Group A streptococcal cysteine protease cleaves epithelial junctions and contributes to bacterial translocation

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.

Serine protease Rv2569c facilitates transmission of Mycobacterium tuberculosis via disrupting the epithelial barrier by cleaving E-cadherin

Epithelial cells function as the primary line of defense against invading pathogens. However, bacterial pathogens possess the ability to compromise this barrier and facilitate the transmigration of bacteria. Nonetheless, the specific molecular mechanism employed by Mycobacterium tuberculosis (M.tb) in this process is not fully understood. Here, we investigated the role of Rv2569c in M.tb translocation by assessing its ability to cleave E-cadherin, a crucial component of cell-cell adhesion junctions that are disrupted during bacterial invasion. By utilizing recombinant Rv2569c expressed in Escherichia coli and subsequently purified through affinity chromatography, we demonstrated that Rv2569c exhibited cell wall-associated serine protease activity. Furthermore, Rv2569c was capable of degrading a range of protein substrates, including casein, fibrinogen, fibronectin, and E-cadherin. We also determined that the optimal conditions for the protease activity of Rv2569c occurred at a temperature of 37°C and a pH of 9.0, in the presence of MgCl2. To investigate the function of Rv2569c in M.tb, a deletion mutant of Rv2569c and its complemented strains were generated and used to infect A549 cells and mice. The results of the A549-cell infection experiments revealed that Rv2569c had the ability to cleave E-cadherin and facilitate the transmigration of M.tb through polarized A549 epithelial cell layers. Furthermore, in vivo infection assays demonstrated that Rv2569c could disrupt E-cadherin, enhance the colonization of M.tb, and induce pathological damage in the lungs of C57BL/6 mice. Collectively, these results strongly suggest that M.tb employs the serine protease Rv2569c to disrupt epithelial defenses and facilitate its systemic dissemination by crossing the epithelial barrier.

Research progress on the microbiota in bladder cancer tumors

The microbiota, also referred to as the microbial community, is a crucial component of the human microenvironment. It is located predominantly in various organs, including the intestines, skin, oral cavity, respiratory tract, and reproductive tract. The microbiota maintains a symbiotic relationship with the human body, influencing physiological and pathological functions to a significant degree. There is increasing evidence linking the microbial flora to human cancers. In contrast to the traditional belief that the urethra and urine of normal individuals are sterile, recent advancements in high-throughput sequencing technology and bacterial cultivation methods have led to the discovery of specific microbial communities in the urethras of healthy individuals. Given the prevalence of bladder cancer (BCa) as a common malignancy of the urinary system, researchers have shifted their focus to exploring the connection between disease development and the unique microbial community within tumors. This shift has led to a deeper investigation into the role of microbiota in the onset, progression, metastasis, prognosis, and potential for early detection of BCa. This article reviews the existing research on the microbiota within BCa tumors and summarizes the findings regarding the roles of different microbes in various aspects of this disease.

Pathogenesis, epidemiology and control of Group A Streptococcus infection

Streptococcus pyogenes (Group A Streptococcus; GAS) is exquisitely adapted to the human host, resulting in asymptomatic infection, pharyngitis, pyoderma, scarlet fever or invasive diseases, with potential for triggering post-infection immune sequelae. GAS deploys a range of virulence determinants to allow colonization, dissemination within the host and transmission, disrupting both innate and adaptive immune responses to infection. Fluctuating global GAS epidemiology is characterized by the emergence of new GAS clones, often associated with the acquisition of new virulence or antimicrobial determinants that are better adapted to the infection niche or averting host immunity. The recent identification of clinical GAS isolates with reduced penicillin sensitivity and increasing macrolide resistance threatens both frontline and penicillin-adjunctive antibiotic treatment. The World Health Organization (WHO) has developed a GAS research and technology road map and has outlined preferred vaccine characteristics, stimulating renewed interest in the development of safe and effective GAS vaccines.

Direct and indirect effects of pathogenic bacteria on the integrity of intestinal barrier

Bacterial translocation is a pathological process involving migration of pathogenic bacteria across the intestinal barrier to enter the systemic circulation and gain access to distant organs. This phenomenon has been linked to a diverse range of diseases including inflammatory bowel disease, pancreatitis, and cancer. The intestinal barrier is an innate structure that maintains intestinal homeostasis. Pathogenic infections and dysbiosis can disrupt the integrity of the intestinal barrier, increasing its permeability, and thereby facilitating pathogen translocation. As translocation represents an essential step in pathogenesis, a clear understanding of how barrier integrity is disrupted and how this disruption facilitates bacterial translocation could identify new routes to effective prophylaxis and therapy. In this comprehensive review, we provide an in-depth analysis of bacterial translocation and intestinal barrier function. We discuss currently understood mechanisms of bacterial-enterocyte interactions, with a focus on tight junctions and endocytosis. We also discuss the emerging concept of bidirectional communication between the intestinal microbiota and other body systems. The intestinal tract has established 'axes' with various organs. Among our regulatory systems, the nervous, immune, and endocrine systems have been shown to play pivotal roles in barrier regulation. A mechanistic understanding of intestinal barrier regulation is crucial for the development of personalized management strategies for patients with bacterial translocation-related disorders. Advancing our knowledge of barrier regulation will pave the way for future research in this field and novel clinical intervention strategies.

Bladder cancer-associated microbiota: Recent advances and future perspectives

Recent evidence suggests that the human genitourinary microbiome plays a significant role in mediating the development and progression of urological tumors, including bladder cancer (BC). Clinicians widely recognize the role of Bacille Calmette Guérin (BCG), an attenuated Mycobacterium tuberculosis vaccine, in the management of intermediate- and high-risk NMIBC. However, compared to the large body of evidence on the gut microbiota and gastrointestinal tumors, limited information is available about the interaction between BC and the genitourinary microbiome. This is an expanding field that merits further investigation. Urologists will need to consider the potential impact of the microbiome in BC diagnosis, prevention of recurrence and progression, and treatment prospects in the future. This review highlights the approaches adopted for microbiome research and the findings and inadequacies of current research on BC.

Investigating the Antibacterial Properties of Prospective Scabicides

Scabies is a dermatological disease found worldwide. Mainly in tropical regions, it is also the cause of significant morbidity and mortality due to its association with potentially severe secondary bacterial infections. Current treatment strategies for scabies do not consider the role of opportunistic bacteria, and here we investigate whether current and emerging scabicides can offer any anti-bacterial protection. Using the broth microdilution method, we examined antimicrobial potential of the current scabicide ivermectin and emerging scabies treatments: abametapir, mānuka oil, and its individual β-triketones. Our results demonstrate that the two novel scabicides abametapir and mānuka oil have antimicrobial properties against common scabies-associated bacteria, specifically Staphylococcus aureus, Streptococcus pyogenes, Streptococcus dysgalactiae subsp. equisimilis and Acinetobacter baumannii. The current scabicide ivermectin offers some antimicrobial activity and is capable of inhibiting the growth aforementioned bacteria. This research is important as it could help to inform future best treatment options of scabies, and scabies-related impetigo.

Secretory Proteases of the Human Skin Microbiome

The human skin is our outermost layer and serves as a protective barrier against external insults. Advances in next generation sequencing have enabled the discoveries of a rich and diverse community of microbes - bacteria, fungi and viruses that are residents of this surface. The genomes of these microbes also revealed the presence of many secretory enzymes. In particular, proteases which are hydrolytic enzymes capable of protein cleavage and degradation are of special interest in the skin environment which is enriched in proteins and lipids. In this minireview, we will focus on the roles of these skin-relevant microbial secreted proteases, both in terms of their widely studied roles as pathogenic agents in tissue invasion and host immune inactivation, and their recently discovered roles in inter-microbial interactions and modulation of virulence factors. From these studies, it has become apparent that while microbial proteases are capable of a wide range of functions, their expression is tightly regulated and highly responsive to the environments the microbes are in. With the introduction of new biochemical and bioinformatics tools to study protease functions, it will be important to understand the roles played by skin microbial secretory proteases in cutaneous health, especially the less studied commensal microbes with an emphasis on contextual relevance.

Playing With Fire: Proinflammatory Virulence Mechanisms of Group A Streptococcus

Group A Streptococcus is an obligate human pathogen that is a major cause of infectious morbidity and mortality. It has a natural tropism for the oropharynx and skin, where it causes infections with excessive inflammation due to its expression of proinflammatory toxins and other virulence factors. Inflammation directly contributes to the severity of invasive infections, toxic shock syndrome, and the induction of severe post-infection autoimmune disease caused by autoreactive antibodies. This review discusses what is known about how the virulence factors of Group A Streptococcus induce inflammation and how this inflammation can promote disease. Understanding of streptococcal pathogenesis and the role of hyper-immune activation during infection may provide new therapeutic targets to treat the often-fatal outcome of severe disease.

Inflammasome activation and IL-1β signalling in group A Streptococcus disease

Group A Streptococcus (GAS) is a Gram-positive bacterial pathogen that causes significant morbidity and mortality worldwide. Recent clinical evidence suggests that the inflammatory marker interleukin-1β (IL-1β) plays an important role in GAS disease progression, and presents a potential target for therapeutic intervention. Interaction with GAS activates the host inflammasome pathway to stimulate production and secretion of IL-1β, but GAS can also stimulate IL-1β production in an inflammasome-independent manner. This review highlights progress that has been made in understanding the importance of host cell inflammasomes and IL-1 signalling in GAS disease, and explores challenges and unsolved problems in this host-pathogen interaction. TAKE AWAY: Inflammasome signalling during GAS infection is an emerging field of research. GAS modulates the NLRP3 inflammasome pathway through multiple mechanisms. SpeB contributes to IL-1β production independently of the inflammasome pathway. IL-1β signalling can be host-protective, but also drive severe GAS disease.

Roles of Porphyromonas gulae proteases in bacterial and host cell biology

Porphyromonas gulae, an animal-derived periodontal pathogen, expresses several virulence factors, including fimbria, lipopolysaccharide (LPS) and proteases. We previously reported that its invasive efficiency was dependent on fimbriae types. In addition, P. gulae LPS increased inflammatory responses via toll-like receptors. The present study was conducted to investigate the involvement of P. gulae proteases in bacterial and host cell biology. Porphyromonas gulae strains showed an ability to agglutinate mouse erythrocytes and also demonstrated co-aggregation with Actinomyces viscosus, while the protease inhibitors antipain, PMSF, TLCK and leupeptin diminished P. gulae proteolytic activity, resulting in inhibition of haemagglutination and co-aggregation with A. viscosus. In addition, specific proteinase inhibitors were found to reduce bacterial cell growth. Porphyromonas gulae inhibited Ca9-22 cell proliferation in a multiplicity of infection- and time-dependent manner. Additionally, P. gulae-induced decreases in cell contact and adhesion-related proteins were accompanied by a marked change in cell morphology from well spread to rounded. In contrast, inhibition of protease activity prevented degradation of proteins, such as E-cadherin, β-catenin and focal adhesion kinase, and also blocked inhibition of cell proliferation. Together, these results indicate suppression of the amount of human proteins, such as γ-globulin, fibrinogen and fibronectin, by P. gulae proteases, suggesting that a novel protease complex contributes to bacterial virulence.

Intracellular Group A Streptococcus Induces Golgi Fragmentation To Impair Host Defenses through Streptolysin O and NAD-Glycohydrolase

Group A Streptococcus (GAS; Streptococcus pyogenes) is a major human pathogen that causes streptococcal pharyngitis, skin and soft tissue infections, and life-threatening conditions such as streptococcal toxic-shock syndrome. During infection, GAS not only invades diverse host cells but also injects effector proteins such as NAD-glycohydrolase (Nga) into the host cells through a streptolysin O (SLO)-dependent mechanism without invading the cells; Nga and SLO are two major virulence factors that are associated with increased bacterial virulence. Here, we have shown that the invading GAS induces fragmentation of the Golgi complex and inhibits anterograde transport in the infected host cells through the secreted toxins SLO and Nga. GAS infection-induced Golgi fragmentation required both bacterial invasion and SLO-mediated Nga translocation into the host cytosol. The cellular Golgi network is critical for the sorting of surface molecules and is thus essential for the integrity of the epithelial barrier and for the immune response of macrophages to pathogens. In epithelial cells, inhibition of anterograde trafficking by invading GAS and Nga resulted in the redistribution of E-cadherin to the cytosol and an increase in bacterial translocation across the epithelial barrier. Moreover, in macrophages, interleukin-8 secretion in response to GAS infection was found to be suppressed by intracellular GAS and Nga. Our findings reveal a previously undescribed bacterial invasion-dependent function of Nga as well as a previously unrecognized GAS-host interaction that is associated with GAS pathogenesis.IMPORTANCE Two prominent virulence factors of group A Streptococcus (GAS), streptolysin O (SLO) and NAD-glycohydrolase (Nga), are linked to enhanced pathogenicity of the prevalent GAS strains. Recent advances show that SLO and Nga are important for intracellular survival of GAS in epithelial cells and macrophages. Here, we found that invading GAS disrupts the Golgi complex in host cells through SLO and Nga. We show that GAS-induced Golgi fragmentation requires bacterial invasion into host cells, SLO pore formation activity, and Nga NADase activity. GAS-induced Golgi fragmentation results in the impairment of the epithelial barrier and chemokine secretion in macrophages. This immune inhibition property of SLO and Nga by intracellular GAS indicates that the invasion of GAS is associated with virulence exerted by SLO and Nga.

Group A Streptococcal S Protein Utilizes Red Blood Cells as Immune Camouflage and Is a Critical Determinant for Immune Evasion

Group A Streptococcus (GAS) is a human-specific pathogen that evades the host immune response through the elaboration of multiple virulence factors. Although many of these factors have been studied, numerous proteins encoded by the GAS genome are of unknown function. Herein, we characterize a biomimetic red blood cell (RBC)-captured protein of unknown function—annotated subsequently as S protein—in GAS pathophysiology. S protein maintains the hydrophobic properties of GAS, and its absence reduces survival in human blood. S protein facilitates GAS coating with lysed RBCs to promote molecular mimicry, which increases virulence in vitro and in vivo. Proteomic profiling reveals that the removal of S protein from GAS alters cellular and extracellular protein landscapes and is accompanied by a decrease in the abundance of several key GAS virulence determinants. In vivo, the absence of S protein results in a striking attenuation of virulence and promotes a robust immune response and immunological memory.

Wierzbicki et al. show that S protein is a major group A Streptococcus (GAS) virulence factor that facilitates bacterial coating with lysed red blood cells to promote molecular mimicry, which increases virulence in vitro and in vivo. Removal of S protein reduces the abundance of multiple virulence factors and attenuates virulence.

The Streptococcal Protease SpeB Antagonizes the Biofilms of the Human Pathogen Staphylococcus aureus USA300 through Cleavage of the Staphylococcal SdrC Protein

Streptococcus pyogenes, or group A Streptococcus (GAS), is both a pathogen and an asymptomatic colonizer of human hosts and produces a large number of surface-expressed and secreted factors that contribute to a variety of infection outcomes. The GAS-secreted cysteine protease SpeB has been well studied for its effects on the human host; however, despite its broad proteolytic activity, studies on how this factor is utilized in polymicrobial environments are lacking. Here, we utilized various forms of SpeB protease to evaluate its antimicrobial and antibiofilm properties against the clinically important human colonizer Staphylococcus aureus, which occupies niches similar to those of GAS. For our investigation, we used a skin-tropic GAS strain, AP53CovS+, and its isogenic ΔspeB mutant to compare the production and activity of native SpeB protease. We also generated active and inactive forms of recombinant purified SpeB for functional studies. We demonstrate that SpeB exhibits potent biofilm disruption activity at multiple stages of S. aureus biofilm formation. We hypothesized that the surface-expressed adhesin SdrC in S. aureus was cleaved by SpeB, which contributed to the observed biofilm disruption. Indeed, we found that SpeB cleaved recombinant SdrC in vitro and in the context of the full S. aureus biofilm. Our results suggest an understudied role for the broadly proteolytic SpeB as an important factor for GAS colonization and competition with other microorganisms in its niche.IMPORTANCEStreptococcus pyogenes (GAS) causes a range of diseases in humans, ranging from mild to severe, and produces many virulence factors in order to be a successful pathogen. One factor produced by many GAS strains is the protease SpeB, which has been studied for its ability to cleave and degrade human proteins, an important factor in GAS pathogenesis. An understudied aspect of SpeB is the manner in which its broad proteolytic activity affects other microorganisms that co-occupy niches similar to that of GAS. The significance of the research reported herein is the demonstration that SpeB can degrade the biofilms of the human pathogen Staphylococcus aureus, which has important implications for how SpeB may be utilized by GAS to successfully compete in a polymicrobial environment.

The M Protein of Streptococcus pyogenes Strain AP53 Retains Cell Surface Functional Plasminogen Binding after Inactivation of the Sortase A Gene

Streptococcus pyogenes (Lancefield group A Streptococcus [GAS]) is a β-hemolytic human-selective pathogen that is responsible for a large number of morbid and mortal infections in humans. For efficient infection, GAS requires different types of surface proteins that provide various mechanisms for evading human innate immune responses, thus enhancing pathogenicity of the bacteria. Many such virulence-promoting proteins, including the major surface signature M protein, are translocated after biosynthesis through the cytoplasmic membrane and temporarily tethered to this membrane via a type 1 transmembrane domain (TMD) positioned near the COOH terminus. In these proteins, a sorting signal, LPXTG, is positioned immediately upstream of the TMD, which is cleaved by the membrane-associated transpeptidase, sortase A (SrtA), leading to the covalent anchoring of these proteins to newly emerging l-Ala-l-Ala cross-bridges of the growing peptidoglycan cell wall. Herein, we show that inactivation of the srtA gene in a skin-tropic pattern D GAS strain (AP53) results in retention of the M protein in the cell membrane. However, while the isogenic AP53 ΔsrtA strain is attenuated in overall pathogenic properties due to effects on the integrity of the cell membrane, our data show that the M protein nonetheless can extend from the cytoplasmic membrane through the cell wall and then to the surface of the bacteria and thereby retain its important properties of productively binding and activating fluid-phase host plasminogen (hPg). The studies presented herein demonstrate an underappreciated additional mechanism of cell surface display of bacterial virulence proteins via their retention in the cell membrane and extension to the GAS surface.IMPORTANCE Group A Streptococcus pyogenes (GAS) is a human-specific pathogen that produces many surface factors, including its signature M protein, that contribute to its pathogenicity. M proteins undergo specific membrane localization and anchoring to the cell wall via the transpeptidase sortase A. Herein, we explored the role of sortase A function on M protein localization, architecture, and function, employing, a skin-tropic GAS isolate, AP53, which expresses a human plasminogen (hPg)-binding M (PAM) Protein. We showed that PAM anchored in the cell membrane, due to the targeted inactivation of sortase A, was nonetheless exposed on the cell surface and functionally interacted with host hPg. We demonstrate that M proteins, and possibly other sortase A-processed proteins that are retained in the cell membrane, can still function to initiate pathogenic processes by this underappreciated mechanism.

Subtiligase-Catalyzed Peptide Ligation

Subtiligase-catalyzed peptide ligation is a powerful approach for site-specific protein bioconjugation, synthesis and semisynthesis of proteins and peptides, and chemoproteomic analysis of cellular N termini. Here, we provide a comprehensive review of the subtiligase technology, including its development, applications, and impacts on protein science. We highlight key advantages and limitations of the tool and compare it to other peptide ligase enzymes. Finally, we provide a perspective on future applications and challenges and how they may be addressed.

Solution structural model of the complex of the binding regions of human plasminogen with its M-protein receptor from Streptococcus pyogenes

VEK50 is a truncated peptide from a Streptococcal pyogenes surface human plasminogen (hPg) binding M-protein (PAM). VEK50 contains the full A-domain of PAM, which is responsible for its low nanomolar binding to hPg. The interaction of VEK50 with kringle 2, the PAM-binding domain in hPg (K2hPg), has been studied by high-resolution NMR spectroscopy. The data show that each VEK50 monomer in solution contains two tight binding sites for K2hPg, one each in the a1- (RH1; R17H18) and a2- (RH2; R30H31) repeats within the A-domain of VEK50. Two mutant forms of VEK50, viz., VEK50[RH1/AA] (VEK50ΔRH1) and VEK50[RH2/AA] (VEK50ΔRH2), were designed by replacing each RH with AA, thus eliminating one of the K2hPg binding sites within VEK50, and allowing separate study of each binding site. Using 13C- and 15N-labeled peptides, NMR-derived solution structures of VEK50 in its complex with K2hPg were solved. We conclude that the A-domain of PAM can accommodate two molecules of K2hPg docked within a short distance of each other, and the strength of the binding is slightly different for each site. The solution structure of the VEK50/K2hPg, complex, which is a reductionist model of the PAM/hPg complex, provides insights for the binding mechanism of PAM to a host protein, a process that is critical to S. pyogenes virulence.

X-ray Structures of Two Bacteroides thetaiotaomicron C11 Proteases in Complex with Peptide-Based Inhibitors

Commensal bacteria secrete proteins and metabolites to influence host intestinal homeostasis, and proteases represent a significant constituent of the components at the host:microbiome interface. Here, we determined the structures of the two secreted C11 cysteine proteases encoded by the established gut commensal Bacteroides thetaiotaomicron. We employed mutational analysis to demonstrate the two proteases, termed "thetapain" and "iotapain", undergo in trans autoactivation after lysine and/or arginine residues, as observed for other C11 proteases. We determined the structures of the active forms of thetapain and iotapain in complex with irreversible peptide inhibitors, Ac-VLTK-AOMK and biotin-VLTK-AOMK, respectively. Structural comparisons revealed key active-site interactions important for peptide recognition are more extensive for thetapain; however, both proteases employ a glutamate residue to preferentially bind small polar residues at the P2 position. Our results will aid in the design of protease-specific probes to ultimately understand the biological role of C11 proteases in bacterial fitness, elucidate their host and/or microbial substrates, and interrogate their involvement in microbiome-related diseases.

Variations in the secondary structures of PAM proteins influence their binding affinities to human plasminogen

M-proteins (M-Prts) are major virulence determinants of Group A Streptococcus pyogenes (GAS) that are covalently anchored to the cell wall at their conserved COOH-termini while the NH₂-terminal regions extend through the capsule into extracellular space. Functional M-Prts are also secreted and/or released from GAS cells where they exist as helical coiled-coil dimers in solution. Certain GAS strains (Pattern D) uniquely express an M-protein (plasminogen-binding group A streptococcal M-protein; PAM) that directly interacts with human plasminogen (hPg), a process strongly implicated in the virulence of these strains. M-Prt expressed by the emm gene is employed to serotype over 250 known strains of GAS, ∼20 of which are hitherto found to express PAMs. We have developed a modular structural model of the PAM dimer that describes the roles of different domains of this protein in various functions. While the helical COOH-terminal domains of PAM are essential for dimerization in solution, regions of its NH₂-terminal domains also exhibit a weak potential to dimerize. We find that temperature controls the open (unwound) or closed (wound) states of the functional NH₂-terminal domains of PAM. As temperature increases, α-helices are dramatically reduced, which concomitantly destabilizes the helical coiled-coil PAM dimers. PAMs with two a-repeats within the variable NH₂-terminal A-domain (class I/III) bind to hPg tightly, but natural PAM isolates with a single a-repeat in this domain (class II) display dramatic changes in hPg binding with temperature. We conclude that coexistence of two a-repeats in PAM is critical to achieve optimal binding to hPg, especially in its monomeric form, at the biologically relevant temperature.

Oxygen induces the expression of invasion and stress response genes in the anaerobic salmon parasite Spironucleus salmonicida

Background

Spironucleus salmonicida is an anaerobic parasite that can cause systemic infections in Atlantic salmon. Unlike other diplomonad parasites, such as the human pathogen Giardia intestinalis, Spironucleus species can infiltrate the blood stream of their hosts eventually colonizing organs, skin and gills. How this presumed anaerobe can persist and invade oxygenated tissues, despite having a strictly anaerobic metabolism, remains elusive.

Results

To investigate how S. salmonicida response to oxygen stress, we performed RNAseq transcriptomic analyses of cells grown in the presence of oxygen or antioxidant-free medium. We found that over 20% of the transcriptome is differentially regulated in oxygen (1705 genes) and antioxidant-depleted (2280 genes) conditions. These differentially regulated transcripts encode proteins related to anaerobic metabolism, cysteine and Fe-S cluster biosynthesis, as well as a large number of proteins of unknown function. S. salmonicida does not encode genes involved in the classical elements of oxygen metabolism (e.g., catalases, superoxide dismutase, glutathione biosynthesis, oxidative phosphorylation). Instead, we found that genes encoding bacterial-like oxidoreductases were upregulated in response to oxygen stress. Phylogenetic analysis revealed some of these oxygen-responsive genes (e.g., nadh oxidase, rubrerythrin, superoxide reductase) are rare in eukaryotes and likely derived from lateral gene transfer (LGT) events into diplomonads from prokaryotes. Unexpectedly, we observed that many host evasion- and invasion-related genes were also upregulated under oxidative stress suggesting that oxygen might be an important signal for pathogenesis.

Conclusion

While oxygen is toxic for related organisms, such as G. intestinalis, we find that oxygen is likely a gene induction signal for host invasion- and evasion-related pathways in S. salmonicida. These data provide the first molecular evidence for how S. salmonicida could tolerate oxic host environments and demonstrate how LGT can have a profound impact on the biology of anaerobic parasites.

Electronic supplementary material

The online version of this article (10.1186/s12915-019-0634-8) contains supplementary material, which is available to authorized users.

Toxins and Superantigens of Group A Streptococci

Streptococcus pyogenes (i.e., the group A Streptococcus ) is a human-restricted and versatile bacterial pathogen that produces an impressive arsenal of both surface-expressed and secreted virulence factors. Although surface-expressed virulence factors are clearly vital for colonization, establishing infection, and the development of disease, the secreted virulence factors are likely the major mediators of tissue damage and toxicity seen during active infection. The collective exotoxin arsenal of S. pyogenes is rivaled by few bacterial pathogens and includes extracellular enzymes, membrane active proteins, and a variety of toxins that specifically target both the innate and adaptive arms of the immune system, including the superantigens; however, despite their role in S. pyogenes disease, each of these virulence factors has likely evolved with humans in the context of asymptomatic colonization and transmission. In this article, we focus on the biology of the true secreted exotoxins of the group A Streptococcus , as well as their roles in the pathogenesis of human disease.

Streptococcus pyogenes CAMP factor promotes calcium ion uptake in RAW264.7 cells

Streptococcus pyogenes is a bacterium that causes systemic diseases such as pharyngitis and toxic shock syndrome. S. pyogenes produces molecules that inhibit the function of the human immune system, thus allowing growth and spread of the pathogen in tissues. It is known that S. pyogenes CAMP factor induces vacuolation in macrophages; however, the mechanism remains unclear. In the current study, the mechanism by which CAMP factor induces vacuolation in macrophages was investigated. CAMP factor was found to induce calcium ion uptake in murine macrophage RAW264.7 cells. In addition, EDTA inhibited calcium ion uptake and vacuolation in the cells. The L-type voltage-dependent calcium ion channel blockers nifedipine and verapamil reduced vacuolation. Furthermore, the phosphoinositide 3-kinase inhibitors LY294002 and wortmannin also inhibited the vacuolation induced by CAMP factor. Fluorescent microscopy revealed that clathrin localized to the vacuoles. These results suggest that the vacuolation is related to calcium ion uptake by RAW264.7 cells via L-type voltage-dependent calcium ion channels. Therefore, it was concluded that the vacuoles induced by S. pyogenes CAMP factor in macrophages are clathrin-dependent endosomes induced by activation of the phosphoinositide 3-kinase signaling pathway through calcium ion uptake.

Molecular Cloning and Docking of speB Gene Encoding Cysteine Protease With Antibiotic Interaction in Streptococcus pyogenes NBMKU12 From the Clinical Isolates

Streptococcus pyogenes causes a variety of diseases ranging from mild diseases to severe invasive infections which result in significant morbidity and mortality. This study focuses on the antibiotic resistance of S. pyogenes and their interaction with cysteine protease. Around 36 beta-hemolytic isolates were collected from the clinical lab, of which seven isolates (19.4%) were identified as Streptococcus pyogenes. One of the seven isolates was collected from a urinary tract infection, which was identified by antibody agglutination and MALTI-TOF-MS, and it is designated as S. pyogenes NBMKU12. Around 8.3 to 66.6 % of the isolates were found to be resistant to one or more antimicrobial agents, especially, penicillin-G resistance was exhibited by 29.1% of the isolates. In the NBMKU12 isolate, the beta lactem (TEM) gene was detected among the 13 antibiotic genes for which it was tested. Furthermore, when analysis for presence of 13 virulence genes were carried out in NBMKU12 isolate, only speJ and speB were detected. The speB (streptococcal pyrogenic exotoxin B) encoding cysteine protease gene was cloned. This was followed by performing DNA sequencing to understand the putative cysteine protease interaction with antibiotics, inhibitors, and substrate. The speB gene consists of 1197 nucleotides and encodes a protein with multiple domains, including a signal peptide (aa 1-22), an inhibitor region (aa 27-156), and a catalytic cysteine domain (aa 160-367). The signal peptide cleavage site is predicted between Ala22 and Asn23. The putative 398 amino acid residues were found to have a theoretical pI of 8.76 and a molecular mass of 43,204.36 Da. The tested culture supernatants of NBMKU12 isolate exhibited the proteolytic activity against casein, papaya and pineapple used as substrates. The proteolytic activity suggests the expression of speB gene. Molecular docking analysis of cysteine protease showed that erythromycin (bond length 2.41 Å), followed by chloramphenicol (2.51 Å), exhibited a strong interaction; while penicillin-G (3.24 Å) exhibited a weak interaction, and this factor could be considered as a cause for penicillin-G resistance. The present study contributes to a better understanding of speB gene encoding cysteine protease, antibiotic resistance, and their interaction in the isolate, S. pyogenes NBMKU12. The antibiotics and cysteine protease interaction study confirms the resistance or sensitivity of S. pyogenes. Hence, it could be hypothesized that the isolate NBMKU12 is resistant to most of the tested antibiotics, and this resistance might be a cause for mutation.

Streptococcal Cysteine Protease-Mediated Cleavage of Desmogleins Is Involved in the Pathogenesis of Cutaneous Infection

Streptococcus pyogenes is responsible for a wide variety of cutaneous infections ranging from superficial impetigo to fulminant invasive necrotizing fasciitis. Dysfunction of desmosomes is associated with the pathogenesis of cutaneous diseases. We identified streptococcal pyrogenic exotoxin B (SpeB) as a proteolytic factor that cleaves the extracellular domains of desmoglein 1 and 3. In an epicutaneous infection model, lesional skin infected with an speB deletion mutant were significantly smaller as compared to those caused by the wild-type strain. Furthermore, immunohistological analysis indicated cleavage of desmogleins that developed around the invasion site of the wild-type strain. In contrast, the speB mutant was preferentially found on the epidermis surface layer. Taken together, our findings provide evidence that SpeB-mediated degradation of desmosomes has a pathogenic role in development of S. pyogenes cutaneous infection.

Conformationally organized lysine isosteres in Streptococcus pyogenes M protein mediate direct high-affinity binding to human plasminogen

The binding of human plasminogen (hPg) to the surface of the human pathogen group A Streptococcus pyogenes (GAS) and subsequent hPg activation to the protease plasmin generate a proteolytic surface that GAS employs to circumvent host innate immunity. Direct high-affinity binding of hPg/plasmin to pattern D GAS is fully recapitulated by the hPg kringle 2 domain (K2hPg) and a short internal peptide region (a1a2) of a specific subtype of bacterial surface M protein, present in all GAS pattern D strains. To better understand the nature of this binding, critical to the virulence of many GAS skin-tropic strains, we used high-resolution NMR to define the interaction of recombinant K2hPg with recombinant a1a2 (VKK38) of the M protein from GAS isolate NS455. We found a 2:1 (m/m) binding stoichiometry of K2hPg/VKK38, with the lysine-binding sites of two K2hPg domains anchored to two regions of monomeric VKK38. The K2hPg/VKK38 binding altered the VKK38 secondary structure from a helical apo-peptide with a flexible center to an end-to-end K2hPg-bound α-helix. The K2hPg residues occupied opposite faces of this helix, an arrangement that minimized steric clashing of K2hPg We conclude that VKK38 provides two conformational lysine isosteres that each interact with the lysine-binding sites in K2hPg Further, the adoption of an α-helix by VKK38 upon binding to K2hPg sterically optimizes the side chains of VKK38 for maximal binding to K2hPg and minimizes steric overlap between the K2hPg domains. The mechanism for hPg/M protein binding uncovered here may facilitate targeting of GAS virulence factors for disease management.

Substrate Profiling and High Resolution Co-complex Crystal Structure of a Secreted C11 Protease Conserved across Commensal Bacteria

Cysteine proteases are among the most abundant hydrolytic enzymes produced by bacteria, and this diverse family of proteins have significant biological roles in bacterial viability and environmental interactions. Members of the clostripain-like (C11) family of cysteine proteases from commensal gut bacterial strains have recently been shown to mediate immune responses by inducing neutrophil phagocytosis and activating bacterial pathogenic toxins. Development of substrates, inhibitors, and probes that target C11 proteases from enteric bacteria will help to establish the role of these proteins at the interface of the host and microbiome in health and disease. We employed a mass spectrometry-based substrate profiling method to identify an optimal peptide substrate of PmC11, a C11 protease secreted by the commensal bacterium Parabacteroides merdae. Using this substrate sequence information, we synthesized a panel of fluorogenic substrates to calculate kcat and KM and to evaluate the importance of the P2 amino acid for substrate turnover. A potent and irreversible tetrapeptide inhibitor with a C-terminal acyloxymethyl ketone warhead, Ac-VLTK-AOMK, was then synthesized. We determined the crystal structure of PmC11 in complex with this inhibitor and uncovered key active-site interactions that govern PmC11 substrate recognition and specificity. This is the first C11 protease structure in complex with a substrate mimetic and is also the highest resolution crystal structure of a C11 protease to date at 1.12 Å resolution. Importantly, subjecting human epithelial cell lysates to PmC11 hydrolysis in combination with subtiligase-based N-terminal labeling and tandem mass spectrometry proteomics complemented the stringent substrate specificity observed in the in vitro substrate profiling experiment. The combination of chemical biological, biophysical, and biochemical techniques presented here to elucidate and characterize PmC11 substrate selectivity can be expanded to other proteases and the development of chemical tools to study these essential proteins in biologically relevant samples, such as the highly complex distal gut microbiome.

Streptococcal pyrogenic exotoxin B inhibits apoptotic cell clearance by macrophages through protein S cleavage

Clearance of apoptotic cells by macrophages plays an important role in maintaining tissue homeostasis. Previous study indicated that streptococcal pyrogenic exotoxin B (SPE B) reduces phagocytic activity in group A streptococcus (GAS) infection. Here, we demonstrate that SPE B causes an inhibitory effect on protein S-mediated phagocytosis. In the presence of SPE B, serum- and purified protein S-mediated phagocytosis of apoptotic cells were significantly inhibited. The binding abilities of protein S to apoptotic cells were decreased by treatment with SPE B. Bacterial culture supernatants from GAS NZ131 strain also caused a reduction of protein S binding to apoptotic cells, but speB mutant strain did not. SPE B directly cleaved protein S in vitro and in vivo, whereas a lower level of cleavage occurred in mice infected with a speB isogenic mutant strain. SPE B-mediated initial cleavage of protein S caused a disruption of phagocytosis, and also resulted in a loss of binding ability of protein S-associated C4b-binding protein to apoptotic cells. Taken together, these results suggest a novel pathogenic role of SPE B that initiates protein S degradation followed by the inhibition of apoptotic cell clearance by macrophages.

The interplay of extracellular matrix and microbiome in urothelial bladder cancer

Many pathological changes in solid tumours are caused by the accumulation of genetic mutations and epigenetic molecular alterations. In addition, tumour progression is profoundly influenced by the environment surrounding the transformed cells. The interplay between tumour cells and their microenvironment has been recognized as one of the key determinants of cancer development and is being extensively investigated. Data suggest that both the extracellular matrix and the microbiota represent microenvironments that contribute to the onset and progression of tumours. Through the introduction of omics technologies and pyrosequencing analyses, a detailed investigation of these two microenvironments is now possible. In urological research, assessment of their dysregulation has become increasingly important to provide diagnostic, prognostic and predictive biomarkers for urothelial bladder cancer. Understanding the roles of the extracellular matrix and microbiota, two key components of the urothelial mucosa, in the sequelae of pathogenic events that occur in the development and progression of urothelial carcinomas will be important to overcome the shortcomings in current bladder cancer treatment strategies.

Group A Streptococcus exploits human plasminogen for bacterial translocation across epithelial barrier via tricellular tight junctions

Group A Streptococcus (GAS) is a human-specific pathogen responsible for local suppurative and life-threatening invasive systemic diseases. Interaction of GAS with human plasminogen (PLG) is a salient characteristic for promoting their systemic dissemination. In the present study, a serotype M28 strain was found predominantly localized in tricellular tight junctions of epithelial cells cultured in the presence of PLG. Several lines of evidence indicated that interaction of PLG with tricellulin, a major component of tricellular tight junctions, is crucial for bacterial localization. A site-directed mutagenesis approach revealed that lysine residues at positions 217 and 252 within the extracellular loop of tricellulin play important roles in PLG-binding activity. Additionally, we demonstrated that PLG functions as a molecular bridge between tricellulin and streptococcal surface enolase (SEN). The wild type strain efficiently translocated across the epithelial monolayer, accompanied by cleavage of transmembrane junctional proteins. In contrast, amino acid substitutions in the PLG-binding motif of SEN markedly compromised those activities. Notably, the interaction of PLG with SEN was dependent on PLG species specificity, which influenced the efficiency of bacterial penetration. Our findings provide insight into the mechanism by which GAS exploits host PLG for acceleration of bacterial invasion into deeper tissues via tricellular tight junctions.

Streptococcal toxins: role in pathogenesis and disease

Group A Streptococcus (Streptococcus pyogenes), group B Streptococcus (Streptococcus agalactiae) and Streptococcus pneumoniae (pneumococcus) are host-adapted bacterial pathogens among the leading infectious causes of human morbidity and mortality. These microbes and related members of the genus Streptococcus produce an array of toxins that act against human cells or tissues, resulting in impaired immune responses and subversion of host physiological processes to benefit the invading microorganism. This toxin repertoire includes haemolysins, proteases, superantigens and other agents that ultimately enhance colonization and survival within the host and promote dissemination of the pathogen.

Campylobacter jejuni outer membrane vesicle-associated proteolytic activity promotes bacterial invasion by mediating cleavage of intestinal epithelial cell E-cadherin and occludin

Outer membrane vesicles (OMVs) play an important role in the pathogenicity of Gram-negative bacteria. Campylobacter jejuni produces OMVs that trigger IL-8, IL-6, hBD-3 and TNF-α responses from T84 intestinal epithelial cells and are cytotoxic to Caco-2 IECs and Galleria mellonella larvae. Proteomic analysis of 11168H OMVs identified the presence of three proteases, HtrA, Cj0511 and Cj1365c. In this study, 11168H OMVs were shown to possess proteolytic activity that was reduced by pretreatment with specific serine protease inhibitors. OMVs isolated from 11168H htrA, Cj0511 or Cj1365c mutants possess significantly reduced proteolytic activity. 11168H OMVs are able to cleave both E-cadherin and occludin, but this cleavage is reduced with OMVs pretreated with serine protease inhibitors and also with OMVs isolated from htrA or Cj1365c mutants. Co-incubation of T84 monolayers with 11168H OMVs results in a visible reduction in both E-cadherin and occludin. The addition of 11168H OMVs to the co-culture of live 11168H bacteria with T84 cells results in enhanced levels of bacterial adhesion and invasion in a time-dependent and dose-dependent manner. Further investigation of the cleavage of host cell structural proteins by C. jejuni OMVs should enhance our understanding of the interactions of this important pathogen with intestinal epithelial cells.

Streptococcus pyogenes CAMP factor attenuates phagocytic activity of RAW 264.7 cells

Streptococcus pyogenes produces molecules that inhibit the function of human immune system, thus allowing the pathogen to grow and spread in tissues. It is known that S. pyogenes CAMP factor increases erythrocytosis induced by Staphylococcus aureus β-hemolysin. However, the effects of CAMP factor for immune cells are unclear. In this study, we investigated the effects of CAMP factor to macrophages. Western blotting analysis demonstrated that all examined strains expressed CAMP factor protein. In the presence of calcium or magnesium ion, CAMP factor was significantly released in the supernatant. In addition, both culture supernatant from S. pyogenes strain SSI-9 and recombinant CAMP factor dose-dependently induced vacuolation in RAW 264.7 cells, but the culture supernatant from Δcfa isogenic mutant strain did not. CAMP factor formed oligomers in RAW 264.7 cells in a time-dependent manner. CAMP factor suppressed cell proliferation via G2 phase cell cycle arrest without inducing cell death. Furthermore, CAMP factor reduced the uptake of S. pyogenes and phagocytic activity indicator by RAW 264.7 cells. These results suggest that CAMP factor works as a macrophage dysfunction factor. Therefore, we conclude that CAMP factor allows S. pyogenes to escape the host immune system, and contribute to the spread of streptococcal infection.

Identification and Co-complex Structure of a New S. pyogenes SpeB Small Molecule Inhibitor

The secreted Streptococcus pyogenes cysteine protease SpeB is implicated in host immune system evasion and bacterial virulence. We present a small molecule inhibitor of SpeB 2477 identified from a high-throughput screen based on the hydrolysis of a fluorogenic peptide substrate Ac-AIK-AMC. 2477 inhibits other SpeB-related proteases but not human caspase-3, suggesting that the molecule targets proteases with the papain-like structural fold. A 1.59 Å X-ray crystal structure of 2477 bound to the SpeB active site reveals the mechanism of inhibition and the essential constituents of 2477 necessary for binding. An assessment against a panel of 2477 derivatives confirms our structural findings and shows that a carbamate and nitrile on 2477 are required for SpeB inhibition, as these moieties provide an extensive network of electrostatic and hydrogen-bonding interactions with SpeB active site residues. Surprisingly, despite 2477 having a reduced inhibitory potential against papain, the majority of 2477-related compounds inhibit papain to a much greater and broader extent than SpeB. These findings indicate that SpeB is more stringently selective than papain for this panel of small molecule inhibitors. On the basis of our structural and biochemical characterization, we propose modifications to 2477 for subsequent rounds of inhibitor design that will impart specificity to SpeB over other papain-like proteases, including alterations of the compound to exploit the differences in CA protease active site pocket sizes and electrostatics.

Application of the C3-binding motif of streptococcal pyrogenic exotoxin B to protect mice from invasive group a streptococcal infection

Group A streptococcus (GAS) is an important human pathogen that produces several extracellular exotoxins to facilitate invasion and infection. Streptococcal pyrogenic exotoxin B (SPE B) has been demonstrated to be an important virulence factor of GAS. Our previous studies indicate that SPE B cleaves complement 3 (C3) and inhibits the activation of complement pathways. In this study, we constructed and expressed recombinant fragments of SPE B to examine the C3-binding site of SPE B. Using enzyme-linked immunosorbent assays and pull-down assays, we found that the C-terminal domain, containing amino-acid residues 345–398, of SPE B was the major binding site of human serum C3. We further identified a major, Ala³⁷⁶-Pro³⁹⁸, and a minor C3-binding motif, Gly³⁴⁶-Gly³⁶⁰, that both mediated the binding of C3 complement. Immunization with the C3-binding motifs protected mice against challenge with a lethal dose of non-invasive M49 strain GAS but not invasive M1 strains. To achieve higher efficiency against invasive M1 GAS infection, a combination of synthetic peptides derived from C-terminal epitope of streptolysin S (SLSpp) and from the major C3-binding motif of SPE B (PP6, Ala³⁷⁶-Pro³⁹⁸) was used to elicit specific immune response to those two important streptococcal exotoxins. Death rates and the severity of skin lesions decreased significantly in PP6/SLSpp-immunized mice that were infected with invasive M1 strains of GAS. These results indicate a combination of the C3-binding motif of SPE B and the protective epitope of SLS could be used as a subunit vaccine against invasive M1 strains group A streptococcal infection.

Molecular and genomic characterization of pathogenic traits of group A Streptococcus pyogenes

Group A streptococcus (GAS) or Streptococcus pyogenes causes various diseases ranging from self-limiting sore throat to deadly invasive diseases. The genome size of GAS is 1.85-1.9 Mb, and genomic rearrangement has been demonstrated. GAS possesses various surface-associated substances such as hyaluronic capsule, M proteins, and fibronectin/laminin/immunoglobulin-binding proteins. These are related to the virulence and play multifaceted and mutually reflected roles in the pathogenesis of GAS infections. Invasion of GAS into epithelial cells and deeper tissues provokes immune and non-immune defense or inflammatory responses including the recruitment of neutrophils, macrophages, and dendritic cells in hosts. GAS frequently evades host defense mechanisms by using its virulence factors. Extracellular products of GAS may perturb cellular and subcellular functions and degrade tissues enzymatically, which leads to the aggravation of local and/or systemic disorders in the host. In this review, we summarize some important cellular and extracellular substances that may affect pathogenic processes during GAS infections, and the host responses to these.

Dendritic cells from aged subjects contribute to chronic airway inflammation by activating bronchial epithelial cells under steady state

The mechanisms underlying the increased susceptibility of the elderly to respiratory infections are not well understood. The crosstalk between the dendritic cells (DCs) and epithelial cells is essential in maintaining tolerance as well as in generating immunity in the respiratory mucosa. DCs from aged subjects display an enhanced basal level of activation, which can affect the function of epithelial cells. Our results suggest that this is indeed the scenario as exposure of primary bronchial epithelial cells (PBECs) to supernatants from unstimulated DCs of aged subjects resulted in activation of PBECs. The expression of CCL20, CCL26, CXCL10, mucin, and CD54 was significantly increased in the PBECs exposed to aged DC supernatants, but not to young DC supernatants. Furthermore, aged DC supernatants also enhanced the permeability of the PBEC barrier. We also found that DCs from aged subjects spontaneously secreted increased levels of pro-inflammatory mediators, interleukin-6, tumor necrosis factor (TNF)-α, and metalloproteinase A disintegrin family of metalloproteinase 10, which can affect the functions of PBECs. Finally, we demonstrated that TNF-α, present in the supernatant of DCs from aged subjects, was the primary pro-inflammatory mediator that affected PBEC functions. Thus, age-associated alterations in DC-epithelial interactions contribute to chronic airway inflammation in the elderly, increasing their susceptibility to respiratory diseases.

Unique genomic arrangements in an invasive serotype M23 strain of Streptococcus pyogenes identify genes that induce hypervirulence

The first genome sequence of a group A Streptococcus pyogenes serotype M23 (emm23) strain (M23ND), isolated from an invasive human infection, has been completed. The genome of this opacity factor-negative (SOF(-)) strain is composed of a circular chromosome of 1,846,477 bp. Gene profiling showed that this strain contained six phage-encoded and 24 chromosomally inherited well-known virulence factors, as well as 11 pseudogenes. The bacterium has acquired four large prophage elements, ΦM23ND.1 to ΦM23ND.4, harboring genes encoding streptococcal superantigen (ssa), streptococcal pyrogenic exotoxins (speC, speH, and speI), and DNases (spd1 and spd3), with phage integrase genes being present at one flank of each phage insertion, suggesting that the phages were integrated by horizontal gene transfer. Comparative analyses revealed unique large-scale genomic rearrangements that result in genomic rearrangements that differ from those of previously sequenced GAS strains. These rearrangements resulted in an imbalanced genomic architecture and translocations of chromosomal virulence genes. The covS sensor in M23ND was identified as a pseudogene, resulting in the attenuation of speB function and increased expression of the genes for the chromosomal virulence factors multiple-gene activator (mga), M protein (emm23), C5a peptidase (scpA), fibronectin-binding proteins (sfbI and fbp54), streptolysin O (slo), hyaluronic acid capsule (hasA), streptokinase (ska), and DNases (spd and spd3), which were verified by PCR. These genes are responsible for facilitating host epithelial cell binding and and/or immune evasion, thus further contributing to the virulence of M23ND. In conclusion, strain M23ND has become highly pathogenic as the result of a combination of multiple genetic factors, particularly gene composition and mutations, prophage integrations, unique genomic rearrangements, and regulated expression of critical virulence factors.

Mutations in the control of virulence sensor gene from Streptococcus pyogenes after infection in mice lead to clonal bacterial variants with altered gene regulatory activity and virulence

The cluster of virulence sensor (CovS)/responder (CovR) two-component operon (CovRS) regulates ∼15% of the genes of the Group A Streptococcal pyogenes (GAS) genome. Bacterial clones containing inactivating mutations in the covS gene have been isolated from patients with virulent invasive diseases. We report herein an assessment of the nature and types of covS mutations that can occur in both virulent and nonvirulent GAS strains, and assess whether a nonvirulent GAS can attain enhanced virulence through this mechanism. A group of mice were infected with a globally-disseminated clonal M1T1 GAS (isolate 5448), containing wild-type (WT) CovRS (5448/CovR⁺S⁺), or less virulent engineered GAS strains, AP53/CovR⁺S⁺ and Manfredo M5/CovR⁺S⁺. SpeB negative GAS clones from wound sites and/or from bacteria disseminated to the spleen were isolated and the covS gene was subjected to DNA sequence analysis. Numerous examples of inactivating mutations were found in CovS in all regions of the gene. The mutations found included frame-shift insertions and deletions, and in-frame small and large deletions in the gene. Many of the mutations found resulted in early translation termination of CovS. Thus, the covS gene is a genomic mutagenic target that gives GAS enhanced virulence. In cases wherein CovS⁻ was discovered, these clonal variants exhibited high lethality, further suggesting that randomly mutated covS genes occur during the course of infection, and lead to the development of a more invasive infection.

Intestinal barrier dysfunction triggered by invasive bacteria

The ability to control uptake across the mucosa and to protect the gut from harmful substances present in the lumen is defined as intestinal barrier function. Two routes are usually distinguished for transepithelial transport. The paracellular route allows the passage of ions and small molecules and is mainly regulated by tight junctions (TJ). The transcellular route concerns large molecules or small particles (including bacteria) and is mediated by cell endocytosis and intracellular vesicular traffic. Enteropathogenic bacteria increase the transcellular permeability, especially in the follicle-associated epithelium. They also modulate TJ opening via the redistribution of TJ proteins and the activation of the myosin light chain kinase (MLCK). This review focuses on the molecular mechanisms involved in the bacteria-induced barrier defect and briefly discusses their consequences in human diseases.

Streptococcal SpeB cleaved PAR-1 suppresses ERK phosphorylation and blunts thrombin-induced platelet aggregation

BACKGROUND

The family of 4 related protease-activated receptors (PAR-1, 2, 3 & 4) expressed by mammalian cells allow to sense for and react to extracellular proteolytic activity. Since major human bacterial pathogens secret a wide array of protease(-s) we investigated whether they interfere with human PAR function.

METHODOLOGY/PRINCIPAL FINDINGS

Supernatants from cultures of major human bacterial pathogens were assayed for the presence of protease(-s) capable to cleave overexpressed human PAR-1, 2, 3 and 4 reporter constructs. Group A streptococcus (GAS) was found to secret a PAR-1-cleaving protease. Experiments involving genetical and pharmacological gain and loss of function identified streptococcal pyrogenic exotoxin B SpeB as the protease responsible. On the host's side analysis of overexpressed PAR-1 carrying alanine substitutions and deletions showed the amino acid residue leucine44 on PAR-1's extracellular N-terminus to be the only cleavage site. Complementary studies on endogenously expressed PAR-1 using PAR-1 blocking antibodies further supported our conclusion. Through PAR-1 cleavage SpeB efficiently blunted thrombin-induced induction of the ERK-pathway in endothelial cells and prevented platelets aggregation in response to thrombin.

CONCLUSIONS/SIGNIFICANCE

Our results identify a novel function of the streptococcal virulence factor SpeB. By cleaving human PAR-1 at the N-terminal amino acid residue leucine44 SpeB rendered endothelial cells unresponsive to thrombin and prevented human platelets from thrombin-induced aggregation. These results suggest that by blunting PAR-1 signaling, SpeB modulates various innate host responses directed against invasive GAS potentially helping the invasive bacteria to escape. This may allow to tailor additional treatments in the future since upon invasion of the blood stream endothelial cells as well as platelets and mononuclear cells respond to PAR-1 agonists aiming to prevent further bacterial dissemination.