Staphylococcal and streptococcal pyrogenic toxins involved in toxic shock syndrome and related illnesses

Toxic Shock Syndrome: A Literature Review

Toxic shock syndrome (TSS) is a rare, life-threatening, toxin-mediated infectious process linked, in the vast majority of cases, to toxin-producing strains of Staphylococcus aureus or Streptococcus pyogenes. The pathophysiology, epidemiology, clinical presentation, microbiological features, management and outcome of TSS are described in this review. Bacterial superantigenic exotoxins induces unconventional polyclonal lymphocyte activation, which leads to rapid shock, multiple organ failure syndrome, and death. The main described superantigenic exotoxins are toxic shock syndrome toxin-1 (TSST-1) and enterotoxins for Staphylococcus aureus and Streptococcal pyrogenic exotoxins (SpE) A, B, and C and streptococcal superantigen A (SsA) for Streptococcus pyogenes. Staphylococcal TSS can be menstrual or nonmenstrual. Streptococcal TSS is linked to a severe group A streptococcal infection and, most frequently, to a necrotizing soft tissue infection. Management of TSS is a medical emergency and relies on early detection, immediate resuscitation, source control and eradication of toxin production, bactericidal antibiotic treatment, and protein synthesis inhibiting antibiotic administration. The interest of polyclonal intravenous immunoglobulin G administration as an adjunctive treatment for TSS requires further evaluation. Scientific literature on TSS mainly consists of observational studies, clinical cases, and in vitro data; although more data on TSS are required, additional studies will be difficult to conduct due to the low incidence of the disease.

Blocking Superantigen-Mediated Diseases: Challenges and Future Trends

Superantigens are virulence factors secreted by microorganisms that can cause various immune diseases, such as overactivating the immune system, resulting in cytokine storms, rheumatoid arthritis, and multiple sclerosis. Some studies have demonstrated that superantigens do not require intracellular processing and instated bind as intact proteins to the antigen-binding groove of major histocompatibility complex II on antigen-presenting cells, resulting in the activation of T cells with different T-cell receptor Vβ and subsequent overstimulation. To combat superantigen-mediated diseases, researchers have employed different approaches, such as antibodies and simulated peptides. However, due to the complex nature of superantigens, these approaches have not been entirely successful in achieving optimal therapeutic outcomes. CD28 interacts with members of the B7 molecule family to activate T cells. Its mimicking peptide has been suggested as a potential candidate to block superantigens, but it can lead to reduced T-cell activity while increasing the host's infection risk. Thus, this review focuses on the use of drug delivery methods to accurately target and block superantigens, while reducing the adverse effects associated with CD28 mimic peptides. We believe that this method has the potential to provide an effective and safe therapeutic strategy for superantigen-mediated diseases.

Toxin exposure and HLA alleles determine serum antibody binding to toxic shock syndrome toxin 1 (TSST-1) of Staphylococcus aureus

Life-threatening toxic shock syndrome is often caused by the superantigen toxic shock syndrome toxin-1 (TSST-1) produced by Staphylococcus aureus. A well-known risk factor is the lack of neutralizing antibodies. To identify determinants of the anti-TSST-1 antibody response, we examined 976 participants of the German population-based epidemiological Study of Health in Pomerania (SHIP-TREND-0). We measured anti-TSST-1 antibody levels, analyzed the colonization with TSST-1-encoding S. aureus strains, and performed a genome-wide association analysis of genetic risk factors. TSST-1-specific serum IgG levels varied over a range of 4.2 logs and were elevated by a factor of 12.3 upon nasal colonization with TSST-1-encoding S. aureus. Moreover, the anti-TSST-1 antibody levels were strongly associated with HLA class II gene loci. HLA-DRB1*03:01 and HLA-DQB1*02:01 were positively, and HLA-DRB1*01:01 as well as HLA-DQB1*05:01 negatively associated with the anti-TSST-1 antibody levels. Thus, both toxin exposure and HLA alleles affect the human antibody response to TSST-1.

Staphylococcal Enterotoxin C2 Mutant-Induced Antitumor Immune Response Is Controlled by CDC42/MLC2-Mediated Tumor Cell Stiffness

As a biological macromolecule, the superantigen staphylococcal enterotoxin C2 (SEC2) is one of the most potent known T-cell activators, and it induces massive cytotoxic granule production. With this property, SEC2 and its mutants are widely regarded as immunomodulating agents for cancer therapy. In a previous study, we constructed an MHC-II-independent mutant of SEC2, named ST-4, which exhibits enhanced immunocyte stimulation and antitumor activity. However, tumor cells have different degrees of sensitivity to SEC2/ST-4. The mechanisms of immune resistance to SEs in cancer cells have not been investigated. Herein, we show that ST-4 could activate more powerful human lymphocyte granule-based cytotoxicity than SEC2. The results of RNA-seq and atomic force microscopy (AFM) analysis showed that, compared with SKOV3 cells, the softer ES-2 cells could escape from SEC2/ST-4-induced cytotoxic T-cell-mediated apoptosis by regulating cell softness through the CDC42/MLC2 pathway. Conversely, after enhancing the stiffness of cancer cells by a nonmuscle myosin-II-specific inhibitor, SEC2/ST-4 exhibited a significant antitumor effect against ES-2 cells by promoting perforin-dependent apoptosis and the S-phase arrest. Taken together, these data suggest that cell stiffness could be a key factor of resistance to SEs in ovarian cancer, and our findings may provide new insight for SE-based tumor immunotherapy.

The safety assessment of tampons: illustration of a comprehensive approach for four different products

Introduction

We illustrate a comprehensive tampon safety assessment approach that assures products can be used safely. Material biocompatibility, vaginal mucosa assessment, vaginal microbiome evaluation, and in vitro assessment of potential risk of staphylococcal toxic shock syndrome expressed through growth of Staphylococcus aureus (S. aureus) and production of TSST-1 are the four essential portions of the approach. Post-marketing surveillance informs of possible health effects that warrant follow up. The approach meets or exceeds US and international regulatory guidance and is described through the example of four tampon products.

Methods/Results

Each product is comprised mostly of large molecular weight components (cotton, rayon, polymers) that cannot pass the vaginal mucosa, are widely used across the industry, and replete with a vast body of safety data and a long history of safe use in the category. Quantitative risk assessment of all small molecular weight components assured a sufficient margin of safety supporting their use. Vaginal mucosa assessment confirmed that pressure points, rough edges and/or sharp contact points were absent. A randomized cross-over clinical trial (ClinicalTrials.gov Identifier: NCT03478371) revealed favorable comfort ratings, and few complaints of irritation, burning, stinging, or discomfort upon insertion, wear, and removal. Adverse events were few, mild in severity, self-limited and resolved without treatment. Vaginal microbiota assessment in vitro presented no adverse effect on microbial growth. Culture-independent microbiome analyses from vaginal swab samples obtained during the clinical trial showed no differences attributable to tampon usage, but instead due to statistically significant subject-to-subject variability. Growth of S. aureus and TSST-1 toxin production in the presence of any of the four products in vitro were statistically significantly reduced when compared to medium control alone.

Discussion

The data from the four elements of the comprehensive safety assessment approach illustrated herein confirm that tampons evaluated using this system can be used safely for menstrual protection. A post-marketing surveillance system that monitors and responds to in-market experiences indicated in-use tolerability of the product among consumers, thus confirming the conclusions of the pre-marketing safety assessment.

Staphylococcal Enterotoxin B and C Mutants and Vaccine Toxoids

Three mutants individually of both staphylococcal enterotoxins B and C were prepared by site-specific mutagenesis of enterotoxin amino acids that contact host T lymphocyte immune cell receptor sites (N23A, Q210A, and N23A/Q210A); these amino acids are shared between the two enterotoxins, and mutations reduce the interaction with the variable part of the β-chain of the T lymphocyte receptor. The mutant proteins, as expressed in Staphylococcus aureus RN4220, lacked biological toxicity as measured by the loss of (i) stimulation of rabbit splenocyte proliferation, (ii) pyrogenicity, and (iii) the ability to enhance the lethality of endotoxin shock, compared to wild-type enterotoxins. In addition, the mutants were able to vaccinate rabbits against pyrogenicity, the enhancement of endotoxin shock, and lethality in a pneumonia model when animals were challenged with methicillin-resistant S. aureus. Three vaccine injections (one primary and two boosters) protected rabbits for at least 3.5 months postvaccination when challenged with wild-type enterotoxins (last time point tested). These mutant proteins have the potential to function as toxoid vaccines against these two causes of nonmenstrual toxic shock syndrome (TSS). IMPORTANCE Toxic shock syndrome toxin 1 (TSST-1) and staphylococcal enterotoxins B and C cause the majority of cases of staphylococcal toxic shock syndrome. Previously, vaccine toxoids of TSST-1 have been prepared. In this study, vaccine toxoids of enterotoxins B and C were prepared. The toxoids lost biological toxicity but were able to vaccinate rabbits against lethal TSS.

TEN mimics: Classification and practical approach to toxic epidermal necrolysis-like dermatoses

Toxic epidermal necrolysis (TEN) is an acute life-threatening dermatologic emergency. However, many dermatoses can present with a TEN-like eruption. Those "TEN-mimics" are a true diagnostic challenge and an alarming differential diagnosis to such a serious condition. Herein, we will expose and classify the landscape of TEN-mimics. Also, the key differentiating clinical and/or laboratory points will be highlighted to help an accurate diagnosis of either a TEN or a TEN-like presentation.

Superantigens, a Paradox of the Immune Response

Staphylococcal enterotoxins are a wide family of bacterial exotoxins with the capacity to activate as much as 20% of the host T cells, which is why they were called superantigens. Superantigens (SAgs) can cause multiple diseases in humans and cattle, ranging from mild to life-threatening infections. Almost all S. aureus isolates encode at least one of these toxins, though there is no complete knowledge about how their production is triggered. One of the main problems with the available evidence for these toxins is that most studies have been conducted with a few superantigens; however, the resulting characteristics are attributed to the whole group. Although these toxins share homology and a two-domain structure organization, the similarity ratio varies from 20 to 89% among different SAgs, implying wide heterogeneity. Furthermore, every attempt to structurally classify these proteins has failed to answer differential biological functionalities. Taking these concerns into account, it might not be appropriate to extrapolate all the information that is currently available to every staphylococcal SAg. Here, we aimed to gather the available information about all staphylococcal SAgs, considering their functions and pathogenicity, their ability to interact with the immune system as well as their capacity to be used as immunotherapeutic agents, resembling the two faces of Dr. Jekyll and Mr. Hyde.

Prospective bacterial and fungal sources of hyaluronic acid: A review

The unique biological and rheological properties make hyaluronic acid a sought-after material for medicine and cosmetology. Due to very high purity requirements for hyaluronic acid in medical applications, the profitability of streptococcal fermentation is reduced. Production of hyaluronic acid by recombinant systems is considered a promising alternative. Variations in combinations of expressed genes and fermentation conditions alter the yield and molecular weight of produced hyaluronic acid. This review is devoted to the current state of hyaluronic acid production by recombinant bacterial and fungal organisms.

Differences in the Accessory Genomes and Methylomes of Strains of Streptococcus equi subsp. equi and of Streptococcus equi subsp. zooepidemicus Obtained from the Respiratory Tract of Horses from Texas

Streptococcus equi subsp. equi (SEE) is a host-restricted equine pathogen considered to have evolved from Streptococcus equi subsp. zooepidemicus (SEZ). SEZ is promiscuous in host range and is commonly recovered from horses as a commensal. Comparison of a single strain each of SEE and SEZ using whole-genome sequencing, supplemented by PCR of selected genes in additional SEE and SEZ strains, was used to characterize the evolution of SEE. But the known genetic variability of SEZ warrants comparison of the whole genomes of multiple SEE and SEZ strains. To fill this knowledge gap, we utilized whole-genome sequencing to characterize the accessory genome elements (AGEs; i.e., elements present in some SEE strains but absent in SEZ or vice versa) and methylomes of 50 SEE and 50 SEZ isolates from Texas. Consistent with previous findings, AGEs consistently found in all SEE isolates were primarily from mobile genetic elements that might contribute to host restriction or pathogenesis of SEE. Fewer AGEs were identified in SEZ because of the greater genomic variability among these isolates. The global methylation patterns of SEE isolates were more consistent than those of the SEZ isolates. Among homologous genes of SEE and SEZ, differential methylation was identified only in genes of SEE encoding proteins with functions of quorum sensing, exopeptidase activity, and transitional metal ion binding. Our results indicate that effects of genetic mobile elements in SEE and differential methylation of genes shared by SEE and SEZ might contribute to the host specificity of SEE.

IMPORTANCE Strangles, caused by the host-specific bacterium Streptococcus equi subsp. equi (SEE), is the most commonly diagnosed infectious disease of horses worldwide. Its ancestor, Streptococcus equi subsp. zooepidemicus (SEZ), is frequently isolated from a wide array of hosts, including horses and humans. A comparison of the genomes of a single strain of SEE and SEZ has been reported, but sequencing of further isolates has revealed variability among SEZ strains. Thus, the importance of this study is that it characterizes genomic and methylomic differences of multiple SEE and SEZ isolates from a common geographic region (viz., Texas). Our results affirm many of the previously described differences between the genomes of SEE and SEZ, including the role of mobile genetic elements in contributing to host restriction. We also provide the first characterization of the global methylome of Streptococcus equi and evidence that differential methylation might contribute to the host restriction of SEE.

Granzyme B and perforin produced by SEC2 mutant-activated human CD4+ T cells and CD8+ T cells induce apoptosis of K562 leukemic cells by the mitochondrial apoptotic pathway

Staphylococcal enterotoxin C2 (SEC2), a classical representative of superantigens, activates T cells that produce massive cytokines. This characteristic makes SEC2 a promising candidate drug for cancer immunotherapy. Previous study showed that ST-4, a SEC2 mutant, enhanced recognition of mouse T-cell receptor Vβ regions, and activated the increased number of T cells that produced more cytokines. However, the underlying molecular mechanism for stimulation of human peripheral blood mononuclear cells (PBMCs) and antitumor effect on human tumor cells remains unknown. Herein, we showed that ST-4 significantly activated TCR Vβ 12, 13A, 14, 15, 17, and 20 CD4⁺ and CD8⁺ T cells, which produced substantial amounts of granzyme B and perforin. These cytokines exhibited antitumor effect on K562 cells by promoting apoptosis and inducing S-phase cell cycle arrest. Conversely, the granzyme B inhibitor or perforin inhibitor significantly weakened antitumor effect of ST-4, accompanied by a decrease of cleaved proapoptotic BAX and cytochrome c, and an increase of antiapoptotic BCL2. Taken together, these data suggest that granzyme B and perforin produced by ST-4-activated CD4⁺ T cells and CD8⁺ T cells play a pivotal role in inducing K562 cell apoptosis by the mitochondrial apoptotic pathway, and support ST-4 as a potential candidate for cancer immunotherapy.

Induction of CD4+ regulatory T cells by stimulation with Staphylococcal Enterotoxin C2 through different signaling pathways

As a member of superantigens, Staphylococcal Enterotoxin C2 (SEC2) can potently activate T cells expressing specific Vβ repertoires and has been applied in clinic for tumor immunotherapy in China for more than 20 years. However, excessive activation of T cells by over-stimulation with superantigen are always followed by eliciting regulatory T cells (Tregs) induction and functional immunosuppression, which brings uncertainties to SEC2 application in tumor immunotherapy. In this study, we found that SEC2 could induce CD4+CD25+Foxp3+ Tregs from the murine splenocytes in dose and time related manners. The induced Tregs with high expression of GITR and CTLA-4 and low expression of CD127 were TCR Vβ8.2-specific and have character of IL-10 production in a SEC2 dose-depended manner. Importantly, SEC2-induced CD4+ Tregs showed the potent capacity of suppressing proliferation of intact murine splenocytes response to SEC2. Furthermore, by using specific inhibitors or neutralizing antibody, we proved that the signaling pathways of TCR-NFAT/AP-1, IL-2-STAT5, and TGF-β-Smad3 play crucial roles in Tregs induction by SEC2. These findings will help us better understand the balance of immune stimulation and immunosuppression mediated by SEC2 and provide valuable guidance for SEC2 application in antitumor immunology.

Superantigen Recognition and Interactions: Functions, Mechanisms and Applications

Superantigens are unconventional antigens which recognise immune receptors outside their usual recognition sites e.g. complementary determining regions (CDRs), to elicit a response within the target cell. T-cell superantigens crosslink T-cell receptors and MHC Class II molecules on antigen-presenting cells, leading to lymphocyte recruitment, induction of cytokine storms and T-cell anergy or apoptosis among many other effects. B-cell superantigens, on the other hand, bind immunoglobulins on B-cells, affecting opsonisation, IgG-mediated phagocytosis, and driving apoptosis. Here, through a review of the structural basis for recognition of immune receptors by superantigens, we show that their binding interfaces share specific physicochemical characteristics when compared with other protein-protein interaction complexes. Given that antibody-binding superantigens have been exploited extensively in industrial antibody purification, these observations could facilitate further protein engineering to optimize the use of superantigens in this and other areas of biotechnology.

Temperate Bacteriophages-The Powerful Indirect Modulators of Eukaryotic Cells and Immune Functions

Bacteriophages are natural biological entities that limit the growth and amplification of bacteria. They are important stimulators of evolutionary variability in bacteria, and currently are considered a weapon against antibiotic resistance of bacteria. Nevertheless, apart from their antibacterial activity, phages may act as modulators of mammalian immune responses. In this paper, we focus on temperate phages able to execute the lysogenic development, which may shape animal or human immune response by influencing various processes, including phagocytosis of bacterial invaders and immune modulation of mammalian host cells.

Update on molecular diversity and multipathogenicity of staphylococcal superantigen toxins

Staphylococcal superantigen (SAg) toxins are the most notable virulence factors associated with Staphylococcus aureus, which is a pathogen associated with serious community and hospital acquired infections in humans and various diseases in animals. Recently, SAg toxins have become a superfamily with 29 types, including staphylococcal enterotoxins (SEs) with emetic activity, SE-like toxins (SEls) that do not induce emesis in primate models or have yet not  been tested, and toxic shock syndrome toxin-1 (TSST-1). SEs and SEls can be subdivided into classical types (SEA to SEE) and novel types (SEG to SElY, SE01, SE02, SEl26 and SEl27). The genes of SAg toxins are located in diverse accessory genetic elements and share certain structural and biological properties. SAg toxins are heat-stable proteins that exhibit pyrogenicity, superantigenicity and capacity to induce lethal hypersensitivity to endotoxin in humans and animals. They have multiple pathogenicities that can interfere with normal immune function of host, increase the chances of survival and transmission of pathogenic bacteria in host, consequently contribute to the occurrence and development of various infections, persistent infections or food poisoning. This review focuses on the following aspects of SAg toxins: (1) superfamily members of classic and novelty discovered staphylococcal SAgs; (2) diversity of gene locations and molecular structural characteristics; (3) biological characteristics and activities; (4) multi-pathogenicity of SAgs in animal and human diseases, including bovine mastitis, swine sepsis, abscesses and skin edema in pig, arthritis and septicemia in poultry, and nosocomial infections and food-borne diseases in humans.

An immunoinformatics approach for the design of a multi-epitope vaccine targeting super antigen TSST-1 of Staphylococcus aureus

Background

TSST-1 is a secretory and pyrogenic superantigen that is being responsible for staphylococcal mediated food poisoning and associated clinical manifestations. It is one of the main targets for the construction of vaccine candidates against Staphylococcus aureus. Most of the vaccines have met failure due to adverse reactions and toxicity reported during late clinical studies. To overcome this, an immunoinformatics approach is being used in the present study for the design of a multi-epitope vaccine to circumvent the problems related to toxicity and allergenicity.

Results

In this study, a multi-epitope vaccine against Staphylococcus aureus targeting TSST-1 was designed through an immunoinformatics approach. B cell and T cell epitopes were predicted in silico and mapped with linkers to avoid junctional immunogenicity and to ensure the efficient presentation of exposed epitopes through HLA. β-defensin and PADRE were adjusted at the N-terminal end of the final vaccine as adjuvants. Physiochemical parameters, antigenicity, and allergenicity of the vaccine construct were determined with the help of online servers. The three-dimensional structure of the vaccine protein was predicted and validated with various tools. The affinity of the vaccine with TLR-3 was studied through molecular docking studies and the interactions of two proteins were visualized using LigPlot⁺. The vaccine was successfully cloned in silico into pET-28a (+) for efficient expression in E. coli K12 system. Population coverage analysis had shown that the vaccine construct can cover 83.15% of the global population. Immune simulation studies showed an increase in the antibody levels, IL-2, IFN-γ, TGF-β, B cell, and T cell populations and induced primary, secondary, and tertiary immune responses.

Conclusion

Multi-epitope vaccine designed through a computational approach is a non-allergic and non-toxic antigen. Preliminary in silico reports have shown that this vaccine could elicit both B cell and T cell responses in the host as desired.

Early intravenous immunoglobulin therapy for group A β-haemolytic streptococcal meningitis with toxic shock syndrome

A woman in her forties was transferred to a Sydney (Australia)-based tertiary hospital, following presentation to a regional hospital with group A Streptococcus (GAS) otomastoiditis; complicated by meningitis, venous sinus thrombosis, haemorrhagic cerebral infarction and subdural empyema. She rapidly deteriorated with profound cardiovascular collapse. Despite initiation of high dose vasoactive therapy, she remained shocked and developed multiorgan dysfunction syndrome. Early intravenous immunoglobulin therapy (140 g in two doses) was initiated as an adjunct to antimicrobial, surgical and supportive care for refractory streptococcal toxic shock syndrome. Over the course of a twelve-day intensive care unit stay she made good progress with de-escalation of her vasoactive supportive care and reversal of her organ injuries. She was subsequently discharged to ward-based care. At her three-month follow-up appointment she had significantly reduced neurological deficit. Five months following her presentation to hospital she had returned to full-time work.

Staphylococcal Enterotoxin C2 Mutant-Directed Fatty Acid and Mitochondrial Energy Metabolic Programs Regulate CD8+ T Cell Activation

CD8⁺ T cells can switch between fatty acid catabolism and mitochondrial energy metabolism to sustain expansion and their cytotoxic functions. ST-4 is a TCR-enhanced mutant derived from superantigen staphylococcal enterotoxin C2 (SEC2), which can hyperactivate CD4⁺ T cells without MHC class II molecules. However, whether ST-4/SEC2 can enhance metabolic reprogramming in CD8⁺ T cells remains poorly understood. In this study, we found that ST-4, but not SEC2, could induce proliferation of purified CD8⁺ T cell from BALB/c mice in Vβ8.2- and -8.3-specific manners. Results of gas chromatography-mass spectroscopy analysis showed that fatty acid contents in CD8⁺ T cells were increased after ST-4 stimulation. Flow cytometry and Seahorse analyses showed that ST-4 significantly promoted mitochondrial energy metabolism in CD8⁺ T cells. We also observed significantly upregulated levels of gene transcripts for fatty acid uptake and synthesis, and significantly increased protein expression levels of fatty acid and mitochondrial metabolic markers of mTOR/PPARγ/SREBP1 and p38-MAPK signaling pathways in ST-4-activated CD8⁺ T cells. However, blocking mTOR, PPARγ, SREBP1, or p38-MAPK signals with specific inhibitors could significantly relieve the enhanced fatty acid catabolism and mitochondrial capacity induced by ST-4. In addition, blocking these signals inhibited ST-4-stimulated CD8⁺ T cell proliferation and effector functions. Taken together, our findings demonstrate that ST-4 enhanced fatty acid and mitochondria metabolic reprogramming through mTOR/PPARγ/SREBP and p38-MAPK signaling pathways, which may be important regulatory mechanisms of CD8⁺ T cell activation. Understanding the effects of ST-4-induced regulatory metabolic networks on CD8⁺ T cells provide important mechanistic insights to superantigen-based tumor therapy.

Molecular interaction between methicillin-resistant Staphylococcus aureus (MRSA) and chicken breast reveals enhancement of pathogenesis and toxicity for food-borne outbreak

To study pathogenesis and toxicity of Staphylococcus aureus in foods, FORC_062 was isolated from a human blood sample and complete genome sequence has a type II SCCmec gene cluster and a type II toxin-antitoxin system, indicating an MRSA strain. Its mobile gene elements has many pathogenic genes involved in host infection, biofilm formation, and various enterotoxin and hemolysin genes. Clinical MRSA is often found in animal foods and ingestion of MRSA-contaminated foods causes human infection. Therefore, it is very important to understand the role of contaminated foods. To elucidate the interaction between clinical MRSA FORC_062 and raw chicken breast, transcriptome analysis was conducted, showing that gene expressions of amino acid biosynthesis and metabolism were specifically down-regulated, suggesting that the strain may import and utilize amino acids from the chicken breast, but not able to synthesize them. However, toxin gene expressions were up-regulated, suggesting that human infection of S. aureus via contaminated food may be more fatal. In addition, the contaminated foods enhance multiple-antibiotic resistance activities and virulence factors in this clinical MRSA. Consequently, MRSA-contaminated food may play a role as a nutritional reservoir as well as in enhancing factor for pathogenesis and toxicity of clinical MRSA for severe food-borne outbreaks.

Toxic Shock Syndrome after Surgery: Case Presentation and Systematic Review of the Literature

Supplemental Digital Content is available in the text.

Toxic shock syndrome (TSS) is an underrecognized but highly fatal cause of septic shock in postoperative patients. Although it may present with no overt source of infection, its course is devastating and rapidly progressive. Surgeon awareness is needed to recognize and treat this condition appropriately. In this paper, we aim to describe a case of postoperative TSS, present a systematic review of the literature, and provide an overview of the disease for the surgeon.

Device-Associated Menstrual Toxic Shock Syndrome

In the 1980s, menstrual toxic shock syndrome (mTSS) became a household topic, particularly among mothers and their daughters. The research performed at the time, and for the first time, exposed the American public as well as the biomedical community, in a major way, to understanding disease progression and investigation. Those studies led to the identification of the cause, Staphylococcus aureus and the pyrogenic toxin superantigen TSS toxin 1 (TSST-1), and many of the risk factors, for example, tampon use. Those studies in turn led to TSS warning labels on the outside and inside of tampon boxes and, as important, uniform standards worldwide of tampon absorbency labeling. This review addresses our understanding of the development and conclusions related to mTSS and risk factors. We leave the final message that even though mTSS is not commonly in the news today, cases continue to occur. Additionally, S. aureus strains cycle in human populations in roughly 10-year intervals, possibly dependent on immune status. TSST-1-producing S. aureus bacteria appear to be reemerging, suggesting that physician awareness of this emergence and mTSS history should be heightened.

Toxic Shock Syndrome Toxin 1 Evaluation and Antibiotic Impact in a Transgenic Model of Staphylococcal Soft Tissue Infection

Staphylococcal toxic shock syndrome (TSS) is a life-threatening illness causing fever, rash, and shock, attributed to toxins produced by the bacterium Staphylococcus aureus, mainly toxic shock syndrome toxin 1 (TSST-1). TSS was in the past commonly linked with menstruation and high-absorbency tampons; now, TSS is more frequently triggered by other staphylococcal infections, particularly of skin and soft tissue. Investigating the progress and treatment of TSS in patients is challenging, as TSS is rare; animal models do not mimic TSS adequately, as toxins interact best with human immune cells. We developed a new model of staphylococcal soft tissue infection in mice producing human immune cell proteins, rendering them TSST-1 sensitive, to investigate TSS. The significance of our research was that TSST-1 was found in soft tissues and immune organs of mice and that early treatment of mice with the antibiotic clindamycin altered TSST-1 production. Therefore, the early treatment of patients suspected of having TSS with clindamycin may influence their response to treatment.

Nonmenstrual toxic shock syndrome (nmTSS), linked to TSST-1-producing CC30 Staphylococcus aureus, is the leading manifestation of toxic shock syndrome (TSS). Due to case rarity and a lack of tractable animal models, TSS pathogenesis is poorly understood. We developed an S. aureus abscess model in HLA class II transgenic mice to investigate pathogenesis and treatment. TSST-1 sensitivity was established using murine spleen cell proliferation assays and cytokine assays following TSST-1 injection in vivo. HLA-DQ8 mice were infected subcutaneously with a tst-positive CC30 methicillin-sensitive S. aureus clinical TSS-associated isolate. Mice received intraperitoneal flucloxacillin, clindamycin, flucloxacillin and clindamycin, or a control reagent. Abscess size, bacterial counts, TSST-1 expression, and TSST-1 bioactivity were measured in tissues. Antibiotic effects were compared with the effects of control reagent. Purified TSST-1 expanded HLA-DQ8 T-cell Vβ subsets 3 and 13 in vitro and instigated cytokine release in vivo, confirming TSST-1 sensitivity. TSST-1 was detected in abscesses (0 to 8.0 μg/ml) and draining lymph nodes (0 to 0.2 μg/ml) of infected mice. Interleukin 6 (IL-6), gamma interferon (IFN-γ), KC (CXCL1), and MCP-1 were consistent markers of inflammation during infection. Clindamycin-containing antibiotic regimens reduced abscess size and TSST-1 production. Infection led to detectable TSST-1 in soft tissues, and TSST-1 was detected in draining lymph nodes, events which may be pivotal to TSS pathogenesis. The reduction in TSST-1 production and lesion size after a single dose of clindamycin underscores a potential role for adjunctive clindamycin at the start of treatment of patients suspected of having TSS to alter disease progression.

IMPORTANCE Staphylococcal toxic shock syndrome (TSS) is a life-threatening illness causing fever, rash, and shock, attributed to toxins produced by the bacterium Staphylococcus aureus, mainly toxic shock syndrome toxin 1 (TSST-1). TSS was in the past commonly linked with menstruation and high-absorbency tampons; now, TSS is more frequently triggered by other staphylococcal infections, particularly of skin and soft tissue. Investigating the progress and treatment of TSS in patients is challenging, as TSS is rare; animal models do not mimic TSS adequately, as toxins interact best with human immune cells. We developed a new model of staphylococcal soft tissue infection in mice producing human immune cell proteins, rendering them TSST-1 sensitive, to investigate TSS. The significance of our research was that TSST-1 was found in soft tissues and immune organs of mice and that early treatment of mice with the antibiotic clindamycin altered TSST-1 production. Therefore, the early treatment of patients suspected of having TSS with clindamycin may influence their response to treatment.

Streptococcal Pyrogenic Exotoxin A-Stimulated Monocytes Mediate Regulatory T-Cell Accumulation through PD-L1 and Kynurenine

Bacterial superantigens (SAgs) are exotoxins that promote a fulminant activation of the immune system. The subsequent intense release of inflammatory cytokines often results in hypotension, shock, and organ failure with high mortality rates. In the current paradigm, the direct and simultaneous binding of SAgs with T-cell receptor (TCR)-bearing Vβ regions and conserved structures on major histocompatibility complex class II (MHC class II) on antigen-presenting cells (APCs) induces the activation of both cell types. However, by crosslinking MHC class II molecules, APCs can be activated by SAgs independently of T lymphocytes. Recently, we showed that streptococcal pyrogenic exotoxin A (SPEA) of Streptococcus pyogenes stimulates an immunogenic APC phenotype with upregulated costimulatory molecules and inflammatory cytokines. Additionally, we revealed that SPEA triggers immunosuppressive programs in monocytes that facilitate the accumulation of regulatory T cells (Tregs) in in vitro monocyte/CD4⁺ T-cell cocultures. Immunosuppressive factors include anti-inflammatory interleukin 10 (IL-10), co-inhibitory surface molecule programmed cell death 1 ligand 1 (PD-L1), and the inhibitory indoleamine 2,3-dioxygenase (IDO)/kynurenine effector system. In the present study, we investigated the underlying mechanism of SPEA-stimulated monocyte-mediated accumulation of Tregs. Blood-derived monocytes from healthy donors were stimulated with SPEA for 48 h (SPEA-monocytes). For the evaluation of SPEA-monocyte-mediated modulation of CD4⁺ T lymphocytes, SPEA was removed from the culture through extensive washing of cells before adding allogeneic CD3/CD28-activated T cells. Results: In coculture with allogeneic CD4⁺ T cells, SPEA-monocytes mediate apoptosis of CD4⁺Foxp3⁻ lymphocytes and accumulation of CD4⁺Foxp3⁺ Tregs. PD-L1 and kynurenine are critically involved in the mediated cell death because blocking both factors diminished apoptosis and decreased the proportion of the CD25⁺/Foxp3⁺ Treg subpopulation significantly. Upregulation of PD-L1 and kynurenine as well as SPEA-monocyte-mediated effects on T cells depend on inflammatory IL-1β. Our study shows that monocytes activated by SPEA mediate apoptosis of CD4⁺Foxp3⁻ T effector cells through PD-L1 and kynurenine. CD4⁺Foxp3⁺ T cells are resistant to apoptosis and accumulate in SPEA-monocyte/CD4⁺ T-cell coculture.

The Role of Streptococcal and Staphylococcal Exotoxins and Proteases in Human Necrotizing Soft Tissue Infections

Necrotizing soft tissue infections (NSTIs) are critical clinical conditions characterized by extensive necrosis of any layer of the soft tissue and systemic toxicity. Group A streptococci (GAS) and Staphylococcus aureus are two major pathogens associated with monomicrobial NSTIs. In the tissue environment, both Gram-positive bacteria secrete a variety of molecules, including pore-forming exotoxins, superantigens, and proteases with cytolytic and immunomodulatory functions. The present review summarizes the current knowledge about streptococcal and staphylococcal toxins in NSTIs with a special focus on their contribution to disease progression, tissue pathology, and immune evasion strategies.

Potent Neutralization of Staphylococcal Enterotoxin B In Vivo by Antibodies that Block Binding to the T-Cell Receptor

To develop an antibody (Ab) therapeutic against staphylococcal enterotoxin B (SEB), a potential incapacitating bioterrorism agent and a major cause of food poisoning, we developed a "class T" anti-SEB neutralizing Ab (GC132) targeting an epitope on SEB distinct from that of previously developed "class M" Abs. A systematic engineering approach was applied to affinity-mature Ab GC132 to yield an optimized therapeutic candidate (GC132a) with sub-nanomolar binding affinity. Mapping of the binding interface by hydrogen-deuterium exchange coupled to mass spectrometry revealed that the class T epitope on SEB overlapped with the T-cell receptor binding site, whereas other evidence suggested that the class M epitope overlapped with the binding site for the major histocompatibility complex. In the IgG format, GC132a showed ∼50-fold more potent toxin-neutralizing efficacy than the best class M Ab in vitro, and fully protected mice from lethal challenge in a toxic shock post-exposure model. We also engineered bispecific Abs (bsAbs) that bound tetravalently by utilizing two class M binding sites and two class T binding sites. The bsAbs displayed enhanced toxin neutralization efficacy compared with the respective monospecific Ab subunits as well as a mixture of the two, indicating that enhanced efficacy was due to heterotypic tetravalent binding to two non-overlapping epitopes on SEB. Together, these results suggest that class T anti-SEB Ab GC132a is an excellent candidate for clinical development and for bsAb engineering.

TBA225, a fusion toxoid vaccine for protection and broad neutralization of staphylococcal superantigens

Superantigens (SAgs) play a major role in the pathogenesis of Staphylococcus aureus and are associated with several diseases, including food poisoning, bacterial arthritis, and toxic shock syndrome. Monoclonal antibodies to these SAgs, primarily TSST-1, SEB and SEA have been shown to provide protection in animal studies and to reduce clinical severity in bacteremic patients. Here we quantify the pre-existing antibodies against SAgs in many human plasma and IVIG samples and demonstrate that in a major portion of the population these antibody titers are suboptimal and IVIG therapy only incrementally elevates the anti-SAg titers. Our in vitro neutralization studies show that a combination of antibodies against SEA, SEB,and TSST-1 can provide broad neutralization of staphylococcal SAgs. We report a single fusion protein (TBA₂₂₅) consisting of the toxoid versions of TSST-1, SEB and SEA and demonstrate its immunogenicity and protective efficacy in a mouse model of toxic shock. Antibodies raised against this fusion vaccine provide broad neutralization of purified SAgs and culture supernatants of multiple clinically relevant S. aureus strains. Our data strongly supports the use of this fusion protein as a component of an anti-virulence based multivalent toxoid vaccine against S. aureus disease.

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.

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.

Clinical and Molecular Epidemiology of Staphylococcal Toxic Shock Syndrome in the United Kingdom

Staphylococcal toxic shock syndrome (TSS) was originally described in menstruating women and linked to TSS toxin 1 (TSST-1)-producing Staphylococcus aureus. Using UK national surveillance data, we ascertained clinical, molecular and superantigenic characteristics of TSS cases. Average annual TSS incidence was 0.07/100,000 population. Patients with nonmenstrual TSS were younger than those with menstrual TSS but had the same mortality rate. Children <16 years of age accounted for 39% of TSS cases, most caused by burns and skin and soft tissue infections. Nonmenstrual TSS is now more common than menstrual TSS in the UK, although both types are strongly associated with the tst+ clonal complex (CC) 30 methicillin-sensitive S. aureus lineage, which accounted for 49.4% of all TSS and produced more TSST-1 and superantigen bioactivity than did tst+ CC30 methicillin-resistant S. aureus strains. Better understanding of this MSSA lineage and infections in children could focus interventions to prevent TSS in the future.

Aetiological Significance of Infectious Stimuli in Kawasaki Disease

Kawasaki disease (KD) is a pediatric vasculitis syndrome that is often involves coronary artery lesions (e. g., coronary artery aneurysms). Although its causal factors and entire pathogenesis remain elusive, the available evidence indicates that the pathogenesis of KD is closely associated with dysregulation of immune responses to various viruses or microbes. In this short review, we address several essential aspects of the etiology of KD with respect to the immune response to infectious stimuli: 1) the role of viral infections, 2) the role of bacterial infections and the superantigen hypothesis, 3) involvement of innate immune response including pathogens/microbe-associated molecular patterns and complement pathways, and 4) the influence of genetic background on the response to infectious stimuli. Based on the clinical and experimental evidence, we discuss the possibility that a wide range of microbes and viruses could cause KD through common and distinct immune processes.

Enhanced interaction between SEC2 mutant and TCR Vβ induces MHC II-independent activation of T cells via PKCθ/NF-κB and IL-2R/STAT5 signaling pathways

SEC2, a major histocompatibility complex class II (MHC II)-dependent T-cell mitogen, binds MHC II and T-cell receptor (TCR) Vβs to induce effective co-stimulating signals for clonal T-cell expansion. We previously characterized a SEC2 mutant with increased recognition of TCR Vβs, ST-4, which could intensify NF-κB signaling transduction, leading to IL-2 production and T-cell activation. In this study, we found that in contrast to SEC2, ST-4 could induce murine CD4⁺ T-cell proliferation in a Vβ8.2- and Vβ8.3-specific manner in the absence of MHC II⁺ antigen-presenting cells (APCs). Furthermore, although IL-2 secretion in response to either SEC2 or ST-4 stimulation was accompanied by up-regulation of protein kinase Cθ (PKCθ), inhibitor of κB (IκB), α and β IκB kinase (IKKα/β), IκBα, and NF-κB in mouse splenocytes, only ST-4 could activate CD4⁺ T cells in the absence of MHC II⁺ APCs through the PKCθ/NF-κB signaling pathway. The PKCθ inhibitor AEB071 significantly suppressed SEC2/ST-4-induced T-cell proliferation, CD69 and CD25 expression, and IL-2 secretion with or without MHC II⁺ APCs. Further, SEC2/ST-4-induced changes in PKCθ/NF-κB signaling were significantly relieved by AEB071 in a dose-dependent manner. Using Lck siRNA, we found that Lck controlled SEC2/ST-4-induced phosphorylation of PKCθ. We also demonstrated that the IL-2R/STAT5 pathway is essential for SEC2/ST-4-induced T-cell activation. Collectively, our data demonstrate that an enhanced ST-4-TCR interaction can compensate for lack of MHC II and stimulate MHC II-free CD4⁺ T-cell proliferation via PKCθ/NF-κB and IL-2R/STAT5 signaling pathways. Compared with SEC2, intensified PKCθ/NF-κB and IL-2R/STAT5 signals induced by ST-4 lead to enhanced T-cell activation. The results of this study will facilitate better understanding of TCR-based immunotherapies for cancer.

Role of Superantigens in Allergic Inflammation: Their Relationship to Allergic Rhinitis, Chronic Rhinosinusitis, Asthma, and Atopic Dermatitis

OBJECTIVES

Our intention was to review all material published to date regarding superantigens (SAgs) and allergy from an otorhinolaryngological viewpoint to understand this association more clearly.

METHODS

We identified all materials published mentioning both SAg and allergic rhinitis (AR), chronic sinusitis, asthma, and atopic dermatitis (AD) that are indexed on PubMed, Google, or the ProQuest Central databases.

RESULTS

Staphylococcus aureus is a significant bacterial pathogen in humans and has the ability to produce enterotoxins with superantigenic features. The inflammatory response in allergy seen in both B cell and T cell may be attributed to SAgs. Sufferers of both allergic asthma with rhinitis and AR alone produce serological evidence of immunoglobulin E formation to SAgs produced by S. aureus. Perennial AR sufferers carry S. aureus more frequently and the presence of the organism within the nasal cavity may exacerbate perennial AR. SAg produced by S. aureus potentially worsens the asthmatic inflammatory response within the airway and may lead to the airways becoming hyperresponsive, as well as possibly activating T cells if asthmatic control is poor. Staphylococcal SAgs potentially increase the risk of developing chronic rhinosinusitis with nasal polyposis, additionally being a marker for more severe disease. If SAgs bring about chronic inflammatory responses in the nose and sinuses, then T cells excreting interferon-gamma may be a crucial mediator. In allergic dermatitis, S. aureus could be a key player in exacerbation of the condition. Even in younger pediatric patients with allergic dermatitis, allergic hypersensitivity to SAgs is frequent and may be a factor explaining how severe the condition becomes.

CONCLUSION

Just as SAgs are known to feature in many allergic conditions, they play their part in AR, chronic rhinosinusitis, asthma, and AD. Further research is required before the relationship between SAgs and allergy can be adequately explained.

Understanding the Role of Biofilms and Superantigens in Chronic Rhinosinusitis

PURPOSE OF REVIEW

This review explores recent discoveries in our understanding of how biofilms and superantigens contribute to the pathogenesis of chronic rhinosinusitis (CRS). It also examines clinical implications and novel treatment approaches for biofilm associated CRS.

RECENT FINDINGS

While the role of biofilms in CRS has been studied for 14 years, research interest has now turned toward elucidating new methods of biofilm detection, microbial diversity, and novel treatment approaches. Recent studies on biofilm superantigens aim to clarify the immunological mechanisms of upper airway inflammation, particularly the type-2 response seen in nasal polyposis.

SUMMARY

Biofilms are a topic of research interest for their role in the pathogenesis of chronic rhinosinusitis, particularly when they elute superantigens. New studies on this topic focus on the molecular and cellular mechanisms at play.

Evaluation and Management of Necrotizing Soft Tissue Infections

Despite advances in antibiotic and surgical management and supportive care for necrotizing soft tissue infections, morbidity and mortality remain substantial. Although there are clinical practice guidelines in place, there still remains much variability in choice and duration of antibiotic therapy, time to initial surgical debridement, and use of adjuvant medical therapies. This article offers an overview of necrotizing soft tissue infections with a focus on current diagnostic and treatment modalities.

The Evaluation and Management of Toxic Shock Syndrome in the Emergency Department: A Review of the Literature

BACKGROUND

Toxic shock syndrome (TSS) is a severe, toxin-mediated illness that can mimic several other diseases and is lethal if not recognized and treated appropriately.

OBJECTIVE

This review provides an emergency medicine evidence-based summary of the current evaluation and treatment of TSS.

DISCUSSION

The most common etiologic agents are Staphylococcus aureus and Streptococcus pyogenes. Sources of TSS include postsurgical wounds, postpartum, postabortion, burns, soft tissue injuries, pharyngitis, and focal infections. Symptoms are due to toxin production and infection focus. Early symptoms include fever, chills, malaise, rash, vomiting, diarrhea, and hypotension. Diffuse erythema and desquamation may occur later in the disease course. Laboratory assessment may demonstrate anemia, thrombocytopenia, elevated liver enzymes, and abnormal coagulation studies. Diagnostic criteria are available to facilitate the diagnosis, but they should not be relied on for definitive diagnosis. Rather, specific situations should trigger consideration of this disease process. Treatment involves intravenous fluids, source control, and antibiotics. Antibiotics should include a penicillinase-resistant penicillin, cephalosporin, or vancomycin (in methicillin-resistant S. aureus prevalent areas) along with either clindamycin or linezolid.

CONCLUSION

TSS is a potentially deadly disease requiring prompt recognition and treatment. Focused history, physical examination, and laboratory testing are important for the diagnosis and management of this disease. Understanding the evaluation and treatment of TSS can assist providers with effectively managing these patients.

Impact of Intravenous Immunoglobulin on Survival in Necrotizing Fasciitis With Vasopressor-Dependent Shock: A Propensity Score-Matched Analysis From 130 US Hospitals

Background

Shock frequently complicates necrotizing fasciitis (NF) caused by group A Streptococcus (GAS) or Staphylococcus aureus. Intravenous immunoglobulin (IVIG) is sometimes administered for presumptive toxic shock syndrome (TSS), but its frequency of use and efficacy are unclear.

Methods

Adult patients with NF and vasopressor-dependent shock undergoing surgical debridement from 2010 to 2014 were identified at 130 US hospitals. IVIG cases were propensity-matched and risk-adjusted. The primary outcome was in-hospital mortality and the secondary outcome was median length of stay (LOS).

Results

Of 4127 cases of debrided NF with shock at 121 centers, only 164 patients (4%) at 61 centers received IVIG. IVIG subjects were younger with lower comorbidity indices, but higher illness severity. Clindamycin and vasopressor intensity were higher among IVIG cases, as was coding for TSS and GAS. In-hospital mortality did not differ between matched IVIG and non-IVIG groups (crude mortality, 27.3% vs 23.6%; adjusted odds ratio, 1.00 [95% confidence interval, .55-1.83]; P = .99). Early IVIG (≤2 days) did not alter this effect (P = .99). Among patients coded for TSS, GAS, and/or S. aureus, IVIG use was still unusual (59/868 [6.8%]) and lacked benefit (P = .63). Median LOS was similar between IVIG and non-IVIG groups (26 [13-49] vs 26 [11-43]; P = .84). Positive predictive values for identifying true NF and debridement among IVIG cases using our algorithms were 97% and 89%, respectively, based on records review at 4 hospitals.

Conclusions

Adjunctive IVIG was administered infrequently in NF with shock and had no apparent impact on mortality or hospital LOS beyond that achieved with debridement and antibiotics.

Staphylococcus aureus strategies to evade the host acquired immune response

Staphylococcus aureus poses a significant public-health problem. Infection caused by S. aureus can manifest as acute or long-lasting persistent diseases that are often refractory to antibiotic and are associated with significant morbidity and mortality. To develop more effective strategies for preventing or treating these infections, it is crucial to understand why the immune response is incapable to eradicate the bacterium. When S. aureus first infect the host, there is a robust activation of the host innate immune responses. Generally, S. aureus can survive this initial interaction due to the expression of a wide array of virulence factors that interfere with the host innate immune defenses. After this initial interaction the acquired immune response is the arm of the host defenses that will try to clear the pathogen. However, S. aureus is capable of maintaining infection in the host even in the presence of a robust antigen-specific immune response. Thus, understanding the mechanisms underlying the ability of S. aureus to escape immune surveillance by the acquired immune response will help uncover potentially important targets for the development of immune-based adjunctive therapies and more efficient vaccines. There are several lines of evidence that lead us to believe that S. aureus can directly or indirectly disable the acquired immune response. This review will discuss the different immune evasion strategies used by S. aureus to modulate the different components of the acquired immune defenses.

An Update on Clinical Burden, Diagnostic Tools, and Therapeutic Options of Staphylococcus aureus

Staphylococcus aureus is an important pathogen responsible for a variety of diseases ranging from mild skin and soft tissue infections, food poisoning to highly serious diseases such as osteomyelitis, endocarditis, and toxic shock syndrome. Proper diagnosis of pathogen and virulence factors is important for providing timely intervention in the therapy. Owing to the invasive nature of infections and the limited treatment options due to rampant spread of antibiotic-resistant strains, the trend for development of vaccines and antibody therapy is increasing at rapid rate than development of new antibiotics. In this article, we have discussed elaborately about the host-pathogen interactions, clinical burden due to S aureus infections, status of diagnostic tools, and treatment options in terms of prophylaxis and therapy.

Staphylococcal β-Toxin Modulates Human Aortic Endothelial Cell and Platelet Function through Sphingomyelinase and Biofilm Ligase Activities

Staphylococcus aureus causes many infections, such as skin and soft tissue, pneumonia, osteomyelitis, and infective endocarditis (IE). IE is an endovascular infection of native and prosthetic valves and the lining of the heart; it is characterized by the formation of cauliflower-like “vegetations” composed of fibrin, platelets, other host factors, bacteria, and bacterial products. β-Toxin is an S. aureus virulence factor that contributes to the microorganism’s ability to cause IE. This cytolysin has two enzymatic activities: sphingomyelinase (SMase) and biofilm ligase. Although both activities have functions in a rabbit model of IE, the mechanism(s) by which β-toxin directly affects human cells and is involved in the infectious process has not been elucidated. Here, we compared the in vitro effects of purified recombinant wild-type β-toxin, SMase-deficient β-toxin (H289N), and biofilm ligase-deficient β-toxin (H162A and/or D163A) on human aortic endothelial cells (HAECs) and platelets. β-Toxin was cytotoxic to HAECs and inhibited the production of interleukin 8 (IL-8) from these cells by both SMase and biofilm ligase activities. β-Toxin altered HAEC surface expression of CD40 and vascular cell adhesion molecule 1 (VCAM-1). HAECs treated with β-toxin displayed granular membrane morphology not seen in treatment with the SMase-deficient mutant. The altered morphology resulted in two possibly separable activities, cell rounding and redistribution of cell membranes into granules, which were not the result of endosome production from the Golgi apparatus or lysosomes. β-Toxin directly aggregated rabbit platelets via SMase activity.

Each year there are up to 100,000 cases of infective endocarditis (IE) in the United States. S. aureus is the most common pathogen in patients with health care-associated IE and the leading cause of community-associated IE in the developed world. Multiple clonal group strains as defined by the Centers for Disease Control and Prevention, particularly USA200 and other clones encoding β-toxin, are highly associated with IE. Considering the strong association and established contribution of β-toxin in animal models of IE, determining how β-toxin directly affects human cell types, including endothelial cells and platelets, is important. In this study, we demonstrate that β-toxin functions to modulate endothelial cells and platelets by both toxin sphingomyelinase and biofilm ligase activities. Our data suggest that these activities modulate inflammation and increase infection severity.

The Pathogenetic Effect of Natural and Bacterial Toxins on Atopic Dermatitis

Atopic dermatitis (AD) is a common allergic skin disease that is associated with chronic, recurrent eczematous and pruritic lesions at the flexural folds caused by interacting factors related to environmental and immune system changes. AD results in dry skin, and immunoglobulin E-mediated allergic reactions to foods and environmental allergens. While steroids and anti-histamines temporarily relieve the symptoms of AD, the possibility of side effects from pharmacological interventions remains. Despite intensive research, the underlying mechanisms for AD have not been clarified. A study of Staphylococcus aureus (S. aureus) established the role of its toxins in the pathogenesis of AD. Approximately 90% of patients with AD experience S. aureus colonization and up to 50%–60% of the colonizing S. aureus is toxin-producing. Any damage to the protective skin barrier allows for the entry of invading allergens and pathogens that further drive the pathogenesis of AD. Some natural toxins (or their components) that have therapeutic effects on AD have been studied. In addition, recent studies on inflammasomes as one component of the innate immune system have been carried out. Additionally, studies on the close relationship between the activation of inflammasomes and toxins in AD have been reported. This review highlights the literature that discusses the pathogenesis of AD, the role of toxins in AD, and the positive and negative effects of toxins on AD. Lastly, suggestions are made regarding the role of inflammasomes in AD.

Differentiation of entC1 from entC2/entC3 with a single primer pair using simple and rapid SYBR Green-based RT-PCR melt curve analysis

In spite of their involvement in foodborne illness, the epidemiological relevance of staphylococcal enterotoxin C (SEC) subtypes is poorly documented may be due to high sequence similarity. Among subtypes, SEC1, SEC2, and SEC3 exhibit more than 97 % homology because of which specific detection tools are seldom available to identify and differentiate them. In this study, a SYBR Green-based RT-PCR followed by melt curve analysis was developed for differentiation of entC1 from entC2/entC3 using a single primer pair. Nucleotide sequences of all three subtypes were analyzed using Clustal Omega program and the region with significant sequence variation/heterogeneity (where utmost SNPs were closely located and accessible for RT-PCR) was selected for amplification by designing a single primer pair that could amplify all three subtypes. In spite of same amplicon size, entC1 showed distinct melt peak at 76 °C. However, due to high similarity between entC2 and entC3, the developed format was deficient to discriminate between them and both showed melt peak at 82 °C. Reliability of developed RT-PCR was evaluated using various naturally contaminated samples and 91 food and clinical Staphylococcus aureus isolates where satisfactory results were obtained in comparison with commercial immunoassay kit and conventional PCRs using validated primers. To the best of our knowledge, this is the first method being reported to differentiate entC1 from entC2/entC3 using single primer pair which is unachievable by conventional PCR due to same amplicon size. As benefits, the method is sensitive, rapid, and inexpensive with no requirement of fluorescent probes, multiple primers, and post-PCR procedures. Thus, the assay might find its utility as a detection tool in epidemiological survey of foodborne outbreaks for simultaneous identification and differentiation of entC1 from entC2/entC3.