Identification of cell-binding adhesins of Leptospira interrogans

Evaluation of binding activities of a putative lipoprotein LIC_13355 of Leptospira spp

Pathogenic Leptospira is the etiological cause of the zoonotic life-threatening infection called leptospirosis. The disease is spread worldwide with higher risk in tropical regions. Although leptospirosis represents a burden to the health of humans and animals, the pathogenic mechanisms of Leptospira infection are yet to be clarified. Leptospirosis infection is multifactorial, involving functionally redundant proteins with the capability to invade, disseminate, and escape the host's immune response. In this work, we describe a putative lipoprotein encoded by the gene LIC_13355, genome annotated as hypothetical of unknown function. The coding sequence is conserved among pathogenic Leptospira spp. with high percentage of coverage and identity. The recombinant protein, rLIC_13355, was expressed in Escherichia coli host system in its insoluble form. The circular dichroism spectrum of the refolded protein showed it containing a mixture of secondary structures. rLIC_13355 interacts with extracellular matrix (ECM) component laminin and binds plasminogen (PLG), generating plasmin (PLA), thus possibly participating during the adhesion and dissemination processes. The rLIC_13355 has the ability to interact with Ea.hy926 and HMEC-1 endothelial cells either in monolayer or suspension. The binding of rLIC_13355 with monolayer cells is dose-dependent on protein concentration. Taken together, our data suggest that this is presumably an adhesion lipoprotein that may play diverse roles in host-Leptospira interactions by mediating the interaction with host components and with endothelial cell.

Cleavage of cell junction proteins as a host invasion strategy in leptospirosis

Infection and invasion are the prerequisites for developing the disease symptoms in a host. While the probable mechanism of host invasion and pathogenesis is known in many pathogens, very little information is available on Leptospira invasion/pathogenesis. For causing systemic infection Leptospira must transmigrate across epithelial barriers, which is the most critical and challenging step. Extracellular and membrane-bound proteases play a crucial role in the invasion process. An extensive search for the proteins experimentally proven to be involved in the invasion process through cell junction cleavage in other pathogens has resulted in identifying 26 proteins. The similarity searches on the Leptospira genome for counterparts of these 26 pathogenesis-related proteins identified at least 12 probable coding sequences. The proteins were either extracellular or membrane-bound with a proteolytic domain to cleave the cell junction proteins. This review will emphasize our current understanding of the pathogenic aspects of host cell junction-pathogenic protein interactions involved in the invasion process. Further, potential candidate proteins with cell junction cleavage properties that may be exploited in the diagnostic/therapeutic aspects of leptospirosis will also be discussed. KEY POINTS: • The review focussed on the cell junction cleavage proteins in bacterial pathogenesis • Cell junction disruptors from Leptospira genome are identified using bioinformatics • The review provides insights into the therapeutic/diagnostic interventions possible.

A comprehensive in silico analysis of putative outer membrane and secretory hydrolases from the pathogenic Leptospira: Possible implications in pathogenesis

Outer surface/membrane and virulent secretory proteins are primarily crucial for pathogenesis. Secreted and outer membrane hydrolases of many pathogens play an important role in attenuating the host immune system. Leptospira expresses many such proteins, and few have been characterized to display various roles, including host immune evasion. However, identification, classification, characterization, and elucidation of the possible role of Leptospira's outer membrane and secretory hydrolases have yet to be explored. In the present study, we used bioinformatics tools to predict exported proteins from the pathogenic Leptospira proteome. Moreover, we focused on secretory and outer membrane putative hydrolases from the exported proteins to generate a deeper understanding. Our analysis yielded four putative outer/secretory hydrolases, LIC_10995, LIC_11183, LIC_11463, and LIC_12988, containing α/β hydrolase fold and displayed similarity with lipase motif. Moreover, their conservation analysis of the predicted hydrolases across the spectrum of different Leptospira species showed high clustering with the pathogenic species. Outer membrane and secretory proteins with lipolytic activity may have a role in pathogenesis. This is the first bioinformatics analysis of secretory and outer membrane α/β hydrolases from leptospiral species. However, experimental studies are indeed required to unravel this possibility.

Leptospira interrogans encodes a canonical BamA and three novel noNterm Omp85 outer membrane protein paralogs

The Omp85 family of outer membrane proteins are ubiquitously distributed among diderm bacteria and play essential roles in outer membrane (OM) biogenesis. The majority of Omp85 orthologs are bipartite and consist of a conserved OM-embedded 16-stranded beta-barrel and variable periplasmic functional domains. Here, we demonstrate that Leptospira interrogans encodes four distinct Omp85 proteins. The presumptive leptospiral BamA, LIC11623, contains a noncanonical POTRA4 periplasmic domain that is conserved across Leptospiraceae. The remaining three leptospiral Omp85 proteins, LIC12252, LIC12254 and LIC12258, contain conserved beta-barrels but lack periplasmic domains. Two of the three 'noNterm' Omp85-like proteins were upregulated by leptospires in urine from infected mice compared to in vitro and/or following cultivation within rat peritoneal cavities. Mice infected with a L. interrogans lic11254 transposon mutant shed tenfold fewer leptospires in their urine compared to mice infected with the wild-type parent. Analyses of pathogenic and saprophytic Leptospira spp. identified five groups of noNterm Omp85 paralogs, including one pathogen- and two saprophyte-specific groups. Expanding our analysis beyond Leptospira spp., we identified additional noNterm Omp85 orthologs in bacteria isolated from diverse environments, suggesting a potential role for these previously unrecognized noNterm Omp85 proteins in physiological adaptation to harsh conditions.

Leptospiral adhesins: from identification to future perspectives

Leptospirosis is a significant zoonosis worldwide, with disease severity ranging from a mild non-specific illness to multi-organ dysfunction and hemorrhage. The disease is caused by pathogenic bacteria of the genus Leptospira, which are classified into pathogenic and saprophytic clades. Bacterial binding to host molecules and cells, coordinated by adhesin proteins, is an important step in pathogenesis. While many leptospiral adhesins have been identified, the vast majority have not been characterized in vivo. Herein, we present an overview of the current methodologies and successes in identifying adhesins in Leptospira, including known biological roles in vivo. We will also identify and discuss potential areas for future research.

Host Cell Binding Mediated by Leptospira interrogans Adhesins

Leptospirosis is a neglected infectious disease with global impact on both humans and animals. The increase in urban development without sanitation planning is one of the main reasons for the disease spreading. The symptoms are similar to those of flu-like diseases, such as dengue, yellow fever, and malaria, which can result in a misleading clinical diagnosis. The characterization of host-pathogen interactions is important in the development of new vaccines, treatments, and diagnostics. However, the pathogenesis of leptospirosis is not well understood, and many gaps remain to be addressed. Here, we aimed to determine if Leptospira strains, virulent, culture-attenuated, and saprophytic, and the major outer membrane proteins OmpL37, OmpL1, LipL21, LipL41, and LipL46 are able to adhere to different endothelial, epithelial and fibroblast cell lines in vitro. We showed that virulent leptospires robustly bind to all cells compared to the culture-attenuated and saprophytic lines. The recombinant proteins exhibited certain adhesion, but only OmpL1 and LipL41 were able to bind to several cell lines, either in monolayer or in cell suspension. Blocking OmpL1 with polyclonal antibodies caused a decrease in bacterial binding to cells, contrasting with an increase observed when anti-LipL41 antibodies were used. The adhesion of OmpL1 to HMEC-1 and EA.hy926 was inhibited when cells were pre-incubated with collagen IV, suggesting that both compete for the same cell receptor. We present here for the first time the interaction of five leptospiral outer membrane proteins with several cell lines, and we conclude that LipL41 and OmpL1 may have an impact on leptospiral adhesion to mammalian cells and may mediate the colonization process in leptospiral pathogenesis.

Characterization of a virulence-modifying protein of Leptospira interrogans identified by shotgun phage display

Pathogenic species of Leptospira are etiologic agents of leptospirosis, an emerging zoonotic disease of worldwide extent and endemic in tropical regions. The growing number of identified leptospiral species sheds light to their genetic diversity and unique virulence mechanisms, many of them still remain unknown. Toxins and adhesins are important virulence factors in several pathogens, constituting promising antigens for the development of vaccines with cross-protection and long-lasting effect against leptospirosis. For this aim, we used the shotgun phage display technique to unravel new proteins with adhesive properties. A shotgun library was constructed using fragmented genomic DNA from Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130 and pG8SAET phagemid vector. Selection of phages bearing new possible cell-binding antigens was performed against VERO cells, using BRASIL biopanning methodology. Analysis of selected clones revealed the hypothetical protein LIC10778, a potentially exposed virulence factor that belongs to the virulence-modifying (VM) protein family (PF07598), composed of 13 members in the leptospiral strain Fiocruz L1-130. Prediction of LIC10778 tertiary structure indicates that the protein contains a cellular-binding domain (N-terminal portion) and an unknown domain of no assigned activity (C-terminal portion). The predicted N-terminal domain shared structural similarities with the cell-binding and internalization domain of toxins like Ricin and Abrin, as well as to the Community-Acquired Respiratory Distress Syndrome (CARDS) toxin in Mycoplasma pneumoniae. Interestingly, recombinant portions of the N-terminal region of LIC10778 protein showed binding to laminin, collagens I and IV, vitronectin, and plasma and cell fibronectins using overlay blotting technique, especially regarding the binding site identified by phage display. These data validate our preliminary phage display biopanning and support the predicted three-dimensional models of LIC10778 protein and other members of PF07598 protein family, confirming the identification of the N-terminal cell-binding domains that are similar to ricin-like toxins. Moreover, fluorescent fused proteins also confirmed that N-terminal region of LIC10778 is capable of binding to VERO and A549 cell lines, further highlighting its virulence role during host-pathogen interaction in leptospirosis probably mediated by its C-terminal domain. Indeed, recent results in the literature confirmed this assumption by demonstrating the cytotoxicity of a closely related PF07598 member.

Heterologous production of the adhesin LIC13411 from pathogenic Leptospira facilitates binding of non-pathogenic Leptospira in vitro and in vivo

Leptospirosis is an important cause of morbidity and mortality worldwide. Disease severity ranges from asymptomatic colonization to widespread hemorrhage and multiorgan dysfunction. The causative agents, Leptospira spp., are zoonotic Gram-negative spirochetes. One important step in pathogenesis is binding of bacterial adhesins to host components. Previously our laboratory identified two L. interrogans candidate adhesins, LIC11574 and LIC13411, that bind to VE-cadherin in vitro. In the current study, we demonstrate the ability of two strains of pathogenic L. interrogans to disrupt the localization of VE-cadherin, a protein important to maintaining inter-endothelial junctions. Purified MBP-LIC11574 and MBP-LIC13411 bind human dermal microvascular endothelial cells in a pattern reminiscent of VE-cadherin, but do not disrupt VE-cadherin localization. Genes encoding the candidate adhesins from pathogenic Leptospira were cloned in an overexpression vector and introduced into non-pathogenic L. biflexa, creating gain-of-function strains producing LIC11574 or LIC13411. Protein production and localization to the outer membrane were confirmed by Triton X-114 fractionation. Although these strains do not disrupt VE-cadherin localization, production of LIC13411 increases binding of non-pathogenic Leptospira to human endothelial cells and specifically to VE-cadherin. In a short-term murine model of infection, LIC13411 production led to increased burdens of the non-pathogen in the lung, liver, kidney, and bladder. These data confirm the role of LIC13411 as an adhesin in Leptospira spp. and implicate it in dissemination to multiple organs. Importantly, anti-adhesin therapy has been shown to have many benefits over classical antibiotics. Taken together, this work provides novel insight into the pathogenesis of Leptospira spp. and identifies LIC13411 as a potential prophylactic and therapeutic target.

Pulmonary haemorrhage as the earliest sign of severe leptospirosis in hamster model challenged with Leptospira interrogans strain HP358

Background

Severe leptospirosis is challenging as it could evolve rapidly and potentially fatal if appropriate management is not performed. An understanding of the progression and pathophysiology of Leptospira infection is important to determine the early changes that could be potentially used to predict the severe occurrence of leptospirosis. This study aimed to understand the kinetics pathogenesis of Leptospira interrogans strain HP358 in the hamster model and identify the early parameters that could be used as biomarkers to predict severe leptospirosis.

Methodology/Principal findings

Male Syrian hamsters were infected with Leptospira interrogans strain HP358 and euthanized after 24 hours, 3, 4, 5, 6 and 7 days post-infection. Blood, lungs, liver and kidneys were collected for leptospiral detection, haematology, serum biochemistry and differential expression of pro- and anti-inflammatory markers. Macroscopic and microscopic organ damages were investigated. Leptospira interrogans strain HP358 was highly pathogenic and killed hamsters within 6–7 days post-infection. Pulmonary haemorrhage and blood vessel congestion in organs were noticed as the earliest pathological changes. The damages in organs and changes in biochemistry value were preceded by changes in haematology and immune gene expression.

Conclusion/Significance

This study deciphered haemorrhage as the earliest manifestation of severe leptospirosis and high levels of IL-1β, CXCL10/IP-10, CCL3/MIP-α, neutrophils and low levels of lymphocytes and platelets serve as a cumulative panel of biomarkers in severe leptospirosis.

As the severe form of leptospirosis could progress rapidly and be potentially fatal if not treated earlier, deciphering the pathophysiology kinetics of infection is crucial to determine the parameters of disease severity. To understand this, we challenged hamsters with the highly virulent Leptospira interrogans strain HP358. Pulmonary haemorrhage was observed as the earliest pathological change followed by liver and kidneys damages. The increased expression of IL-1β, CXCL10/IP-10, CCL3/MIP-α, high neutrophils and low lymphocytes and platelets production observed in the present study indicate that these parameters could serve as a cumulative panel of biomarkers in severe leptospirosis.

A Review on Host-Leptospira Interactions: What We Know and Future Expectations

Leptospirosis is a widespread zoonosis caused by pathogenic Leptospira spp. It is considered a neglected infectious disease of human and veterinary concern. Our group has been investigating proteins annotated as hypothetical, predicted to be located on the leptospiral surface. Because of their location, these proteins may have the ability to interact with various host components, which could allow establishment of the infection. These proteins act as adherence factors by binding to host receptor molecules, such as the extracellular matrix (ECM) components laminin and glycosaminoglycans to help bacterial colonization. Leptospira also interacts with the host fibrinolytic system, which has been demonstrated to be a powerful tool for invasion mechanisms. The interaction with fibrinogen and thrombin has been shown to reduce fibrin clot formation. Additionally, the degradation of coagulation cascade components by secreted proteases or by acquired surface plasmin could also play a role in reducing clot formation, hence facilitating dissemination during infection. Interaction with host complement system regulators also plays a role in helping bacteria to evade the immune system, facilitating invasion. Interaction of Leptospira to cell receptors, such as cadherins, can contribute to investigate molecules that participate in virulence. To achieve a better understanding of the host-pathogen interaction, leptospiral mutagenesis tools have been developed and explored. This work presents several proteins that mediate binding to components of the ECM, plasma, components of the complement system and cells, to gather research achievements that can be helpful in better understanding the mechanisms of leptospiral-host interactions and discuss genetic manipulation for Leptospira spp. aimed at protein function validation.

Gamma Delta TCR and the WC1 Co-Receptor Interactions in Response to Leptospira Using Imaging Flow Cytometry and STORM

The WC1 cell surface family of molecules function as hybrid gamma delta (γδ) TCR co-receptors, augmenting cellular responses when cross-linked with the TCR, and as pattern recognition receptors, binding pathogens. It is known that following activation, key tyrosines are phosphorylated in the intracytoplasmic domains of WC1 molecules and that the cells fail to respond when WC1 is knocked down or, as shown here, when physically separated from the TCR. Based on these results we hypothesized that the colocalization of WC1 and TCR will occur following cellular activation thereby allowing signaling to ensue. We evaluated the spatio-temporal dynamics of their interaction using imaging flow cytometry and stochastic optical reconstruction microscopy. We found that in quiescent γδ T cells both WC1 and TCR existed in separate and spatially stable protein domains (protein islands) but after activation using Leptospira, our model system, that they concatenated. The association between WC1 and TCR was close enough for fluorescence resonance energy transfer. Prior to concatenating with the WC1 co-receptor, γδ T cells had clustering of TCR-CD3 complexes and exclusion of CD45. γδ T cells may individually express more than one variant of the WC1 family of molecules and we found that individual WC1 variants are clustered in separate protein islands in quiescent cells. However, the islands containing different variants merged following cell activation and before merging with the TCR islands. While WC1 was previously shown to bind Leptospira in solution, here we showed that Leptospira bound WC1 proteins on the surface of γδ T cells and that this could be blocked by anti-WC1 antibodies. In conclusion, γδ TCR, WC1 and Leptospira interact directly on the γδ T cell surface, further supporting the role of WC1 in γδ T cell pathogen recognition and cellular activation.

Crystal structure of Leptospira leucine-rich repeat 20 reveals a novel E-cadherin binding protein to induce NGAL expression in HK2 cells

Leptospirosis is the most common zoonotic disease caused by pathogenic Leptospira, which is classified into three groups according to virulence. Its pathogenic and intermediate species contain leucine-rich repeat (LRR) proteins that are rarely expressed in non-pathogenic strains. In this study, we presented the crystal structure of LSS_11580 (rLRR20) from pathogenic L. santarosai serovar Shermani. X-ray diffraction at a resolution of 1.99 Å revealed a horseshoe-shaped structure containing seven α-helices and five β-sheets. Affinity assays indicated that rLRR20 interacts with E-cadherin on the cell surface. Interestingly, its binds to the extracellular (EC) 1 domain in human epithelial (E)-cadherin, which is responsible for binding to another E-cadherin molecule in neighboring cells. Several charged residues on the concave face of LRR20 were predicted to interact with EC1 domain. In the affinity assays, these charged residues were replaced by alanine, and their affinities to E-cadherin were measured. Three vital residues and mutation variants of LRR20, namely D56A, E59A, and E123A, demonstrated significantly reduced affinity to E-cadherin compared with the control. Besides, we also demonstrated that rLRR20 induced the expression of neutrophil gelatinase-associated lipocalin (NGAL) in HK2 cells. The low ability of the three mutation variants to induce NGAL expression further demonstrates this induction. The present findings indicate that LRR20 from pathogenic Leptospira binds to E-cadherin and interacts with its EC1 domain. In addition, its induction of NGAL expression in HK2 cells is associated with acute kidney injury in human.

The interaction of two novel putative proteins of Leptospira interrogans with E-cadherin, plasminogen and complement components with potential role in bacterial infection

Leptospirosis is a worldwide zoonosis caused by pathogenic species of Leptospira. Leptospires are able to adhere to exposed extracellular matrix in injured tissues and, once in the bloodstream, can survive the attack of the immune system and spread to colonize target organs. In this work, we report that two novel putative proteins, coded by the genes LIC11711 and LIC12587 of L. interrogans serovar Copenhageni are conserved among pathogenic strains, and probably exposed in the bacterial surface. Soluble recombinant proteins were expressed in Escherichia coli, purified and characterized. Both recombinant proteins bound to laminin and E-cadherin, suggesting an initial adhesion function in host epithelial cells. The recombinant protein LIC11711 (rLIC11711) was able to capture plasminogen (PLG) from normal human serum and convert to enzymatically active plasmin (PLA), in the presence of PLG activator. rLIC12587 (recombinant protein LIC12587) displayed a dose dependent and saturable interaction with components C7, C8, and C9 of the complement system, reducing the bactericidal effect of the complement. Binding to C9 may have consequences such as C9 polymerization inhibition, interfering with the membrane attack complex formation. Blocking LIC11711 and LIC12587 on bacterial cells by the respective antiserum reduced leptospiral cell viability when exposed to normal human serum (NHS). Both recombinant proteins could be recognized by serum samples of confirmed leptospirosis, but not of unrelated diseases, suggesting that the native proteins are immunogenic and expressed during leptospirosis. Taken together, our data suggest that these proteins may have a role in leptospiral pathogenesis, participating in immune evasion strategies.

Role of Supramolecule ErpY-Like Lipoprotein of Leptospira in Thrombin-Catalyzed Fibrin Clot Inhibition and Binding to Complement Factors H and I, and Its Diagnostic Potential

Leptospirosis is one of the most widespread zoonoses caused by pathogenic Leptospira spp. In this study, we report that the LIC11966/ErpY-like lipoprotein is a surface-exposed outer membrane protein exclusively present in pathogenic species of Leptospira The recombinant ErpY (rErpY)-like protein is recognized by the immunoglobulins of confirmed leptospirosis sera of diverse hosts (human, bovine, and canine), suggesting the expression of the native leptospiral surface protein during infection. Circular dichroism of pure rErpY-like protein showed the secondary structural integrity to be uncompromised during the purification process. Analysis of the rErpY-like protein by native polyacrylamide gel electrophoresis, chemical cross-linking, dynamic light scattering, and field emission transmission electron microscopy demonstrated it undergoes supramolecular assembly. The rErpY-like protein can bind to diverse host extracellular matrices, and it presented a saturable and strong binding affinity (dissociation constant [K_D ] of 70.45 ± 4.13 nM) to fibrinogen, a central host plasma component involved in blood clotting. In the presence of the rErpY-like supramolecule, thrombin-catalyzed fibrin clot formation is inhibited up to 7%, implying its role in inhibiting blood coagulation during Leptospira infection. In addition, binding of the rErpY-like supramolecule to complement factors H and I suggests the protein also contributes to Leptospira evading innate host defense during infection by inactivating alternative complement pathways. This study reveals that rErpY-like protein is functionally active in the supramolecular state and performs moonlighting activity under the given in vitro conditions.

An extracellular Leptospira interrogans leucine-rich repeat protein binds human E- and VE-cadherins

Pathogenic Leptospira bacteria are the causative agents of leptospirosis, a zoonotic disease affecting animals and humans worldwide. These pathogenic species have the ability to rapidly cross host tissue barriers by a yet unknown mechanism. A comparative analysis of pathogens and saprophytes revealed a higher abundance of genes encoding proteins with leucine-rich repeat (LRR) domains in the genomes of pathogens. In other bacterial pathogens, proteins with LRR domains have been shown to be involved in mediating host cell attachment and invasion. One protein from the pathogenic species Leptospira interrogans, LIC10831, has been previously analysed via X-ray crystallography, with findings suggesting it may be an important bacterial adhesin. Herein we show that LIC10831 elicits an antibody response in infected animals, is actively secreted by the bacterium, and binds human E- and VE-cadherins. These results provide biochemical and cellular evidences of LRR protein-mediated host-pathogen interactions and identify a new multireceptor binding protein from this infectious Leptospira species.

Pathology and pathogenesis of human leptospirosis: a commented review

Leptospirosis is an acute bacterial septicemic febrile disease caused by pathogenic leptospires, which affect humans and animals in all parts of the world. Transmission can occur by direct contact with infected animals or, more commonly, through indirect contact with water or soil contaminated with urine from infected animals. Leptospires enter the body by penetrating mucous membranes or skin abrasions and disseminate through the hematogenic route. In humans, leptospirosis may cause a wide spectrum of symptoms. Most cases have a biphasic clinical presentation, which begins with the septicemic phase followed by immune manifestations. The severe forms of the disease may be life threatening with multisystem damage including renal failure, hepatic dysfunction, vascular damage, pulmonary hemorrhage and muscle lesions. In this review, we present and discuss the pathogenesis of the human disease and the mechanisms of cell membrane injuries, which occur mainly due to the presence of leptospires and/or their antigen/s in the host tissues.

Leptospirosis: Molecular trial path and immunopathogenesis correlated with dengue, malaria and mimetic hemorrhagic infections

Immuno-pathogenesis of leptospirosis can be recounted well by following its trail path from entry to exit, while inducing disastrous damages in various tissues of the host. Dysregulated, inappropriate and excessive immune responses are unanimously blamed in fatal leptospirosis. The inherent abilities of the pathogen and inabilities of the host were debated targeting the severity of the disease. Hemorrhagic manifestation through various mechanisms leading to a fatal end is observed when this disease is unattended. The similar vascular destructions and hemorrhage manifestations are noted in infections with different microbes in endemic areas. The simultaneous infection in a host with more than one pathogen or parasite is referred as the coinfection. Notably, common endemic infections such as leptospirosis, dengue, chikungunya, and malaria, harbor favorable environments to flourish in similar climates, which is aggregated with stagnated water and aggravated with the poor personal and environmental hygiene of the inhabitants. These factors aid the spread of pathogens and parasites to humans and potential vectors, eventually leading to outbreaks of public health relevance. Malaria, dengue and chikungunya need mosquitoes as vectors, in contrast with leptospirosis, which directly invades human, although the environmental bacterial load is maintained through other mammals, such as rodents. The more complicating issue is that infections by different pathogens exhibiting similar symptoms but require different treatment management. The current review explores different pathogens expressing specific surface proteins and their ability to bind with array of host proteins with or without immune response to enter into the host tissues and their ability to evade the host immune responses to invade and their affinity to certain tissues leading to the common squeal of hemorrhage. Furthermore, at the host level, the increased susceptibility and inability of the host to arrest the pathogens' and parasites' spread in different tissues, various cytokines accumulated to eradicate the microorganisms and their cellular interactions, the antibody dependent defense and the susceptibility of individual organs bringing the manifestation of the diseases were explored. Lastly, we provided a discussion on the immune trail path of pathogenesis from entry to exit to narrate the similarities and dissimilarities among various hemorrhagic fevers mentioned above, in order to outline future possibilities of prevention, diagnosis, and treatment of coinfections, with special reference to endemic areas.

Leptospira interrogans causes quantitative and morphological disturbances in adherens junctions and other biological groups of proteins in human endothelial cells

Pathogenic Leptospira transmits from animals to humans, causing the zoonotic life-threatening infection called leptospirosis. This infection is reported worldwide with higher risk in tropical regions. Symptoms of leptospirosis range from mild illness to severe illness such as liver damage, kidney failure, respiratory distress, meningitis, and fatal hemorrhagic disease. Invasive species of Leptospira rapidly disseminate to multiple tissues where this bacterium damages host endothelial cells, increasing vascular permeability. Despite the burden in humans and animals, the pathogenic mechanisms of Leptospira infection remain to be elucidated. The pathogenic leptospires adhere to endothelial cells and permeabilize endothelial barriers in vivo and in vitro. In this study, human endothelial cells were infected with the pathogenic L. interrogans serovar Copenhageni or the saprophyte L. biflexa serovar Patoc to investigate morphological changes and other distinctive phenotypes of host cell proteins by fluorescence microscopy. Among those analyzed, 17 proteins from five biological classes demonstrated distinctive phenotypes in morphology and/or signal intensity upon infection with Leptospira. The affected biological groups include: 1) extracellular matrix, 2) intercellular adhesion molecules and cell surface receptors, 3) intracellular proteins, 4) cell-cell junction proteins, and 5) a cytoskeletal protein. Infection with the pathogenic strain most profoundly disturbed the biological structures of adherens junctions (VE-cadherin and catenins) and actin filaments. Our data illuminate morphological disruptions and reduced signals of cell-cell junction proteins and filamentous actin in L. interrogans-infected endothelial cells. In addition, Leptospira infection, regardless of pathogenic status, influenced other host proteins belonging to multiple biological classes. Our data suggest that this zoonotic agent may damage endothelial cells via multiple cascades or pathways including endothelial barrier damage and inflammation, potentially leading to vascular hyperpermeability and severe illness in vivo. This work provides new insights into the pathophysiological mechanisms of Leptospira infection.

Multifunctional and Redundant Roles of Leptospira interrogans Proteins in Bacterial-Adhesion and fibrin clotting inhibition

Pathogenic Leptopira is the etiological agent of leptospirosis, the most widespread zoonotic infection in the world. The disease represents a major public health problem, especially in tropical countries. The present work focused on two hypothetical proteins of unknown function, encoded by the genes LIC13059 and LIC10879, and predicted to be surface-exposed proteins. The genes were cloned and the proteins expressed using E. coli as a host system. We report that the recombinant proteins interacted with extracellular matrix (ECM) laminin, in a dose-dependent fashion and are novel potential adhesins. The recombinant proteins were called Lsa25.6 (rLIC13059) and Lsa16 (rLIC10879), for Leptospiral surface adhesins, followed by the respective molecular masses. The proteins attached to plasminogen (PLG), generating plasmin, in the presence of PLG-activator uPA. Both proteins bind to fibrinogen (Fg), but only Lsa25.6 inhibited fibrin clotting by thrombin-catalyzed reaction. Moreover, Lsa16 interacts with the mammalian cell receptor E-cadherin, and could contribute to bacterial attachment to epithelial cells. The proteins were recognized by confirmed leptospirosis serum samples, suggesting that they are expressed during infection. The corresponding leptospiral proteins are surface exposed based on proteinase K accessibility assay, being LIC10879 most probably exposed in its dimer form. The data of this study extend the spectrum of surface-exposed proteins of L. interrogans and indicate a possible role of the originally annotated hypothetical proteins in infection processes.

Discovery of Novel Leptospirosis Vaccine Candidates Using Reverse and Structural Vaccinology

Leptospira spp. are diderm (two membranes) bacteria that infect mammals causing leptospirosis, a public health problem with global implications. Thousands of people die every year due to leptospirosis, especially in developing countries with tropical climates. Prophylaxis is difficult due to multiple factors, including the large number of asymptomatic hosts that transmit the bacteria, poor sanitation, increasing numbers of slum dwellers, and the lack of an effective vaccine. Several leptospiral recombinant antigens were evaluated as a replacement for the inactivated (bacterin) vaccine; however, success has been limited. A prospective vaccine candidate is likely to be a surface-related protein that can stimulate the host immune response to clear leptospires from blood and organs. In this study, a comprehensive bioinformatics approach based on reverse and structural vaccinology was applied toward the discovery of novel leptospiral vaccine candidates. The Leptospira interrogans serovar Copenhageni strain L1-130 genome was mined in silico for the enhanced identification of conserved β-barrel (βb) transmembrane proteins and outer membrane (OM) lipoproteins. Orthologs of the prospective vaccine candidates were screened in the genomes of 20 additional Leptospira spp. Three-dimensional structural models, with a high degree of confidence, were created for each of the surface-exposed proteins. Major histocompatibility complex II (MHC-II) epitopes were identified, and their locations were mapped on the structural models. A total of 18 βb transmembrane proteins and 8 OM lipoproteins were identified. These proteins were conserved among the pathogenic Leptospira spp. and were predicted to have epitopes for several variants of MHC-II receptors. A structural and functional analysis of the sequence of these surface proteins demonstrated that most βb transmembrane proteins seem to be TonB-dependent receptors associated with transportation. Other proteins identified included, e.g., TolC efflux pump proteins, a BamA-like OM component of the βb transmembrane protein assembly machinery, and the LptD-like LPS assembly protein. The structural mapping of the immunodominant epitopes identified the location of conserved, surface-exposed, immunogenic regions for each vaccine candidate. The proteins identified in this study are currently being evaluated for experimental evidence for their involvement in virulence, disease pathogenesis, and physiology, in addition to vaccine development.

A Universal Vaccine against Leptospirosis: Are We Going in the Right Direction?

Leptospirosis is the most widespread zoonosis in the world and a neglected tropical disease estimated to cause severe infection in more than one million people worldwide every year that can be combated by effective immunization. However, no significant progress has been made on the leptospirosis vaccine since the advent of bacterins over 100 years. Although protective against lethal infection, particularly in animals, bacterin-induced immunity is considered short term, serovar restricted, and the vaccine can cause serious side effects. The urgent need for a new vaccine has motivated several research groups to evaluate the protective immune response induced by recombinant vaccines. Significant protection has been reported with several promising outer membrane proteins, including LipL32 and the leptospiral immunoglobulin-like proteins. However, efficacy was variable and failed to induce a cross-protective response or sterile immunity among vaccinated animals. As hundreds of draft genomes of all known Leptospira species are now available, this should aid novel target discovery through reverse vaccinology (RV) and pangenomic studies. The identification of surface-exposed vaccine candidates that are highly conserved among infectious Leptospira spp. is a requirement for the development of a cross-protective universal vaccine. However, the lack of immune correlates is a major drawback to the application of RV to Leptospira genomes. In addition, as the protective immune response against leptospirosis is not fully understood, the rational use of adjuvants tends to be a process of trial and error. In this perspective, we discuss current advances, the pitfalls, and possible solutions for the development of a universal leptospirosis vaccine.

Leptospiral outer membrane protein LipL32 induces inflammation and kidney injury in zebrafish larvae

Leptospirosis is an often overlooked cause of acute kidney injury that can lead to multiple organ failure and even death. The principle protein that conserved in many pathogenic leptospires is the outer membrane protein LipL32. However, the role of LipL32 in the pathogenesis of renal injury in leptospirosis is not entirely clear. Here we studied the effects of LipL32 on the developing kidney in zebrafish larvae. Incubation of zebrafish larvae with Leptospira santarosai serovar Shermani induced acute tubular injury predominantly in the proximal pronephric ducts. Furthermore, microinjection of lipl32 mRNA or recombinant LipL32 protein into zebrafish larvae increased macrophage accumulation and disrupted the basolateral location of NA-K-ATPase in pronephric ducts. These changes led to substantial impairment of the pronephric kidney structure. We further demonstrated that morpholino knockdown of tlr2, but not tlr4, reduced the LipL32-induced leukocyte infiltration and kidney injury. These data demonstrate that LipL32 contributes to the renal pathology in leptospirosis and gives some clues to the potential virulence of LipL32. Our results support the use of zebrafish as a model organism for studying the disease mechanism of leptospiral infection. This model might permit the future exploration of the virulence and molecular pathways of different leptospiral outer membrane proteins.

Exploring the Secretomes of Microbes and Microbial Communities Using Filamentous Phage Display

Microbial surface and secreted proteins (the secretome) contain a large number of proteins that interact with other microbes, host and/or environment. These proteins are exported by the coordinated activities of the protein secretion machinery present in the cell. A group of bacteriophage, called filamentous phage, have the ability to hijack bacterial protein secretion machinery in order to amplify and assemble via a secretion-like process. This ability has been harnessed in the use of filamentous phage of Escherichia coli in biotechnology applications, including screening large libraries of variants for binding to “bait” of interest, from tissues in vivo to pure proteins or even inorganic substrates. In this review we discuss the roles of secretome proteins in pathogenic and non-pathogenic bacteria and corresponding secretion pathways. We describe the basics of phage display technology and its variants applied to discovery of bacterial proteins that are implicated in colonization of host tissues and pathogenesis, as well as vaccine candidates through filamentous phage display library screening. Secretome selection aided by next-generation sequence analysis was successfully applied for selective display of the secretome at a microbial community scale, the latter revealing the richness of secretome functions of interest and surprising versatility in filamentous phage display of secretome proteins from large number of Gram-negative as well as Gram-positive bacteria and archaea.

Analysis of LexA binding sites and transcriptomics in response to genotoxic stress in Leptospira interrogans

We determined the effects of DNA damage caused by ultraviolet radiation on gene expression in Leptospira interrogans using DNA microarrays. These data were integrated with DNA binding in vivo of LexA1, a regulator of the DNA damage response, assessed by chromatin immunoprecipitation and massively parallel DNA sequencing (ChIP-seq). In response to DNA damage, Leptospira induced expression of genes involved in DNA metabolism, in mobile genetic elements and defective prophages. The DNA repair genes involved in removal of photo-damage (e.g. nucleotide excision repair uvrABC, recombinases recBCD and resolvases ruvABC) were not induced. Genes involved in various metabolic pathways were down regulated, including genes involved in cell growth, RNA metabolism and the tricarboxylic acid cycle. From ChIP-seq data, we observed 24 LexA1 binding sites located throughout chromosome 1 and one binding site in chromosome 2. Expression of many, but not all, genes near those sites was increased following DNA damage. Binding sites were found as far as 550 bp upstream from the start codon, or 1 kb into the coding sequence. Our findings indicate that there is a shift in gene expression following DNA damage that represses genes involved in cell growth and virulence, and induces genes involved in mutagenesis and recombination.

What Makes a Bacterial Species Pathogenic?:Comparative Genomic Analysis of the Genus Leptospira

Leptospirosis, caused by spirochetes of the genus Leptospira, is a globally widespread, neglected and emerging zoonotic disease. While whole genome analysis of individual pathogenic, intermediately pathogenic and saprophytic Leptospira species has been reported, comprehensive cross-species genomic comparison of all known species of infectious and non-infectious Leptospira, with the goal of identifying genes related to pathogenesis and mammalian host adaptation, remains a key gap in the field. Infectious Leptospira, comprised of pathogenic and intermediately pathogenic Leptospira, evolutionarily diverged from non-infectious, saprophytic Leptospira, as demonstrated by the following computational biology analyses: 1) the definitive taxonomy and evolutionary relatedness among all known Leptospira species; 2) genomically-predicted metabolic reconstructions that indicate novel adaptation of infectious Leptospira to mammals, including sialic acid biosynthesis, pathogen-specific porphyrin metabolism and the first-time demonstration of cobalamin (B12) autotrophy as a bacterial virulence factor; 3) CRISPR/Cas systems demonstrated only to be present in pathogenic Leptospira, suggesting a potential mechanism for this clade's refractoriness to gene targeting; 4) finding Leptospira pathogen-specific specialized protein secretion systems; 5) novel virulence-related genes/gene families such as the Virulence Modifying (VM) (PF07598 paralogs) proteins and pathogen-specific adhesins; 6) discovery of novel, pathogen-specific protein modification and secretion mechanisms including unique lipoprotein signal peptide motifs, Sec-independent twin arginine protein secretion motifs, and the absence of certain canonical signal recognition particle proteins from all Leptospira; and 7) and demonstration of infectious Leptospira-specific signal-responsive gene expression, motility and chemotaxis systems. By identifying large scale changes in infectious (pathogenic and intermediately pathogenic) vs. non-infectious Leptospira, this work provides new insights into the evolution of a genus of bacterial pathogens. This work will be a comprehensive roadmap for understanding leptospirosis pathogenesis. More generally, it provides new insights into mechanisms by which bacterial pathogens adapt to mammalian hosts.

European consensus statement on leptospirosis in dogs and cats

Leptospirosis is a zoonotic disease with a worldwide distribution affecting most mammalian species. Clinical leptospirosis is common in dogs but appears to be rare in cats. Both dogs and cats, however, can shed leptospires in the urine. This is problematic as it can lead to exposure of humans. The control of leptospirosis, therefore, is important not only from an animal but also from a public health perspective. The aim of this consensus statement is to raise awareness of leptospirosis and to outline the current knowledge on the epidemiology, clinical features, diagnostic tools, prevention and treatment measures relevant to canine and feline leptospirosis in Europe.

Exploitation of plasmin(ogen) by bacterial pathogens of veterinary significance

The plasminogen (Plg) system plays an important homeostatic role in the degradation of fibrin clots, extracellular matrices and tissue barriers important for cellular migration, as well as the promotion of neurotransmitter release. Plg circulates in plasma at physiologically high concentrations (150-200μg ml(-1)) as an inactive proenzyme. Proteins enriched in lysine and other positively charged residues (histidine and arginine) as well as glycosaminoglycans and gangliosides bind Plg. The binding interaction initiates a structural adjustment to the bound Plg that facilitates cleavage by proteases (plasminogen activators tPA and uPA) that activate Plg to the active serine protease plasmin. Both pathogenic and commensal bacteria capture Plg onto their cell surface and promote its conversion to plasmin. Many microbial Plg-binding proteins have been described underpinning the importance this process plays in how bacteria interact with their hosts. Bacteria exploit the proteolytic capabilities of plasmin by (i) targeting the mammalian fibrinolytic system and degrading fibrin clots, (ii) remodeling the extracellular matrix and generating bioactive cleavage fragments of the ECM that influence signaling pathways, (iii) activating matrix metalloproteinases that assist in the destruction of tissue barriers and promote microbial metastasis and (iv) destroying immune effector molecules. There has been little focus on the exploitation of the fibrinolytic system by veterinary pathogens. Here we describe several pathogens of veterinary significance that possess adhesins that bind plasmin(ogen) onto their cell surface and promote its activation to plasmin. Cumulative data suggests that these attributes provide pathogenic and commensal bacteria with a means to colonize and persist within the host environment.

Evaluation of cell binding activities of Leptospira ECM adhesins

Pathogenic spirochetes of the genus Leptospira are the causative agents of leptospirosis, a zoonotic infection that occurs globally. The bacteria colonize the renal proximal tubules of many animals and are shed in the urine. Contact with the urine, or with water contaminated with the urine of infected animals can cause infection of new host animals, including humans. Mechanisms of colonization of the proximal tubule and other tissues are not known, but specific interactions between bacterial adhesins and host substrates are likely to be critical in this process. Several extracellular matrix (ECM) adhesins have been previously identified, but more recently, it has been shown that Leptospira bind more efficiently to cells than ECM. In this work, recombinant forms of five putative Leptospira ECM adhesins, namely LipL32, Loa22, OmpL1, p31/LipL45, and LenA were evaluated for binding to cells as well as an expanded variety of ECM components. Reproducible and significant adhesin activity was demonstrated only for OmpL1, which bound to both mammalian cell lines tested and to glycosaminoglycans (GAGs). While determination of biologically significant bacterial adhesion activity will require generation of site-directed mutant strains, our results suggest that OmpL1 is a strong candidate for future evaluation regarding the roles of the adhesin activity of the protein during L. interrogans infection.

Leptospirosis is the most widespread zoonotic infection in the world and represents a major public health problem, especially in tropical climates. The processes by which some Leptospira species cause infection, disease, and colonization of carrier animals remains poorly understood. Specific binding of Leptospira molecules and host molecules are likely important for infection and colonization. To identify Leptospira molecules that mediate attachment to host substrates, prior studies have evaluated Leptospira membrane proteins for binding to extracellular matrix (ECM) proteins. More recent data, however, show that Leptospira bind more efficiently to cells than to ECM. In search of adhesins mediating the latter activity, our study evaluated the direct cell binding activity of recombinant forms of a group of previously reported Leptospira ECM adhesins. Only one of these proteins, OmpL1, demonstrated reproducible direct cell binding activity. Further work will focus on identification of the mammalian receptor for OmpL1 and determining the biological significance of this activity during infection.