecules that posttranscriptionally regulate gene expression by imperfectly binding to the 3′ untranslated region (UTR), the 5′ UTR, or the coding region within a gene. In our study, muscle-specific miRNA targets (miRT) were incorporated into the CVB3 genome. Replication of the engineered viruses was restricted in the important heart tissue of infected mice, which reduced cardiac pathology and increased mouse survival. Meanwhile, replication ability was retained in other tissues, thus inducing a strong humoral immune response and providing long-term protection against CVB3 rechallenge. This study suggests that a microRNA-targeting strategy can potentially control CVB3 tissue tropism and pathogenesis and may be useful for viral attenuation and vaccine development.
High-Throughput DNA Sequencing Analysis of Antibody Repertoires
Authors: Boyd Scott D. , Joshi Shilpa A.
Published: October 2014

New high-throughput DNA sequencing (HTS) technologies developed in the past decade have begun to be applied to the study of the complex gene rearrangements that encode human antibodies. This article first reviews the genetic features of Ig loci and the HTS technologies that have been applied to human repertoire studies, then discusses key choices for experimental design and data analysis in these experiments and the insights gained in immunological and infectious disease studies with the use of these approaches.
Efficient Methods To Isolate Human Monoclonal Antibodies from Memory B Cells and Plasma Cells
Authors: Corti Davide , Lanzavecchia Antonio
Published: October 2014

In this article, we highlight the advantages of isolating human monoclonal antibodies from the human memory B cells and plasma cell repertoires by using high-throughput cellular screens. Memory B cells are immortalized with high efficiency using Epstein-Barr virus (EBV) in the presence of a toll-like receptor (TLR) agonist, while plasma cells are maintained in single-cell cultures by using interleukin 6 (IL-6) or stromal cells. In both cases, multiple parallel assays, including functional assays, can be used to identify rare cells that produce antibodies with unique properties. Using these methods, we have isolated potent and broadly neutralizing antibodies against a variety of viruses, in particular, a pan-influenza-A-neutralizing antibody and an antibody that neutralizes four different paramyxoviruses. Given the high throughput and the possibility of directly screening for function (rather than just binding), these methods are instrumental to implement a target-agnostic approach to identify the most effective antibodies and, consequently, the most promising targets for vaccine design. This approach is exemplified by the identification of unusually potent cytomegalovirus-neutralizing antibodies that led to the identification of the target, a pentameric complex that we are developing as a candidate vaccine.
The Locus of Enterocyte Effacement and Associated Virulence Factors of Enterohemorrhagic
Escherichia coli
Authors: Stevens Mark P. , Frankel Gad M.
Published: October 2014

A subset of Shiga toxin-producing
Escherichia coli
strains, termed enterohemorrhagic
E. coli
(EHEC), is defined in part by the ability to produce attaching and effacing (A/E) lesions on intestinal epithelia. Such lesions are characterized by intimate bacterial attachment to the apical surface of enterocytes, cytoskeletal rearrangements beneath adherent bacteria, and destruction of proximal microvilli. A/E lesion formation requires the locus of enterocyte effacement (LEE), which encodes a Type III secretion system that injects bacterial proteins into host cells. The translocated proteins, termed effectors, subvert a plethora of cellular pathways to the benefit of the pathogen, for example, by recruiting cytoskeletal proteins, disrupting epithelial barrier integrity, and interfering with the induction of inflammation, phagocytosis, and apoptosis. The LEE and selected effectors play pivotal roles in intestinal persistence and virulence of EHEC, and it is becoming clear that effectors may act in redundant, synergistic, and antagonistic ways during infection. Vaccines that target the function of the Type III secretion system limit colonization of reservoir hosts by EHEC and may thus aid control of zoonotic infections. Here we review the features and functions of the LEE-encoded Type III secretion system and associated effectors of
E. coli
O157:H7 and other Shiga toxin-producing
E. coli
strains.
The Interplay between the Microbiota and Enterohemorrhagic
Escherichia coli
Authors: Pifer Reed , Sperandio Vanessa
Published: October 2014

The gastrointestinal tract of mammals is home to a plethora of microbial species that comprise the microbiota. The role of the microbiota in human health is at the forefront of science in recent years, because it is now appreciated that this intricate microbe-host association shapes the host's immune response and physiology. Many diseases are associated with changes in the microbiota, called dysbiosis. Dysbiosis is associated with obesity, metabolic syndromes, inflammatory bowel-disease, inflammatory bowel syndrome, cancer, diabetes, allergies, and autism. The microbiota is largely regarded as a barrier to enteric infections, such as with enterohemorrhagic
Escherichia coli
(EHEC). However, the interactions between pathogens and the microbiota are largely unknown, as is how these interactions influence the outcome of enteric disease. The microbial composition of the gastrointestinal tract shapes the landscape in which EHEC survives within the host. This organism competes for nutrients derived from the host diet, liberates additional resources from dietary and host sources, and produces signaling molecules sensed by EHEC to direct gene expression. To successfully colonize the recto-anal junction of a ruminant, the EHEC reservoir, or the colon of a human, an accidental host, EHEC must alter its physiology to survive within the host digestive tract. In this article, we explore the classes of molecules produced or modified by the microbiota that appear to be instrumental in governing virulence gene expression of EHEC. We also explore how interaction with different microbiotas influences EHEC infectivity and host interaction.
Taxonomy Meets Public Health: The Case of Shiga Toxin-Producing
Escherichia coli
Authors: Scheutz Flemming
Published: October 2014

To help assess the clinical and public health risks associated with different Shiga toxin-producing
Escherichia coli
(STEC) strains, an empirical classification scheme was used to classify STEC into five “seropathotypes” (seropathotype A [high risk] to seropathotypes D and E [minimal risk]). This definition is of considerable value in cases of human infection but is also problematic because not all STEC infections are fully characterized and coupled to reliable clinical information. Outbreaks with emerging hybrid strains continuously challenge our understanding of virulence potential and may result in incorrect classification of specific pathotypes; an example is the hybrid strain that caused the 2011 outbreak in Germany, STEC/EAggEC O104:H4, which may deserve an alternative seropathotype designation. The integration of mobile virulence factors in the stepwise and parallel evolution of pathogenic lineages of STEC collides with the requirements of a good taxonomy, which separates elements of each group into subgroups that are mutually exclusive, unambiguous, and, together, include all possibilities. The concept of (sero)-pathotypes is therefore challenged, and the need to identify factors of STEC that absolutely predict the potential to cause human disease is obvious. Because the definition of hemolytic-uremic syndrome (HUS) is distinct, a basic and primary definition of HUS-associated
E. coli
(HUSEC) for first-line public health action is proposed:
stx2
in a background of an
eae-
or
aggR
-positive
E. coli
followed by a second-line subtyping of
stx
genes that refines the definition of HUSEC to include only
stx2a
and
stx2d
. All other STEC strains are considered “low-risk” STEC.
EHEC Genomics: Past, Present, and Future
Authors: Sadiq Shah M. , Hazen Tracy H. , Rasko David A. , Eppinger Mark
Published: October 2014

This article examines the role of genomics in the understanding and identification of O157:H7 enterohemorrhagic
Escherichia coli
(EHEC). We highlight the development of novel molecular typing systems that are based on the genomic sequence that has been generated for this pathotype. The genomic comparisons of EHEC to other
E. coli
strains highlight the close relatedness of the O157 and O55 isolates and also identify other non-O157 clades of isolates that appear to have a different genomic history. Analysis within the EHEC isolates must be completed on a fine scale using whole-genome sequence-based approaches to assess both the conserved and lateral acquired gene content. The plethora of genomic data for EHEC isolates has provided the ability to examine this pathotype in detail, which has provided opportunities for novel surveillance, detection, and diagnostics.
Shiga Toxin (Stx) Classification, Structure, and Function
Authors: Melton-Celsa Angela R.
Published: October 2014

Shiga toxin (Stx) is one of the most potent bacterial toxins known. Stx is found in
Shigella dysenteriae
1 and in some serogroups of
Escherichia coli
(called Stx1 in
E. coli
). In addition to or instead of Stx1, some
E. coli
strains produce a second type of Stx, Stx2, that has the same mode of action as Stx/Stx1 but is antigenically distinct. Because subtypes of each toxin have been identified, the prototype toxin for each group is now designated Stx1a or Stx2a. The Stxs consist of two major subunits, an A subunit that joins noncovalently to a pentamer of five identical B subunits. The A subunit of the toxin injures the eukaryotic ribosome and halts protein synthesis in target cells. The function of the B pentamer is to bind to the cellular receptor, globotriaosylceramide, Gb3, found primarily on endothelial cells. The Stxs traffic in a retrograde manner within the cell, such that the A subunit of the toxin reaches the cytosol only after the toxin moves from the endosome to the Golgi and then to the endoplasmic reticulum. In humans infected with Stx-producing
E. coli
, the most serious manifestation of the disease, hemolytic-uremic syndrome, is more often associated with strains that produce Stx2a rather than Stx1a, and that relative toxicity is replicated in mice and baboons. Stx1a and Stx2a also exhibit differences in cytotoxicity to various cell types, bind dissimilarly to receptor analogs or mimics, induce differential chemokine responses, and have several distinctive structural characteristics.
Animal Reservoirs of Shiga Toxin-ProducingEscherichia coli
Authors: Persad Anil K. , LeJeune Jefrey T.
Published: October 2014

Shiga toxin-producingEscherichia coli(STEC) strains have been detected in a wide diversity of mammals, birds, fish, and several insects. Carriage by most animals is asymptomatic, thus allowing for dissemination of the bacterium in the environment without detection. Replication of the organism may occur in the gastrointestinal tract of some animals, notably ruminants. Carriage may also be passive or transient, without significant amplification of bacterial numbers while in the animal host. Animals may be classified as reservoir species, spillover hosts, or dead-end hosts. This classification is based on the animal's ability to (i) transmit STEC to other animal species and (ii) maintain STEC infection in the absence of continuous exposure. Animal reservoirs are able to maintain STEC infections in the absence of continuous STEC exposure and transmit infection to other species. Spillover hosts, although capable of transmitting STEC to other animals, are unable to maintain infection in the absence of repeated exposure. The large diversity of reservoir and spillover host species and the survival of the organism in environmental niches result in complex pathways of transmission that are difficult to interrupt.
The Molecular Genetics of Mycolic Acid Biosynthesis
Authors: PaweŁczyk Jakub , Kremer Laurent
Published: October 2014

Mycolic acids are major and specific long-chain fatty acids that represent essential components of the
Mycobacterium tuberculosis
cell envelope. They play a crucial role in the cell wall architecture and impermeability, hence the natural resistance of mycobacteria to most antibiotics, and represent key factors in mycobacterial virulence. Biosynthesis of mycolic acid precursors requires two types of fatty acid synthases (FASs), the eukaryotic-like multifunctional enzyme FAS I and the acyl carrier protein (ACP)–dependent FAS II systems, which consists of a series of discrete mono-functional proteins, each catalyzing one reaction in the pathway. Unlike FAS II synthases of other bacteria, the mycobacterial FAS II is incapable of
de novo
fatty acid synthesis from acetyl-coenzyme A, but instead elongates medium-chain-length fatty acids previously synthesized by FAS I, leading to meromycolic acids. In addition, mycolic acid subspecies with defined biological properties can be distinguished according to the chemical modifications decorating the meromycolate. Nearly all the genetic components involved in both elongation and functionalization of the meromycolic acid have been identified and are generally clustered in distinct transcriptional units. A large body of information has been generated on the enzymology of the mycolic acid biosynthetic pathway and on their genetic and biochemical/structural characterization as targets of several antitubercular drugs. This chapter is a comprehensive overview of mycolic acid structure, function, and biosynthesis. Special emphasis is given to recent work addressing the regulation of mycolic acid biosynthesis, adding new insights to our understanding of how pathogenic mycobacteria adapt their cell wall composition in response to environmental changes.
Evasion of Innate and Adaptive Immunity byMycobacterium tuberculosis
Authors: Goldberg Michael F. , Saini Neeraj K. , Porcelli Steven A.
Published: October 2014

Through thousands of years of reciprocal coevolution,Mycobacterium tuberculosishas become one of humanity's most successful pathogens, acquiring the ability to establish latent or progressive infection and persist even in the presence of a fully functioning immune system. The ability ofM. tuberculosisto avoid immune-mediated clearance is likely to reflect a highly evolved and coordinated program of immune evasion strategies that interfere with both innate and adaptive immunity. These include the manipulation of their phagosomal environment within host macrophages, the selective avoidance or engagement of pattern recognition receptors, modulation of host cytokine production, and the manipulation of antigen presentation to prevent or alter the quality of T-cell responses. In this article we review an extensive array of published studies that have begun to unravel the sophisticated program of specific mechanisms that enableM. tuberculosisand other pathogenic mycobacteria to persist and replicate in the face of considerable immunological pressure from their hosts. Unraveling the mechanisms by whichM. tuberculosisevades or modulates host immune function is likely to be of major importance for the development of more effective new vaccines and targeted immunotherapy against tuberculosis.
Metallobiology of Tuberculosis
Authors: Marcela Rodriguez G. , Neyrolles Olivier
Published: October 2014

Transition metals are essential constituents of all living organisms, playing crucial structural and catalytic parts in many enzymes and transcription factors. However, transition metals can also be toxic when present in excess. Their uptake and efflux rates must therefore be carefully controlled by biological systems. In this chapter, we summarize the current knowledge about uptake and efflux systems in
Mycobacterium tuberculosis
for mainly three of these metals, namely iron, zinc, and copper. We also propose questions for future research in the field of metallobiology of host-pathogen interactions in tuberculosis.
Energetics of Respiration and Oxidative Phosphorylation in Mycobacteria
Authors: Cook Gregory M. , Hards Kiel , Vilchèze Catherine , Hartman Travis , Berney Michael
Published: October 2014

Mycobacteria inhabit a wide range of intracellular and extracellular environments. Many of these environments are highly dynamic, and therefore mycobacteria are faced with the constant challenge of redirecting their metabolic activity to be commensurate with either replicative growth or a nonreplicative quiescence. A fundamental feature in this adaptation is the ability of mycobacteria to respire, regenerate reducing equivalents, and generate ATP via oxidative phosphorylation. Mycobacteria harbor multiple primary dehydrogenases to fuel the electron transport chain, and two terminal respiratory oxidases, an
aa
3
-type cytochrome
c
oxidase and a cytochrome
bd
-type menaquinol oxidase, are present for dioxygen reduction coupled to the generation of a proton motive force (PMF). Hypoxia leads to the downregulation of key respiratory complexes, but the molecular mechanisms regulating this expression are unknown. Despite being obligate aerobes, mycobacteria have the ability to metabolize in the absence of oxygen, and a number of reductases are present to facilitate the turnover of reducing equivalents under these conditions (e.g., nitrate reductase, succinate dehydrogenase/fumarate reductase). Hydrogenases and ferredoxins are also present in the genomes of mycobacteria, suggesting the ability of these bacteria to adapt to an anaerobic type of metabolism in the absence of oxygen. ATP synthesis by the membrane-bound F
1
F
0
-ATP synthase is essential for growing and nongrowing mycobacteria, and the enzyme is able to function over a wide range of PMF values (aerobic to hypoxic). The discovery of lead compounds that target respiration and oxidative phosphorylation in
Mycobacterium tuberculosis
highlights the importance of this area for the generation of new frontline drugs to combat tuberculosis.
Genetics of Capsular Polysaccharides and Cell Envelope (Glyco)lipids
Authors: Daffé Mamadou , Crick Dean C. , Jackson Mary
Published: October 2014

This article summarizes what is currently known of the structures, physiological roles, involvement in pathogenicity, and biogenesis of a variety of noncovalently bound cell envelope lipids and glycoconjugates of
Mycobacterium tuberculosis
and other
Mycobacterium
species. Topics addressed in this article include phospholipids; phosphatidylinositol mannosides; triglycerides; isoprenoids and related compounds (polyprenyl phosphate, menaquinones, carotenoids, noncarotenoid cyclic isoprenoids); acyltrehaloses (lipooligosaccharides, trehalose mono- and di-mycolates, sulfolipids, di- and poly-acyltrehaloses); mannosyl-beta-1-phosphomycoketides; glycopeptidolipids; phthiocerol dimycocerosates, para-hydroxybenzoic acids, and phenolic glycolipids; mycobactins; mycolactones; and capsular polysaccharides.
Genetics of Peptidoglycan Biosynthesis
Authors: Pavelka Jr. Martin S. , Mahapatra Sebabrata , Crick Dean C.
Published: October 2014

The complex cell envelope is a hallmark of mycobacteria and is anchored by the peptidoglycan layer, which is similar to that of
Escherichia coli
and a number of other bacteria but with modifications to the monomeric units and other structural complexities that are likely related to a role for the peptidoglycan in stabilizing the mycolyl-arabinogalactan-peptidoglycan complex (MAPc). In this article, we will review the genetics of several aspects of peptidoglycan biosynthesis in mycobacteria, including the production of monomeric precursors in the cytoplasm, assembly of the monomers into the mature wall, cell wall turnover, and cell division. Finally, we will touch upon the resistance of mycobacteria to β-lactam antibiotics, an important class of drugs that, until recently, have not been extensively exploited as potential antimycobacterial agents. We will also note areas of research where there are still unanswered questions.
Molecular Basis of Drug Resistance in
Mycobacterium tuberculosis
Authors: Cohen Keira A. , Bishai William R. , Pym Alexander S.
Published: October 2014

In this chapter we review the molecular mechanisms of drug resistance to the major first- and second-line antibiotics used to treat tuberculosis.
Virulence Plasmids of Nonsporulating Gram-Positive Pathogens
Authors: Van Tyne Daria , Gilmore Michael S.
Published: October 2014

Gram-positive bacteria are leading causes of many types of human infection, including pneumonia, skin and nasopharyngeal infections, as well as urinary tract and surgical wound infections among hospitalized patients. These infections have become particularly problematic because many of the species causing them have become highly resistant to antibiotics. The role of mobile genetic elements, such as plasmids, in the dissemination of antibiotic resistance among Gram-positive bacteria has been well studied; less well understood is the role of mobile elements in the evolution and spread of virulence traits among these pathogens. While these organisms are leading agents of infection, they are also prominent members of the human commensal ecology. It appears that these bacteria are able to take advantage of the intimate association between host and commensal organism, via virulence traits that exacerbate infection and cause disease. However, evolution into an obligate pathogen has not occurred, presumably because it would lead to rejection of pathogenic organisms from the host ecology. Instead, in organisms that exist as both commensal and pathogen, selection has favored the development of mechanisms for variability. As a result, many virulence traits are localized on mobile genetic elements, such as virulence plasmids and pathogenicity islands. Virulence traits may occur within a minority of isolates of a given species, but these minority populations have nonetheless emerged as a leading problem in infectious disease. This chapter reviews virulence plasmids in nonsporulating Gram-positive bacteria and examines their contribution to disease pathogenesis.
Plasmids as Tools for Containment
Authors: GarcíA José L. , Díaz Eduardo
Published: October 2014

Active containment systems are a major tool for reducing the uncertainty associated with the introduction of monocultures, genetically engineered or not, into target habitats for a large number of biotechnological applications (e.g., bioremediation, bioleaching, biopesticides, biofuels, biotransformations, live vaccines, etc.). While biological containment reduces the survival of the introduced organism outside the target habitat and/or upon completion of the projected task, gene containment strategies reduce the lateral spread of the key genetic determinants to indigenous microorganisms. In fundamental research, suicide circuits become relevant tools to address the role of gene transfer, mainly plasmid transfer, in evolution and how this transfer contributes to genome plasticity and to the rapid adaptation of microbial communities to environmental changes. Many lethal functions and regulatory circuits have been used and combined to design efficient containment systems. As many new genomes are being sequenced, novel lethal genes and regulatory elements are available, e.g., new toxin-antitoxin modules, and they could be used to increase further the current containment efficiencies and to expand containment to other organisms. Although the current containment systems can increase the predictability of genetically modified organisms in the environment, containment will never be absolute, due to the existence of mutations that lead to the appearance of surviving subpopulations. In this sense, orthogonal systems (xenobiology) appear to be the solution for setting a functional genetic firewall that will allow absolute containment of recombinant organisms.
Spore Resistance Properties
Authors: Setlow Peter
Published: October 2014

Spores of various
Bacillus
and
Clostridium
species are among the most resistant life forms known. Since the spores of some species are causative agents of much food spoilage, food poisoning, and human disease, and the spores of
Bacillus anthracis
are a major bioweapon, there is much interest in the mechanisms of spore resistance and how these spores can be killed. This article will discuss the factors involved in spore resistance to agents such as wet and dry heat, desiccation, UV and γ-radiation, enzymes that hydrolyze bacterial cell walls, and a variety of toxic chemicals, including genotoxic agents, oxidizing agents, aldehydes, acid, and alkali. These resistance factors include the outer layers of the spore, such as the thick proteinaceous coat that detoxifies reactive chemicals; the relatively impermeable inner spore membrane that restricts access of toxic chemicals to the spore core containing the spore's DNA and most enzymes; the low water content and high level of dipicolinic acid in the spore core that protect core macromolecules from the effects of heat and desiccation; the saturation of spore DNA with a novel group of proteins that protect the DNA against heat, genotoxic chemicals, and radiation; and the repair of radiation damage to DNA when spores germinate and return to life. Despite their extreme resistance, spores can be killed, including by damage to DNA, crucial spore proteins, the spore's inner membrane, and one or more components of the spore germination apparatus.
Physiology and Sporulation in
Clostridium
Authors: Dürre Peter
Published: October 2014

Clostridia are Gram-positive, anaerobic, endospore-forming bacteria, incapable of dissimilatory sulfate reduction. Comprising approximately 180 species, the genus
Clostridium
is one of the largest bacterial genera. Physiology is mostly devoted to acid production. Numerous pathways are known, such as the homoacetate fermentation by acetogens, the propionate fermentation by
Clostridium propionicum
, and the butyrate/butanol fermentation by
C. acetobutylicum
, a well-known solvent producer. Clostridia degrade sugars, alcohols, amino acids, purines, pyrimidines, and polymers such as starch and cellulose. Energy conservation can be performed by substrate-level phosphorylation as well as by the generation of ion gradients. Endospore formation resembles the mechanism elucidated in
Bacillus
. Morphology, contents, and properties of spores are very similar to bacilli endospores. Sporulating clostridia usually form swollen mother cells and accumulate the storage substance granulose. However, clostridial sporulation differs by not employing the so-called phosphorelay. Initiation starts by direct phosphorylation of the master regulator Spo0A. The cascade of sporulation-specific sigma factors is again identical to what is known from
Bacillus
. The onset of sporulation is coupled in some species to either solvent (acetone, butanol) or toxin (e.g.,
C. perfringens
enterotoxin) formation. The germination of spores is often induced by various amino acids, often in combination with phosphate and sodium ions. In medical applications,
C. butyricum
spores are used as a
C. difficile
prophylaxis and as treatment against diarrhea. Recombinant spores are currently under investigation and testing as antitumor agents, because they germinate only in hypoxic tissues (i.e., tumor tissue), allowing precise targeting and direct killing of tumor cells.
Graves’ disease and coeliac disease: screening and treatment dilemmas
Authors: Joshi Ameya S , Varthakavi Premlata K , Bhagwat Nikhil M , Thiruvengadam Narendhran Ramaswamy
Published: October 2014

The association between autoimmune thyroid disorders (AITD) and coeliac disease (CD) is well known, however, most of the literature concentrates on hypothyroidism and CD. We report a case of a 37-year-old woman with Graves’ disease (GD) who presented with thyrotoxicosis that was not responsive to medical management. The screening for coeliac autoimmunity (CA) was positive. After initiation of a gluten-free diet the patient’s thyrotoxicosis responded to medical management. She was given radioiodine therapy and is currently hypothyroid on a stable dose of thyroxine.
Endotracheal intubation of a paediatric patient with an umbrella wire embedded in the palate to the posterior wall of the nasopharynx using a GlideScope video laryngoscope
Authors: Saricicek Vahap , Sahin Levent , Mizrak Ayse , Sen Elzem
Published: October 2014

The penetration of foreign bodies into the oropharynx can be life-threatening. Airway management in patients who have a foreign body penetrated into their oropharynx is a challenging problem for the anaesthetist. In this case report, we aimed to share our experience of endotracheal intubation performed with GlideScope video laryngoscopy in a 3-year-old, 15 kg patient. The patient underwent general anaesthesia to facilitate the removal of an umbrella wire that had become embedded in her soft palate.
Endovascular treatment of a rare cause of secondary hypertension in an elderly woman
Authors: Chadha Davinder , Malani Susheel , Hasija Pradeep , Naveen A J
Published: October 2014

A 70-year-old woman on four antihypertensive drugs including diuretics presented with accelerated hypertension and acute pulmonary oedema. She had a bounding brachial pulse with feeble femoral pulses. A 256 slice CT scan revealed the presence of severe diffuse thoracoabdominal atherosclerosis. Cardiac catheterisation revealed 125 mm Hg gradient across the atherosclerotic segment at the level of thoracic 10–11 vertebrae. A self-deploying stent was implanted in the thoracoabdominal segment reducing the gradient across the disease segment to 20 mm Hg with a significant improvement in the luminal diameter of the aorta. Her upper limb blood pressure normalised on two antihypertensive drugs 6 weeks later.
An unusual case of dysphasia and seizures
Authors: Williams Mark Robert , Easson Anne , Khwaja Sadie , Aucott Will
Published: October 2014

Defects in the tegmen tympani can have serious consequences such as intracranial infection and seizures, however, they can be difficult to diagnose due to their subtlety on cross-sectional imaging and the non-specific way in which they can present. Repair of such defects can be undertaken via a middle fossa or transmastoid approach; both, however, usually necessitate a general anaesthetic and, furthermore, middle cranial fossa surgery carries the risk of epilepsy while transmastoid repair can result in the loss of hearing. We present a novel method of repair in a patient who would otherwise have been managed conservatively.
Anomalous origin of the right coronary artery with concomitant myxomatous mitral valve disease: a rare coexistence
Authors: Imori Yoichi , Murakami Masato , Tanaka Masashi , Saito Shigeru
Published: October 2014

A 45-year-old man previously diagnosed with myxomatous mitral valve disease was admitted to our hospital with chest pain at rest and on effort. Contrast-enhanced CT revealed that the patient's right coronary artery originated from the left sinus Valsalva, which was compressed between the aortic and pulmonary roots. This anatomical abnormality can be associated with sudden death, syncope and chest pain. Ultrasonography showed mitral valve prolapse with severe regurgitation. Surgical repair was performed, which included coronary artery bypass graft and mitral valvoplasty with tricuspid annuloplasty. The postoperative course was uneventful and the patient remains asymptomatic. This is the first description of the coexistence of an anomalous origin of the right coronary artery with myxomatous mitral valve disease.
Postcoital visual loss due to valsalva retinopathy
Authors: Michaels Luke , Tint Naing Latt , Alexander Philip
Published: October 2014

A 29-year-old male patient presented to eye emergency clinic after noticing a left paracentral scotoma on waking. On direct questioning the patient revealed an episode of vigorous sexual intercourse the preceding evening. During orgasm the valsalva manoeuvre can produce a sudden increase in retinal venous pressure resulting in vessel rupture and haemorrhagic retinopathy. Valsalva retinopathy is managed conservatively and the patient's symptoms resolved spontaneously without intervention. This case report highlights the importance of focused history taking of patients which can thereby obviate the need for further investigations. This case also emphasises the importance of considering sexual activity as a cause of stress-induced pathology.