Strategies of Intracellular Pathogens for Obtaining Iron from the Environment

Upstream land use with microbial downstream consequences: Iron and humic substances link to Legionella spp

Intensified land use can disturb water quality, potentially increasing the abundance of bacterial pathogens, threatening public access to clean water. This threat involves both direct contamination of faecal bacteria as well as indirect factors, such as disturbed water chemistry and microbiota, which can lead to contamination. While direct contamination has been well described, the impact of indirect factors is less explored, despite the potential of severe downstream consequences on water supply. To assess direct and indirect downstream effects of buildings, farms, pastures and fields on potential water sources, we studied five Swedish lakes and their inflows. We analysed a total of 160 samples in a gradient of anthropogenic activity spanning four time points, including faecal and water-quality indicators. Through species distribution modelling, Random Forest and network analysis using 16S rRNA amplicon sequencing data, our findings highlight that land use indirectly impacts lakes via inflows. Land use impacted approximately one third of inflow microbiota taxa, in turn impacting ∼20-50 % of lake taxa. Indirect effects via inflows were also suggested by causal links between e.g. water colour and lake bacterial taxa, where this influenced the abundance of several freshwater bacteria, such as Polynucleobacter and Limnohabitans. However, it was not possible to identify direct effects on the lakes based on analysis of physiochemical- or microbial parameters. To avoid potential downstream consequences on water supply, it is thus important to consider possible indirect effects from upstream land use and inflows, even when no direct effects can be observed on lakes. Legionella (a genus containing bacterial pathogens) illustrated potential consequences, since the genus was particularly abundant in inflows and was shown to increase by the presence of pastures, fields, and farms. The approach presented here could be used to assess the suitability of lakes as alternative raw water sources or help to mitigate contaminations in important water catchments. Continued broad investigations of stressors on the microbial network can identify indirect effects, avoid enrichment of pathogens, and help secure water accessibility.

Targeting Intracellular Bacteria with Dual Drug-loaded Lactoferrin Nanoparticles

Treatment of microbial infections is becoming daunting because of widespread antimicrobial resistance. The treatment challenge is further exacerbated by the fact that certain infectious bacteria invade and localize within host cells, protecting the bacteria from antimicrobial treatments and the host's immune response. To survive in the intracellular niche, such bacteria deploy surface receptors similar to host cell receptors to sequester iron, an essential nutrient for their virulence, from host iron-binding proteins, in particular lactoferrin and transferrin. In this context, we aimed to target lactoferrin receptors expressed by macrophages and bacteria; as such, we prepared and characterized lactoferrin nanoparticles (Lf-NPs) loaded with a dual drug combination of antimicrobial natural alkaloids, berberine or sanguinarine, with vancomycin or imipenem. We observed increased uptake of drug-loaded Lf-NPs by differentiated THP-1 cells with up to 90% proportion of fluorescent cells, which decreased to about 60% in the presence of free lactoferrin, demonstrating the targeting ability of Lf-NPs. The encapsulated antibiotic drug cocktail efficiently cleared intracellular Staphylococcus aureus (Newman strain) compared to the free drug combinations. However, the encapsulated drugs and the free drugs alike exhibited a bacteriostatic effect against the hard-to-treat Mycobacterium abscessus (smooth variant). In conclusion, the results of this study demonstrate the potential of lactoferrin nanoparticles for the targeted delivery of antibiotic drug cocktails for the treatment of intracellular bacteria.

Confronting the complexities of antimicrobial management for Staphyloccous aureus causing bovine mastitis: an innovative paradigm

Globally, Mastitis is a disease commonly affecting dairy cattle which leads to the use of antimicrobials. The majority of mastitis etiological agents are bacterial pathogens and Staphylococcus aureus is the predominant causative agent. Antimicrobial treatment is administered mainly via intramammary and intramuscular routes. Due to increasing antimicrobial resistance (AMR) often associated with antimicrobial misuse, the treatment of mastitis is becoming challenging with less alternative treatment options. Besides, biofilms formation and ability of mastitis-causing bacteria to enter and adhere within the cells of the mammary epithelium complicate the treatment of bovine mastitis. In this review article, we address the challenges in treating mastitis through conventional antibiotic treatment because of the rising AMR, biofilms formation, and the intracellular survival of bacteria. This review article describes different alternative treatments including phytochemical compounds, antimicrobial peptides (AMPs), phage therapy, and Graphene Nanomaterial-Based Therapy that can potentially be further developed to complement existing antimicrobial therapy and overcome the growing threat of AMR in etiologies of mastitis.

Targeting Mycobacterium tuberculosis iron-scavenging tools: a recent update on siderophores inhibitors

Among the various bacterial infections, tuberculosis (TB) remains a life-threatening infectious disease responsible as the most significant cause of mortality and morbidity worldwide. The co-infection of human immunodeficiency virus (HIV) in association with TB burdens the healthcare system substantially. Notably, M.tb possesses defence against most antitubercular antibiotic drugs, and the efficacy of existing frontline anti-TB drugs is waning. Also, new and recurring cases of TB from resistant bacteria such as multidrug-resistant TB (MDR), extensively drug-resistant TB (XDR), and totally drug-resistant TB (TDR) strains are increasing. Hence, TB begs the scientific community to explore the new therapeutic class of compounds with their novel mechanism. M.tb requires iron from host cells to sustain, grow, and carry out several biological processes. M.tb has developed strategic methods of acquiring iron from the surrounding environment. In this communication, we discuss an overview of M.tb iron-scavenging tools. Also, we have summarized recently identified MbtA and MbtI inhibitors, which prevent M.tb from scavenging iron. These iron-scavenging tool inhibitors have the potential to be developed as anti-TB agents/drugs.

Hepcidin and ferritin levels as markers of immune cell activation during septic shock, severe COVID-19 and sterile inflammation

Introduction

Major clinically relevant inflammatory events such as septic shock and severe COVID-19 trigger dynamic changes in the host immune system, presenting promising candidates for new biomarkers to improve precision diagnostics and patient stratification. Hepcidin, a master regulator of iron metabolism, has been intensively studied in many pathologies associated with immune system activation, however these data have never been compared to other clinical settings. Thus, we aimed to reveal the dynamics of iron regulation in various clinical settings and to determine the suitability of hepcidin and/or ferritin levels as biomarkers of inflammatory disease severity.

Cohorts

To investigate the overall predictive ability of hepcidin and ferritin, we enrolled the patients suffering with three different diagnoses - in detail 40 patients with COVID-19, 29 patients in septic shock and eight orthopedic patients who were compared to nine healthy donors and all cohorts to each other.

Results

We showed that increased hepcidin levels reflect overall immune cell activation driven by intrinsic stimuli, without requiring direct involvement of infection vectors. Contrary to hepcidin, ferritin levels were more strongly boosted by pathogen-induced inflammation - in septic shock more than four-fold and in COVID-19 six-fold in comparison to sterile inflammation. We also defined the predictive capacity of hepcidin-to-ferritin ratio with AUC=0.79 and P = 0.03.

Discussion

Our findings confirm that hepcidin is a potent marker of septic shock and other acute inflammation-associated pathologies and demonstrate the utility of the hepcidin-to-ferritin ratio as a predictor of mortality in septic shock, but not in COVID-19.

Moonlighting in Rickettsiales: Expanding Virulence Landscape

The order Rickettsiales includes species that cause a range of human diseases such as human granulocytic anaplasmosis (Anaplasma phagocytophilum), human monocytic ehrlichiosis (Ehrlichia chaffeensis), scrub typhus (Orientia tsutsugamushi), epidemic typhus (Rickettsia prowazekii), murine typhus (R. typhi), Mediterranean spotted fever (R. conorii), or Rocky Mountain spotted fever (R. rickettsii). These diseases are gaining a new momentum given their resurgence patterns and geographical expansion due to the overall rise in temperature and other human-induced pressure, thereby remaining a major public health concern. As obligate intracellular bacteria, Rickettsiales are characterized by their small genome sizes due to reductive evolution. Many pathogens employ moonlighting/multitasking proteins as virulence factors to interfere with multiple cellular processes, in different compartments, at different times during infection, augmenting their virulence. The utilization of this multitasking phenomenon by Rickettsiales as a strategy to maximize the use of their reduced protein repertoire is an emerging theme. Here, we provide an overview of the role of various moonlighting proteins in the pathogenicity of these species. Despite the challenges that lie ahead to determine the multiple potential faces of every single protein in Rickettsiales, the available examples anticipate this multifunctionality as an essential and intrinsic feature of these obligates and should be integrated into available moonlighting repositories.

Dual RNA sequencing reveals dendritic cell reprogramming in response to typhoidal Salmonella invasion

Salmonella enterica represent a major disease burden worldwide. S. enterica serovar Typhi (S. Typhi) is responsible for potentially life-threatening Typhoid fever affecting 10.9 million people annually. While non-typhoidal Salmonella (NTS) serovars usually trigger self-limiting diarrhoea, invasive NTS bacteraemia is a growing public health challenge. Dendritic cells (DCs) are key professional antigen presenting cells of the human immune system. The ability of pathogenic bacteria to subvert DC functions and prevent T cell recognition contributes to their survival and dissemination within the host. Here, we adapted dual RNA-sequencing to define how different Salmonella pathovariants remodel their gene expression in tandem with that of infected DCs. We find DCs harness iron handling pathways to defend against invading Salmonellas, which S. Typhi is able to circumvent by mounting a robust response to nitrosative stress. In parallel, we uncover the alternative strategies invasive NTS employ to impair DC functions.

Aulicino, Antanaviciute et al investigate the transcriptional response to invasive Salmonella strains in dendritic cells (DCs). They show that S. Typhi mount a response against nitrosative stress pathways and propose a role of iron uptake and transport in preventing infection, which the pathogen can bypass. In parallel, they find that invasive Salmonella employs several mechanisms targeting more classic aspects of immunity to impair DC function.

Host glyceraldehyde-3-phosphate dehydrogenase-mediated iron acquisition is hijacked by intraphagosomal Mycobacterium tuberculosis

Availability of iron is a key factor in the survival and multiplication of Mycobacterium tuberculosis (M.tb) within host macrophage phagosomes. Despite host cell iron regulatory machineries attempts to deny supply of this essential micronutrient, intraphagosomal M.tb continues to access extracellular iron. In the current study, we report that intracellular M.tb exploits mammalian secreted Glyceraldehyde 3-phosphate dehydrogenase (sGAPDH) for the delivery of host iron carrier proteins lactoferrin (Lf) and transferrin (Tf). Studying the trafficking of iron carriers in infected cells we observed that sGAPDH along with the iron carrier proteins are preferentially internalized into infected cells and trafficked to M.tb containing phagosomes where they are internalized by resident mycobacteria resulting in iron delivery. Collectively our findings provide a new mechanism of iron acquisition by M.tb involving the hijack of host sGAPDH. This may contribute to its successful pathogenesis and provide an option for targeted therapeutic intervention.

Antibiotic-Loaded Polymersomes for Clearance of Intracellular Burkholderia thailandensis

Melioidosis caused by the facultative intracellular pathogen Burkholderia pseudomallei is difficult to treat due to poor intracellular bioavailability of antibiotics and antibiotic resistance. In the absence of novel compounds, polymersome (PM) encapsulation may increase the efficacy of existing antibiotics and reduce antibiotic resistance by promoting targeted, infection-specific intracellular uptake. In this study, we developed PMs composed of widely available poly(ethylene oxide)-polycaprolactone block copolymers and demonstrated their delivery to intracellular B. thailandensis infection using multispectral imaging flow cytometry (IFC) and coherent anti-Stokes Raman scattering microscopy. Antibiotics were tightly sequestered in PMs and did not inhibit the growth of free-living B. thailandensis. However, on uptake of antibiotic-loaded PMs by infected macrophages, IFC demonstrated PM colocalization with intracellular B. thailandensis and a significant inhibition of their growth. We conclude that PMs are a viable approach for the targeted antibiotic treatment of persistent intracellular Burkholderia infection.

Innate Lymphoid Cells in Response to Intracellular Pathogens: Protection Versus Immunopathology

Innate lymphoid cells (ILCs) are a heterogeneous group of cytokine-producing lymphocytes which are predominantly located at mucosal barrier surfaces, such as skin, lungs, and gastrointestinal tract. ILCs contribute to tissue homeostasis, regulate microbiota-derived signals, and protect against mucosal pathogens. ILCs are classified into five major groups by their developmental origin and distinct cytokine production. A recently emerged intriguing feature of ILCs is their ability to alter their phenotype and function in response to changing local environmental cues such as pathogen invasion. Once the pathogen crosses host barriers, ILCs quickly activate cytokine production to limit the spread of the pathogen. However, the dysregulated ILC responses can lead to tissue inflammation and damage. Furthermore, the interplay between ILCs and other immune cell types shapes the outcome of the immune response. Recent studies highlighted the important role of ILCs for host defense against intracellular pathogens. Here, we review recent advances in understanding the mechanisms controlling protective and pathogenic ILC responses to intracellular pathogens. This knowledge can help develop new ILC-targeted strategies to control infectious diseases and immunopathology.

Detection and Sequencing of Iron Superoxide Dismutase Gene in Entamoeba histolytica Isolated from Patients with Diarrhea in Iraq

Parasites are among serious health problems that threaten the public health of humans. Entamoeba histolytica is considered the second or third most common cause of death among parasitic diseases. The present study was conducted to determine the molecular detection and sequencing of iron-containing superoxide dismutase (FeSOD) genes of E. histolytica. This cross-sectional study was carried out within March-August 2020. Genomic DNA from stool samples was extracted using an AccuPrep® stool DNA Extraction Kit. Afterward, four DNA samples were subjected to sequence alignment analysis of the FeSOD gene in local E. histolytica human isolated using a Clustal W alignment tool (Mega 6.0).The iron-containing superoxide dismutase gene was present at 62.8% in 15 out of 24 E. histolytica samples. The results of sequence alignment analysis of the FeSOD gene in local E.histolytica human isolates indicated the number of mutations in each of the 4 isolates. Accordingly, there were 2 (16.66%) silent mutations and 1(6.66%) nonsense mutation. There are a variety of genetic strains of E. histolytica associated with diarrheal illness in Iraqi patients, which are unique to this country.

The Transporter-Mediated Cellular Uptake and Efflux of Pharmaceutical Drugs and Biotechnology Products: How and Why Phospholipid Bilayer Transport Is Negligible in Real Biomembranes

Over the years, my colleagues and I have come to realise that the likelihood of pharmaceutical drugs being able to diffuse through whatever unhindered phospholipid bilayer may exist in intact biological membranes in vivo is vanishingly low. This is because (i) most real biomembranes are mostly protein, not lipid, (ii) unlike purely lipid bilayers that can form transient aqueous channels, the high concentrations of proteins serve to stop such activity, (iii) natural evolution long ago selected against transport methods that just let any undesirable products enter a cell, (iv) transporters have now been identified for all kinds of molecules (even water) that were once thought not to require them, (v) many experiments show a massive variation in the uptake of drugs between different cells, tissues, and organisms, that cannot be explained if lipid bilayer transport is significant or if efflux were the only differentiator, and (vi) many experiments that manipulate the expression level of individual transporters as an independent variable demonstrate their role in drug and nutrient uptake (including in cytotoxicity or adverse drug reactions). This makes such transporters valuable both as a means of targeting drugs (not least anti-infectives) to selected cells or tissues and also as drug targets. The same considerations apply to the exploitation of substrate uptake and product efflux transporters in biotechnology. We are also beginning to recognise that transporters are more promiscuous, and antiporter activity is much more widespread, than had been realised, and that such processes are adaptive (i.e., were selected by natural evolution). The purpose of the present review is to summarise the above, and to rehearse and update readers on recent developments. These developments lead us to retain and indeed to strengthen our contention that for transmembrane pharmaceutical drug transport "phospholipid bilayer transport is negligible".

Vitamin D - A host directed autophagy mediated therapy for tuberculosis

According to the WHO report 2019, Tuberculosis (TB) is an ancient disease of humanity that is curable. TB has caused significant morbidity and mortality even in 2018. The etiological agent of TB, Mycobacterium tuberculosis (MTB) exploits its virulence factors to escape from host immunity and therapeutic drugs. Host Directed Therapy (HDT) is an adjunctive therapy where repurposed drugs, small molecules, vitamins, cytokines, and monoclonal antibodies are used to overcome the pathogen exploited pathways in the host. One of the HDTs, i.e. induction of autophagy is a highly regulated intracellular self-degradative process in which pathogens are sequestered in double-layered autophagosomes and targeted to the lysosome for degradation. Apart from the pathogen clearance, autophagy involves the release of nutrients during starvation, removal of damaged organelles and aggregated proteins, antigen presentation, tumor suppression, and anti-aging mechanisms. Xenophagy is a type of selective autophagy against microbes induced by ubiquitin receptors (p62/SQSTM1, NDP52, NBR1, OPTN, Parkin and Smurf proteins) after pathogen recognition. ULK1/2, Beclin-1, ATG5-ATG12-ATG16 L and LC-II-PE complexes along with two nutrient-sensing protein complexes, mTOR and AMPK activate autophagy mechanisms to limit infection. Pattern Recognition Receptors (PRRs) such as TLR2, recognize lipopolysaccharide (LPS) of MTB and triggers vitamin D₃ activating enzymes. Activated vitamin D₃ induces the synthesis of antimicrobial peptide, LL-37, which further enhances xenophagy. Apart from vitamin D, few micronutrients such as zinc and iron also regulate autophagy. In this review, we discuss current knowledge, advances and perspectives of autophagy against TB.

YdiV regulates Escherichia coli ferric uptake by manipulating the DNA-binding ability of Fur in a SlyD-dependent manner

Iron is essential for all bacteria. In most bacteria, intracellular iron homeostasis is tightly regulated by the ferric uptake regulator Fur. However, how Fur activates the iron-uptake system during iron deficiency is not fully elucidated. In this study, we found that YdiV, the flagella gene inhibitor, is involved in iron homeostasis in Escherichia coli. Iron deficiency triggers overexpression of YdiV. High levels of YdiV then transforms Fur into a novel form which does not bind DNA in a peptidyl-prolyl cis-trans isomerase SlyD dependent manner. Thus, the cooperation of YdiV, SlyD and Fur activates the gene expression of iron-uptake systems under conditions of iron deficiency. Bacterial invasion assays also demonstrated that both ydiV and slyD are necessary for the survival and growth of uropathogenic E. coli in bladder epithelial cells. This reveals a mechanism where YdiV not only represses flagella expression to make E. coli invisible to the host immune system, but it also promotes iron acquisition to help E. coli overcome host nutritional immunity.

Iron trafficking in patients with Indian Post kala-azar dermal leishmaniasis

Background

During infections involving intracellular pathogens, iron performs a double-edged function by providing the pathogen with nutrients, but also boosts the host’s antimicrobial arsenal. Although the role of iron has been described in visceral leishmaniasis, information regarding its status in the dermal sequel, Post Kala-azar Dermal Leishmaniasis (PKDL) remains limited. Accordingly, this study aimed to establish the status of iron within monocytes/macrophages of PKDL cases.

Methodology/Principal findings

The intramonocytic labile iron pool (LIP), status of CD163 (hemoglobin-haptoglobin scavenging receptor) and CD71 (transferrin receptor, Tfr) were evaluated within CD14⁺ monocytes by flow cytometry, and soluble CD163 by ELISA. At the lesional sites, Fe³⁺ status was evaluated by Prussian blue staining, parasite load by qPCR, while the mRNA expression of Tfr (TfR1/CD71), CD163, divalent metal transporter-1 (DMT-1), Lipocalin-2 (Lcn-2), Heme-oxygenase-1 (HO-1), Ferritin, Natural resistance-associated macrophage protein (NRAMP-1) and Ferroportin (Fpn-1) was evaluated by droplet digital PCR. Circulating monocytes demonstrated elevated levels of CD71, CD163 and soluble CD163, which corroborated with an enhanced lesional mRNA expression of TfR, CD163, DMT1 and Lcn-2. Additionally, the LIP was raised along with an elevated mRNA expression of ferritin and HO-1, as also iron exporters NRAMP-1 and Fpn-1.

Conclusions/Significance

In monocytes/macrophages of PKDL cases, enhancement of the iron influx gateways (TfR, CD163, DMT-1 and Lcn-2) possibly accounted for the enhanced LIP. However, enhancement of the iron exporters (NRAMP-1 and Fpn-1) defied the classical Ferritin^low/Ferroportin^high phenotype of alternatively activated macrophages. The creation of such a pro-parasitic environment suggests incorporation of chemotherapeutic strategies wherein the availability of iron to the parasite can be restricted.

Post kala-azar dermal leishmaniasis (PKDL), a dermal sequel of Visceral Leishmaniasis (VL) is caused by the digenetic protozoan parasite Leishmania donovani. The parasite infects humans and replicates intracellularly within macrophages, cells normally engaged in protecting the host from pathogens. Iron plays a crucial role in microbes and mammalian cells, being needed by the former for its growth and survival, while the latter uses it for activation of the immune system by facilitating generation of reactive oxygen species. Therefore, the availability of iron needs to be tightly regulated to ensure its accessibility for core biological functions, and yet prevent its utilization by intracellular pathogens. Here we investigated the status of intra-macrophage iron along with expression of its transporters in patients with PKDL. Our study suggests that within monocytes/macrophages there is an enhanced entry of iron via the upregulation of CD71 and CD163 that translates into an enhanced labile iron pool and Ferritin. However, the concomitant increase in expression of iron exporters NRAMP-1 and Fpn-1 suggested the host’s attempt to deny the pathogen access to iron. This Ferritin^high/Ferroportin^high phenotype was in contrast to the conventional Ferritin^low/Ferroportin^high phenotype present in alternatively activated M2 macrophages. Taken together, the control of iron homeostasis is one of the contributors in the host-pathogen interplay as it influences the course of an infectious disease by favouring either the mammalian host or the invading pathogen.

The Role of Iron Regulation in Immunometabolism and Immune-Related Disease

Immunometabolism explores how the intracellular metabolic pathways in immune cells can regulate their function under different micro-environmental and (patho-)-physiological conditions (Pearce, 2010; Buck et al., 2015; O'Neill and Pearce, 2016). In the last decade great advances have been made in studying and manipulating metabolic programs in immune cells. Immunometabolism has primarily focused on glycolysis, the TCA cycle and oxidative phosphorylation (OXPHOS) as well as free fatty acid synthesis and oxidation. These pathways are important for providing the energy needs of cell growth, membrane rigidity, cytokine production and proliferation. In this review, we will however, highlight the specific role of iron metabolism at the cellular and organismal level, as well as how the bioavailability of this metal orchestrates complex metabolic programs in immune cell homeostasis and inflammation. We will also discuss how dysregulation of iron metabolism contributes to alterations in the immune system and how these novel insights into iron regulation can be targeted to metabolically manipulate immune cell function under pathophysiological conditions, providing new therapeutic opportunities for autoimmunity and cancer.

Host inflammatory responses to intracellular invaders: Review study

As soon as a pathogen invades through the physical barriers of its corresponding host, host mounts a series of protective immune response to get rid of the invading pathogen. Host's pattern recognition receptors (PRR), localized at the cellular surface, cytoplasm and also in the nucleus; recognises pathogen associated molecular patterns (PAMPs) and plays crucial role in directing the immune response to be specific. Inflammatory responses are among the earliest strategies to tackle the pathogen by the host and are tightly regulated by multiple molecular pathways. Inflammasomes are multi-subunit protein complex consisting of a receptor molecule viz. NLRP3, an adaptor molecule- Apoptosis-associated speck-like protein containing a CARD (ASC) and an executioner caspase. Upon infection and/or injury; inflammasome components assemble and oligomerizes leading to the auto cleavage of the pro-caspase-1 to its active form. The activated caspase-1 cleaves immature form of the pro-inflammatory cytokines to their mature form e.g. IL1-β and IL-18 which mount inflammatory response. Moreover, C-terminal end of the Gasdermin D molecule is also cleaved by the caspase-1. The activated N-terminal Gasdermin D molecule form pores in the infected cells leading to their pyroptosis. Hence, inflammasomes drive inflammation during infection and controls the establishment of the pathogen by mounting inflammatory response and activation of the pyroptotic cell death.

Autophagy in intracellular bacterial infection

Autophagy is a conserved intracellular degradation process enclosing the bulk of cytosolic components for lysosomal degradation to maintain cellular homeostasis. Accumulating evidences showed that a specialized form of autophagy, known as xenophagy, could serve as an innate immune response to defend against pathogens invading inside the host cells. Correspondingly, infectious pathogens have developed a variety of strategies to disarm xenophagy, leading to a prolonged and persistent intracellular colonization. In this review, we first summarize the current knowledge about the general mechanisms of intracellular bacterial infections and xenophagy. We then focus on the ongoing battle between these two processes.

Integrating Genomic and Morphological Approaches in Fish Pathology Research: The Case of Turbot (Scophthalmus maximus) Enteromyxosis

Enteromyxosis, caused by Enteromyxum scophthalmi, is one of the most devastating diseases stemming from myxozoan parasites in turbot (Scophthalmus maximus L.), being a limiting factor for its production. The disease develops as a cachectic syndrome, associated to catarrhal enteritis and leukocytic depletion, with morbidity and mortality rates usually reaching 100%. To date, no effective treatment exists and there are different unknown issues concerning its pathogenesis. The gross and microscopic lesions associated to enteromyxosis have been thoroughly described, and several morphopathological studies have been carried out to elucidate the mechanisms of this host-parasite interaction. More recently, efforts have been focused on a multidisciplinary approach, combining histopathology and transcriptome analysis, which has provided significant advances in the understanding of the pathogenesis of this parasitosis. RNA-Seq technology was applied at early and advanced stages of the disease on fishes histologically evaluated and classified based on their lesional degree. In the same way, the transcriptomic data were analyzed in relation to the morphopathological picture and the course of the disease. In this paper, a comprehensive review of turbot enteromyxosis is presented, starting from the disease description up to the most novel information extracted by an integrated approach on the infection mechanisms and host response. Further, we discuss ongoing strategies toward a full understanding of host-pathogen interaction and the identification of suitable biomarkers for early diagnosis and disease management strategies.

Proteomic Profiling of Burkholderia thailandensis During Host Infection Using Bio-Orthogonal Noncanonical Amino Acid Tagging (BONCAT)

Burkholderia pseudomallei and B. mallei are the causative agents of melioidosis and glanders, respectively, and are often fatal to humans and animals. Owing to the high fatality rate, potential for spread by aerosolization, and the lack of efficacious therapeutics, B. pseudomallei and B. mallei are considered biothreat agents of concern. In this study, we investigate the proteome of Burkholderia thailandensis, a closely related surrogate for the two more virulent Burkholderia species, during infection of host cells, and compare to that of B. thailandensis in culture. Studying the proteome of Burkholderia spp. during infection is expected to reveal molecular mechanisms of intracellular survival and host immune evasion; but proteomic profiling of Burkholderia during host infection is challenging. Proteomic analyses of host-associated bacteria are typically hindered by the overwhelming host protein content recovered from infected cultures. To address this problem, we have applied bio-orthogonal noncanonical amino acid tagging (BONCAT) to B. thailandensis, enabling the enrichment of newly expressed bacterial proteins from virtually any growth condition, including host cell infection. In this study, we show that B. thailandensis proteins were selectively labeled and efficiently enriched from infected host cells using BONCAT. We also demonstrate that this method can be used to label bacteria in situ by fluorescent tagging. Finally, we present a global proteomic profile of B. thailandensis as it infects host cells and a list of proteins that are differentially regulated in infection conditions as compared to bacterial monoculture. Among the identified proteins are quorum sensing regulated genes as well as homologs to previously identified virulence factors. This method provides a powerful tool to study the molecular processes during Burkholderia infection, a much-needed addition to the Burkholderia molecular toolbox.

Iron-modulated virulence factors of Entamoeba histolytica

Entamoeba histolytica is a human parasite that causes amoebiasis, a disease that affects the colon and liver and is prevalent worldwide. This protozoan requires a high concentration of iron to survive and reproduce. Iron modulates the expression of parasite virulence factors, including hemoglobinases, hemoglobin-binding proteins and cysteine proteases, as well as proteins related to the amoebic cytoskeleton. This review summarizes the virulence factors that are affected by iron, resulting in upregulation or downregulation of E. histolytica genes. This review also discusses the functionality of iron in the mechanisms of pathogenesis.

Metabolic adaptation of intracellular bacteria and fungi to macrophages

The mature phagosome of macrophages is a hostile environment for the vast majority of phagocytosed microbes. In addition to active destruction of the engulfed microbes by antimicrobial compounds, restriction of essential nutrients in the phagosomal compartment contributes to microbial growth inhibition and killing. However, some pathogenic microorganisms have not only developed various strategies to efficiently withstand or counteract antimicrobial activities, but also to acquire nutrients within macrophages for intracellular replication. Successful intracellular pathogens are able to utilize host-derived amino acids, carbohydrates and lipids as well as trace metals and vitamins during intracellular growth. This requires sophisticated strategies such as phagosome modification or escape, efficient nutrient transporters and metabolic adaptation. In this review, we discuss the metabolic adaptation of facultative intracellular bacteria and fungi to the intracellular lifestyle inside macrophages.

Comparative Genomics of Sibling Species of Fonsecaea Associated with Human Chromoblastomycosis

Fonsecaea and Cladophialophora are genera of black yeast-like fungi harboring agents of a mutilating implantation disease in humans, along with strictly environmental species. The current hypothesis suggests that those species reside in somewhat adverse microhabitats, and pathogenic siblings share virulence factors enabling survival in mammal tissue after coincidental inoculation driven by pathogenic adaptation. A comparative genomic analysis of environmental and pathogenic siblings of Fonsecaea and Cladophialophora was undertaken, including de novo assembly of F. erecta from plant material. The genome size of Fonsecaea species varied between 33.39 and 35.23 Mb, and the core genomes of those species comprises almost 70% of the genes. Expansions of protein domains such as glyoxalases and peptidases suggested ability for pathogenicity in clinical agents, while the use of nitrogen and degradation of phenolic compounds was enriched in environmental species. The similarity of carbohydrate-active vs. protein-degrading enzymes associated with the occurrence of virulence factors suggested a general tolerance to extreme conditions, which might explain the opportunistic tendency of Fonsecaea sibling species. Virulence was tested in the Galleria mellonella model and immunological assays were performed in order to support this hypothesis. Larvae infected by environmental F. erecta had a lower survival. Fungal macrophage murine co-culture showed that F. erecta induced high levels of TNF-α contributing to macrophage activation that could increase the ability to control intracellular fungal growth although hyphal death were not observed, suggesting a higher level of extremotolerance of environmental species.

Lower incidence of respiratory infections among iron-deficient children in Kilimanjaro, Tanzania

Objective: We posited a trade-off in iron nutrition, with iron deficiency decreasing risk for infection by depriving infectious agents of iron while increasing risk for infection by compromising immune protection. We described associations between iron deficiency and prevalent and incident infectious disease episodes and cell-mediated immunity (CMI) among 283 children in Kilimanjaro, Tanzania.

Methodology: Whole blood specimens were evaluated for hemoglobin and dried blood spots (DBS) were evaluated for biomarkers of iron deficiency (transferrin receptor) and inflammation (C-reactive protein and α₁-acid glycoprotein). Prevalent and incident infectious disease episodes were identified by physician’s diagnosis. CMI was evaluated as delayed-type hypersensitivity to Candida albicans (DTH-Candida). Associations between iron status and elevated inflammation, prevalent infectious disease episodes and DTH-Candida were described with logistic regression models; associations between iron status and incident infectious disease episodes were described with Cox proportional hazards models.

Results: Elevated inflammation and diagnosed infectious diseases were more common among children with iron-deficiency anemia (IDA, severe iron deficiency), but not significantly so. The incidence of infectious disease was lowest among children with moderate iron deficiency (iron-deficient erythropoiesis, IDE); this pattern was most apparent for respiratory infections (aHR: 0.24; p: 0.030). DTH-Candida was not compromised among children with any degree of iron deficiency.

Conclusions and implications: We observed no adverse effect of iron deficiency on CMI, but did observe patterns consistent with the hypothesis that moderate iron deficiency protects against respiratory infections and may represent a nutritional adaptation to infectious disease. This suggests that interventions targeting iron deficiency should be coupled with effective infectious disease control measures.

Iron Metabolism and the Inflammatory Response

Iron (Fe) is essential to almost all organisms, as required by cells to satisfy metabolic needs and accomplish specialized functions. Its ability to exchange electrons between different substrates, however, renders it potentially toxic. Fine tune-mechanisms are necessary to maintain Fe homeostasis and, as such, to prevent its participation into the Fenton reaction and generation of oxidative stress. These are particularly important in the context of inflammation/infection, where restricting Fe availability to invading pathogens is one, if not, the main host defense strategy against microbial growth. The ability of Fe to modulate several aspects of the immune response is associated with a number of "costs" and "benefits", some of which have been described in this review. © 2017 IUBMB Life, 69(6):442-450, 2017.

FmvB: A Francisella tularensis Magnesium-Responsive Outer Membrane Protein that Plays a Role in Virulence

Francisella tularensis is the causative agent of the lethal disease tularemia. Despite decades of research, little is understood about why F. tularensis is so virulent. Bacterial outer membrane proteins (OMPs) are involved in various virulence processes, including protein secretion, host cell attachment, and intracellular survival. Many pathogenic bacteria require metals for intracellular survival and OMPs often play important roles in metal uptake. Previous studies identified three F. tularensis OMPs that play roles in iron acquisition. In this study, we examined two previously uncharacterized proteins, FTT0267 (named fmvA, for Francisellametal and virulence) and FTT0602c (fmvB), which are homologs of the previously studied F. tularensis iron acquisition genes and are predicted OMPs. To study the potential roles of FmvA and FmvB in metal acquisition and virulence, we first examined fmvA and fmvB expression following pulmonary infection of mice, finding that fmvB was upregulated up to 5-fold during F. tularensis infection of mice. Despite sequence homology to previously-characterized iron-acquisition genes, FmvA and FmvB do not appear to be involved iron uptake, as neither fmvA nor fmvB were upregulated in iron-limiting media and neither ΔfmvA nor ΔfmvB exhibited growth defects in iron limitation. However, when other metals were examined in this study, magnesium-limitation significantly induced fmvB expression, ΔfmvB was found to express significantly higher levels of lipopolysaccharide (LPS) in magnesium-limiting medium, and increased numbers of surface protrusions were observed on ΔfmvB in magnesium-limiting medium, compared to wild-type F. tularensis grown in magnesium-limiting medium. RNA sequencing analysis of ΔfmvB revealed the potential mechanism for increased LPS expression, as LPS synthesis genes kdtA and wbtA were significantly upregulated in ΔfmvB, compared with wild-type F. tularensis. To provide further evidence for the potential role of FmvB in magnesium uptake, we demonstrated that FmvB was outer membrane-localized. Finally, ΔfmvB was found to be attenuated in mice and cytokine analyses revealed that ΔfmvB-infected mice produced lower levels of pro-inflammatory cytokines, including GM-CSF, IL-3, and IL-10, compared with mice infected with wild-type F. tularensis. Taken together, although the function of FmvA remains unknown, FmvB appears to play a role in magnesium uptake and F. tularensis virulence. These results may provide new insights into the importance of magnesium for intracellular pathogens.

RNA-seq analysis of early enteromyxosis in turbot (Scophthalmus maximus): new insights into parasite invasion and immune evasion strategies

Enteromyxum scophthalmi, an intestinal myxozoan parasite, is the causative agent of a threatening disease for turbot (Scophthalmus maximus, L.) aquaculture. The colonisation of the digestive tract by this parasite leads to a cachectic syndrome associated with high morbidity and mortality rates. This myxosporidiosis has a long pre-patent period and the first detectable clinical and histopathological changes are subtle. The pathogenic mechanisms acting in the early stages of infection are still far from being fully understood. Further information on the host-parasite interaction is needed to assist in finding efficient preventive and therapeutic measures. Here, a RNA-seq-based transcriptome analysis of head kidney, spleen and pyloric caeca from experimentally-infected and control turbot was performed. Only infected fish with early signs of infection, determined by histopathology and immunohistochemical detection of E. scophthalmi, were selected. The RNA-seq analysis revealed, as expected, less intense transcriptomic changes than those previously found during later stages of the disease. Several genes involved in IFN-related pathways were up-regulated in the three organs, suggesting that the IFN-mediated immune response plays a main role in this phase of the disease. Interestingly, an opposite expression pattern had been found in a previous study on severely infected turbot. In addition, possible strategies for immune system evasion were suggested by the down-regulation of different genes encoding complement components and acute phase proteins. At the site of infection (pyloric caeca), modulation of genes related to different structural proteins was detected and the expression profile indicated the inhibition of cell proliferation and differentiation. These transcriptomic changes provide indications regarding the mechanisms of parasite attachment to and invasion of the host. The current results contribute to a better knowledge of the events that characterise the early stages of turbot enteromyxosis and provide valuable information to identify molecular markers for early detection and control of this important parasitosis.