Staphylococcal and streptococcal superantigens: molecular, biological and clinical aspects

The pathogenicity and virulence of the opportunistic pathogen Staphylococcus epidermidis

The pervasive presence of Staphylococcus epidermidis and other coagulase-negative staphylococci on the skin and mucous membranes has long underpinned a casual disregard for the infection risk that these organisms pose to vulnerable patients in healthcare settings. Prior to the recognition of biofilm as an important virulence determinant in S. epidermidis, isolation of this microorganism in diagnostic specimens was often overlooked as clinically insignificant with potential delays in diagnosis and onset of appropriate treatment, contributing to the establishment of chronic infection and increased morbidity or mortality. While impressive progress has been made in our understanding of biofilm mechanisms in this important opportunistic pathogen, research into other virulence determinants has lagged S. aureus. In this review, the broader virulence potential of S. epidermidis including biofilm, toxins, proteases, immune evasion strategies and antibiotic resistance mechanisms is surveyed, together with current and future approaches for improved therapeutic interventions.

Hand infection: a management approach based on a new understanding of combined bacterial and neutrophil mediated tissue damage

Concepts of tissue damage from sepsis are rooted in the works of Pasteur regarding colonization by microorganisms, and Lister's observation of avoiding suppuration by their exclusion. The reactive inflammation has been considered a beneficial defence mechanism. A more complex biology is now unfolding of pathogenic mechanisms with toxins produced by the organisms now being placed in a broad category of virulence factors. Neutrophils are key cells in providing innate immunity and their trafficking to sites of infection results in entry to the extracellular space where they attack pathogens by release of the contents of neutrophil granules and neutrophil extracellular traps. There is now considerable evidence that much of the tissue damage in infection is due to excessive host innate immunological reaction; a hyperinflammatory response, whether localized or systemic. In addition to traditional surgical methods of drainage and decompression there is now a focus on dilution of inflammatory mediators. This emerging knowledge can potentially alter the way we approach hand infections.

High-progesterone environment preserves T cell competency by evading glucocorticoid effects on immune regulation

Progesterone (P4) and glucocorticoid (GC) play crucial roles in the immunoregulation of a mother to accept and maintain a semi-allogenic fetus. P4 concentration increases during pregnancy and becomes much higher in the placenta than in the other peripheral tissues, wherein the concentration of cortisol (COR), the most abundant GC and a strong immunosuppressor, remains uniform throughout the rest of the body. Here, we evaluated the effect of a high-P4 environment on pregnant immunity by comparing it with COR. Naïve T cell proportion increased transiently in peripheral blood of pregnant women just after delivery and decreased after one month. T cells stimulated with superantigen toxic-shock-syndrome-1 (TSST-1) in the presence of P4 stayed in the naïve state and did not increase, irrespective of the presence of COR, and reactive T cells could not survive. Treatment of T cells with P4 without T cell receptor (TCR) stimulation transiently suppressed T cell activation and proliferation, whereas the levels remain unaltered if P4 was not given before stimulation. Comparison of the engraftment and response against specific antigens using hu-PBL-NOG-hIL-4-Tg mice showed that P4-pretreated lymphocytes preserved CD62L expression and engrafted effectively in the spleen. Moreover, they produced antigen-specific antibodies, whereas COR-pretreated lymphocytes did not. These results suggest that a high-P4 environment suppresses T cell activation and induces T cell migration into lymphoid tissues, where they maintain the ability to produce anti-pathogen antibodies, whereas COR does not preserve T cell function. The mechanism may be pivotal in maintaining non-fetus-specific T cell function in pregnancy.

Coccomyxa sp.KJ extract affects the fate of T cells stimulated by toxic shock syndrome toxin-1, a superantigen secreted by Staphylococcus aureus

T cell stimulation by bacterial superantigens induces a cytokine storm. After T cell activation and inflammatory cytokine secretion, regulatory T cells (Treg) are produced to suppress the immune response. Coccomyxa sp.KJ (IPOD FERM BP‐22254), a green alga, is reported to regulate immune reactions. Therefore, we examined the effects of Coccomyxa sp.KJ extract (CE) on the superantigen‐induced immune response. When human peripheral blood mononuclear cells (PBMCs) were stimulated with toxic shock syndrome‐1 (TSST‐1) in the presence of CE, the number of activated T cells decreased moderately. Purified T cells stimulated in the presence of CE comprised more non‐proliferating cells than those stimulated in the absence of CE, whereas some T cells proliferated more quickly. The levels of activation markers on the stimulated T cells increased in the presence of CE. Most of the inflammatory cytokines did not change but IL‐1β, IL‐17, IL‐4, and IL‐13 secretion increased, whereas that of IL‐2, TNF‐α, and IL‐18 decreased. IL‐10 secretion was also decreased by CE treatment, suggesting that the immune response was not suppressed by Treg cells. CE enhanced the expression of stem cell‐like memory cell markers in T cells. These results suggest that CE can regulate the fate of T cells and can help to ameliorate superantigen‐induced T cell hyperactivation and immune suppression.

SARS-CoV-2-Specific Immune Response and the Pathogenesis of COVID-19

The review aims to consolidate research findings on the molecular mechanisms and virulence and pathogenicity characteristics of coronavirus disease (COVID-19) causative agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and their relevance to four typical stages in the development of acute viral infection. These four stages are invasion; primary blockade of antiviral innate immunity; engagement of the virus's protection mechanisms against the factors of adaptive immunity; and acute, long-term complications of COVID-19. The invasion stage entails the recognition of the spike protein (S) of SARS-CoV-2 target cell receptors, namely, the main receptor (angiotensin-converting enzyme 2, ACE2), its coreceptors, and potential alternative receptors. The presence of a diverse repertoire of receptors allows SARS-CoV-2 to infect various types of cells, including those not expressing ACE2. During the second stage, the majority of the polyfunctional structural, non-structural, and extra proteins SARS-CoV-2 synthesizes in infected cells are involved in the primary blockage of antiviral innate immunity. A high degree of redundancy and systemic action characterizing these pathogenic factors allows SARS-CoV-2 to overcome antiviral mechanisms at the initial stages of invasion. The third stage includes passive and active protection of the virus from factors of adaptive immunity, overcoming of the barrier function at the focus of inflammation, and generalization of SARS-CoV-2 in the body. The fourth stage is associated with the deployment of variants of acute and long-term complications of COVID-19. SARS-CoV-2's ability to induce autoimmune and autoinflammatory pathways of tissue invasion and development of both immunosuppressive and hyperergic mechanisms of systemic inflammation is critical at this stage of infection.

Host-microbe metatranscriptome reveals differences between acute and chronic infections in diabetes-related foot ulcers

Virtually all diabetes-related foot ulcers (DRFUs) will become colonized by microorganisms that may increase the risk of developing an infection. The reasons why some ulcerations develop acute clinical infections (AI-DRFUs) whilst others develop chronic infection (CI-DRFUs) and the preceding host-microbe interactions in vivo remain largely unknown. Establishing that acute and chronic infections are distinct processes requires demonstrating that these are two different strategies employed by microbes when interacting with a host. In this study, dual-RNA seq was employed to differentiate the host-microbe metatranscriptome between DRFUs that had localized chronic infection or acute clinical infection. Comparison of the host metatranscriptome in AI-DRFUs relative to CI-DRFUs identified upregulated differentially expressed genes (DEGs) that functioned as regulators of vascular lymphatic inflammatory responses, T-cell signalling and olfactory receptors. Conversely, CI-DRFUs upregulated DEGs responsible for cellular homeostasis. Gene set enrichment analysis using Hallmark annotations revealed enrichment of immune and inflammatory profiles in CI-DRFUs relative to AI-DRFUs. Analysis of the microbial metatranscriptome identified the DEGs being enriched within AI-DRFUs relative to CI-DRFUs included several toxins, two-component systems, bacterial motility, secretion systems and genes encoding for energy metabolism. Functions relevant to DRFU pathology were further explored, including biofilm and bacterial pathogenesis. This identified that the expression of biofilm-associated genes was higher within CI-DRFUs compared to that of AI-DRFUs, with mucR being the most highly expressed gene. Collectively, these data provide insights into the host-microbe function in two clinically-distinct infective phenotypes that affect DRFUs. The data reveal that bacteria in acutely infected DRFUs prioritize motility over biofilm and demonstrate greater pathogenicity and mechanisms, which likely subvert host cellular and immune pathways to establish infection. Upregulation of genes for key vascular inflammatory mediators in acutely infected ulcers may contribute, in part, to the clinical picture of a red, hot, swollen foot, which differentiates an acutely infected ulcer from that of a chronic infection.

The Role of Bacterial Superantigens in the Immune Response: From Biology to Cancer Treatment

Aims:

Encouraging results have been indicated preclinically and in patients using the bacterial superantigen. This review article intends to summarize the role of the superantigens that have been recently used in the treatment of cancer. In addition, the vector systems, including lentiviral vectors, adeno-associated vector systems and retroviral vectors that are increasingly being used in basic and applied research, were discussed. Most importantly, the new CRISPR technique has also been discussed in this literature review.

Discussion:

More successful therapies can be achieved by manipulating bacterial vector systems through incorporating genes related to the superantigens and cytokines. The products of SAg and cytokine genes contribute to the strong stimulation of the immune system against tumor cells. They bind to MHC II molecules as well as the V beta regions of TCR and lead to the production of IL2 and other cytokines, the activation of antigen-presenting cells and T lymphocytes. Additionally, superantigens can be used to eradicate tumor cells. Better results in cancer treatment can be achieved by transferring superantigen genes and subsequent strong immune stimulation along with other cancer immunotherapy agents.

Conclusion:

Superantigens induce the proliferation of T lymphocytes and antigen-presenting cells by binding to MHCII molecules and V beta regions in T cell receptors. Therefore, the presentation of tumor cell antigens is increased. Additionally, the production of important cytokines by T cells and APCs contributes to the stimulation of immune response against tumor cells. The manipulation of bacterial vector systems through incorporating genesrelated to SAgs and other immune response factors is a good strategy for the immune system stimulating and eradicating tumor cells along with other immunotherapy agents.

Toxic shock syndrome with a cytokine storm caused by Staphylococcus simulans: a case report

Background

Exotoxins secreted from Staphylococcus aureus or Streptococcus pyogenes act as superantigens that induce systemic release of inflammatory cytokines and are a common cause of toxic shock syndrome (TSS). However, little is known about TSS caused by coagulase-negative staphylococci (CoNS) and the underlying mechanisms. Here, we present a rare case of TSS caused by Staphylococcus simulans (S. simulans).

Case presentation

We report the case of a 75-year-old woman who developed pneumococcal pneumonia and bacteremia from S. simulans following an influenza infection. The patient met the clinical criteria for probable TSS, and her symptoms included fever of 39.5 °C, diffuse macular erythroderma, conjunctival congestion, vomiting, diarrhea, liver dysfunction, and disorientation. Therefore, the following treatment was initiated for bacterial pneumonia complicating influenza A with suspected TSS: meropenem (1 g every 8 h), vancomycin (1 g every 12 h), and clindamycin (600 mg every 8 h). Blood cultures taken on the day after admission were positive for CoNS, whereas sputum and pharyngeal cultures grew Streptococcus pneumoniae (Geckler group 4) and methicillin-sensitive S. aureus, respectively. However, exotoxins thought to cause TSS, such as TSS toxin-1 and various enterotoxins, were not detected. The patient’s therapy was switched to cefazolin (2 g every 8 h) and clindamycin (600 mg every 8 h) for 14 days based on microbiologic test results. She developed desquamation of the fingers on hospital day 8 and was diagnosed with TSS. Conventional exotoxins, such as TSST-1, and S. aureus enterotoxins were not detected in culture samples. The serum levels of inflammatory cytokines, such as neopterin and IL-6, were high. CD8+ T cells were activated in peripheral blood. Vβ2+ population activation, which is characteristic for TSST-1, was not observed in the Vβ usage of CD8+ T cells in T cell receptor Vβ repertoire distribution analysis.

Conclusions

We present a case of S. simulans-induced TSS. Taken together, we speculate that no specific exotoxins are involved in the induction of TSS in this patient. A likely mechanism is uncontrolled cytokine release (i.e., cytokine storm) induced by non-specific immune reactions against CoNS proliferation.

Microbial communities and gene contributions in smokeless tobacco products

Smokeless tobacco products (STP) contain bacteria, mold, and fungi due to exposure from surrounding environments and tobacco processing. This has been a cause for concern since the presence of microorganisms has been linked to the formation of highly carcinogenic tobacco-specific nitrosamines. These communities have also been reported to produce toxins and other pro-inflammatory molecules that can cause mouth lesions and elicit inflammatory responses in STP users. Moreover, microbial species in these products could transfer to the mouth and gastrointestinal tract, potentially altering the established respective microbiotas of the consumer. Here, we present the first metagenomic analysis of select smokeless tobacco products, specifically US domestic moist and dry snuff. Bacterial, eukaryotic, and viral species were found in all tobacco products where 68% of the total species was comprised of Bacteria with 3 dominant phyla but also included 32% Eukarya and 1% share abundance for Archaea and Viruses. Furthermore, 693,318 genes were found to be present and included nitrate and nitrite reduction and transport enzymes, antibiotic resistance genes associated with resistance to vancomycin, β-lactamases, their derivatives, and other antibiotics, as well as genes encoding multi-drug transporters and efflux pumps. Additional analyses showed the presence of endo- and exotoxin genes in addition to other molecules associated with inflammatory responses. Our results present a novel aspect of the smokeless tobacco microbiome and provide a better understanding of these products' microbiology. KEY POINTS: • The findings presented will help understand microbial contributions to overall STP chemistries. • Gene function categorization reveals harmful constituents outside canonical forms. • Pathway genes for TSNA precursor activity may occur at early stages of production. • Bacteria in STPs carry antibiotic resistance genes and gene transfer mechanisms.

Staphylococcal and Streptococcal Superantigens Trigger B7/CD28 Costimulatory Receptor Engagement to Hyperinduce Inflammatory Cytokines

Staphylococcal and streptococcal superantigens are virulence factors that cause toxic shock by hyperinducing inflammatory cytokines. Effective T-cell activation requires interaction between the principal costimulatory receptor CD28 and its two coligands, B7-1 (CD80) and B7-2 (CD86). To elicit an inflammatory cytokine storm, bacterial superantigens must bind directly into the homodimer interfaces of CD28 and B7-2. Recent evidence revealed that by engaging CD28 and B7-2 directly at their dimer interface, staphylococcal enterotoxin B (SEB) potently enhances intercellular synapse formation mediated by B7-2 and CD28, resulting in T-cell hyperactivation. Here, we addressed the question, whether diverse bacterial superantigens share the property of triggering B7-2/CD28 receptor engagement and if so, whether they are capable of enhancing also the interaction between B7-1 and CD28, which occurs with an order-of-magnitude higher affinity. To this end, we compared the ability of distinct staphylococcal and streptococcal superantigens to enhance intercellular B7-2/CD28 engagement. Each of these diverse superantigens promoted B7-2/CD28 engagement to a comparable extent. Moreover, they were capable of triggering the intercellular B7-1/CD28 interaction, analyzed by flow cytometry of co-cultured cell populations transfected separately to express human CD28 or B7-1. Streptococcal mitogenic exotoxin Z (SMEZ), the most potent superantigen known, was as sensitive as SEB, SEA and toxic shock syndrome toxin-1 (TSST-1) to inhibition of inflammatory cytokine induction by CD28 and B7-2 dimer interface mimetic peptides. Thus, superantigens act not only by mediating unconventional interaction between MHC-II molecule and T-cell receptor but especially, by strongly promoting engagement of CD28 by its B7-2 and B7-1 coligands, a critical immune checkpoint, forcing the principal costimulatory axis to signal excessively. Our results show that the diverse superantigens use a common mechanism to subvert the inflammatory response, strongly enhancing B7-1/CD28 and B7-2/CD28 costimulatory receptor engagement.

Group A Streptococcus-Mediated Host Cell Signaling

In the past decade, the field of the cellular microbiology of group A Streptococcus (S. pyogenes) infection has made tremendous advances and touched upon several important aspects of pathogenesis, including receptor biology, invasive and evasive phenomena, inflammasome activation, strain-specific autophagic bacterial killing, and virulence factor-mediated programmed cell death. The noteworthy aspect of S. pyogenes-mediated cell signaling is the recognition of the role of M protein in a variety of signaling events, starting with the targeting of specific receptors on the cell surface and on through the induction and evasion of NETosis, inflammasome, and autophagy/xenophagy to pyroptosis and apoptosis. Variations in reports on S. pyogenes-mediated signaling events highlight the complex mechanism of pathogenesis and underscore the importance of the host cell and S. pyogenes strain specificity, as well as in vitro/in vivo experimental parameters. The severity of S. pyogenes infection is, therefore, dependent on the virulence gene expression repertoire in the host environment and on host-specific dynamic signaling events in response to infection. Commonly known as an extracellular pathogen, S. pyogenes finds host macrophages as safe havens wherein it survives and even multiplies. The fact that endothelial cells are inherently deficient in autophagic machinery compared to epithelial cells and macrophages underscores the invasive nature of S. pyogenes and its ability to cause severe systemic diseases. S. pyogenes is still one of the top 10 causes of infectious mortality. Understanding the orchestration of dynamic host signaling networks will provide a better understanding of the increasingly complex mechanism of S. pyogenes diseases and novel ways of therapeutically intervening to thwart severe and often fatal infections.

Sepsis: mechanisms of bacterial injury to the patient

In bacteremia the majority of bacterial species are killed by oxidation on the surface of erythrocytes and digested by local phagocytes in the liver and the spleen. Sepsis-causing bacteria overcome this mechanism of human innate immunity by versatile respiration, production of antioxidant enzymes, hemolysins, exo- and endotoxins, exopolymers and other factors that suppress host defense and provide bacterial survival. Entering the bloodstream in different forms (planktonic, encapsulated, L-form, biofilm fragments), they cause different types of sepsis (fulminant, acute, subacute, chronic, etc.). Sepsis treatment includes antibacterial therapy, support of host vital functions and restore of homeostasis. A bacterium killing is only one of numerous aspects of antibacterial therapy. The latter should inhibit the production of bacterial antioxidant enzymes and hemolysins, neutralize bacterial toxins, modulate bacterial respiration, increase host tolerance to bacterial products, facilitate host bactericidal mechanism and disperse bacterial capsule and biofilm.

Pediatric rhinosinusitis and asthma

Both asthma and rhinosinusitis are complex and heterogeneous diseases and, importantly, they often coexist: these diseases can be concomitant in 35-65% of affected children, according to different studies. Thus, evaluating this comorbidity in the clinical practice should be paramount. In this review, we focused our discussion on the multiple pathophysiological aspects that may link rhinosinusitis and asthma in the pediatric population. Although rhinosinusitis may exacerbate asthma through several mechanisms occurring by contiguity, actually this aspect seems to be only one component of the complex interplay between upper and lower airways. In particular, the onset of an important and persistent Th2-driven inflammatory process dominated by eosinophils presence at one site of the airways, may release into the bloodstream several cytokines; in their turn, those can lead to the stimulation of the bone marrow, which may function as a systemic amplifier of such an eosinophilic inflammation.

Staphylococcal Exotoxins and Nasal Polyposis: Analysis of Systemic and Local Responses

Background

Staphylococcal exotoxins have been implicated in the pathogenesis of several chronic inflammatory diseases including atopic dermatitis (AD), asthma, and, most recently, chronic rhinosinusitis with nasal polyposis (CRS/NP). In severe AD, these toxins act both as superantigens (SAg), triggering massive T-cell activation, and as conventional allergens, triggering toxin-specific immunoglobulin E (IgE) in the serum. In CRS/NP, evidence for both processes has been reported but it is unclear whether these processes are linked. The aim of this study was to correlate SAg activity as inferred by staphylococcal-specific T-cell receptor (TCR) V-β expansion in the polyp and blood of CRS/NP patients with staphylococcal-specific anti-IgE antibodies in the serum.

Methods

IgE antibodies to staphylococcal exotoxin A (SEA), staphylococcal exotoxin B (SEB), and toxic shock syndrome toxin (TSST) 1 were measured in the serum of 12 individuals with CRS/NP before functional endoscopic sinus surgery. Flow cytometry was used to analyze the SEA, SEB, and TSST-1–specific TCR V-β domains on the T cells from the polyp and blood of these patients.

Results

Serum SEA-, SEB-, and TSST-1-specific IgE antibodies were detected in 0/12 (0%), 6/12 (50.0%), and 9/12 (75%) of CRS/NP patients, respectively. Evidence of SAg effect in the polyp lymphocytes (TCR V-β expansion in both CD4+ and CD8+ subsets) was noted in 7/12 (58.3%) patients. Five of 6 CRS/NP patients had overlapping evidence of a systemic IgE response and TCR V-β expansion, suggestive of exposure to the same exotoxin. No patients had evidence a SAg effect in blood lymphocytes. Nine of 12 subjects also had coexistent asthma.

Conclusion

These results provide evidence for a local SAg effect in 7/12 (58.3%) polyp patients and establish a positive correlation of V-β expansion with the presence of corresponding toxin-specific IgE in the serum.

Competing scaffolding proteins determine capsid size during mobilization of Staphylococcus aureus pathogenicity islands

Staphylococcus aureus pathogenicity islands (SaPIs), such as SaPI1, exploit specific helper bacteriophages, like 80α, for their high frequency mobilization, a process termed 'molecular piracy'. SaPI1 redirects the helper's assembly pathway to form small capsids that can only accommodate the smaller SaPI1 genome, but not a complete phage genome. SaPI1 encodes two proteins, CpmA and CpmB, that are responsible for this size redirection. We have determined the structures of the 80α and SaPI1 procapsids to near-atomic resolution by cryo-electron microscopy, and show that CpmB competes with the 80α scaffolding protein (SP) for a binding site on the capsid protein (CP), and works by altering the angle between capsomers. We probed these interactions genetically and identified second-site suppressors of lethal mutations in SP. Our structures show, for the first time, the detailed interactions between SP and CP in a bacteriophage, providing unique insights into macromolecular assembly processes.

A Systemic Review on Staphylococcal Scalded Skin Syndrome (SSSS): A Rare and Critical Disease of Neonates

The symptoms of Staphylococcal scalded skin syndrome (SSSS) include blistering of skin on superficial layers due to the exfoliative toxins released from Staphylococcus aureus. After the acute exfoliation of skin surface, erythematous cellulitis occurs. The SSSS may be confined to few blisters localized to the infection site and spread to severe exfoliation affecting complete body. The specific antibodies to exotoxins and increased clearence of exotoxins decrease the frequency of SSSS in adults. Immediate medication with parenteral anti-staphylococcal antibiotics is mandatory. Mostly, SSSS are resistant to penicillin. Penicillinase resistant synthetic penicillins such as Nafcillin or Oxacillin are prescribed as emergency treatment medicine. If Methicillin-resistant Staphylococcus aureus (MRSA) is suspected), antibiotics with MRSA coverage (e.g., Vancomycin or Linezolid) are indicated. Clindamycin is considered as drug of choice to stop the production of exotoxin from bacteria ribosome. The use of Ringer solution to to balance the fluid loss, followed by maintainence therapy with an objective to maintain the fluid loss from exfoliation of skin, application of Cotrimoxazole on topical surface are greatlly considered to treat the SSSS. The drugs that reduce renal function are avoided. Through this article, an attempt has been made to focus the source, etiology, mechanism, outbreaks, mechanism, clinical manisfestation, treatment and other detail of SSSS.

Healthcare- and Community-Associated Methicillin-Resistant Staphylococcus aureus (MRSA) and Fatal Pneumonia with Pediatric Deaths in Krasnoyarsk, Siberian Russia: Unique MRSA's Multiple Virulence Factors, Genome, and Stepwise Evolution

Methicillin-resistant Staphylococcus aureus (MRSA) is a common multidrug-resistant (MDR) pathogen. We herein discussed MRSA and its infections in Krasnoyarsk, Siberian Russia between 2007 and 2011. The incidence of MRSA in 3,662 subjects was 22.0% and 2.9% for healthcare- and community-associated MRSA (HA- and CA-MRSA), respectively. The 15-day mortality rates for MRSA hospital- and community-acquired pneumonia (HAP and CAP) were 6.5% and 50%, respectively. MRSA CAP cases included pediatric deaths; of the MRSA pneumonia episodes available, ≥27.3% were associated with bacteremia. Most cases of HA-MRSA examined exhibited ST239/spa3(t037)/SCCmecIII.1.1.2 (designated as ST239_Kras), while all CA-MRSA cases examined were ST8/spa1(t008)/SCCmecIV.3.1.1(IVc) (designated as ST8_Kras). ST239_Kras and ST8_Kras strongly expressed cytolytic peptide (phenol-soluble modulin α, PSMα; and δ-hemolysin, Hld) genes, similar to CA-MRSA. ST239_Kras pneumonia may have been attributed to a unique set of multiple virulence factors (MVFs): toxic shock syndrome toxin-1 (TSST-1), elevated PSMα/Hld expression, α-hemolysin, the staphylococcal enterotoxin SEK/SEQ, the immune evasion factor SCIN/SAK, and collagen adhesin. Regarding ST8_Kras, SEA was included in MVFs, some of which were common to ST239_Kras. The ST239_Kras (strain OC3) genome contained: a completely unique phage, φSa7-like (W), with no att repetition; S. aureus pathogenicity island SaPI2R, the first TSST-1 gene-positive (tst⁺) SaPI in the ST239 lineage; and a super copy of IS256 (≥22 copies/genome). ST239_Kras carried the Brazilian SCCmecIII.1.1.2 and United Kingdom-type tst. ST239_Kras and ST8_Kras were MDR, with the same levofloxacin resistance mutations; small, but transmissible chloramphenicol resistance plasmids spread widely enough to not be ignored. These results suggest that novel MDR and MVF⁺ HA- and CA-MRSA (ST239_Kras and ST8_Kras) emerged in Siberian Russia (Krasnoyarsk) associated with fatal pneumonia, and also with ST239_Kras, a new (Siberian Russian) clade of the ST239 lineage, which was created through stepwise evolution during its potential transmission route of Brazil-Europe-Russia/Krasnoyarsk, thereby selective advantages from unique MVFs and the MDR.

Novel relationships between oxidative stress and angiogenesis-related factors in sepsis: New biomarkers and therapies

Sepsis is a systemic uncontrolled inflammatory response in the presence of an infection. It remains a major cause of morbidity and mortality in hospitalized patients. According to its severity, sepsis can progress to three different states: severe sepsis, septic shock, and multiple organ dysfunction syndrome, related to organ dysfunction and/or tissue hypoperfusion. Different processes underlie its pathophysiology; among them are oxidative stress, endothelial and mitochondrial dysfunction, and angiogenesis-related factors. However, no studies have integrated these elements in sepsis. The main difficulty in sepsis is its diagnosis. Currently, the potential of inflammatory biomarkers in septic patients remains weak. In this context, the research into new biomarkers is essential to aid with sepsis diagnosis and prognostication. Furthermore, even though the current management of severe forms of sepsis has been effective, morbimortality remains elevated. Therefore, it is essential to explore alternative approaches to therapy development. The aim of this review is to present an update of evidence supporting the role of oxidative stress and angiogenesis-related factors in the pathophysiology of the different forms of sepsis. It proposes a novel convergence between both elements in their role in the disease, and it will cover their utility as new diagnostic tools, predictors of outcome, and as novel therapeutic targets.

Detection of the staphylococcal enterotoxin D-like gene from staphylococcal food poisoning isolates over the last two decades in Tokyo

The plasmid is a very well-known mobile genetic element that participates in the acquisition of virulence genes, such as staphylococcal enterotoxins (SEs), via horizontal transfer. SEs are emetic toxins and causative agents in staphylococcal food poisoning (SFP). We herein identified the types of plasmids harbored by seven SFP isolates and examined their production of plasmid-related SE/SEl to determine whether the new types of plasmid-related SE or SE-like (SEl) toxins (i.e. SElJ and SER) were involved in SFP. These isolates harbored pIB485-like plasmids, and all, except for one isolate, produced SElJ and SER. The amount of SER produced by each isolate accounted for the highest or second highest percentage of the total amount of SE/SEl produced. These new types of plasmid-related SE/SEls as well as classical SE may play a role in SFP. The seven isolates were classified into two SED-production types; a high SED-production type (>500 ng/ml) and no SED-production type. A nucleotide sequencing analysis revealed that three plasmids harbored by the SED-non-producing isolates had a single-base deletion in the sed gene with a resulting stop codon (from 233 amino acids of the intact SED to 154 amino acids of the mutant SED (mSED)). A real-time reverse transcription-PCR analysis showed that the mRNA of the msed gene was transcribed in the isolates. If the msed gene was translated as a protein, mSED may act as an emetic toxin instead of intact SED.

Δ(9) Tetrahydrocannabinol attenuates Staphylococcal enterotoxin B-induced inflammatory lung injury and prevents mortality in mice by modulation of miR-17-92 cluster and induction of T-regulatory cells

BACKGROUND AND PURPOSE

Staphylococcal enterotoxin B (SEB) is a potent activator of Vβ8+T-cells resulting in the clonal expansion of ∼30% of the T-cell pool. Consequently, this leads to the release of inflammatory cytokines, toxic shock, and eventually death. In the current study, we investigated if Δ(9) tetrahydrocannabinol (THC), a cannabinoid known for its anti-inflammatory properties, could prevent SEB-induced mortality and alleviate symptoms of toxic shock.

EXPERIMENTAL APPROACH

We investigated the efficacy of THC against the dual administration (intranasal and i.p.) of SEB into C3H/HeJ mice based on the measurement of SEB-mediated clinical parameters, including cytokine production, cellular infiltration, vascular leak, and airway resistance. In addition, the molecular mechanism of action was elucidated in vitro by the activation of splenocytes with SEB.

KEY RESULTS

Exposure to SEB resulted in acute mortality, while THC treatment led to 100% survival of mice. SEB induced the miRNA-17-92 cluster, specifically miRNA-18a, which targeted Pten (phosphatase and tensin homologue), an inhibitor of the PI3K/Akt signalling pathway, thereby suppressing T-regulatory cells. In contrast, THC treatment inhibited the individual miRNAs in the cluster, reversing the effects of SEB.

CONCLUSIONS AND IMPLICATIONS

We report, for the first time a role for the miRNA 17-92 cluster in SEB-mediated inflammation. Furthermore, our results suggest that THC is a potent anti-inflammatory compound that may serve as a novel therapeutic to suppress SEB-induced pulmonary inflammation by modulating critical miRNA involved in SEB-induced toxicity and death.

Detection of Staphylococcal Exotoxins in Antrochoanal Polyps and Chronic Rhinosinusitis with Nasal Polyps

Objective

Staphylococcal exotoxins have been reported in the pathogenesis of many chronic inflammatory diseases. Recent reports have hypothesized that staphylococcal exotoxins might be related to inflammatory mucosal changes seen in chronic sinusitis with nasal polyps (CRS-NPs). Staphylococcal exotoxins have the capacity to act as superantigens (SAgs), bypassing normal antigen processing and directly stimulating a massive inflammatory response. The objective of this study was to analyze polyp tissue samples from patients with antrochoanal polyps (ACPs) and CRS-NPs for the presence of staphylococcal exotoxins.

Study Design

Prospective cohort study.

Setting

Tertiary medical center.

Subjects and Methods

Tissue samples were obtained from 29 patients and 16 controls. Thirteen of 29 patients had ACPs, and 16 had CRS-NPs. Specimens were analyzed for the presence of 5 staphylococcal exotoxins (SEA, SEB, SEC, SED, and toxic shock syndrome toxin–1) using enzyme-linked immunosorbent assay (ELISA).

Results

At least 1 toxin was detected in 7 of 13 patients with ACPs and in 13 of 16 patients with CRS-NPs, whereas it was detected in only 4 controls. There were no statistically significant differences between ACP and control groups ( P = .063). Our results showed a statistically significant association between toxin detection and patients with CRS-NPs ( P = .003).

Conclusion

Inflammatory triggers in ACP remain a subject of debate, and this study does not support the hypothesis that staphylococcal exotoxins may play a role in ACP ethiopathogenesis. Our research is consistent with the possibility of SAgs as etiological agents in the development of bilateral nasal polyposis.

Treatment of septic shock with continuous HDF using 2 PMMA hemofilters for enhanced intensity

PURPOSE

Cytokines play pivotal roles in the pathophysiology of severe sepsis/septic shock, and continuous hemodiafiltration using a polymethylmethacrylate membrane hemofilter (PMMA-CHDF) removes cytokines efficiently and continuously, mainly through adsorption to a hemofilter membrane. The aim of this study was to investigate the clinical efficacy of enhanced intensity PMMA-CHDF in treating refractory septic shock.

METHODS

Seventy-two septic shock patients admitted to the intensive care unit (ICU) underwent critical care including PMMA-CHDF. We employed enhanced intensity PMMA-CHDF to improve the cytokine removal rate by increasing the hemofilter membrane area in 10 refractory septic shock patients (enhanced intensity group, EI group; 2 extracorporeal CHDF circuits using the hemofilter with a larger membrane area of 2.1 m2). Other patients undergoing conventional PMMA-CHDF and matched for severity with the EI group, comprised a matched conventional group (MC group; using a PMMA membrane hemofilter with a membrane area of 1.0 m2; n=15). The case-control comparison was performed between the 2 groups.

RESULTS

Enhanced intensity PMMA-CHDF significantly increased mean arterial pressure by 23.8% in 1 hour (p=0.037), decreased the blood lactate level by 28.6% in 12 hours (p=0.006), and reduced blood IL-6 level in 24 hours (p=0.005). The ICU survival rate in the EI group was significantly better than that in the MC group (60% vs. 13.3%, p=0.028).

CONCLUSION

Enhanced intensity PMMA-CHDF may improve hemodynamics and survival rate in patients with refractory septic shock.

Multifaceted interactions of bacterial toxins with the gastrointestinal mucosa

The digestive tract is one of the ecosystems that harbors the largest number and greatest variety of bacteria. Among them, certain bacteria have developed various strategies, including the synthesis of virulence factors such as toxins, to interact with the intestinal mucosa, and are responsible for various pathologies. A large variety of bacterial toxins of different sizes, structures and modes of action are able to interact with the gastrointestinal mucosa. Some toxins, termed enterotoxins, directly stimulate fluid secretion in enterocytes or cause their death, whereas other toxins pass through the intestinal barrier and disseminate by the general circulation to remote organs or tissues, where they are active. After recognition of a membrane receptor on target cells, toxins can act at the cell membrane by transducing a signal across the membrane in a hormone-like manner, by pore formation or by damaging membrane compounds. Other toxins can enter the cells and modify an intracellular target leading to a disregulation of certain physiological processes or disorganization of some structural architectures and cell death. Toxins are fascinating molecules, which mimic or interfere with eukaryotic physiological processes. Thereby, they have permitted the identification and characterization of new natural hormones or regulatory pathways. Besides use as protective antigens in vaccines, toxins offer multiple possibilities in pharmacology, such as immune modulation or specific delivery of a protein of interest into target cells.

GenHtr: a tool for comparative assessment of genetic heterogeneity in microbial genomes generated by massive short-read sequencing

Background

Microevolution is the study of short-term changes of alleles within a population and their effects on the phenotype of organisms. The result of the below-species-level evolution is heterogeneity, where populations consist of subpopulations with a large number of structural variations. Heterogeneity analysis is thus essential to our understanding of how selective and neutral forces shape bacterial populations over a short period of time. The Solexa Genome Analyzer, a next-generation sequencing platform, allows millions of short sequencing reads to be obtained with great accuracy, allowing for the ability to study the dynamics of the bacterial population at the whole genome level. The tool referred to as Gen^Htr was developed for genome-wide heterogeneity analysis.

Results

For particular bacterial strains, Gen^Htr relies on a set of Solexa short reads on given bacteria pathogens and their isogenic reference genome to identify heterogeneity sites, the chromosomal positions with multiple variants of genes in the bacterial population, and variations that occur in large gene families. Gen^Htr accomplishes this by building and comparatively analyzing genome-wide heterogeneity genotypes for both the newly sequenced genomes (using massive short-read sequencing) and their isogenic reference (using simulated data). As proof of the concept, this approach was applied to SRX007711, the Solexa sequencing data for a newly sequenced Staphylococcus aureus subsp. USA300 cell line, and demonstrated that it could predict such multiple variants. They include multiple variants of genes critical in pathogenesis, e.g. genes encoding a LysR family transcriptional regulator, 23 S ribosomal RNA, and DNA mismatch repair protein MutS. The heterogeneity results in non-synonymous and nonsense mutations, leading to truncated proteins for both LysR and MutS.

Conclusion

Gen^Htr was developed for genome-wide heterogeneity analysis. Although it is much more time-consuming when compared to Maq, a popular tool for SNP analysis, Gen^Htr is able to predict potential multiple variants that pre-exist in the bacterial population as well as SNPs that occur in the highly duplicated gene families. It is expected that, with the proper experimental design, this analysis can improve our understanding of the molecular mechanism underlying the dynamics and the evolution of drug-resistant bacterial pathogens.

Superantigens

Superantigens (SAgs) are derived from diverse sources, including bacteria, viruses, and human hepatic tissue. SAgs initially cause lymphocyte activation but then result in clonal deletion and anergy, leading to immune tolerance. They can also act as superallergens by stimulating a broad spectrum of mast cells and basophils in patients with allergic conditions. The newly described staphylococcal SAg-like proteins subvert innate immune function by several mechanisms, which are distinct from SAgs' effects on lymphocytes and other acquired immune processes. There is mounting evidence to suggest that SAgs play a role in the pathophysiology of inflammatory airway disease. The pathophysiologic role of SAg-like proteins awaits clarification.

Procession to pediatric bacteremia and sepsis: covert operations and failures in diplomacy

Despite advances in diagnosis and treatment, bacterial sepsis remains a major cause of pediatric morbidity and mortality, particularly among neonates, the critically ill, and the growing immunocompromised patient population. Sepsis is the end point of a complex and dynamic series of events in which both host and microbial factors drive high morbidity and potentially lethal physiologic alterations. In this article we provide a succinct overview of the events that lead to pediatric bloodstream infections (BSIs) and sepsis, with a focus on the molecular mechanisms used by bacteria to subvert host barriers and local immunity to gain access to and persist within the systemic circulation. In the events preceding and during BSI and sepsis, Gram-positive and Gram-negative pathogens use a battery of factors for translocation, inhibition of immunity, molecular mimicry, intracellular survival, and nutrient scavenging. Gaps in understanding the molecular pathogenesis of bacterial BSIs and sepsis are highlighted as opportunities to identify and develop new therapeutics.

HIV-1 neutralization profile and plant-based recombinant expression of actinohivin, an Env glycan-specific lectin devoid of T-cell mitogenic activity

The development of a topical microbicide blocking the sexual transmission of HIV-1 is urgently needed to control the global HIV/AIDS pandemic. The actinomycete-derived lectin actinohivin (AH) is highly specific to a cluster of high-mannose-type glycans uniquely found on the viral envelope (Env). Here, we evaluated AH's candidacy toward a microbicide in terms of in vitro anti-HIV-1 activity, potential side effects, and recombinant producibility. Two validated assay systems based on human peripheral blood mononuclear cell (hPBMC) infection with primary isolates and TZM-bl cell infection with Env-pseudotyped viruses were employed to characterize AH's anti-HIV-1 activity. In hPMBCs, AH exhibited nanomolar neutralizing activity against primary viruses with diverse cellular tropisms, but did not cause mitogenicity or cytotoxicity that are often associated with other anti-HIV lectins. In the TZM-bl-based assay, AH showed broad anti-HIV-1 activity against clinically-relevant, mucosally transmitting strains of clades B and C. By contrast, clade A viruses showed strong resistance to AH. Correlation analysis suggested that HIV-1's AH susceptibility is significantly linked to the N-glycans at the Env C2 and V4 regions. For recombinant (r)AH expression, we evaluated a tobacco mosaic virus-based system in Nicotiana benthamiana plants as a means to facilitate molecular engineering and cost-effective mass production. Biochemical analysis and an Env-mediated syncytium formation assay demonstrated high-level expression of functional rAH within six days. Taken together, our study revealed AH's cross-clade anti-HIV-1 activity, apparent lack of side effects common to lectins, and robust producibility using plant biotechnology. These findings justify further efforts to develop rAH toward a candidate HIV-1 microbicide.

Streptococcus suis: a new emerging or an old neglected zoonotic pathogen?

Infections caused by Streptococcus suis are considered a global and an economical problem in the swine industry. Moreover, S. suis is an agent of zoonosis that afflicts people in close contact with infected pigs or pork-derived products. Although sporadic cases of S. suis infections in humans (mainly meningitis) have been reported during the last 40 years, a large outbreak due to this pathogen emerged in the summer of 2005 in China. The severity of the infection in humans during the outbreak, such as a shorter incubation time, more rapid disease progression and higher rate of mortality, attracted a lot of attention from the scientific community and the general press. In fact, the number of publications on S. suis (including the number of reported human cases) has significantly increased during recent years. In this article we critically review the present knowledge on S. suis infection in humans, we discuss the hypotheses that may explain the 2005 outbreak and the repercussion of such an episode on the scientific community.

Contribution of the flexible loop region to the function of staphylococcal enterotoxin B

Staphylococcal enterotoxin B (SEB), a toxin produced by Staphylococcus aureus, causes food poisoning and other fatal diseases by inducing high levels of pro-inflammatory cytokines. These cytokines are released from CD4+ T cells and major histocompatibility complex (MHC) class II antigen-presenting cells, which are activated through binding of wild-type (WT) SEB to both the MHC class II molecule and specific T-cell receptor Vbeta chains. Here, we focused on a trypsin/cathepsin cleavage site of WT SEB, which is known to be cleaved in vivo between Lys97 and Lys98, located within the loop region. To know the function of the cleavage, an SEB mutant, in which both of these Lys residues have been changed to Ser, was examined. This mutant showed prolonged tolerance to protease cleavage at a different site between Thr107 and Asp108, and structural analyses revealed no major conformational differences between WT SEB and the mutant protein. However, differential scanning calorimetric analysis showed an increase in enthalpy upon thermal denaturation of the mutant protein, which correlated with the speed of cleavage between Thr107 and Asp108. The mutant protein also had slightly increased affinity for MHC. In the in vivo experiment, the SEB mutant showed lower proliferative response in peripheral blood mononuclear cells and had lower cytokine-induction activity, compared with WT SEB. These results highlight the importance of the flexible loop region for the functional, physical and chemical properties of WT SEB, thus providing insight into the nature of WT SEB that was unrevealed previously.

Preparation and in-vitro bioactivity of a novel superantigen conjugate targeting bladder carcinoma

Objectives

Superantigens have shown potent effects against bladder tumours by inducing Vβ-specific T-lymphocyte proliferation and massive cytokine release but therapeutic benefit is compromised by cytotoxicity towards non-malignant cells and hypotoxicity to major histocompability complex (MHC) II-negative tumour cells. We are therefore interested in a conjugate preparation of a monoclonal antibody (MAb)—superantigens conjugate for which these drawbacks would be resolved.

Methods

The Fab fragment of the anti-bladder carcinoma MAb BDI-1 was conjugated to one member of the staphylococcal enterotoxin A (SEA) superantigen using the chemical conjugating reagent, N-succinimidyl 3-(2-pyridyldithio) propionate.

Results

After HPLC purification through a Superdex-200 gel column, another peak with a molecular mass of 250 KDa was observed before Fab and SEA were eluted. Indirect immunocytochemical analysis and immunofluorescence tests showed that the cell membranes of most human bladder cancer cells were positively stained only by the conjugate, confirming the ability of the conjugate to target human bladder carcinoma. Peripheral blood mononuclear cell proliferation and cytokine release were similar with the conjugate and SEA. Cytotoxicity targeting in MHC II-negative bladder cancer cell lines, evaluated by flow cytometry, showed significant differences between the conjugate and SEA, whereas there was no difference in the Lovo colon cancer cell line.

Conclusions

These findings indicate the conjugate of SEA protein and BDI-1 Fab fragment was prepared successfully and targeted bladder carcinoma in vitro.

Streptococcus adherence and colonization

Streptococci readily colonize mucosal tissues in the nasopharynx; the respiratory, gastrointestinal, and genitourinary tracts; and the skin. Each ecological niche presents a series of challenges to successful colonization with which streptococci have to contend. Some species exist in equilibrium with their host, neither stimulating nor submitting to immune defenses mounted against them. Most are either opportunistic or true pathogens responsible for diseases such as pharyngitis, tooth decay, necrotizing fasciitis, infective endocarditis, and meningitis. Part of the success of streptococci as colonizers is attributable to the spectrum of proteins expressed on their surfaces. Adhesins enable interactions with salivary, serum, and extracellular matrix components; host cells; and other microbes. This is the essential first step to colonization, the development of complex communities, and possible invasion of host tissues. The majority of streptococcal adhesins are anchored to the cell wall via a C-terminal LPxTz motif. Other proteins may be surface anchored through N-terminal lipid modifications, while the mechanism of cell wall associations for others remains unclear. Collectively, these surface-bound proteins provide Streptococcus species with a "coat of many colors," enabling multiple intimate contacts and interplays between the bacterial cell and the host. In vitro and in vivo studies have demonstrated direct roles for many streptococcal adhesins as colonization or virulence factors, making them attractive targets for therapeutic and preventive strategies against streptococcal infections. There is, therefore, much focus on applying increasingly advanced molecular techniques to determine the precise structures and functions of these proteins, and their regulatory pathways, so that more targeted approaches can be developed.

Gram-positive toxic shock syndromes

Toxic shock syndrome (TSS) is an acute, multi-system, toxin-mediated illness, often resulting in multi-organ failure. It represents the most fulminant expression of a spectrum of diseases caused by toxin-producing strains of Staphylococcus aureus and Streptococcus pyogenes (group A streptococcus). The importance of Gram-positive organisms as pathogens is increasing, and TSS is likely to be underdiagnosed in patients with staphylococcal or group A streptococcal infection who present with shock. TSS results from the ability of bacterial toxins to act as superantigens, stimulating immune-cell expansion and rampant cytokine expression in a manner that bypasses normal MHC-restricted antigen processing. A repetitive cycle of cell stimulation and cytokine release results in a cytokine avalanche that causes tissue damage, disseminated intravascular coagulation, and organ dysfunction. Specific therapy focuses on early identification of the illness, source control, and administration on antimicrobial agents including drugs capable of suppressing toxin production (eg, clindamycin, linezolid). Intravenous immunoglobulin has the potential to neutralise superantigen and to mitigate subsequent tissue damage.

Diagnosis of toxic shock syndrome by two different systems; clinical criteria and monitoring of TSST-1-reactive T cells

Two methods of TSS diagnosis were evaluated: comparison of symptoms with clinical criteria and monitoring for evidence of selective activation of Vbeta2(+) T cells by the causative toxin, TSS toxin-1 (TSST-1). Ten patients with acute and systemic febrile infections caused by Staphylococcus aureus were monitored for increase in TSST-1-reactive Vbeta2(+) T cells during their clinical courses. Nine of the ten patients were diagnosed with TSS based on evidence of selective activation of Vbeta2(+) T cells by TSST-1; however, clinical symptoms met the clinical criteria for TSS in only six of these nine patients. In the remaining patient, clinical symptoms met the clinical criteria, but selective activation of Vbeta2(+) T cells was not observed. Time taken to reach the diagnosis of TSS could be significantly shortened by utilizing the findings from tracing Vbeta2(+) T cells. In vitro studies showed that TSST-1- reactive T cells from TSS patients were anergic in the early phase of their illness. Examining selective activation of Vbeta2(+) T cells could be a useful tool to supplement clinical criteria for early diagnosis of TSS.

Measurement of proliferative responses of cultured lymphocytes

Measurement of proliferative responses of human lymphocytes is a fundamental technique for the assessment of their biological responses to various stimuli. Most simply, this involves measurement of the number of cells present in a culture before and after the addition of a stimulating agent. This unit contains several different prototype protocols to measure the proliferative response of lymphocytes following exposure to mitogens, antigens, allogeneic or autologous cells, or soluble factors. Each of these protocols can be used in conjunction with an accompanying support protocol which contains methods for pulsing cultures with [3H]thymidine and determining incorporation of [3H]thymidine into DNA or assessing cell proliferation by nonradioactive methods, e.g., reduction of tetrazolium salts (MTT). The protocols described here provide an estimate of DNA synthesis and cell proliferation in an entire cell population, but do not provide information on the proliferation of individual cells. A protocol for CFSE labeling allows specific subpopulations of cells to be separated viably for further analysis.

Streptococcus sp. and Staphylococcus aureus isolates from patients with psoriasis possess genes that code for toxins (superantigens): clinical and therapeutic implications

Superantigens are powerful T lymphocyte-stimulating agents that are believed to contribute to the pathogenesis of certain diseases such as psoriasis. Toxins produced by Streptococcus pyogenes and Staphylococcus aureus are superantigens. The aim of this study was to detect genes that code for superantigens in Streptococcus and Staphylococcus aureus isolates from psoriatic patients. Primers to amplify streptococcal pyrogenic exotoxin A, B, and C and streptolysin O genes and staphylococcal enterotoxin A, B, C, and D genes were used. Streptococcal exotoxin B was detected in five streptococcal isolates. Staphyloccocus aureus enterotoxin A and/or C genes were detected in nine S. aureus isolates. Isolates from 13 of 22 patients possesed gene(s) that code for toxin(s) (superantigens). These results might support the role of superantigens in the exacerbation of psoriasis.

Activation of TAFI on the surface of Streptococcus pyogenes evokes inflammatory reactions by modulating the kallikrein/kinin system

Bacteria-controlled regulation of host responses to infection is an important virulence mechanism that has been demonstrated to contribute to disease progression. Here we report that the human pathogen Streptococcus pyogenes employs the procarboxypeptidase TAFI (thrombin-activatable fibrinolysis inhibitor) to modulate the kallikrein/kinin system. To this end, bacteria initiate a chain of events starting with the recruitment and activation of TAFI. This is followed by the assembly and induction of the contact system at the streptococcal surface, eventually triggering the release of bradykinin (BK). BK is then carboxyterminally truncated by activated TAFI, which converts the peptide from a kinin B(2) receptor ligand to a kinin B(1) receptor (B1R) agonist. Finally, we show that streptococcal supernatants indirectly amplify the B1R response as they act on peripheral blood mononuclear cells to secrete inflammatory cytokines that in turn stimulate upregulation of the B1R on human fibroblasts. Taken together our findings implicate a critical and novel role for streptococci-bound TAFI, as it processes BK to a B1R agonist at the bacterial surface and thereby may redirect inflammation from a transient to a chronic state.

Capsid size determination by Staphylococcus aureus pathogenicity island SaPI1 involves specific incorporation of SaPI1 proteins into procapsids

The Staphylococcus aureus pathogenicity island SaPI1 carries the gene for the toxic shock syndrome toxin (TSST-1) and can be mobilized by infection with S. aureus helper phage 80alpha. SaPI1 depends on the helper phage for excision, replication and genome packaging. The SaPI1-transducing particles comprise proteins encoded by the helper phage, but have a smaller capsid commensurate with the smaller size of the SaPI1 genome. Previous studies identified only 80alpha-encoded proteins in mature SaPI1 virions, implying that the presumptive SaPI1 capsid size determination function(s) must act transiently during capsid assembly or maturation. In this study, 80alpha and SaPI1 procapsids were produced by induction of phage mutants lacking functional 80alpha or SaPI1 small terminase subunits. By cryo-electron microscopy, these procapsids were found to have a round shape and an internal scaffolding core. Mass spectrometry was used to identify all 80alpha-encoded structural proteins in 80alpha and SaPI1 procapsids, including several that had not previously been found in the mature capsids. In addition, SaPI1 procapsids contained at least one SaPI1-encoded protein that has been implicated genetically in capsid size determination. Mass spectrometry on full-length phage proteins showed that the major capsid protein and the scaffolding protein are N-terminally processed in both 80alpha and SaPI1 procapsids.