Relative roles of pneumolysin and hydrogen peroxide from Streptococcus pneumoniae in inhibition of ependymal ciliary beat frequency

Hydrogen peroxide is responsible for the cytotoxic effects of Streptococcus pneumoniae on primary microglia in the absence of pneumolysin

INTRODUCTION

Streptococcus pneumoniae is the most common cause of bacterial meningitis and meningoencephalitis in humans. The bacterium produces numerous virulence determinants, among them hydrogen peroxide (H2O2) and pneumolysin (Ply), which contribute to bacterial cytotoxicity. Microglia, the resident phagocytes in the brain, are distinct from other macrophages, and we thus compared their susceptibility to pneumococcal toxicity and their ability to phagocytose pneumococci with those of bone marrow-derived macrophages (BMDM).

METHODS

Microglia and BMDM were co-incubated with S. pneumoniae D39 to analyze survival of phagocytes by fluorescence microscopy, bacterial growth by quantitative plating, and phagocytosis by an antibiotic protection assay. Ply was detected by hemolysis assay and Western blot analysis.

RESULTS

We found that microglia were killed during pneumococcal infection with a wild-type and an isogenic ply-deficient mutant, whereas viability of BMDM was not affected by pneumococci. Treatment with recombinant Ply showed a dose-dependent cytotoxic effect on microglia and BMDM. However, high concentrations of recombinant Ply were required and under the chosen experimental conditions, Ply was not detectable in the supernatant during infection of microglia. Inactivation of H2O2 by exogenously added catalase abolished its cytotoxic effect. Consequently, infection of microglia with pneumococci deficient for the pyruvate oxidase SpxB, primarily producing H2O2, resulted in reduced killing of microglia.

CONCLUSION

Taken together, in the absence of Ply, H2O2 caused cell death in primary phagocytes in concentrations produced by pneumococci.

High-Speed Video Microscopy of Ependymal Cilia in Brain Organotypic and Cell Culture Models

The wall of the ventricular system within the neuraxis is lined almost entirely by E1 ependymal cells, each of which projects multiple motile cilia from their apical surface into the cerebrospinal fluid (CSF). This specialized layer of E1 cells constitutes the border between the CSF and the brain interstitial fluid (BIF), and by controlling influx and efflux across the CSF to BIF interface, it is increasingly recognized to play an integral role in modulating and maintaining the brain microenvironment. The motile cilia have been shown to be responsive to changes in the CSF microenvironment, and while the physiological role of this mechanism remains incompletely understood, manipulating this control mechanism may influence the brain microenvironment potentially opening a new frontier in therapeutic intervention.In this paper, we describe our techniques for preparing organotypic slices from the murine brain parenchyma and establishing cell cultures of multiciliated ependymal cells from mouse and rat neonatal brain tissue. Our methodology generates a functional readout of ciliary function, specifically high-speed video microscopy (HSVM) enables the quantification of ciliary beat frequency (CBF), and characterization of ciliary beat pattern.

Oxidation of hemoproteins by Streptococcus pneumoniae collapses the cell cytoskeleton and disrupts mitochondrial respiration leading to cytotoxicity of human lung cells

Streptococcus pneumoniae (Spn) causes pneumonia that kills millions through acute toxicity and invasion of the lung parenchyma. During aerobic respiration, Spn releases hydrogen peroxide (Spn-H 2 O 2 ), as a by-product of enzymes SpxB and LctO, and causes cell death with signs of both apoptosis and pyroptosis by oxidizing unknown cell targets. Hemoproteins are molecules essential for life and prone to oxidation by H 2 O 2 . We recently demonstrated that during infection-mimicking conditions, Spn-H 2 O 2 oxidizes the hemoprotein hemoglobin (Hb), releasing toxic heme. In this study, we investigated details of the molecular mechanism(s) by which the oxidation of hemoproteins by Spn-H 2 O 2 causes human lung cell death. Spn strains, but not H 2 O 2 -deficient SpnΔ spxB Δ lctO strains caused time-dependent cell cytotoxicity characterized by the rearrangement of the actin, the loss of the microtubule cytoskeleton and nuclear contraction. Disruption of the cell cytoskeleton correlated with the presence of invasive pneumococci and an increase of intracellular reactive oxygen species. In cell culture, the oxidation of Hb or cytochrome c (Cyt c ) caused DNA degradation and mitochondrial dysfunction from inhibition of complex I-driven respiration, which was cytotoxic to human alveolar cells. Oxidation of hemoproteins resulted in the creation of a radical, which was identified as a protein derived side chain tyrosyl radical by using electron paramagnetic resonance (EPR). Thus, we demonstrate that Spn invades lung cells, releasing H 2 O 2 that oxidizes hemoproteins, including Cyt c , catalyzing the formation of a tyrosyl side chain radical on Hb and causing mitochondrial disruption, that ultimately leads to the collapse of the cell cytoskeleton.

Transforming Growth Factor-β1 and Bone Morphogenetic Protein-2 Inhibit Differentiation into Mature Ependymal Multiciliated Cells

Ependymal cilia play pivotal roles in cerebrospinal fluid flow. In the primary culture system, undifferentiated glial cells differentiate well into ependymal multiciliated cells (MCCs) in the absence of fetal bovine serum (FBS). However, the substances included in FBS which inhibit this differentiation process have not been clarified yet. Here, we constructed the polarized primary culture system of ependymal cells using a permeable filter in which they retained ciliary movement. We found that transforming growth factor-β1 (TGF-β1) as well as Bone morphogenetic protein (BMP)-2 inhibited the differentiation with ciliary movement. The inhibition on the differentiation by FBS was recovered by the TGF-β1 and BMP-2 inhibitors in combination.

Streptococcus pneumoniae: 'captain of the men of death' and financial burden

Streptococcus pneumoniae may inhabit the upper respiratory tract of humans without causing harm but it also causes diseases with high morbidity and mortality. It has excellent adaptive capabilities thanks to its ability to shuffle its genetic content by acquiring and incorporating DNA from other bacteria and is highly competent for genetic transformation. Sugar sensing, cleavage and transport ensure its fitness and survival in the host, and intracellular survival in macrophages has been linked to virulence. The polysaccharide capsule and toxin pneumolysin are the most important virulence determinants. Polysaccharide-based vaccines provide protection against the serotypes represented in vaccine formulations.

Therapeutic Potential of Small Molecules Targeting Oxidative Stress in the Treatment of Chronic Obstructive Pulmonary Disease (COPD): A Comprehensive Review

Chronic obstructive pulmonary disease (COPD) is an increasing and major global health problem. COPD is also the third leading cause of death worldwide. Oxidative stress (OS) takes place when various reactive species and free radicals swamp the availability of antioxidants. Reactive nitrogen species, reactive oxygen species (ROS), and their counterpart antioxidants are important for host defense and physiological signaling pathways, and the development and progression of inflammation. During the disturbance of their normal steady states, imbalances between antioxidants and oxidants might induce pathological mechanisms that can further result in many non-respiratory and respiratory diseases including COPD. ROS might be either endogenously produced in response to various infectious pathogens including fungi, viruses, or bacteria, or exogenously generated from several inhaled particulate or gaseous agents including some occupational dust, cigarette smoke (CS), and air pollutants. Therefore, targeting systemic and local OS with therapeutic agents such as small molecules that can increase endogenous antioxidants or regulate the redox/antioxidants system can be an effective approach in treating COPD. Various thiol-based antioxidants including fudosteine, erdosteine, carbocysteine, and N-acetyl-L-cysteine have the capacity to increase thiol content in the lungs. Many synthetic molecules including inhibitors/blockers of protein carbonylation and lipid peroxidation, catalytic antioxidants including superoxide dismutase mimetics, and spin trapping agents can effectively modulate CS-induced OS and its resulting cellular alterations. Several clinical and pre-clinical studies have demonstrated that these antioxidants have the capacity to decrease OS and affect the expressions of several pro-inflammatory genes and genes that are involved with redox and glutathione biosynthesis. In this article, we have summarized the role of OS in COPD pathogenesis. Furthermore, we have particularly focused on the therapeutic potential of numerous chemicals, particularly antioxidants in the treatment of COPD.

The Yin and Yang of Pneumolysin During Pneumococcal Infection

Pneumolysin (PLY) is a pore-forming toxin produced by the human pathobiont Streptococcus pneumoniae, the major cause of pneumonia worldwide. PLY, a key pneumococcal virulence factor, can form transmembrane pores in host cells, disrupting plasma membrane integrity and deregulating cellular homeostasis. At lytic concentrations, PLY causes cell death. At sub-lytic concentrations, PLY triggers host cell survival pathways that cooperate to reseal the damaged plasma membrane and restore cell homeostasis. While PLY is generally considered a pivotal factor promoting S. pneumoniae colonization and survival, it is also a powerful trigger of the innate and adaptive host immune response against bacterial infection. The dichotomy of PLY as both a key bacterial virulence factor and a trigger for host immune modulation allows the toxin to display both "Yin" and "Yang" properties during infection, promoting disease by membrane perforation and activating inflammatory pathways, while also mitigating damage by triggering host cell repair and initiating anti-inflammatory responses. Due to its cytolytic activity and diverse immunomodulatory properties, PLY is integral to every stage of S. pneumoniae pathogenesis and may tip the balance towards either the pathogen or the host depending on the context of infection.

Hydrogen Peroxide Is Crucial for NLRP3 Inflammasome-Mediated IL-1β Production and Cell Death in Pneumococcal Infections of Bronchial Epithelial Cells

Epithelial cells play a crucial role in detection of the pathogens as well as in initiation of the host immune response. Streptococcus pneumoniae (pneumococcus) is a typical colonizer of the human nasopharynx, which can disseminate to the lower respiratory tract and subsequently cause severe invasive diseases such as pneumonia, sepsis, and meningitis. Hydrogen peroxide (H2O2) is produced by pneumococci as a product of the pyruvate oxidase SpxB. However, its role as a virulence determinant in pneumococcal infections of the lower respiratory tract is not well understood. In this study, we investigated the role of pneumococcal-derived H2O2 in initiating epithelial cell death by analyzing the interplay between 2 key cell death pathways, namely, apoptosis and pyroptosis. We demonstrate that H2O2 primes as well as activates the NLRP3 inflammasome and thereby mediates IL-1β production and release. Furthermore, we show that pneumococcal H2O2 causes cell death via the activation of both apoptotic as well as pyroptotic pathways which are mediated by the activation of caspase-3/7 and caspase-1, respectively. However, H2O2-mediated IL-1β release itself occurs mainly via apoptosis.

Arginine Decarboxylase Is Essential for Pneumococcal Stress Responses

Polyamines such as putrescine, cadaverine, and spermidine are small cationic molecules that play significant roles in cellular processes, including bacterial stress responses and host–pathogen interactions. Streptococcus pneumoniae is an opportunistic human pathogen, which causes several diseases that account for significant morbidity and mortality worldwide. As it transits through different host niches, S. pneumoniae is exposed to and must adapt to different types of stress in the host microenvironment. We earlier reported that S. pneumoniae TIGR4, which harbors an isogenic deletion of an arginine decarboxylase (ΔspeA), an enzyme that catalyzes the synthesis of agmatine in the polyamine synthesis pathway, has a reduced capsule. Here, we report the impact of arginine decarboxylase deletion on pneumococcal stress responses. Our results show that ΔspeA is more susceptible to oxidative, nitrosative, and acid stress compared to the wild-type strain. Gene expression analysis by qRT-PCR indicates that thiol peroxidase, a scavenger of reactive oxygen species and aguA from the arginine deiminase system, could be important for peroxide stress responses in a polyamine-dependent manner. Our results also show that speA is essential for endogenous hydrogen peroxide and glutathione production in S. pneumoniae. Taken together, our findings demonstrate the critical role of arginine decarboxylase in pneumococcal stress responses that could impact adaptation and survival in the host.

Understanding Primary Ciliary Dyskinesia and Other Ciliopathies

Ciliopathies are a collection of disorders related to cilia dysfunction. Cilia are specialized organelles that project from the surface of most cells. Motile and primary (sensory) cilia are essential structures and have wide ranging functions. Our understanding of the genetics, pathophysiology, and clinical manifestations of motile ciliopathies, including primary ciliary dyskinesia (PCD), has rapidly advanced since the disease was linked to ciliary ultrastructural defects nearly five decades ago. We will provide an overview of different types of cilia, their role in child health and disease, focusing on motile ciliopathies, and describe recent advances that have led to improved diagnostics and may yield therapeutic targets to restore ciliary structure and function.

Interactions of Bacteriophages and Bacteria at the Airway Mucosa: New Insights Into the Pathophysiology of Asthma

The airway epithelium is the primary site where inhaled and resident microbiota interacts between themselves and the host, potentially playing an important role on allergic asthma development and pathophysiology. With the advent of culture independent molecular techniques and high throughput technologies, the complex composition and diversity of bacterial communities of the airways has been well-documented and the notion of the lungs' sterility definitively rejected. Recent studies indicate that the microbial composition of the asthmatic airways across the spectrum of disease severity, differ significantly compared with healthy individuals. In parallel, a growing body of evidence suggests that bacterial viruses (bacteriophages or simply phages), regulating bacterial populations, are present in almost every niche of the human body and can also interact directly with the eukaryotic cells. The triptych of airway epithelial cells, bacterial symbionts and resident phages should be considered as a functional and interdependent unit with direct implications on the respiratory and overall homeostasis. While the role of epithelial cells in asthma pathophysiology is well-established, the tripartite interactions between epithelial cells, bacteria and phages should be scrutinized, both to better understand asthma as a system disorder and to explore potential interventions.

First contact: the role of respiratory cilia in host-pathogen interactions in the airways

Respiratory cilia are the driving force of the mucociliary escalator, working in conjunction with secreted airway mucus to clear inhaled debris and pathogens from the conducting airways. Respiratory cilia are also one of the first contact points between host and inhaled pathogens. Impaired ciliary function is a common pathological feature in patients with chronic airway diseases, increasing susceptibility to respiratory infections. Common respiratory pathogens, including viruses, bacteria, and fungi, have been shown to target cilia and/or ciliated airway epithelial cells, resulting in a disruption of mucociliary clearance that may facilitate host infection. Despite being an integral component of airway innate immunity, the role of respiratory cilia and their clinical significance during airway infections are still poorly understood. This review examines the expression, structure, and function of respiratory cilia during pathogenic infection of the airways. This review also discusses specific known points of interaction of bacteria, fungi, and viruses with respiratory cilia function. The emerging biological functions of motile cilia relating to intracellular signaling and their potential immunoregulatory roles during infection will also be discussed.

Pneumolysin: Pathogenesis and Therapeutic Target

Streptococcus pneumoniae is an opportunistic pathogen responsible for widespread illness and is a major global health issue for children, the elderly, and the immunocompromised population. Pneumolysin (PLY) is a cholesterol-dependent cytolysin (CDC) and key pneumococcal virulence factor involved in all phases of pneumococcal disease, including transmission, colonization, and infection. In this review we cover the biology and cytolytic function of PLY, its contribution to S. pneumoniae pathogenesis, and its known interactions and effects on the host with regard to tissue damage and immune response. Additionally, we review statins as a therapeutic option for CDC toxicity and PLY toxoid as a vaccine candidate in protein-based vaccines.

Acacetin inhibits Streptococcus pneumoniae virulence by targeting pneumolysin

OBJECTIVES

Streptococcus pneumoniae (S. pneumoniae) is an important commensal and pathogenic bacterium responsible for pneumonia, meningitis and other invasive diseases. Pneumolysin (PLY) is the major virulence factor that contributes significantly to the interaction between S. pneumoniae and the host.

KEY FINDINGS

In this study, the results of antibacterial analysis, the haemolysis test and the Western blotting assay showed that acacetin inhibited PLY-mediated pore-forming activity caused by S. pneumoniae culture precipitates and purified PLY without anti-S. pneumoniae activity. In addition, acacetin treatment inhibited PLY oligomerization without affecting the expression of PLY in S. pneumoniae culture supernatants. Live/dead cells and cytotoxicity assays suggested that acacetin significantly enhanced the survival rate of injured cells by inhibiting the biological toxicity of PLY without cytotoxicity in the coculture system. The in vivo mouse model of S. pneumoniae infection further demonstrated that acacetin treatment could significantly reduce the levels of inflammatory factors (INF-γ and IL-β) in bronchoalveolar lavage fluid (BALF) and alleviate the pathological damage of lung injury.

CONCLUSIONS

Taken together, the results presented in this study indicated that acacetin inhibited the pore-forming activity of PLY and reduced the virulence of S. pneumoniae in vivo and in vitro, which may provide a leading compound for the treatment of S. pneumoniae infection.

Streptococcus pneumoniae: Invasion and Inflammation

Streptococcus pneumoniae (the pneumoccus) is the leading cause of otitis media, community-acquired pneumonia, and bacterial meningitis. The success of the pneumococcus stems from its ability to persist in the population as a commensal and avoid killing by immune system. This chapter first reviews the molecular mechanisms that allow the pneumococcus to colonize and spread from one anatomical site to the next. Then, it discusses the mechanisms of inflammation and cytotoxicity during emerging and classical pneumococcal infections.

Redox regulation of motile cilia in airway disease

Motile cilia on airway cells are necessary for clearance of mucus-trapped particles out of the lung. Ciliated airway epithelial cells are uniquely exposed to oxidants through trapping of particles, debris and pathogens in mucus and the direct exposure to inhaled oxidant gases. Dynein ATPases, the motors driving ciliary motility, are sensitive to the local redox environment within each cilium. Several redox-sensitive cilia-localized proteins modulate dynein activity and include Protein Kinase A, Protein Kinase C, and Protein Phosphatase 1. Moreover, cilia are rich in known redox regulatory proteins and thioredoxin domain-containing proteins that are critical in maintaining a balanced redox environment. Importantly, a nonsense mutation in TXNDC3, which contains a thioredoxin motif, has recently been identified as disease-causing in Primary Ciliary Dyskinesia, a hereditary motile cilia disease resulting in impaired mucociliary clearance. Here we review current understanding of the role(s) oxidant species play in modifying airway ciliary function. We focus on oxidants generated in the airways, cilia redox targets that modulate ciliary beating and imbalances in redox state that impact health and disease. Finally, we review disease models such as smoking, asthma, alcohol drinking, and infections as well as the direct application of oxidants that implicate redox balance as a modulator of cilia motility.

Oxidative stress associated with aging activates protein kinase Cε, leading to cilia slowing

Older people are four times more likely to develop pneumonia than younger people. As we age, many components of pulmonary innate immunity are impaired, including slowing of mucociliary clearance. Ciliary beat frequency (CBF) is a major determinant of mucociliary clearance, and it slows as we age. We hypothesized that CBF is slowed in aging because of increased oxidative stress, which activates PKCε signaling. We pharmacologically inhibited PKCε in ex vivo mouse models of aging. We measured a slowing of CBF with aging that was reversed with inhibition using the novel PKC inhibitor, Ro-31-8220, as well as the PKCε inhibitor, PKCe141. Inhibition of PKCε using siRNA in mouse trachea also returned CBF to normal. In addition, antioxidants decrease PKCε activity and speed cilia. We also aged wild-type and PKCε KO mice and measured CBF. The PKCε KO mice were spared from the CBF slowing of aging. Using human airway epithelial cells from younger and older donors at air-liquid interface (ALI), we inhibited PKCε with siRNA. We measured a slowing of CBF with aging that was reversed with siRNA inhibition of PKCε. In addition, we measured bead clearance speeds in human ALI, which demonstrated a decrease in bead velocity with aging and a return to baseline after inhibition of PKCε. In summary, in human and mouse models, aging is associated with increased oxidant stress, which activates PKCε and slows CBF.

Choroid plexus glutathione peroxidases are instrumental in protecting the brain fluid environment from hydroperoxides during postnatal development

Hydrogen peroxide, released at low physiological concentration, is involved in different cell signaling pathways during brain development. When released at supraphysiological concentrations in brain fluids following an inflammatory, hypoxic, or toxic stress, it can initiate lipid peroxidation, protein, and nucleic acid damage and contribute to long-term neurological impairment associated with perinatal diseases. We found high glutathione peroxidase and glutathione reductase enzymatic activities in both lateral and fourth ventricle choroid plexus tissue isolated from developing rats, in comparison to the cerebral cortex and liver. Consistent with these, a high protein expression of glutathione peroxidases 1 and 4 was observed in choroid plexus epithelial cells, which form the blood-cerebrospinal fluid barrier. Live choroid plexuses isolated from newborn rats were highly efficient in detoxifying H2O2 from mock cerebrospinal fluid, illustrating the capacity of the choroid plexuses to control H2O2 concentration in the ventricular system of the brain. We used a differentiated cellular model of the blood-cerebrospinal fluid barrier coupled to kinetic and inhibition analyses to show that glutathione peroxidases are more potent than catalase to detoxify extracellular H2O2 at concentrations up to 250 µM. The choroidal cells also formed an enzymatic barrier preventing blood-borne hydroperoxides to reach the cerebrospinal fluid. These data point out the choroid plexuses as key structures in the control of hydroperoxide levels in the cerebral fluid environment during development, at a time when the protective glial cell network is still immature. Glutathione peroxidases are the main effectors of this choroidal hydroperoxide inactivation.

Glucose Levels Alter the Mga Virulence Regulon in the Group A Streptococcus

Many bacterial pathogens coordinately regulate genes encoding important metabolic pathways during disease progression, including the phosphoenolpyruvate (PEP)-phosphotransferase system (PTS) for uptake of carbohydrates. The Gram-positive Group A Streptococcus (GAS) is a pathogen that infects multiple tissues in the human host. The virulence regulator Mga in GAS can be phosphorylated by the PTS, affecting Mga activity based on carbohydrate availability. Here, we explored the effects of glucose availability on the Mga regulon. RNA-seq was used to identify transcriptomic differences between the Mga regulon grown to late log phase in the presence of glucose (THY) or after glucose has been expended (C media). Our results revealed a correlation between the genes activated in C media with those known to be repressed by CcpA, indicating that C media mimics a non-preferred sugar environment. Interestingly, we found very little overlap in the Mga regulon from GAS grown in THY versus C media beyond the core virulence genes. We also observed an alteration in the phosphorylation status of Mga, indicating that the observed media differences in the Mga regulon may be directly attributed to glucose levels. Thus, these results support an in vivo link between glucose availability and virulence regulation in GAS.

Anatomical site-specific contributions of pneumococcal virulence determinants

Streptococcus pneumoniae is an opportunistic pathogen globally associated with significant morbidity and mortality. It is capable of causing a wide range of diseases including sinusitis, conjunctivitis, otitis media, pneumonia, bacteraemia, sepsis, and meningitis. While its capsular polysaccharide is indispensible for invasive disease, and opsonising antibodies against the capsule are the basis for the current vaccines, a long history of biomedical research indicates that other components of this Gram-positive bacterium are also critical for virulence. Herein we review the contribution of pneumococcal virulence determinants to survival and persistence in the context of distinct anatomical sites. We discuss how these determinants allow the pneumococcus to evade mucociliary clearance during colonisation, establish lower respiratory tract infection, resist complement deposition and opsonophagocytosis in the bloodstream, and invade secondary tissues such as the central nervous system leading to meningitis. We do so in a manner that highlights both the critical role of the capsular polysaccharide and the accompanying and necessary protein determinants. Understanding the complex interplay between host and pathogen is necessary to find new ways to prevent pneumococcal infection. This review is an attempt to do so with consideration for the latest research findings.

Primary ciliary dyskinesia and associated sensory ciliopathies

Primary ciliary dyskinesia (PCD) is a genetic disease of motile cilia, which belongs to a group of disorders resulting from dysfunction of cilia, collectively known as ciliopathies. Insights into the genetics and phenotypes of PCD have grown over the last decade, in part propagated by the discovery of a number of novel cilia-related genes. These genes encode proteins that segregate into structural axonemal, regulatory, as well as cytoplasmic assembly proteins. Our understanding of primary (sensory) cilia has also expanded, and an ever-growing list of diverse conditions has been linked to defective function and signaling of the sensory cilium. Recent multicenter clinical and genetic studies have uncovered the heterogeneity of motile and sensory ciliopathies, and in some cases, the overlap between these conditions. Here, we will describe the genetics and pathophysiology of ciliopathies in children, focusing on PCD, review emerging genotype-phenotype relationships, and diagnostic tools available for the clinician.

NADPH Oxidase-4 Overexpression Is Associated With Epithelial Ciliary Dysfunction in Neutrophilic Asthma

BACKGROUND

Bronchial epithelial ciliary dysfunction is an important feature of asthma. We sought to determine the role in asthma of neutrophilic inflammation and nicotinamide adenine dinucleotide phosphate (NADPH) oxidases in ciliary dysfunction.

METHODS

Bronchial epithelial ciliary function was assessed by using video microscopy in fresh ex vivo epithelial strips from patients with asthma stratified according to their sputum cell differentials and in culture specimens from healthy control subjects and patients with asthma. Bronchial epithelial oxidative damage was determined by 8-oxo-dG expression. Nicotinamide adenine dinucleotide phosphate oxidase (NOX)/dual oxidase (DUOX) expression was assessed in bronchial epithelial cells by using microarrays, with NOX4 and DUOX1/2 expression assessed in bronchial biopsy specimens. Ciliary dysfunction following NADPH oxidase inhibition, using GKT137831, was evaluated in fresh epithelial strips from patients with asthma and a murine model of ovalbumin sensitization and challenge.

RESULTS

Ciliary beat frequency was impaired in patients with asthma with sputum neutrophilia (n = 11) vs those without (n = 10) (5.8 [0.6] Hz vs 8.8 [0.5] Hz; P = .003) and was correlated with sputum neutrophil count (r = -0.70; P < .001). Primary bronchial epithelial cells expressed DUOX1/2 and NOX4. Levels of 8-oxo-dG and NOX4 were elevated in patients with neutrophilic vs nonneutrophilic asthma, DUOX1 was elevated in both, and DUOX2 was elevated in nonneutrophilic asthma in vivo. In primary epithelial cultures, ciliary dysfunction did not persist, although NOX4 expression and reactive oxygen species generation was increased from patients with neutrophilic asthma. GKT137831 both improved ciliary function in ex vivo epithelial strips (n = 13), relative to the intensity of neutrophilic inflammation, and abolished ciliary dysfunction in the murine asthma model with no reduction in inflammation.

CONCLUSIONS

Ciliary dysfunction is increased in neutrophilic asthma associated with increased NOX4 expression and is attenuated by NADPH oxidase inhibition.

Streptococcus pneumoniae proteomics: determinants of pathogenesis and vaccine development

Streptococcus pneumoniae is a major pathogen that is responsible for a variety of invasive diseases. The bacteria gain entry initially by establishing a carriage state in the nasopharynx from where they migrate to other sites in the body. The worldwide distribution of the bacteria and the severity of the diseases have led to a significant level of interest in the development of vaccines against the bacteria. Current vaccines, based on the bacterial polysaccharide, have a number of limitations including poor immunogenicity and limited effectiveness against all pneumococcal serotypes. There are many challenges in developing vaccines that will be effective against the diverse range of isolates and serotypes for this highly variable bacterial pathogen. This review considers how proteomic technologies have extended our understanding of the pathogenic mechanisms of nasopharyngeal colonization and disease development as well as the critical areas in developing protein-based vaccines.

Mycoplasma iowae: relationships among oxygen, virulence, and protection from oxidative stress

The poultry-associated bacterium Mycoplasma iowae colonizes multiple sites in embryos, with disease or death resulting. Although M. iowae accumulates in the intestinal tract, it does not cause disease at that site, but rather only in tissues that are exposed to atmospheric O₂. The activity of M. iowae catalase, encoded by katE, is capable of rapid removal of damaging H₂O₂ from solution, and katE confers a substantial reduction in the amount of H₂O₂ produced by Mycoplasma gallisepticum katE transformants in the presence of glycerol. As catalase-producing bacteria are often beneficial to hosts with inflammatory bowel disease, we explored whether M. iowae was exclusively protective against H₂O₂-producing bacteria in a Caenorhabditis elegans model, whether its protectiveness changed in response to O₂ levels, and whether expression of genes involved in H₂O₂ metabolism and virulence changed in response to O₂ levels. We observed that M. iowae was in fact protective against H₂O₂-producing Streptococcus pneumoniae, but not HCN-producing Pseudomonas aeruginosa, and that M. iowae cells grown in 1% O₂ promoted survival of C. elegans to a greater extent than M. iowae cells grown in atmospheric O₂. Transcript levels of an M. iowae gene encoding a homolog of Mycoplasma pneumoniae CARDS toxin were 5-fold lower in cells grown in low O₂. These data suggest that reduced O₂, representing the intestinal environment, triggers M. iowae to reduce its virulence capabilities, effecting a change from a pathogenic mode to a potentially beneficial one.

Respiratory syncytial virus increases the virulence of Streptococcus pneumoniae by binding to penicillin binding protein 1a. A new paradigm in respiratory infection

RATIONALE

Respiratory syncytial virus (RSV) and Streptococcus pneumoniae are major respiratory pathogens. Coinfection with RSV and S. pneumoniae is associated with severe and often fatal pneumonia but the molecular basis for this remains unclear.

OBJECTIVES

To determine if interaction between RSV and pneumococci enhances pneumococcal virulence.

METHODS

We used confocal microscopy and Western blot to identify the receptors involved in direct binding of RSV and pneumococci, the effects of which were studied in both in vivo and in vitro models of infection. Human ciliated respiratory epithelial cell cultures were infected with RSV for 72 hours and then challenged with pneumococci. Pneumococci were collected after 2 hours exposure and changes in gene expression determined using quantitative real-time polymerase chain reaction.

MEASUREMENTS AND MAIN RESULTS

Following incubation with RSV or purified G protein, pneumococci demonstrated a significant increase in the inflammatory response and bacterial adherence to human ciliated epithelial cultures and markedly increased virulence in a pneumonia model in mice. This was associated with extensive changes in the pneumococcal transcriptome and significant up-regulation in the expression of key pneumococcal virulence genes, including the gene for the pneumococcal toxin, pneumolysin. We show that mechanistically this is caused by RSV G glycoprotein binding penicillin binding protein 1a.

CONCLUSIONS

The direct interaction between a respiratory virus protein and the pneumococcus resulting in increased bacterial virulence and worsening disease outcome is a new paradigm in respiratory infection.

Picking up speed: advances in the genetics of primary ciliary dyskinesia

Abnormal ciliary axonemal structure and function are linked to the growing class of genetic disorders collectively known as ciliopathies, and our understanding of the complex genetics and functional phenotypes of these conditions has rapidly expanded. While progress in genetics and biology has uncovered numerous cilia-related syndromes, primary ciliary dyskinesia (PCD) remains the sole genetic disorder of motile cilia dysfunction. The first disease-causing mutation was described just 13 y ago, and since that time, the pace of gene discovery has quickened. These mutations separate into genes that encode axonemal motor proteins, structural and regulatory elements, and cytoplasmic proteins that are involved in assembly and preassembly of ciliary elements. These findings have yielded novel insights into the processes involved in ciliary assembly, structure, and function, which will allow us to better understand the clinical manifestations of PCD. Moreover, advances in techniques for genetic screening and sequencing are improving diagnostic approaches. In this article, we will describe the structure, function, and emerging genetics of respiratory cilia, review the genotype-phenotype relationships of motor ciliopathies, and explore the implications of recent discoveries for diagnostic testing for PCD.

Contribution of different pneumococcal virulence factors to experimental meningitis in mice

Background

Pneumococcal meningitis (PM) is a life-threatening disease with a high case-fatality rate and elevated risk for serious neurological sequelae. In this study, we investigated the contribution of three major virulence factors of Streptococcus pneumoniae, the capsule, pneumococcal surface protein A (PspA) and C (PspC), to the pathogenesis of experimental PM.

Methods

Mice were challenged by the intracranial route with the serotype 4 TIGR4 strain (wt) and three isogenic mutants devoid of PspA, PspC, and the capsule. Survival, bacterial counts, and brain histology were carried out. To study the interaction between S. pneumoniae mutants and microglia, phagocytosis and survival experiments were performed using the BV2 mouse microglial cell line.

Results

Virulence of the PspC mutant was comparable to that of TIGR4. In contrast, survival of animals challenged with the PspA mutant was significantly increased compared with the wt, and the mutant was also impaired at replicating in the brain and blood of infected mice. Brain histology indicated that all strains, except for the unencapsulated mutant, caused PM. Analysis of inflammation and damage in the brain of mice infected with TIGR4 or its unencapsulated mutant demonstrated that the rough strain was unable to induce inflammation and neuronal injury, even at high challenge doses. Results with BV2 cells showed no differences in phagocytic uptake between wt and mutants. In survival assays, however, the PspA mutant showed significantly reduced survival in microglia compared with the wt.

Conclusions

PspA contributed to PM pathogenesis possibly by interacting with microglia at early infection stages, while PspC had limited importance in the disease. The rough mutant did not cause brain inflammation, neuronal damage or mouse death, strengthening the key role of the capsule in PM.

Pyruvate oxidase influences the sugar utilization pattern and capsule production in Streptococcus pneumoniae

Pyruvate oxidase is a key function in the metabolism and lifestyle of many lactic acid bacteria and its activity depends on the presence of environmental oxygen. In Streptococcus pneumoniae the protein has been suggested to play a major role in metabolism and has been implicated in virulence, oxidative stress survival and death in stationary phase. Under semi-aerobic conditions, transcriptomic and metabolite profiling analysis of a spxB mutant grown on glucose showed minor changes compared to the wild type, apart from the significant induction of two operons involved in carbohydrate uptake and processing. This induction leads to a change in the sugar utilization capabilities of the bacterium, as indicated by the analysis of the growth profiles of the D39 parent and spxB mutant on alternative carbohydrates. Metabolic analysis and growth experiments showed that inactivation of SpxB has no effect on the glucose fermentation pattern, except under aerobic conditions. More importantly, we show that mutation of spxB results in the production of increased amounts of capsule, the major virulence factor of S. pneumoniae. Part of this increase can be attributed to induction of capsule operon (cps) transcription. Therefore, we propose that S. pneumoniae utilizes pyruvate oxidase as an indirect sensor of the oxygenation of the environment, resulting in the adaption of its nutritional capability and the amount of capsule to survive in the host.

Mucociliary clearance defects in a murine in vitro model of pneumococcal airway infection

Mucociliary airway clearance is an innate defense mechanism that protects the lung from harmful effects of inhaled pathogens. In order to escape mechanical clearance, airway pathogens including Streptococcus pneumoniae (pneumococcus) are thought to inactivate mucociliary clearance by mechanisms such as slowing of ciliary beating and lytic damage of epithelial cells. Pore-forming toxins like pneumolysin, may be instrumental in these processes. In a murine in vitro airway infection model using tracheal epithelial cells grown in air-liquid interface cultures, we investigated the functional consequences on the ciliated respiratory epithelium when the first contact with pneumococci is established. High-speed video microscopy and live-cell imaging showed that the apical infection with both wildtype and pneumolysin-deficient pneumococci caused insufficient fluid flow along the epithelial surface and loss of efficient clearance, whereas ciliary beat frequency remained within the normal range. Three-dimensional confocal microscopy demonstrated that pneumococci caused specific morphologic aberrations of two key elements in the F-actin cytoskeleton: the junctional F-actin at the apical cortex of the lateral cell borders and the apical F-actin, localized within the planes of the apical cell sides at the ciliary bases. The lesions affected the columnar shape of the polarized respiratory epithelial cells. In addition, the planar architecture of the entire ciliated respiratory epithelium was irregularly distorted. Our observations indicate that the mechanical supports essential for both effective cilia strokes and stability of the epithelial barrier were weakened. We provide a new model, where - in pneumococcal infection - persistent ciliary beating generates turbulent fluid flow at non-planar distorted epithelial surface areas, which enables pneumococci to resist mechanical cilia-mediated clearance.

Microglia and a functional type I IFN pathway are required to counter HSV-1-driven brain lateral ventricle enlargement and encephalitis

HSV-1 is the leading cause of sporadic viral encephalitis, with mortality rates approaching 30% despite treatment with the antiviral drug of choice, acyclovir. Permanent neurologic deficits are common in patients that survive, but the mechanism leading to this pathology is poorly understood, impeding clinical advancements in treatment to reduce CNS morbidity. Using magnetic resonance imaging and type I IFN receptor-deficient mouse chimeras, we demonstrate HSV-1 gains access to the murine brain stem and subsequently brain ependymal cells, leading to enlargement of the cerebral lateral ventricle and infection of the brain parenchyma. A similar enlargement in the lateral ventricles is found in a subpopulation of herpes simplex encephalitic patients. Associated with encephalitis is an increase in CXCL1 and CXCL10 levels in the cerebral spinal fluid, TNF-α expression in the ependymal region, and the influx of neutrophils of encephalitic mouse brains. Reduction in lateral ventricle enlargement using anti-secretory factor peptide 16 reduces mortality significantly in HSV-1-infected mice without any effect on expression of inflammatory mediators, infiltration of leukocytes, or changes in viral titer. Microglial cells but not infiltrating leukocytes or other resident glial cells or neurons are the principal source of resistance in the CNS during the first 5 d postinfection through a Toll/IL-1R domain-containing adapter inducing IFN-β-dependent, type I IFN pathway. Our results implicate lateral ventricle enlargement as a major cause of mortality in mice and speculate such an event transpires in a subpopulation of human HSV encephalitic patients.

Thiol peroxidase is an important component of Streptococcus pneumoniae in oxygenated environments

Streptococcus pneumoniae is an aerotolerant gram-positive bacterium that causes an array of diseases, including pneumonia, otitis media, and meningitis. During aerobic growth, S. pneumoniae produces high levels of H(2)O(2). Since S. pneumoniae lacks catalase, the question of how it controls H(2)O(2) levels is of critical importance. The psa locus encodes an ABC Mn(2+)-permease complex (psaBCA) and a putative thiol peroxidase, tpxD. This study shows that tpxD encodes a functional thiol peroxidase involved in the adjustment of H(2)O(2) homeostasis in the cell. Kinetic experiments showed that recombinant TpxD removed H(2)O(2) efficiently. However, in vivo experiments revealed that TpxD detoxifies only a fraction of the H(2)O(2) generated by the pneumococcus. Mass spectrometry analysis demonstrated that TpxD Cys(58) undergoes selective oxidation in vivo, under conditions where H(2)O(2) is formed, confirming the thiol peroxidase activity. Levels of TpxD expression and synthesis in vitro were significantly increased in cells grown under aerobic versus anaerobic conditions. The challenge with D39 and TIGR4 with H(2)O(2) resulted in tpxD upregulation, while psaBCA expression was oppositely affected. However, the challenge of ΔtpxD mutants with H(2)O(2) did not affect psaBCA, implying that TpxD is involved in the regulation of the psa operon, in addition to its scavenging activity. Virulence studies demonstrated a notable difference in the survival time of mice infected intranasally with D39 compared to that of mice infected intranasally with D39ΔtpxD. However, when bacteria were administered directly into the blood, this difference disappeared. The findings of this study suggest that TpxD constitutes a component of the organism's fundamental strategy to fine-tune cellular processes in response to H(2)O(2).

Identification of a novel pneumococcal vaccine antigen preferentially expressed during meningitis in mice

Streptococcus pneumoniae is the most common cause of severe bacterial meningitis in children, the elderly, and immunocompromised individuals. To identify virulence factors preferentially expressed during meningitis, we conducted niche-specific genome-wide in vivo transcriptomic analysis after intranasal infection of mice with serotype 4 or 6A pneumococci. The expression of 34 bacterial genes was substantially altered in brain tissue of mice infected with either of the 2 strains. Ten upregulated genes were common to both strains, 7 of which were evaluated for their role in the development of meningitis. One previously uncharacterized protein, α-glycerophosphate oxidase (GlpO), was cytotoxic for human brain microvascular endothelial cells (HBMECs) via generation of H(2)O(2). A glpO deletion mutant was defective in adherence to HBMECs in vitro as well as in progression from the blood to the brain in vivo. Mutant bacteria also induced markedly reduced meningeal inflammation and brain pathology compared with wild type, despite similar levels of bacteremia. Immunization of mice with GlpO protected against invasive pneumococcal disease and provided additive protection when formulated with pneumolysin toxoid. Our results provide the basis of a strategy that can be adapted to identify genes that contribute to the development of meningitis caused by other pathogens.

Pneumococcal gene complex involved in resistance to extracellular oxidative stress

Streptococcus pneumoniae is a gram-positive bacterium which is a member of the normal human nasopharyngeal flora but can also cause serious disease such as pneumonia, bacteremia, and meningitis. Throughout its life cycle, S. pneumoniae is exposed to significant oxidative stress derived from endogenously produced hydrogen peroxide (H(2)O(2)) and from the host through the oxidative burst. How S. pneumoniae, an aerotolerant anaerobic bacterium that lacks catalase, protects itself against hydrogen peroxide stress is still unclear. Bioinformatic analysis of its genome identified a hypothetical open reading frame belonging to the thiol-specific antioxidant (TlpA/TSA) family, located in an operon consisting of three open reading frames. For all four strains tested, deletion of the gene resulted in an approximately 10-fold reduction in survival when strains were exposed to external peroxide stress. However, no role for this gene in survival of internal superoxide stress was observed. Mutagenesis and complementation analysis demonstrated that all three genes are necessary and sufficient for protection against oxidative stress. Interestingly, in a competitive index mouse pneumonia model, deletion of the operon had no impact shortly after infection but was detrimental during the later stages of disease. Thus, we have identified a gene complex involved in the protection of S. pneumoniae against external oxidative stress, which plays an important role during invasive disease.

Pathogenesis of A Clinical Ocular Strain of Streptococcus pneumoniae and the Interaction of Pneumolysin with Corneal Cells

Streptococcus pneumoniae is an important cause of bacterial keratitis, an infectious disease of the cornea. This study aimed to determine the importance of pneumolysin (PLY), a pneumococcal virulence factor, in keratitis using a clinical keratitis isolate (K1263) and its isogenic mutant deficient in PLY (K1263ΔPLY) and determine the effect of these strains on primary rabbit corneal epithelial (RCE) cells. Each strain was injected into the corneal stromas of rabbits, clinical examinations were performed, and the recovered bacterial loads were determined. Bacterial extracts were exposed to RCE cells, and morphology and viability were assessed. The mutant strain deficient in PLY, K1263ΔPLY, caused significantly lower ocular disease scores than the parent strain (K1263), although a higher bacterial load was recovered from corneas infected with the mutant strain. Histological examination showed increased inflammatory cells in the anterior chamber and increased edema in eyes infected with the parent strain. RCE cells exposed to the parent strain had significantly decreased cell viability and showed increased evidence of cellular damage. This study confirms that in a strain that can cause clinical keratitis, PLY is a significant cause of the damage associated with pneumococcal keratitis. It also shows for the first time that the results from an in vitro model using RCE cells correlates with in vivo results thereby establishing a less invasive way to study the mechanisms of pneumococcal keratitis.

Activation of adenosine A2B receptors enhances ciliary beat frequency in mouse lateral ventricle ependymal cells

BACKGROUND

Ependymal cells form a protective monolayer between the brain parenchyma and cerebrospinal fluid (CSF). They possess motile cilia important for directing the flow of CSF through the ventricular system. While ciliary beat frequency in airway epithelia has been extensively studied, fewer reports have looked at the mechanisms involved in regulating ciliary beat frequency in ependyma. Prior studies have demonstrated that ependymal cells express at least one purinergic receptor (P2X7). An understanding of the full range of purinergic receptors expressed by ependymal cells, however, is not yet complete. The objective of this study was to identify purinergic receptors which may be involved in regulating ciliary beat frequency in lateral ventricle ependymal cells.

METHODS

High-speed video analysis of ciliary movement in the presence and absence of purinergic agents was performed using differential interference contrast microscopy in slices of mouse brain (total number of animals = 67). Receptor identification by this pharmacological approach was corroborated by immunocytochemistry, calcium imaging experiments, and the use of two separate lines of knockout mice.

RESULTS

Ciliary beat frequency was enhanced by application of a commonly used P2X7 agonist. Subsequent experiments, however, demonstrated that this enhancement was observed in both P2X7+/+ and P2X7-/- mice and was reduced by pre-incubation with an ecto-5'-nucleotidase inhibitor. This suggested that enhancement was primarily due to a metabolic breakdown product acting on another purinergic receptor subtype. Further studies revealed that ciliary beat frequency enhancement was also induced by adenosine receptor agonists, and pharmacological studies revealed that ciliary beat frequency enhancement was primarily due to A2B receptor activation. A2B expression by ependymal cells was subsequently confirmed using A2B-/-/beta-galactosidase reporter gene knock-in mice.

CONCLUSION

This study demonstrates that A2B receptor activation enhances ciliary beat frequency in lateral ventricle ependymal cells. Ependymal cell ciliary beat frequency regulation may play an important role in cerebral fluid balance and cerebrospinal fluid dynamics.

CcpA and LacD.1 affect temporal regulation of Streptococcus pyogenes virulence genes

Production of H(2)O(2) follows a growth phase-dependent pattern that mimics that of many virulence factors of Streptococcus pyogenes. To gain greater insight into mechanisms coupling virulence factor expression to growth phase, we investigated the molecular basis for H(2)O(2) generation and its regulation. Deletion of the gene encoding lactate oxidase (lctO) or culture in the presence of glucose eliminated H(2)O(2) production, implicating carbohydrate regulation of lctO as a key element of growth phase control. In examining known carbohydrate-responsive regulators, deletion of the gene encoding CcpA but not that encoding LacD.1 resulted in both derepression and an uncoupling of lctO transcription from its growth phase pattern. Expanding this analysis to additional virulence factors demonstrated both negative (cfa, encoding CAMP factor) and positive (speB, encoding a cysteine protease) regulation by CcpA and that CcpA mutants were highly cytotoxic for cultured macrophages. This latter property resulted from enhanced transcription of the streptolysin S biogenesis operon. Examination of CcpA-promoter interactions using a DNA pull-down assay mimicking physiological conditions showed direct binding to the promoters of lctO and speB but not those of sagA. CcpA but not LacD.1 mutants were attenuated in a murine model of soft-tissue infection, and analysis of gene expression in infected tissue indicated that CcpA mutants had altered expression of lctO, cfa, and speB but not the indirectly regulated sagA gene. Taken together, these data show that CcpA regulates virulence genes via at least three distinct mechanisms and that disruption of growth phase regulation alters transcriptional patterns in infected tissues.

The role of Streptococcus pneumoniae virulence factors in host respiratory colonization and disease

Streptococcus pneumoniae is a Gram-positive bacterial pathogen that colonizes the mucosal surfaces of the host nasopharynx and upper airway. Through a combination of virulence-factor activity and an ability to evade the early components of the host immune response, this organism can spread from the upper respiratory tract to the sterile regions of the lower respiratory tract, which leads to pneumonia. In this Review, we describe how S. pneumoniae uses its armamentarium of virulence factors to colonize the upper and lower respiratory tracts of the host and cause disease.

The effect of protein expression of Streptococcus pneumoniae by blood

During infection, the common respiratory tract pathogen Streptococcus pneumoniae encounters several environmental conditions, such as upper respiratory tract, lung tissue, and blood stream, etc. In this study, we examined the effects of blood on S. pneumoniae protein expression using a combination of highly sensitive 2-dimensional electrophoresis (DE) and MALDI-TOF MS and/or LC/ESI-MS/MS. A comparison of expression profiles between the growth in THY medium and THY supplemented with blood allowed us to identify 7 spots, which increased or decreased two times or more compared with the control group: tyrosyl-tRNA synthetase, lactate oxidase, glutamyl-aminopeptidase, L-lactate dehydrogenase, cysteine synthase, ribose-phosphate pyrophosphokinase, and orotate phosphoribosyltransferase. This global approach can provide a better understanding of S. pneumoniae adaptation to its human host and a clue for its pathogenicity.

Hyaluronidase augments pneumolysin-mediated injury to human ciliated epithelium

OBJECTIVES

The main objective of this study was to investigate the effects of pneumococcal hyaluronidase (0.1-10microg/ml), alone and in combination with pneumolysin (50 and 100ng/ml), on human ciliated epithelium.

METHODS

Ciliary beat frequency (CBF) and structural integrity of human ciliated respiratory epithelium in vitro were studied using a phototransistor technique and a visual scoring index, respectively.

RESULTS

Hyaluronidase per se did not affect either CBF or the structural integrity of the epithelium. However, preincubation of the epithelial strips with hyaluronidase (10microg/ml) for 30min at 37 degrees C significantly potentiated pneumolysin-mediated ciliary slowing and epithelial damage. Hyaluronan, a substrate of hyaluronidase, had no effects on the ciliated respiratory epithelium in concentrations up to 100microg/ml and did not antagonize the injurious effects of pneumolysin on the epithelium. However, preincubation of the epithelial strips with hyaluronan (100microg/ml) was associated with attenuation of the ciliary slowing and epithelial damage induced by incubation of the strips with hyaluronidase (10microg/ml) for 30min at 37 degrees C followed by addition of pneumolysin (50ng/ml).

CONCLUSIONS

Although having no direct effects alone, hyaluronidase may contribute to pneumolysin-mediated damage and dysfunction to respiratory epithelium, thereby favoring colonization and subsequently extra-pulmonary dissemination of the pneumococcus.

PavA of Streptococcus pneumoniae modulates adherence, invasion, and meningeal inflammation

Pneumococcal adherence and virulence factor A (PavA) is displayed to the cell outer surface of Streptococcus pneumoniae and mediates pneumococcal binding to immobilized fibronectin. PavA, which lacks a typical gram-positive signal sequence and cell surface anchorage motif, is essential for pneumococcal virulence in a mouse infection model of septicemia. In this report the impact of PavA on pneumococcal adhesion to and invasion of eukaryotic cells and on experimental pneumococcal meningitis was investigated. In the experimental mouse meningitis model, the virulence of the pavA knockout mutant of S. pneumoniae D39, which did not show alterations of subcellular structures as indicated by electron microscopic studies, was strongly decreased. Pneumococcal strains deficient in PavA showed substantially reduced adherence to and internalization of epithelial cell lines A549 and HEp-2. Similar results were obtained with human brain-derived microvascular endothelial cells and human umbilical vein-derived endothelial cells. Attachment and internalization of pneumococci were not significantly affected by preincubation or cocultivations of pneumococci with anti-PavA antisera. Pneumococcal adherence was also not significantly affected by the addition of PavA protein. Complementation of the pavA knockout strain with exogenously added PavA polypeptide did not restore adherence of the mutant. These data suggest that PavA affects pneumococcal colonization by modulating expression or function of important virulence determinants of S. pneumoniae.

Pneumococcal vaccines: an update on current strategies

Streptococcus pneumoniae is a major cause of morbidity and mortality in infants, children and the elderly. Despite the availability of excellent antimicrobial therapy and adequate health care systems, respiratory diseases and invasive infections caused by pneumococci still comprise a major health problem. The emerging resistance to penicillin and other commonly used antibiotics underscores the importance of the development of novel vaccine strategies to combat pneumococcal disease. Although the 23-valent polysaccharide (PS) vaccine is immunogenic and protective in most adults and children over 5 years of age, they fail to protect children under 2 years of age. Fortunately, the recent conjugate vaccines have shown to be highly efficacious in preventing invasive diseases in this risk group. Moreover, promising results regarding prevention of pneumonia and acute otitis media have been published. Unfortunately, protection is raised against a limited number of pneumococcal serotypes, and serotype replacement and subsequent vaccine failure have become a serious concern. Currently, several pneumococcal surface proteins are considered as alternative vaccine candidates because of their serotype-independence. Thus far, pneumococcal surface adhesin A (PsaA) has proven to be highly protective against colonization in animal models. Moreover, pneumococcal surface protein A (PspA) and pneumolysin have shown to elicit protection against invasive diseases. Future research will elucidate their true potential in protecting humans. In this paper we discuss the present knowledge on pneumococcal vaccines and the current status of novel vaccine strategies.

The role of pneumolysin in pneumococcal pneumonia and meningitis

Diseases caused by Streptococcus pneumoniae include pneumonia, septicaemia and meningitis. All these are associated with high morbidity and mortality. The pneumococcus can colonize the nasopharynx, and this can be a prelude to bronchopneumonia and invasion of the vasculature space. Proliferation in the blood can result in a breach of the blood-brain barrier and entry into the cerebrospinal fluid (CSF) where the bacteria cause inflammation of the meningeal membranes resulting in meningitis. The infected host may develop septicaemia and/or meningitis secondary to bronchopneumonia. Also septicaemia is a common precursor of meningitis. The mechanisms surrounding the sequence of infection are unknown, but will be dependent on the properties of both the host and bacterium. Treatment of these diseases with antibiotics leads to clearance of the bacteria from the infected tissues, but the bacteriolytic nature of antibiotics leads to an acute release of bacterial toxins and thus after antibiotic therapy the patients can be left with organ-specific deficits. One of the main toxins released from pneumococci is the membrane pore forming toxin pneumolysin. Here we review the extensive studies on the role of pneumolysin in the pathogenesis of pneumococcal diseases.

Streptococcus pneumoniae-induced inhibition of rat ependymal cilia is attenuated by antipneumolysin antibody

Ciliated ependymal cells line the ventricular surfaces and aqueducts of the brain. In ex vivo experiments, pneumolysin caused rapid inhibition of the ependymal ciliary beat frequency and caused ependymal cell disruption. Wild-type pneumococci and pneumococci deficient in pneumolysin caused ciliary slowing, but penicillin lysis of wild-type, not pneumolysin-deficient, pneumococci increased the extent of ciliary inhibition. This effect was abolished by antipneumolysin antibody. Ependymal ciliary stasis by purified pneumolysin was also blocked by the addition of antipneumolysin monoclonal antibodies. These data show that antibiotic lysis of Streptococcus pneumoniae can be detrimental to the ciliated ependyma and that antipneumolysin antibody may have a therapeutic potential.

Cytotoxicity of hydrogen peroxide produced by Enterococcus faecium

Although the opportunistic bacterial pathogen Enterococcus faecium is a leading source of nosocomial infections, it appears to lack many of the overt virulence factors produced by other bacterial pathogens, and the underlying mechanism of pathogenesis is not clear. Using E. faecium-mediated killing of the nematode worm Caenorhabditis elegans as an indicator of toxicity, we determined that E. faecium produces hydrogen peroxide at levels that cause cellular damage. We identified E. faecium transposon insertion mutants with altered C. elegans killing activity, and these mutants were altered in hydrogen peroxide production. Mutation of an NADH oxidase-encoding gene eliminated nearly all NADH oxidase activity and reduced hydrogen peroxide production. Mutation of an NADH peroxidase-encoding gene resulted in the enhanced accumulation of hydrogen peroxide. E. faecium is able to produce hydrogen peroxide by using glycerol-3-phosphate oxidase, and addition of glycerol to the culture medium enhanced the killing of C. elegans. Conversely, addition of glucose, which leads to the down-regulation of glycerol metabolism, prevented both C. elegans killing and hydrogen peroxide production. Lastly, detoxification of hydrogen peroxide either by exogenously added catalase or by a C. elegans transgenic strain overproducing catalase prevented E. faecium-mediated killing. These results suggest that hydrogen peroxide produced by E. faecium has cytotoxic effects and highlight the utility of C. elegans pathogenicity models for identifying bacterial virulence factors.

Differences in clinical manifestation of Streptococcus pneumoniae infection are not correlated with in vitro production and release of the virulence factors pneumolysin and lipoteichoic and teichoic acids

Production and release of the pneumococcal virulence factors pneumolysin and lipoteichoic and teichoic acid in 75 clinical isolates were investigated. No difference was found between strains causing systemic infection or localized respiratory infection and isolates from asymptomatic carriers. This suggests that the presence of pneumolysin and lipoteichoic and teichoic acid is a necessary but not a sufficient condition for pneumococcal infection and development of invasive disease.

Hydrogen peroxide production in Streptococcus pyogenes: involvement of lactate oxidase and coupling with aerobic utilization of lactate

Streptococcus pyogenes strains can be divided into two classes, one capable and the other incapable of producing H2O2 (M. Saito, S. Ohga, M. Endoh, H. Nakayama, Y. Mizunoe, T. Hara, and S. Yoshida, Microbiology 147:2469-2477, 2001). In the present study, this dichotomy was shown to parallel the presence or absence of H2O2-producing lactate oxidase activity in permeabilized cells. Both lactate oxidase activity and H2O2 production under aerobic conditions were detectable only after glucose in the medium was exhausted. Thus, the glucose-repressible lactate oxidase is likely responsible for H2O2 production in S. pyogenes. Of the other two potential H2O2-producing enzymes of this bacterium, NADH and alpha-glycerophosphate oxidase, only the former exhibited low but significant activity in either class of strains. This activity was independent of the growth phase, suggesting that the protein may serve in vivo as a subunit of the H2O2-scavenging enzyme NAD(P)H-linked alkylhydroperoxide reductase. The activity of lactate oxidase was associated with the membrane while that of NADH oxidase was in the soluble fraction, findings consistent with their respective physiological roles, i.e., the production and scavenging of H2O2. Analyses of fermentation end products revealed that the concentration of lactate initially increased with time and decreased on glucose exhaustion, while that of acetate increased during the culture. These results suggest that the lactate oxidase activity of H2O2-producing cells oxidizes lactate to pyruvate, which is in turn converted to acetate. This latter process proceeds presumably via acetyl coenzyme A and acetyl phosphate with formation of extra ATP.