Bacterial metastasis: the host plasminogen system in bacterial invasion

Evaluation of immune effect to recombinant potential protective antigens of Mycoplasma ovipneumoniae in mice

Mycoplasma ovipneumoniae is a primary causative agent of pneumonia in ruminants, causing chronic non-progressive pneumonia in domestic sheep and goats, but leading to higher morbidity and mortality in bighorn sheep and wild small ruminants. This disease has become a widespread epidemic, resulting in significant losses to the sheep industry. In this study, we evaluated the immunogenicity and initial protective effects of four antigenic proteins of M. ovipneumoniae, namely Eno, EF-Tu, Ulad, and T4SS. These proteins were used to immunize BALB/c mice either individually or in a combination (rProteins group). The mice were intranasally infected with 109 CCU50/mL M. ovipneumoniae strain NJ01 twice, on days 28 and 30 after immunization. Among the four recombinant proteins, rEno demonstrated the most promising results in terms of inducing specific humoral and cellular immune responses. It also resulted in the lowest lung lesion scores and the lowest M. ovipneumoniae loads in the lungs and bronchoalveolar lavage fluid (BALF). Compared to the other three proteins, rEno provided superior protection. Furthermore, the rEno vaccine significantly reduced the inflammatory response in the lungs of mice, as evidenced by the evaluation of pro-inflammatory cytokines. The expression of IL-1β and NF-κB was significantly reduced, while the expression of IL-4 was significantly increased. In conclusion, the rEno vaccine elicited a favorable immunological response and conferred protection against M. ovipneumoniae. This finding presents a novel approach to controlling the global spread of this pathogen.

Hijacking of plasminogen by dengue virus: The kringle-4 and -5 domains of plasminogen binds synergistically to the domain I of envelope protein

Dengue fever is a serious health issue, particularly in tropical countries like Singapore. We have previously found that dengue virus (DENV) recruits human plasmin in blood meal to enhance the permeability of the mosquito midgut for infection. Here, using biolayer interferometry, we found that neither kringle-4 nor kringle-5 plasmin domains alone binds well to dengue virus. However, the domains together lead to a synergistic effect, with both kringle-4 and -5 domains required and sufficient for binding. Site-directed mutagenesis experiments showed that the N-terminal and C-terminal aspartic acid residues in the "DXD" acidic motifs of the kringle-4 and -5 domains likely have different roles when engaged with DENV. Hydrogen deuterium exchange mass spectrometry experiments on the plasmin:DENV complex led to the identification of two Lys-containing regions on domain I of the E-protein of DENV that are buried by plasmin and could be potential plasmin binding sites. These findings contradict with published literature that domain III of the DENV E-protein interacts with the kringle-1-3 domains of plasmin. We provide a plausible explanation for the observed discrepancies.

The Effect of Local Papaverine Use in an Experimental High-Risk Colonic Anastomosis Model: Reduced Inflammatory Findings and Less Necrosis

Objectives: To assess the impact of topical papaverine administration in complete and incomplete colonic anastomosis, by examining bursting pressure, hydroxyproline concentration, collagen content, inflammation levels, inflammatory cell infiltration, neoangiogenesis, and necrosis grades. Methods: We performed an experimental study on rats, in which they were divided into the following 4 groups of 16 subjects each. Group 1 [complete anastomosis (CA) without papaverine (CA -P) group], Group 2 [CA with papaverine (CA +P) group], Group 3 [incomplete anastomosis (ICA) without papaverine (ICA -P) group], and Group 4 [ICA with papaverine (ICA +P) group]. Results: The lymphocyte infiltration score of the ICA +P3 (day 3) group was significantly higher compared to the ICA -P3 group (p = 0.018). The median Ehrlich-Hunt score (p = 0.012), inflammation score (p = 0.026), and neutrophil infiltration score (p = 0.041) of the CA +P7 (day 7) group were significantly lower than the corresponding data of the CA -P7 group. Additionally, the necrosis score of the ICA +P7 group was significantly lower than that of the ICA -P7 group (p = 0.014). Conclusions: Data from the current study reveal that, although topical papaverine seems to suppress inflammation in anastomosis tissue and reduce necrosis at 7 days, definite conclusions regarding its impact on anastomotic leak cannot be drawn without further studies investigating anastomotic wound healing and anastomotic leak, preferably with both shorter- and longer-term evaluations.

Macrophage-to-osteocyte communication: Impact in a 3D in vitro implant-associated infection model

Macrophages and osteocytes are important regulators of inflammation, osteogenesis and osteoclastogenesis. However, their interactions under adverse conditions, such as biomaterial-associated infection (BAI) are not fully understood. We aimed to elucidate how factors released from macrophages modulate osteocyte responses in an in vitro indirect 3D co-culture model. Human monocyte-derived macrophages were cultured on etched titanium disks and activated with either IL-4 cytokine (anti-inflammatory M2 phenotype) or Staphylococcus aureus secreted virulence factors to simulate BAI (pro-inflammatory M1 phenotype). Primary osteocytes in collagen gels were then stimulated with conditioned media (CM) from these macrophages. The osteocyte response was analyzed by gene expression, protein secretion, and immunostaining. M1 phenotype macrophages were confirmed by IL-1β and TNF-α secretion, and M2 macrophages by ARG-1 and MRC-1.Osteocytes receiving M1 CM revealed bone inhibitory effects, denoted by reduced secretion of bone formation osteocalcin (BGLAP) and increased secretion of the bone inhibitory sclerostin (SOST). These osteocytes also downregulated the pro-mineralization gene PHEX and upregulated the anti-mineralization gene MEPE. Additionally, exhibited pro-osteoclastic potential by upregulating pro-osteoclastic gene RANKL expression. Nonetheless, M1-stimulated osteocytes expressed a higher level of the potent pro-osteogenic factor BMP-2 in parallel with the downregulation of the bone inhibitor genes DKK1 and SOST, suggesting a compensatory feedback mechanisms. Conversely, M2-stimulated osteocytes mainly upregulated anti-osteoclastic gene OPG expression, suggesting an anti-catabolic effect. Altogether, our findings demonstrate a strong communication between M1 macrophages and osteocytes under M1 (BAI)-simulated conditions, suggesting that the BAI adverse effects on osteoblastic and osteoclastic processes in vitro are partly mediated via this communication. STATEMENT OF SIGNIFICANCE: Biomaterial-associated infections are major challenges and the underlying mechanisms in the cellular interactions are missing, especially among the major cells from the inflammatory side (macrophages as the key cell in bacterial clearance) and the regenerative side (osteocyte as main regulator of bone). We evaluated the effect of macrophage polarization driven by the stimulation with bacterial virulence factors on the osteocyte function using an indirect co-culture model, hence mimicking the scenario of a biomaterial-associated infection. The results suggest that at least part of the adverse effects of biomaterial associated infection on osteoblastic and osteoclastic processes in vitro are mediated via macrophage-to-osteocyte communication.

The Pneumococcal Protein SufC Binds to Host Plasminogen and Promotes Its Conversion into Plasmin

Streptococcus pneumoniae causes otitis media, sinusitis, and serious diseases such as pneumonia and bacteremia. However, the in vivo dynamics of S. pneumoniae infections and disease severity are not fully understood. In this study, we investigated pneumococcal proteins detected in the bronchoalveolar lavage fluid of an S. pneumoniae-infected mouse, which were assumed to be expressed during infection. Analysis of three proteins with unknown infection-related functions revealed that recombinant Fe-S cluster assembly ATP-binding protein (SufC) binds to the host plasminogen and promotes its conversion into plasmin. SufC was detected in the bacterial cell-surface protein fraction, but it had no extracellular secretory signal. This study suggests that S. pneumoniae releases SufC extracellularly through LytA-dependent autolysis, binding to the bacterial cell surface and host plasminogen and promoting its conversion into plasmin. The recruitment of plasmin by S. pneumoniae is considered useful for bacterial survival and spread, and SufC is suggested to facilitate this process.

Probiotics in vaginal health

Bacterial vaginosis, a type of vaginal inflammation, can be considered the main reason for abnormal discharges of the vagina and vaginal dysbiosis during reproductive years. Epidemiological investigations of females suffering from vaginitis demonstrated that at least 30% to 50% of all women had Bacterial vaginosis (BV). One of the fields of treatment is the use of probiotics, probiotics are commonly defined as viable microorganisms (yeasts or bacteria) that can positively affect the health of their hosts. They are used in foods, notably fermented milk products, and medicine-related products. The development of new probiotic strains is aimed at more active advantageous organisms. Lactobacillus species are the dominant bacteria in a normal vagina that can decrease the pH of the vagina by the production of lactic acid. A number of lactobacilli types can produce hydrogen peroxide as well. The presence of hydrogen peroxide-induced low pH can prevent the growth of several other microorganisms. The vaginal flora of BV cases can modify by replacing the Lactobacillus species with a high density of anaerobic bacteria (i.e. Mobiluncus sp. Bacteroides sp.), Mycoplasma hominis, and Gardnerella vaginalis. More vaginal infections are treated with medications, while there is a possibility of recurrence and chronic infection because of the adverse effects on the indigenous lactobacilli. Probiotics and prebiotics have shown capacities for optimizing, maintaining, and restoring the vaginal microflora. Therefore, biotherapeutics can offer alternative approaches to reduce infections of the vagina and thus promote consumers' health.

New understanding of gut microbiota and colorectal anastomosis leak: A collaborative review of the current concepts

Anastomotic leak (AL) is a life-threatening postoperative complication following colorectal surgery, which has not decreased over time. Until now, no specific risk factors or surgical technique could be targeted to improve anastomotic healing. In the past decade, gut microbiota dysbiosis has been recognized to contribute to AL, but the exact effects are still vague. In this context, interpretation of the mechanisms underlying how the gut microbiota contributes to AL is significant for improving patients' outcomes. This review concentrates on novel findings to explain how the gut microbiota of patients with AL are altered, how the AL-specific pathogen colonizes and is enriched on the anastomosis site, and how these pathogens conduct their tissue breakdown effects. We build up a framework between the gut microbiota and AL on three levels. Firstly, factors that shape the gut microbiota profiles in patients who developed AL after colorectal surgery include preoperative intervention and surgical factors. Secondly, AL-specific pathogenic or collagenase bacteria adhere to the intestinal mucosa and defend against host clearance, including the interaction between bacterial adhesion and host extracellular matrix (ECM), the biofilm formation, and the weakened host commercial bacterial resistance. Thirdly, we interpret the potential mechanisms of pathogen-induced poor anastomotic healing.

The Mycoplasma spp. ‘Releasome’: A New Concept for a Long-Known Phenomenon

The bacterial secretome comprises polypeptides expressed at the cell surface or released into the extracellular environment as well as the corresponding secretion machineries. Despite their reduced coding capacities, Mycoplasma spp. are able to produce and release several components into their environment, including polypeptides, exopolysaccharides and extracellular vesicles. Technical difficulties in purifying these elements from the complex broth media used to grow mycoplasmas have recently been overcome by optimizing growth conditions and switching to chemically defined culture media. However, the secretion pathways responsible for the release of these structurally varied elements are still poorly described in mycoplasmas. We propose the use of the term ‘releasome,’ instead of secretome, to refer to molecules released by mycoplasmas into their environment. The aim of this review is to more precisely delineate the elements that should be considered part of the mycoplasmal releasome and their role in the interplay of mycoplasmas with host cells and tissues.

A multifunctional enolase mediates cytoadhesion and interaction with host plasminogen and fibronectin in Mycoplasma hyorhinis

Mycoplasma hyorhinis may cause systemic inflammation of pigs, typically polyserositis and arthritis, and is also associated with several types of human cancer. However, the pathogenesis of M. hyorhinis colonizing and breaching the respiratory barrier to establish systemic infection is poorly understood. Glycolytic enzymes are important moonlighting proteins and virulence-related factors in various bacteria. In this study, we investigated the functions of a glycolytic critical enzyme, enolase in the infection and systemic spread of M. hyorhinis. Bacterial surface localization of enolase was confirmed by flow cytometry and colony hybridization assay. Recombinant M. hyorhinis enolase (rEno) was found to adhere to pig kidney (PK-15) cells, and anti-rEno serum significantly decreased adherence. The enzyme was also found to bind host plasminogen and fibronectin, and interactions were specific and strong, with dissociation constant (K_D) values of 1.4 nM and 14.3 nM, respectively, from surface plasmon resonance analysis. Activation of rEno-bound plasminogen was confirmed by its ability to hydrolyze plasmin-specific substrates and to degrade a reconstituted extracellular matrix. To explore key sites during these interactions, C-terminal lysine residues of enolase were replaced with leucine, and the resulting single-site and double-site mutants show significantly reduced interaction with plasminogen in far-Western blotting and surface plasmon resonance tests. The binding affinities of all mutants to fibronectin were reduced as well. Collectively, these results imply that enolase moonlights as an important adhesin of M. hyorhinis, and interacts with plasminogen and fibronectin. The two lysine residues in the C-terminus are important binding sites for its multiple binding activities.

DnaK Functions as a Moonlighting Protein on the Surface of Mycoplasma hyorhinis Cells

Mycoplasma hyorhinis is a common pathogen of swine and is also associated with various human tumors. It causes systemic inflammation, typically polyserositis and polyarthritis, in some infected pigs. However, the pathogenic mechanism of M. hyorhinis remains unclear. DnaK is a highly conserved protein belonging to the heat-shock protein 70 family of molecular chaperones, which plays important roles as a moonlighting protein in various bacteria. In the present study, we identified the surface exposure of M. hyorhinis DnaK. Two virulent strains expressed more DnaK on their surface than the avirulent strain. Thereafter, the potential moonlighting functions of DnaK were investigated. Recombinant M. hyorhinis DnaK (rMhr-DnaK) was found to be able to adhere to swine PK-15 cells and human NCI-H292 cells. It also bound to four extracellular matrix components-fibronectin, laminin, type IV collagen, and vitronectin-in a dose-dependent manner. ELISA demonstrated an interaction between rMhr-DnaK and plasminogen, which was significantly inhibited by a lysine analog, ε-aminocaproic acid. rMhr-DnaK-bound plasminogen was activated by tissue-type plasminogen activator (tPA), and the addition of rMhr-DnaK significantly enhanced the activation. Finally, a DnaK-specific antibody was detected in the serum of pigs immunized with inactivated vaccines, which indicated good immunogenicity of it. In summary, our findings imply that DnaK is an important multifunctional moonlighting protein in M. hyorhinis and likely participates extensively in the infection and pathogenesis processes of M. hyorhinis.

Enolase of Staphylococcus lugdunensis Is a Surface-Exposed Moonlighting Protein That Binds to Extracellular Matrix and the Plasminogen/Plasmin System

The coagulase-negative staphylococcal (CoNS) species Staphylococcus lugdunensis is unique in causing serious infections in humans that resemble those of Staphylococcus aureus rather than those of other CoNS species. The colonization and invasion of host tissue presupposes the presence of adherence factors, but only a few proteins mediating adhesion of S. lugdunensis to biotic surfaces are known yet. Here, we report on the functionality of the S. lugdunensis enolase (SlEno), which performs two distinct roles, first, as the metabolic enzyme of the glycolysis, and second, as an adherence factor to the extracellular matrix (ECM) of cells. Phylogenetic analyses of the SlEno confirmed their high conservation to enolases of other species and revealed a closer relationship to Staphylococcus epidermidis than to S. aureus. Using matrix-assisted laser desorption/ionization time of flight mass spectrometry and Western blot experiments, we identified SlEno to be located in the cytoplasm as well as on the cell surface of S. lugdunensis. Recombinantly generated and surface-associated SlEno showed the usual enolase activity by catalyzing the conversion of 2-phosphoglycerate to phosphoenolpyruvate but, in addition, also displayed strong binding to immobilized laminin, fibronectin, fibrinogen, and collagen type IV in a dose-dependent manner. We also showed a strong binding of SlEno to plasminogen (Plg) and observed a tissue plasminogen activator (tPA)-dependent conversion of Plg to plasmin (Pln) whereby the Plg activation significantly increased in the presence of SlEno. This interaction might be dependent on lysines of the SlEno protein as binding to Plg was inhibited by ε-aminocaproic acid. Furthermore, the enhanced activation of the Plg/Pln system by SlEno enabled S. lugdunensis to migrate through a fibrin matrix. This migration was about 10-fold higher than without exogenously added SlEno. Finally, we observed a significantly higher clearance of S. lugdunensis by freshly prepared granulocytes and in the presence of anti-SlEno antibodies. In conclusion, these data demonstrate for the first time a moonlighting function of the S. lugdunensis enolase, which is an underrated virulence factor for colonization and invasion of tissues. Hence, SlEno might be a potential vaccine candidate to prevent severe infections caused by this pathogen.

Multifunctional Fructose 1,6-Bisphosphate Aldolase as a Therapeutic Target

Fructose 1,6-bisphosphate aldolase is a ubiquitous cytosolic enzyme that catalyzes the fourth step of glycolysis. Aldolases are classified into three groups: Class-I, Class-IA, and Class-II; all classes share similar structural features but low amino acid identity. Apart from their conserved role in carbohydrate metabolism, aldolases have been reported to perform numerous non-enzymatic functions. Here we review the myriad "moonlighting" functions of this classical enzyme, many of which are centered on its ability to bind to an array of partner proteins that impact cellular scaffolding, signaling, transcription, and motility. In addition to the cytosolic location, aldolase has been found the extracellular surface of several pathogenic bacteria, fungi, protozoans, and metazoans. In the extracellular space, the enzyme has been reported to perform virulence-enhancing moonlighting functions e.g., plasminogen binding, host cell adhesion, and immunomodulation. Aldolase's importance has made it both a drug target and vaccine candidate. In this review, we note the several inhibitors that have been synthesized with high specificity for the aldolases of pathogens and cancer cells and have been shown to inhibit classical enzyme activity and moonlighting functions. We also review the many trials in which recombinant aldolases have been used as vaccine targets against a wide variety of pathogenic organisms including bacteria, fungi, and metazoan parasites. Most of such trials generated significant protection from challenge infection, correlated with antigen-specific cellular and humoral immune responses. We argue that refinement of aldolase antigen preparations and expansion of immunization trials should be encouraged to promote the advancement of promising, protective aldolase vaccines.

Mycobacterium tuberculosis glyceraldehyde-3-phosphate dehydrogenase plays a dual role-As an adhesin and as a receptor for plasmin(ogen)

The spread of infection is directly determined by the ability of a pathogen to invade and infect host tissues. The process involves adherence due to host-pathogen interactions and traversal into deeper tissues. Mycobacterium tuberculosis (Mtb) primarily infects the lung but is unique in its ability to infect almost any other organ of the human host including immune privileged sites such as the central nervous system (CNS). The extreme invasiveness of this bacterium is not fully understood. In the current study, we report that cell surface Mtb glyceraldehyde-3-phosphate dehydrogenase (GAPDH) functions as a virulence factor by multiple mechanisms. Firstly, it serves as a dual receptor for both plasminogen (Plg) and plasmin (Plm). CRISPRi-mediated silencing of this essential enzyme confirmed its role in the recruitment of Plg/Plm. Our studies further demonstrate that soluble GAPDH can re-associate on Mtb bacilli to promote plasmin(ogen) recruitment. The direct association of plasmin(ogen) via cell surface GAPDH or by the re-association of soluble GAPDH enhanced bacterial adherence to and traversal across lung epithelial cells. Furthermore, the association of GAPDH with host extracellular matrix (ECM) proteins coupled with its ability to recruit plasmin(ogen) may endow cells with the ability of directed proteolytic activity vital for tissue invasion.

Epitope-specific immunity against Staphylococcus aureus coproporphyrinogen III oxidase

Staphylococcus aureus represents a serious infectious threat to global public health and a vaccine against S. aureus represents an unmet medical need. We here characterise two S. aureus vaccine candidates, coproporphyrinogen III oxidase (CgoX) and triose phosphate isomerase (TPI), which fulfil essential housekeeping functions in heme synthesis and glycolysis, respectively. Immunisation with rCgoX and rTPI elicited protective immunity against S. aureus bacteremia. Two monoclonal antibodies (mAb), CgoX-D3 and TPI-H8, raised against CgoX and TPI, efficiently provided protection against S. aureus infection. MAb-CgoX-D3 recognised a linear epitope spanning 12 amino acids (aa), whereas TPI-H8 recognised a larger discontinuous epitope. The CgoX-D3 epitope conjugated to BSA elicited a strong, protective immune response against S. aureus infection. The CgoX-D3 epitope is highly conserved in clinical S. aureus isolates, indicating its potential wide usability against S. aureus infection. These data suggest that immunofocusing through epitope-based immunisation constitutes a strategy for the development of a S. aureus vaccine with greater efficacy and better safety profile.

Preventing Candida albicans from subverting host plasminogen for invasive infection treatment

Candida albicans is a common fungal pathogen in humans that colonizes the skin and mucosal surfaces of the majority healthy individuals. How C. albicans disseminates into the bloodstream and causes life-threatening systemic infections in immunocompromised patients remains unclear. Plasminogen system activation can degrade a variety of structural proteins in vivo and is involved in several homeostatic processes. Here, for the first time, we characterized that C. albicans could capture and “subvert” host plasminogen to invade host epithelial cell surface barriers through cell-wall localized Eno1 protein. We found that the “subverted” plasminogen system plays an important role in development of invasive infection caused by C. albicans in mice. Base on this finding, we discovered a mouse monoclonal antibody (mAb) 12D9 targeting C. albicans Eno1, with high affinity to the ₂₅₄FYKDGKYDL₂₆₂ motif in α-helices 6, β-sheet 6 (H6S6) loop and direct blocking activity for C. albicans capture host plasminogen. mAb 12D9 could prevent C. albicans from invading human epithelial and endothelial cells, and displayed antifungal activity and synergistic effect with anidulafungin or fluconazole in proof-of-concept in vivo studies, suggesting that blocking the function of cell surface Eno1 was effective for controlling invasive infection caused by Candida spp. In summary, our study provides the evidence of C. albicans invading host by “subverting” plasminogen system, suggesting a potential novel treatment strategy for invasive fungal infections.

Human Plasminogen Exacerbates Clostridioides difficile Enteric Disease and Alters the Spore Surface

BACKGROUND & AIMS

The protease plasmin is an important wound healing factor, but it is not clear how it affects gastrointestinal infection-mediated damage, such as that resulting from Clostridioides difficile. We investigated the role of plasmin in C difficile-associated disease. This bacterium produces a spore form that is required for infection, so we also investigated the effects of plasmin on spores.

METHODS

C57BL/6J mice expressing the precursor to plasmin, the zymogen human plasminogen (hPLG), or infused with hPLG were infected with C difficile, and disease progression was monitored. Gut tissues were collected, and cytokine production and tissue damage were analyzed by using proteomic and cytokine arrays. Antibodies that inhibit either hPLG activation or plasmin activity were developed and structurally characterized, and their effects were tested in mice. Spores were isolated from infected patients or mice and visualized using super-resolution microscopy; the functional consequences of hPLG binding to spores were determined.

RESULTS

hPLG localized to the toxin-damaged gut, resulting in immune dysregulation with an increased abundance of cytokines (such as interleukin [IL] 1A, IL1B, IL3, IL10, IL12B, MCP1, MP1A, MP1B, GCSF, GMCSF, KC, TIMP-1), tissue degradation, and reduced survival. Administration of antibodies that inhibit plasminogen activation reduced disease severity in mice. C difficile spores bound specifically to hPLG and active plasmin degraded their surface, facilitating rapid germination.

CONCLUSIONS

We found that hPLG is recruited to the damaged gut, exacerbating C difficile disease in mice. hPLG binds to C difficile spores, and, upon activation to plasmin, remodels the spore surface, facilitating rapid spore germination. Inhibitors of plasminogen activation might be developed for treatment of C difficile or other infection-mediated gastrointestinal diseases.

Construction of a Live-Attenuated Vaccine Strain of Yersinia pestis EV76-B-SHUΔpla and Evaluation of Its Protection Efficacy in a Mouse Model by Aerosolized Intratracheal Inoculation

Plague, which is caused by Yersinia pestis, is one of the most dangerous infectious diseases. No FDA-approved vaccine against plague is available for human use at present. To improve the immune safety of Y. pestis EV76 based live attenuated vaccine and to explore the feasibility of aerosolized intratracheal inoculation (i.t.) route for vaccine delivery, a plasminogen activator protease (pla) gene deletion mutant of the attenuated Y. pestis strain EV76-B-SHU was constructed, and its residual virulence and protective efficacy were evaluated in a mouse model via aerosolized intratracheal inoculation (i.t.) or via subcutaneous injection (s.c.). The residual virulence of EV76-B-SHUΔpla was significantly reduced compared to that of the parental strain EV76-B-SHU following i.t. and s.c. infection. The EV76-B-SHUΔpla induced higher levels of mucosal antibody sIgA in the bronchoalveolar lavage fluid of mice immunized by i.t. but not by s.c.. Moreover, after lethal challenge with Y. pestis biovar Microtus strain 201 (avirulent in humans), the protective efficacy and bacterial clearance ability of the EV76-B-SHUΔpla-i.t. group were comparable to those of the EV76-B-SHUΔpla-s.c. and EV76-B-SHU immunized groups. Thus, the EV76-B-SHUΔpla represents an excellent live-attenuated vaccine candidate against pneumonic plague and aerosolized i.t. represents a promising immunization route in mouse model.

Combined Transcriptome Sequencing of Mycoplasma hyopneumoniae and Infected Pig Lung Tissue Reveals Up-Regulation of Bacterial F1-Like ATPase and Down-Regulation of the P102 Cilium Adhesin in vivo

Mycoplasma hyopneumoniae (M. hyopneumoniae) causes enzootic pneumonia in pigs but it is still largely unknown which host-pathogen interactions enable persistent infection and cause disease. In this study, we analyzed the host and bacterial transcriptomes during infection using RNA sequencing. Comparison of the transcriptome of lung lesion tissue from infected pigs with lung tissue from non-infected animals, identified 424 differentially expressed genes (FDR < 0.01 and fold change > 1.5LOG2). These genes were part of the following major pathways of the immune system: interleukin signaling (type 4, 10, 13, and 18), regulation of Toll-like receptors by endogenous ligand and activation of C3 and C5 in the complement system. Besides analyzing the lung transcriptome, a sampling protocol was developed to obtain enough bacterial mRNA from infected lung tissue for RNA sequencing. This was done by flushing infected lobes in the lung, and subsequently enriching for bacterial RNA. On average, 2.2 million bacterial reads were obtained per biological replicate to analyze the bacterial in vivo transcriptome. We compared the in vivo bacterial transcriptome with the transcriptome of bacteria grown in vitro and identified 22 up-regulated and 30 down-regulated genes (FDR < 0.01 and fold change > 2LOG2). Six out of seven genes in the operon encoding the mycoplasma specific F1-like ATPase (MHP_RS02445-MHP_RS02475) and all genes in the operon MHP_RS01965-MHP_RS01990 with functions related to nucleotide metabolism, spermidine transport and glycerol-3-phoshate transport were up-regulated in vivo. Down-regulated in vivo were genes related to glycerol uptake, cilium adhesion (P102), cell division and myo-inositol metabolism. In addition to providing a novel method to isolate bacterial mRNA from infected lung, this study provided insights into changes in gene expression during infection, which could help development of novel treatment strategies against enzootic pneumonia caused by M. hyopneumoniae.

Surface Protein Dispersin of Enteroaggregative Escherichia coli Binds Plasminogen That Is Converted Into Active Plasmin

Dispersin is a 10.2 kDa-immunogenic protein secreted by enteroaggregative Escherichia coli (EAEC). In the prototypical EAEC strain 042, dispersin is non-covalently bound to the outer membrane, assisting dispersion across the intestinal mucosa by overcoming electrostatic attraction between the AAF/II fimbriae and the bacterial surface. Also, dispersin facilitates penetration of the intestinal mucus layer. Initially characterized in EAEC, dispersin has been detected in other E. coli pathotypes, including those isolated from extraintestinal sites. In this study we investigated the binding capacity of purified dispersin to extracellular matrix (ECM), since dispersin is exposed on the bacterial surface and is involved in intestinal colonization. Binding to plasminogen was also investigated due to the presence of conserved carboxy-terminal lysine residues in dispersin sequences, which are involved in plasminogen binding in several bacterial proteins. Moreover, some E. coli components can interact with this host protease, as well as with tissue plasminogen activator, leading to plasmin production. Recombinant dispersin was produced and used in binding assays with ECM molecules and coagulation cascade compounds. Purified dispersin bound specifically to laminin and plasminogen. Interaction with plasminogen occurred in a dose-dependent and saturable manner. In the presence of plasminogen activator, bound plasminogen was converted into plasmin, its active form, leading to fibrinogen and vitronectin cleavage. A collection of E. coli strains isolated from human bacteremia was screened for the presence of aap, the dispersin-encoding gene. Eight aap-positive strains were detected and dispersin production could be observed in four of them. Our data describe new attributes for dispersin and points out to possible roles in mechanisms of tissue adhesion and dissemination, considering the binding capacity to laminin, and the generation of dispersin-bound plasmin(ogen), which may facilitate E. coli spread from the colonization site to other tissues and organs. The cleavage of fibrinogen in the bloodstream, may also contribute to the pathogenesis of sepsis caused by dispersin-producing E. coli.

Anastomotic leak in colorectal cancer patients: New insights and perspectives

Anastomotic leak (AL) remains a potentially life-threatening sequela of colorectal surgery impacting on mortality, short- and long-term morbidity, quality of life, local recurrence (LR) and disease-free survival. Despite technical improvements and the identification of several surgery- and patient-related factors associated to the risk of AL, its incidence has not significantly changed over time. In this context, the clarification of the mechanisms underlying anastomotic healing remains an important unmet need, crucial for improving patients' outcomes. This review concentrates on novel key findings in the etiopathogenesis of AL, how they can contribute in determining LR, and measures which may contribute to reducing its incidence. AL results from a complex, dynamic interplay of several factors and biological processes, including host genetics, gut microbiome, inflammation and the immune system. Many of these factors seem to act in concert to drive both AL and LR, even if the exact mechanisms remain to be elucidated. The next generation sequencing technology, including the microbial metagenomics, could lead to tailored bowel preparations targeting only those pathogens that can cause AL. Significant progress is being made in each of the reviewed areas, moving toward translational and targeted therapeutic strategies to prevent the difficult complication of AL.

Enterococcus faecalis exploits the human fibrinolytic system to drive excess collagenolysis: implications in gut healing and identification of druggable targets

Perforations, anastomotic leak, and subsequent intra-abdominal sepsis are among the most common and feared complications of invasive interventions in the colon and remaining intestinal tract. During physiological healing, tissue protease activity is finely orchestrated to maintain the strength and integrity of the submucosa collagen layer in the wound. We (Shogan, BD et al. Sci Trans Med 7: 286ra68, 2015.) have previously demonstrated in both mice and humans that the commensal microbe Enterococcus faecalis selectively colonizes wounded colonic tissues and disrupts the healing process by amplifying collagenolytic matrix-metalloprotease activity toward excessive degradation. Here, we demonstrate for the first time, to our knowledge, a novel collagenolytic virulence mechanism by which E. faecalis is able to bind and locally activate the human fibrinolytic protease plasminogen (PLG), a protein present in high concentrations in healing colonic tissue. E. faecalis-mediated PLG activation leads to supraphysiological collagen degradation; in this study, we demonstrate this concept both in vitro and in vivo. This pathoadaptive response can be mitigated with the PLG inhibitor tranexamic acid (TXA) in a fashion that prevents clinically significant complications in validated murine models of both E. faecalis- and Pseudomonas aeruginosa-mediated colonic perforation. TXA has a proven clinical safety record and is Food and Drug Administration approved for topical application in invasive procedures, albeit for the prevention of bleeding rather than infection. As such, the novel pharmacological effect described in this study may be translatable to clinical trials for the prevention of infectious complications in colonic healing.NEW & NOTEWORTHY This paper presents a novel mechanism for virulence in a commensal gut microbe that exploits the human fibrinolytic system and its principle protease, plasminogen. This mechanism is targetable by safe and effective nonantibiotic small molecules for the prevention of infectious complications in the healing gut.

Prevention of Anastomotic Leak Via Local Application of Tranexamic Acid to Target Bacterial-mediated Plasminogen Activation: A Practical Solution to a Complex Problem

OBJECTIVE

To investigate the role of bacterial- mediated plasminogen (PLG) activation in the pathogenesis of anastomotic leak (AL) and its mitigation by tranexamic acid (TXA).

BACKGROUND

AL is the most feared complication of colorectal resections. The pathobiology of AL in the setting of a technically optimal procedure involves excessive submucosal collagen degradation by resident microbes. We hypothesized that activation of the host PLG system by pathogens is a central and targetable pathway in AL.

METHODS

We employed kinetic analysis of binding and activation of human PLG by microbes known to cause AL, and collagen degradation assays to test the impact of PLG on bacterial collagenolysis. Further, we measured the ability of the antifibrinolytic drug TXA to inhibit this process. Finally, using mouse models of pathogen-induced AL, we locally applied TXA via enema and measured its ability to prevent a clinically relevant AL.

RESULTS

PLG is deposited rapidly and specifically at the site of colorectal anastomoses. TXA inhibited PLG activation and downstream collagenolysis by pathogens known to have a causal role in AL. TXA enema reduced collagenolytic bacteria counts and PLG deposition at anastomotic sites. Postoperative PLG inhibition with TXA enema prevented clinically and pathologically apparent pathogen-mediated AL in mice.

CONCLUSIONS

Bacterial activation of host PLG is central to collagenolysis and pathogen-mediated AL. TXA inhibits this process both in vitro and in vivo. TXA enema represents a promising method to prevent AL in high-risk sites such as the colorectal anastomoses.

The contact system proteases play disparate roles in streptococcal sepsis

Sepsis causes an activation of the human contact system, an inflammatory response mechanism against foreign surfaces, proteins and pathogens. The serine proteases of the contact system, factor XII and plasma kallikrein, are decreased in plasma of septic patients, which was previously associated with an unfavorable outcome. However, the precise mechanisms and roles of contact system factors in bacterial sepsis are poorly understood. We, therefore, studied the physiological relevance of factor XII and plasma kallikrein in a mouse model of experimental sepsis. We show that decreased plasma kallikrein concentration in septic mice is a result of reduced mRNA expression plasma prekallikrein gene, indicating that plasma kallikrein belong to negative acute phase proteins. Investigations regarding the pathophysiological function of contact system proteases during sepsis revealed different roles for factor XII and plasma kallikrein. In vitro, factor XII decelerated bacteria induced fibrinolysis, whereas plasma kallikrein supported it. Remarkably, depletion of plasma kallikrein (but not factor XII) by treatment with antisense-oligonucleotides, dampens bacterial dissemination and growth in multiple organs in the mouse sepsis model. These findings identify plasma kallikrein as a novel host pathogenicity factor in Streptococcus pyogenes sepsis.

Staphylococcus aureus versus neutrophil: Scrutiny of ancient combat

Staphylococcus aureus (S.aureus) is a Gram-positive bacterium that causes many infections and diseases. This pathogen can cause many types of infections such as impetigo, toxic shock syndrome toxin (TSST1), pneumonia, endocarditis, and autoimmune diseases like lupus erythematosus and can infect other healthy individuals. In the pathogenic process, colonization is a main risk factor for invasive diseases. Various factors including the cell wall-associated factors and receptors of the epithelial cells facilitate adhesion and colonization of this pathogen. S. aureus has many enzymes, toxins, and strategies to evade from the immune system either by an enzyme that lyses cellular component or by hiding from the immune system via surface antigens like protein A and second immunoglobulin-binding protein (Sbi). The strategies of this bacterium can be divided into five groups: A: Inhibit neutrophil recruitment B: Inhibit phagocytosis C: Inhibit killing by ROS, D: Neutrophil killing, and E: Resistance to antimicrobial peptide. On the other hand, innate immune system via neutrophils, the most important polymorphonuclear leukocytes, fights against bacterial cells by neutrophil extracellular trap (NET). In this review, we try to explain the role of each factor in immune evasion.

New Promising Targets for Synthetic Omptin-Based Peptide Vaccine against Gram-Negative Pathogens

Omptins represent a family of proteases commonly found in various Gram-negative pathogens. These proteins play an important role in host-pathogen interaction and have been recognized as key virulence factors, highlighting the possibility of developing an omptin-based broad-spectrum vaccine. The prototypical omptin, His-tagged recombinant Pla, was used as a model target antigen. In total, 46 linear and 24 conformational epitopes for the omptin family were predicted by the use of ElliPro service. Among these we selected highly conserved, antigenic, non-allergenic, and immunogenic B-cell epitopes. Five epitopes (2, 6, 8, 10, and 11 corresponding to Pla regions 52-60, 146-150, 231-234, 286-295, and 306-311, respectively) could be the first choice for the development of the new generation of target-peptide-based vaccine against plague. The partial residues of omptin epitopes 6, 8, and 10 (regions 136-145, 227-230, and 274-285) could be promising targets for the multi-pathogen vaccine against a group of enterobacterial infections. The comparative analysis and 3D modeling of amino acid sequences of several omptin family proteases, such as Pla (Yersinia pestis), PgtE (Salmonella enterica), SopA (Shigella flexneri), OmpT, and OmpP (Escherichia coli), confirmed their high cross-homology with respect to the identified epitope clusters and possible involvement of individual epitopes in host-pathogen interaction.

Functional characterization of a matrix metalloproteinase 2 gene in Litopenaeus vannamei

Matrix metalloproteinases (MMPs) contribute to both normal and pathological tissue remodeling. They act as regulatory molecules by working in enzyme cascades as well as processing matrix proteins, cytokines, growth factors and adhesion molecules to generate fragments with biological effects. So MMPs could play distrinct roles in the process of pathogen infection. In present study, we cloned a MMP-2 (LvMMP-2) gene from Litopenaeus vannamei. LvMMP-2, highly expressed in epidermis, located to endoplasmic reticulum in S2 cells. Results of real-time RT-PCR assay showed that LvMMP-2 was induced in shrimp hemocytes upon unfolded protein response or oxidative stress, but not via heat shock treatment. It is proved that the promoter activity of LvMMP-2 was enhanced by NF-E2-related factor 2 and AP-1 factor c-Jun. Further research showed that down-regulated LvMMP-2 contributing to oxidative stress injury, could reduce the cumulative mortality of shrimps under oxidative stress. Besides, our study also indicated that LvMMP-2 was accelerated by lipopolysaccharides injection. LvMMP-2 in S2 could increase the promoter activity of several antimicrobial peptide genes, and knocked-down expression of LvMMP-2 depressed the expression of penaeidin2 and β-Defensin. Moreover, we showed that down-regulated LvMMP-2 suppressed the cumulative mortality of shrimp infected with white spot syndrome virus (WSSV) or with Vibrio alginolyticus. Collecting results suggested that LvMMP-2 involves in shrimp innate immune response, and also contributes to tissue injury caused by WSSV infection.

Mycoplasma hyopneumoniae resides intracellularly within porcine epithelial cells

Enzootic pneumonia incurs major economic losses to pork production globally. The primary pathogen and causative agent, Mycoplasma hyopneumoniae, colonises ciliated epithelium and disrupts mucociliary function predisposing the upper respiratory tract to secondary pathogens. Alleviation of disease is reliant on antibiotics, vaccination, and sound animal husbandry, but none are effective at eliminating M. hyopneumoniae from large production systems. Sustainable pork production systems strive to lower reliance on antibiotics but lack of a detailed understanding of the pathobiology of M. hyopneumoniae has curtailed efforts to develop effective mitigation strategies. M. hyopneumoniae is considered an extracellular pathogen. Here we show that M. hyopneumoniae associates with integrin β1 on the surface of epithelial cells via interactions with surface-bound fibronectin and initiates signalling events that stimulate pathogen uptake into clathrin-coated vesicles (CCVs) and caveosomes. These early events allow M. hyopneumoniae to exploit an intracellular lifestyle by commandeering the endosomal pathway. Specifically, we show: (i) using a modified gentamicin protection assay that approximately 8% of M. hyopneumoniae cells reside intracellularly; (ii) integrin β1 expression specifically co-localises with the deposition of fibronectin precisely where M. hyopneumoniae cells assemble extracellularly; (iii) anti-integrin β1 antibodies block entry of M. hyopneumoniae into porcine cells; and (iv) M. hyopneumoniae survives phagolysosomal fusion, and resides within recycling endosomes that are trafficked to the cell membrane. Our data creates a paradigm shift by challenging the long-held view that M. hyopneumoniae is a strict extracellular pathogen and calls for in vivo studies to determine if M. hyopneumoniae can traffic to extrapulmonary sites in commercially-reared pigs.

A complex interplay between the extracellular matrix and the innate immune response to microbial pathogens

The role of the host extracellular matrix (ECM) in infection tends to be neglected. However, the complex interactions between invading pathogens, host tissues and immune cells occur in the context of the ECM. On the pathogen side, a variety of surface and secreted molecules, including microbial surface components recognizing adhesive matrix molecules and tissue-degrading enzymes, are employed that interact with different ECM proteins to effectively establish an infection at specific sites. Microbial pathogens can also hijack or misuse host proteolytic systems to modify the ECM, evade immune responses or process biologically active molecules such as cell surface receptors and cytokines that direct cell behaviour and immune defence. On the host side, the ECM composition and three-dimensional ultrastructure undergo significant modifications, which have a profound impact on the specific signals that the ECM conveys to immune cells at the forefront of infection. Unexpectedly, activated immune cells participate in the remodelling of the local ECM by synthesizing ECM glycoproteins, proteoglycans and collagen molecules. The close interplay between the ECM and the innate immune response to microbial pathogens ultimately affects the outcome of infection. This review explores and discusses recent data that implicate an active role for the ECM in the immune response to infection, encompassing antimicrobial activities, microbial recognition, macrophage activation, phagocytosis, leucocyte population balance, and transcriptional and post-transcriptional regulation of inflammatory networks, and may foster novel antimicrobial approaches.

Identification of targets of monoclonal antibodies that inhibit adhesion and growth in Mycoplasma mycoides subspecies mycoides

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A panel of anti-Mmm mAbs was produced and screened for host-pathogen inhibition.

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13 mAbs inhibited adhesion of Mmm to host target cells.

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Anti-capsular polysaccharide inhibited growth and caused agglutination of Mmm.

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Anti-PDHC inhibited adherence of Mmm cells showing the possible role of glycolytic enzymes in host-pathogen interaction.

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One novel antigen that is a promising vaccine candidate against CBPP identified.

Mycoplasma mycoides subspecies mycoides (Mmm) adhesion is tissue and host specific. Inhibition of adhesion will prevent Mmm from binding to lung cells and hence prevent colonization and disease. The aim of this study was to develop a panel of Mmm monoclonal antibodies against Mmm and use these antibodies to investigate their inhibitory effect on the adherence of Mmm to bovine lung epithelial cells (BoLEC), and to further identify an antigen to any of the inhibitory antibodies. Thirteen anti-Mycoplasma mycoides subsp. mycoides (AMMY) monoclonal antibodies (mAbs) inhibited adhesion by at least 30% and ten of the mAbs bound to multiple bands on Western blots suggesting that the antibodies bound to proteins of variable sizes. AMMY 10, a previously characterized Mmm- capsular polysaccharide (CPS) specific antibody, inhibited growth of Mmm in vitro and also caused agglutination of Mmm total cell lysate. AMMY 5, a 2-oxo acid dehydrogenase acyltransferase (Catalytic domain) (MSC_0267) specific antibody, was identified and polyclonal rabbit serum against recombinant MSC_0267 blocked adhesion of Mmm to BoLEC by 41%. Antigens recognized by these antibodies could be vaccine candidate(s) and should be subsequently tested for their ability to induce a protective immune response in vivo.

Fructose-1,6-bisphosphate aldolase of Mycoplasma bovis is a plasminogen-binding adhesin

Mycoplasma bovis is an extremely small cell wall-deficient pathogenic bacterium in the genus Mycoplasma that causes serious economic losses to the cattle industry worldwide. Fructose-1,6-bisphosphate aldolase (FBA), a key enzyme in the glycolytic pathway, is a multifunctional protein in several pathogenic bacterial species, but its role in M. bovis remains unknown. Herein, the FBA gene of the M. bovis was amplified by PCR, and subcloned into the prokaryotic expression vector pET28a (+) to generate the pET28a-FBA plasmid for recombinant expression in Escherichia coli Transetta. Expression of the 34 kDa recombinant rMbFBA protein was confirmed by electrophoresis, and enzymatic activity assays based on conversion of NADH to NAD+ revealed Km and Vmax values of 48 μM and 43.8 μmoL/L/min, respectively. Rabbit anti-rMbFBA and anti-M. bovis serum were generated by inoculation with rMbFBA and M. bovis, and antigenicity and immunofluorescence assay demonstrated that FBA is an immunogenic protein expressed on the cell membrane in M. bovis cells. Enzyme-linked immunosorbent assays revealed equal distribution of FBA in the cell membrane and cytoplasm. Complement-dependent mycoplasmacidal assays showed that rabbit anti-rMbFBA serum killed 44.1% of M. bovis cells in the presence of complement. Binding and ELISA assays demonstrated that rMbFBA binds native bovine plasminogen and in a dose-dependent manner. Fluorescent microscopy revealed that pre-treatment with antibodies against rMbFBA decreased the adhesion of M. bovis to embryonic bovine lung (EBL) cells. Furthermore, adherence inhibition assays revealed 34.4% inhibition of M. bovis infection of EBL cells following treatment with rabbit anti-rMbFBA serum, suggesting rMbFBA participates in bacterial adhesion to EBL cells.

Humoral and cellular immune responses to Yersinia pestis Pla antigen in humans immunized with live plague vaccine

Background

To establish correlates of human immunity to the live plague vaccine (LPV), we analyzed parameters of cellular and antibody response to the plasminogen activator Pla of Y. pestis. This outer membrane protease is an essential virulence factor that is steadily expressed by Y. pestis.

Methodology/Principal findings

PBMCs and sera were obtained from a cohort of naïve (n = 17) and LPV-vaccinated (n = 34) donors. Anti-Pla antibodies of different classes and IgG subclasses were determined by ELISA and immunoblotting. The analysis of antibody response was complicated with a strong reactivity of Pla with normal human sera. The linear Pla B-cell epitopes were mapped using a library of 15-mer overlapping peptides. Twelve peptides that reacted specifically with sera of vaccinated donors were found together with a major cross-reacting peptide IPNISPDSFTVAAST located at the N-terminus. PBMCs were stimulated with recombinant Pla followed by proliferative analysis and cytokine profiling. The T-cell recall response was pronounced in vaccinees less than a year post-immunization, and became Th17-polarized over time after many rounds of vaccination.

Conclusions/Significance

The Pla protein can serve as a biomarker of successful vaccination with LPV. The diagnostic use of Pla will require elimination of cross-reactive parts of the antigen.

Yersinia pestis, the causative agent of plague, has been recognized as one of the most devastating pathogen experienced by mankind. It remains endemic in many parts of the world, and is considered emerging pathogen. A live attenuated Y. pestis strain EV line NIIEG has been used for decades in the former Soviet Union for human vaccination and has proven effective against all forms of plague. We began characterizing the Y. pestis-specific antibody and T cell-mediated immune responses in people immunized with live plague vaccine. The long term goal of our research is to understand the protective mechanisms underlying immunity to plague in humans and to discover novel protective antigens for their incorporation into a subunit vaccine. Here, we describe our study on immune responses in vaccinees to one of the essential virulence factors of Y. pestis, namely Pla antigen. The results of the study shed light on the development of the optimal markers to assess the correlation with vaccine-induced protection.

Suppression of Staphylococcus aureus biofilm formation and virulence by a benzimidazole derivative, UM-C162

Staphylococcus aureus is a major cause of nosocomial infections and secretes a diverse spectrum of virulence determinants as well as forms biofilm. The emergence of antibiotic-resistant S. aureus highlights the need for alternative forms of therapeutics other than conventional antibiotics. One route to meet this need is screening small molecule derivatives for potential anti-infective activity. Using a previously optimized C. elegans – S. aureus small molecule screen, we identified a benzimidazole derivative, UM-C162, which rescued nematodes from a S. aureus infection. UM-C162 prevented the formation of biofilm in a dose-dependent manner without interfering with bacterial viability. To examine the effect of UM-C162 on the expression of S. aureus virulence genes, a genome-wide transcriptome analysis was performed on UM-C162-treated pathogen. Our data indicated that the genes associated with biofilm formation, particularly those involved in bacterial attachment, were suppressed in UM-C162-treated bacteria. Additionally, a set of genes encoding vital S. aureus virulence factors were also down-regulated in the presence of UM-C162. Further biochemical analysis validated that UM-C162-mediated disruption of S. aureus hemolysins, proteases and clumping factors production. Collectively, our findings propose that UM-C162 is a promising compound that can be further developed as an anti-virulence agent to control S. aureus infections.

Erysipelothrix rhusiopathiae recruits host plasminogen via the major protective antigen SpaA

Erysipelothrix rhusiopathiae is the causative agent of animal erysipelas and human erysipeloid. Some pathogenic bacteria are able to recruit host plasminogen and then use the plasminogen system for migration across tissue barriers or for nutritional demands during infection. However, there is no study on E. rhusiopathiae recruitment of plasminogen. SpaA has long been known to be a major protective antigen of E. rhusiopathiae, but its roles in virulence have not yet been well clarified. The aim of this study was to detect the activity of E. rhusiopathiae to recruit host plasminogen and evaluate the ability of SpaA to act as a receptor in the recruitment process. It was found that E. rhusiopathiae could recruit host plasminogen. SpaA could specifically bind host plasminogen. Anti-SpaA serum could significantly decrease the activity of E. rhusiopathiae to recruit plasminogen. In addition, this binding activity was lysine dependent. In conclusion, E. rhusiopathiae was able to recruit host plasminogen via SpaA. To our knowledge, this is the first report on E. rhusiopathiae recruitment of host plasminogen and the receptor in the process.

Structural Principles in the Development of Cyclic Peptidic Enzyme Inhibitors

This review summarizes our studies in the development of small cyclic peptides for specifically modulating enzyme activity. Serine proteases share highly similar active sites but perform diverse physiological and pathological functions. From a phage-display peptide library, we isolated two mono-cyclic peptides, upain-1 (CSWRGLENHRMC) and mupain-1 (CPAYSRYLDC), which inhibit the activity of human and murine urokinase-type plasminogen activators (huPA and muPA) with K_i values in the micromolar or sub-micromolar range, respectively. The following affinity maturations significantly enhanced the potencies of the two peptides, 10-fold and >250-fold for upain-1 and mupain-1, respectively. The most potent muPA inhibitor has a potency (K_i = 2 nM) and specificity comparable to mono-clonal antibodies. Furthermore, we also found an unusual feature of mupain-1 that its inhibitory potency can be enhanced by increasing the flexibility, which challenges the traditional viewpoint that higher rigidity leading to higher affinity. Moreover, by changing a few key residues, we converted mupain-1 from a uPA inhibitor to inhibitors of other serine proteases, including plasma kallikrein (PK) and coagulation factor XIa (fXIa). PK and fXIa inhibitors showed K_i values in the low nanomolar range and high specificity. Our studies demonstrate the versatility of small cyclic peptides to engineer inhibitory potency against serine proteases and to provide a new strategy for generating peptide inhibitors of serine proteases.

Defence factors of vaginal lactobacilli

Accurate knowledge of the composition and ecology of the vaginal microbial environment in healthy women is necessary for understanding lactobacilli-dominated normal microbiota and the mechanisms by which it reduces disease risk. The vagina and its microbiota form a balanced ecosystem; any movement outside the normal range for this ecosystem of obligate and/or facultative microbes, termed dysbacteriosis, can lead to infection and disease. This review summarizes recent research on the vaginal ecosystem, the Lactobacillus species that dominate it, and the means by which they suppress the growth, development, and/or proliferation of pathogenic microbial species. Lactobacilli colonization is believed to be beneficial since it prevents other microorganisms from colonizing the vaginal epithelium via competitive adhesion, interactions with the local immunity and plasminogen-plasmin system, and the production of lactic acid, hydrogen peroxide, and antibacterial substances. In addition, lactobacilli also constitute an important part of the urogenital tract microbiota and the lactobacilli-dominated vaginal microbiome is a major determinant for female urogenital health.

Complete Molecular and Immunoprotective Characterization of Babesia microti Enolase

The apicomplexan Babesia microti is the primary causative agent of human babesiosis, one of the most broadly distributed tick-borne diseases worldwide. B. microti undergoes a complex lifecycle within both the mammalian host and the tick vector, and employs several different specific molecular mechanisms to enter host cells. Enolase, the key glycolytic enzyme in intracellular glucose metabolism, can also be expressed on the parasite’s outer surface, binds to human plasminogen, and coordinates apicomplexan parasite invasion of host cells, however, it lacks sorting sequences or lipoprotein anchor sites. In the present study, we isolated the coding gene of B. microti enolase (BmEno), expressed it within E. coli and purified the recombinant BmEno protein (rBmEno). Consequently, we confirmed cytoplasmic and surface localization of BmEno via immunofluorescence, and demonstrated that rBmEno catalyzes the dehydration of 2-phospho-D-glycerate to phosphoenolpyruvate. Moreover, our results showed that rBmEno binds to human plasminogen, and that the lysine analog ε-aminocaproic acid significantly inhibited this binding. Furthermore plasminogen bound to rBmEno converts to active plasmin. Additionally, actively immunizing mice with rBmEno could evoke a partial protective immunity against B. microti infection following challenge. In conclusion, B. microti enolase is a multifunctional cytoplasmic protein which is also expressed at the parasitic outer surface, facilitates binding to host plasminogen, and could partially protect hosts against parasite infection.

Listeria monocytogenes remodels the cell surface in the blood-stage

After crossing the intestinal barrier, the bacterial pathogen Listeria monocytogenes disseminates via the blood to the liver, spleen, brain and placenta. Transcriptomic studies have shown that L. monocytogenes changes expression of many genes during this blood-stage. However, no comparable data at the protein level are known. As main interactors with the environment, we focused in surface proteins produced by L. monocytogenes in an ex vivo bovine blood model. Bacteria exposed to blood alter selectively the amount of several surface proteins compared with bacteria grown in laboratory media. Increased levels were detected for Lmo0514 and Internalin A, two surface proteins covalently bound to peptidoglycan, and the moonlighting protein alcohol-acetaldehyde dehydrogenase, also known as Lap for 'Listeria adhesion protein'. Lmo0514, induced by L. monocytogenes inside epithelial cells, is required for survival in plasma and for virulence in mice at early infection stages. Lmo0514 is also important to cope with low pH stress. By contrast, L. monocytogenes down-regulates other surface proteins following exposure to blood and plasma such as Internalin I. These data provide evidence for remodelling of the L. monocytogenes cell surface during the blood-stage, which it could facilitate pathogen dissemination to deep organs.

Identification and characterisation of elongation factor Tu, a novel protein involved in Paracoccidioides brasiliensis-host interaction

Paracoccidioides spp., which are temperature-dependent dimorphic fungi, are responsible for the most prevalent human systemic mycosis in Latin America, the paracoccidioidomycosis. The aim of this study was to characterise the involvement of elongation factor Tu (EF-Tu) in Paracoccidioides brasiliensis-host interaction. Adhesive properties were examined using recombinant PbEF-Tu proteins and the respective polyclonal anti-rPbEF-Tu antibody. Immunogold analysis demonstrated the surface location of EF-Tu in P. brasiliensis. Moreover, PbEF-Tu was found to bind to fibronectin and plasminogen by enzyme-linked immunosorbent assay, and it was determined that the binding to plasminogen is at least partly dependent on lysine residues and ionic interactions. To verify the participation of EF-Tu in the interaction of P. brasiliensis with pneumocytes, we blocked the respective protein with an anti-rPbEF-Tu antibody and evaluated the consequences on the interaction index by flow cytometry. During the interaction, we observed a decrease of 2- and 3-fold at 8 and 24 h, respectively, suggesting the contribution of EF-Tu in fungal adhesion/invasion.

Enolase of Mycobacterium tuberculosis is a surface exposed plasminogen binding protein

BACKGROUND

Enolase, a glycolytic enzyme, has long been studied as an anchorless protein present on the surface of many pathogenic bacteria that aids in tissue remodeling and invasion by binding to host plasminogen.

METHODS

Anti-Mtb enolase antibodies in human sera were detected using ELISA. Immunoelectron microscopy, immunofluorescence microscopy and flow cytometry were used to show surface localization of Mtb enolase. SPR was used to determine the affinity of enolase-plasminogen interaction. Plasmin formation upon plasminogen binding to enolase and Mtb surface was measured by ELISA. Mice challenge and histopathological studies were undertaken to determine the protective efficacy of enolase immunization.

RESULTS

Enolase of Mtb is present on its surface and binds human plasminogen with high affinity. There was an average of 2-fold increase in antibody mediated recognition of Mtb enolase in human sera from TB patients with an active disease over control individuals. Substitution of C-terminal lysine to alanine in rEno decreased its binding affinity with human plasminogen by >2-folds. Enolase bound plasminogen showed urokinase mediated conversion into plasmin. Binding of plasminogen to the surface of Mtb and its conversion into fibrinolytic plasmin was significantly reduced in the presence of anti-rEno antibodies. Immunization with rEno also led to a significant decrease in lung CFU counts of mice upon infection with Mtb H37Rv.

CONCLUSIONS

Mtb enolase is a surface exposed plasminogen binding protein which upon immunization confers significant protection against Mtb challenge.

GENERAL SIGNIFICANCE

Plasminogen binding has been recognized for Mtb, however, proteins involved have not been characterized. We show here that Mtb enolase is a moonlighting plasminogen binding protein.

A Moonlighting Enolase from Lactobacillus gasseri does not Require Enzymatic Activity to Inhibit Neisseria gonorrhoeae Adherence to Epithelial Cells

Enolases are generally thought of as cytoplasmic enzymes involved in glycolysis and gluconeogenesis. However, several bacteria have active forms of enolase associated with the cell surface and these proteins are utilized for functions other than central metabolism. Recently, a surface-associated protein produced by Lactobacillus gasseri ATCC 33323 with homology to enolase was found to inhibit the adherence of the sexually transmitted pathogen, Neisseria gonorrhoeae, to epithelial cells in culture. Here, we show that the protein is an active enolase in vitro. A recombinantly expressed, C-terminal His-tagged version of the protein, His6-Eno3, inhibited gonococcal adherence. Assays utilizing inhibitors of enolase enzymatic activity showed that this inhibitory activity required the substrate-binding site to be in an open conformation; however, the enolase enzymatic activity of the protein was not necessary for inhibition of gonococcal adherence. An L. gasseri strain carrying an insertional mutation in eno3 was viable, indicating that eno3 is not an essential gene in L. gasseri 33323. This observation, along with the results of the enzyme assays, is consistent with reports that this strain encodes more than one enolase. Here we show that the three L. gasseri genes annotated as encoding an enolase are expressed. The L. gasseri eno3 mutant exhibited reduced, but not abolished, inhibition of gonococcal adherence, which supports the hypothesis that L. gasseri inhibition of gonococcal adherence is a multifactorial process.

Penicillin binding protein 3 of Staphylococcus aureus NCTC 8325-4 binds and activates human plasminogen

Background

Staphylococcus aureus is a versatile pathogen expressing a number of virulence-associated adhesive molecules. In a previous study, we generated in a secretion-competent Escherichia coli strain a library of random FLAG-tag positive (FTP) polypeptides of S. aureus. To identify adhesive proteins and gain additional knowledge on putative virulence factors of S. aureus, we here screened the FTP library against human serum proteins.

Findings

Staphylococcus aureus NCTC 8325-4, origin of the FTP library, adhered to immobilized plasminogen in vitro. In an enzyme-linked immunoassay a C-terminal part of penicillin binding protein 3 (PBP3), included in the FTP library, bound to immobilized plasminogen. We expressed and purified full-length PBP3 and its C-terminal fragments as recombinant proteins. In a time-resolved fluorometry—based assay the PBP3 polypeptides bound to immobilized plasminogen. The polypeptides enhanced formation of plasmin from plasminogen as analyzed by cleavage of a chromogenic plasmin substrate.

Conclusions

The present findings, although preliminary, demonstrate reliably that S. aureus NCTC 8325-4 adheres to immobilized plasminogen in vitro and that the adhesion may be mediated by a C-terminal fragment of the PBP3 protein. The full length PBP3 and the penicillin binding C-terminal domain of PBP3 expressed as recombinant proteins bound plasminogen and activated plasminogen to plasmin. These phenomena were inhibited by the lysine analogue ε-aminocaproic acid suggesting that the binding is mediated by lysine residues. A detailed molecular description of surface molecules enhancing the virulence of S. aureus will aid in understanding of its pathogenicity and help in design of antibacterial drugs in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-2190-4) contains supplementary material, which is available to authorized users.

In vitro safety assessments and antimicrobial activities of Lactobacillus rhamnosus strains isolated from a fermented mare's milk

Safety and probiotic characteristics such as antimicrobial activities of three Lactobacillus rhamnosus strains, FSMM15, FSMM22 and FSMM26, previously isolated as potential probiotics from fermented mare's milk were investigated. The three FSMM strains were susceptible to ampicillin, gentamycin, kanamycin, streptomycin, tetracycline and chloramphenicol, whereas they were resistant to erythromycin (minimal inhibitory concentration (MIC) = 4-8 µg/mL) and clindamycin (MIC = 4 µg/mL); bioconversion of bile salts, hemolytic activity and mucin degradation activity were negative; enzymatic activities of α-chymotrypsin and β-glucosidase were detected, but those of α-galactosidase, β-glucuronidase and N-acetyl-β-glucosaminidase, were undetectable. Among the strains, strain FSMM15 was chosen as a safer probiotic candidate due mainly to the lack of plasminogen binding ability. Despite lower acid production of strain FSMM15 than others, its cell-free culture supernatant inhibited growths of Salmonella Typhimurium LT-2, Shigella sonnei, Listeria monocytogenes, and Escherichia coli O157 with comparable levels of ampicillin, suggesting a favorable aspect of strain FSMM15 as a probiotic strain.

Plasmin cleaves fibrinogen and the human complement proteins C3b and C5 in the presence of Leptospira interrogans proteins: A new role of LigA and LigB in invasion and complement immune evasion

Plasminogen is a single-chain glycoprotein found in human plasma as the inactive precursor of plasmin. When converted to proteolytically active plasmin, plasmin(ogen) regulates both complement and coagulation cascades, thus representing an important target for pathogenic microorganisms. Leptospira interrogans binds plasminogen, which is converted to active plasmin. Leptospiral immunoglobulin-like (Lig) proteins are surface exposed molecules that interact with extracellular matrix components and complement regulators, including proteins of the FH family and C4BP. In this work, we demonstrate that these multifunctional molecules also bind plasminogen through both N- and C-terminal domains. These interactions are dependent on lysine residues and are affected by ionic strength. Competition assays suggest that plasminogen does not share binding sites with C4BP or FH on Lig proteins at physiological molar ratios. Plasminogen bound to Lig proteins is converted to proteolytic active plasmin in the presence of urokinase-type plasminogen activator (uPA). Lig-bound plasmin is able to cleave the physiological substrates fibrinogen and the complement proteins C3b and C5. Taken together, our data point to a new role of LigA and LigB in leptospiral invasion and complement immune evasion. Plasmin(ogen) acquisition by these versatile proteins may contribute to Leptospira infection, favoring bacterial survival and dissemination inside the host.

Fructose-1,6-bisphosphate aldolase of Neisseria meningitidis binds human plasminogen via its C-terminal lysine residue

Neisseria meningitidis is a leading cause of fatal sepsis and meningitis worldwide. As for commensal species of human neisseriae, N. meningitidis inhabits the human nasopharynx and asymptomatic colonization is ubiquitous. Only rarely does the organism invade and survive in the bloodstream leading to disease. Moonlighting proteins perform two or more autonomous, often dissimilar, functions using a single polypeptide chain. They have been increasingly reported on the surface of both prokaryotic and eukaryotic organisms and shown to interact with a variety of host ligands. In some organisms moonlighting proteins perform virulence‐related functions, and they may play a role in the pathogenesis of N. meningitidis. Fructose‐1,6‐bisphosphate aldolase (FBA) was previously shown to be surface‐exposed in meningococci and involved in adhesion to host cells. In this study, FBA was shown to be present on the surface of both pathogenic and commensal neisseriae, and surface localization and anchoring was demonstrated to be independent of aldolase activity. Importantly, meningococcal FBA was found to bind to human glu‐plasminogen in a dose‐dependent manner. Site‐directed mutagenesis demonstrated that the C‐terminal lysine residue of FBA was required for this interaction, whereas subterminal lysine residues were not involved.

Dengue Virus Nonstructural Protein 1-Induced Antibodies Cross-React with Human Plasminogen and Enhance Its Activation

Dengue virus (DENV) infection is the most common mosquito-borne viral disease, and it can cause life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Abnormal activation of the coagulation and fibrinolysis system is one of the hallmarks of DHF/DSS. However, the mechanism underlying hemorrhage in DHF/DSS remains elusive. In previous studies, plasminogen (Plg) cross-reactive Abs, which can recognize DENV nonstructural protein (NS) 1, have been found in dengue patients. However, it is unclear whether these Abs are indeed induced by DENV NS1. Thus, we immunized mice with recombinant NS1 from both bacteria and drosophila to determine whether NS1 can induce Plg cross-reactive Abs. The results from the NS1-immunized mouse sera indicated that NS1 immunization induced Abs that could cross-react with Plg. To study the effects of these NS1-induced Plg cross-reactive Abs on fibrinolysis, we isolated several Plg cross-reactive anti-NS1 mAbs from these mice and found that some of them could enhance Plg activation. In addition, epitope mapping with a phage-displayed random peptide library revealed that one of these mAbs (2A5) could recognize NS1 C-terminal residues 305-311, which share sequence homology with Plg residues 590-597. A synthetic peptide of NS1 residues 305-311 could inhibit the binding of both 2A5 and its Fab to Plg and its enhanced activation. Thus, our results suggest that DENV NS1 can induce Plg cross-reactive Abs through molecular mimicry, which can enhance Plg activation and may contribute to the pathogenesis of DHF/DSS.

Complement regulatory protein genes in channel catfish and their involvement in disease defense response

Complement system is one of the most important defense systems of innate immunity, which plays a crucial role in disease defense responses in channel catfish. However, inappropriate and excessive complement activation could lead to potential damage to the host cells. Therefore the complement system is controlled by a set of complement regulatory proteins to allow normal defensive functions, but prevent hazardous complement activation to host tissues. In this study, we identified nine complement regulatory protein genes from the channel catfish genome. Phylogenetic and syntenic analyses were conducted to determine their orthology relationships, supporting their correct annotation and potential functional inferences. The expression profiles of the complement regulatory protein genes were determined in channel catfish healthy tissues and after infection with the two main bacterial pathogens, Edwardsiella ictaluri and Flavobacterium columnare. The vast majority of complement regulatory protein genes were significantly regulated after bacterial infections, but interestingly were generally up-regulated after E. ictaluri infection while mostly down-regulated after F. columnare infection, suggesting a pathogen-specific pattern of regulation. Collectively, these findings suggested that complement regulatory protein genes may play complex roles in the host immune responses to bacterial pathogens in channel catfish.