Novel structurally designed vaccine for S. aureus α-hemolysin: protection against bacteremia and pneumonia

Story of Pore-Forming Proteins from Deadly Disease-Causing Agents to Modern Applications with Evolutionary Significance

Animal venoms are a complex mixture of highly specialized toxic molecules. Among them, pore-forming proteins (PFPs) or toxins (PFTs) are one of the major disease-causing toxic elements. The ability of the PFPs in defense and toxicity through pore formation on the host cell surface makes them unique among the toxin proteins. These features made them attractive for academic and research purposes for years in the areas of microbiology as well as structural biology. All the PFPs share a common mechanism of action for the attack of host cells and pore formation in which the selected pore-forming motifs of the host cell membrane-bound protein molecules drive to the lipid bilayer of the cell membrane and eventually produces water-filled pores. But surprisingly their sequence similarity is very poor. Their existence can be seen both in a soluble state and also in transmembrane complexes in the cell membrane. PFPs are prevalent toxic factors that are predominately produced by all kingdoms of life such as virulence bacteria, nematodes, fungi, protozoan parasites, frogs, plants, and also from higher organisms. Nowadays, multiple approaches to applications of PFPs have been conducted by researchers both in basic as well as applied biological research. Although PFPs are very devastating for human health nowadays researchers have been successful in making these toxic proteins into therapeutics through the preparation of immunotoxins. We have discussed the structural, and functional mechanism of action, evolutionary significance through dendrogram, domain organization, and practical applications for various approaches. This review aims to emphasize the PFTs to summarize toxic proteins together for basic knowledge as well as to highlight the current challenges, and literature gap along with the perspective of promising biotechnological applications for their future research.

Emerging strategies and therapeutic innovations for combating drug resistance in Staphylococcus aureus strains: A comprehensive review

In recent years, antibiotic therapy has encountered significant challenges due to the rapid emergence of multidrug resistance among bacteria responsible for life-threatening illnesses, creating uncertainty about the future management of infectious diseases. The escalation of antimicrobial resistance in the post-COVID era compared to the pre-COVID era has raised global concern. The prevalence of nosocomial-related infections, especially outbreaks of drug-resistant strains of Staphylococcus aureus, have been reported worldwide, with India being a notable hotspot for such occurrences. Various virulence factors and mutations characterize nosocomial infections involving S. aureus. The lack of proper alternative treatments leading to increased drug resistance emphasizes the need to investigate and examine recent research to combat future pandemics. In the current genomics era, the application of advanced technologies such as next-generation sequencing (NGS), machine learning (ML), and quantum computing (QC) for genomic analysis and resistance prediction has significantly increased the pace of diagnosing drug-resistant pathogens and insights into genetic intricacies. Despite prompt diagnosis, the elimination of drug-resistant infections remains unattainable in the absence of effective alternative therapies. Researchers are exploring various alternative therapeutic approaches, including phage therapy, antimicrobial peptides, photodynamic therapy, vaccines, host-directed therapies, and more. The proposed review mainly focuses on the resistance journey of S. aureus over the past decade, detailing its resistance mechanisms, prevalence in the subcontinent, innovations in rapid diagnosis of the drug-resistant strains, including the applicants of NGS and ML application along with QC, it helps to design alternative novel therapeutics approaches against S. aureus infection.

Dry and liquid formulations of IBT-V02, a novel multi-component toxoid vaccine, are effective against Staphylococcus aureus isolates from low-to-middle income countries

Staphylococcus aureus is the leading cause of skin and soft tissue infections (SSTIs) in the U.S. as well as more serious invasive diseases, including bacteremia, sepsis, endocarditis, surgical site infections, osteomyelitis, and pneumonia. These infections are exacerbated by the emergence of antibiotic-resistant clinical isolates such as methicillin-resistant S. aureus (MRSA), highlighting the need for alternatives to antibiotics to treat bacterial infections. We have previously developed a multi-component toxoid vaccine (IBT-V02) in a liquid formulation with efficacy against multiple strains of Staphylococcus aureus prevalent in the industrialized world. However, liquid vaccine formulations are not compatible with the paucity of cold chain storage infrastructure in many low-to-middle income countries (LMICs). Furthermore, whether our IBT-V02 vaccine formulations are protective against S. aureus isolates from LMICs is unknown. To overcome these limitations, we developed lyophilized and spray freeze-dried formulations of IBT-V02 vaccine and demonstrated that both formulations had comparable biophysical attributes as the liquid formulation, including similar levels of toxin neutralizing antibodies and protective efficacy against MRSA infections in murine and rabbit models. To enhance the relevancy of our findings, we then performed a multi-dimensional screen of 83 S. aureus clinical isolates from LMICs (e.g., Democratic Republic of Congo, Palestine, and Cambodia) to rationally down-select strains to test in our in vivo models based on broad expression of IBT-V02 targets (i.e., pore-forming toxins and superantigens). IBT-V02 polyclonal antisera effectively neutralized toxins produced by the S. aureus clinical isolates from LMICs. Notably, the lyophilized IBT-V02 formulation exhibited significant in vivo efficacy in various preclinical infection models against the S. aureus clinical isolates from LMICs, which was comparable to our liquid formulation. Collectively, our findings suggested that lyophilization is an effective alternative to liquid vaccine formulations of our IBT-V02 vaccine against S. aureus infections, which has important implications for protection from S. aureus isolates from LMICs.

Eighteen iridoids from the roots and rhizomes of Valeriana jatamansi and their protective effects against α-hemolysin

Thirteen previously undescribed iridoids (1-13), together with five known iridoids (14-18) were isolated from the roots and rhizomes of Valeriana jatamansi Jones. Their structures with absolute configurations were elucidated by analysis of MS, NMR, optical rotation and their experimental and calculated electronic circular dichroism spectra. All of the isolated compounds were tested for their protective effects against α-hemolysin-induced cell death in A549 cells. Compounds 14, 16 and 17 showed moderate protective effects, and compounds 15 and 18 showed weak protective effects.

Infection prevention-how can we prevent transmission of community-onset methicillin-resistant Staphylococcus aureus?

BACKGROUND

Staphylococcus aureus is a versatile organism, capable of existing as a commensal organism while also possessing pathogenic potential. The emergence of clinically and genetically distinct strains of methicillin-resistant S. aureus (MRSA), termed community-onset MRSA (CO-MRSA), resulted in an epidemic of invasive and skin and soft tissue infections (SSTI) in otherwise healthy individuals without traditional risk factors. Colonization with S. aureus is a risk factor for developing infection and also a source of transmission to close contacts. Outbreaks of S. aureus SSTI have been described in crowded settings and within households. Thus, preventive strategies are essential to interrupt recurrent infections.

OBJECTIVES

The objective of this narrative review is to provide a comprehensive, evidence-based approach to prevent transmission of CO-MRSA. We highlight key clinical trials that emphasize the importance of household and environmental S. aureus colonization in propagating household transmission. Finally, we highlight research priorities to prevent S. aureus infection.

SOURCES

We cite primary literature from peer-reviewed publications as sources for this review.

CONTENT

Our recommended approach to the management of individuals presenting with skin abscesses includes optimal treatment of the initial infection and hygiene education. Decolonization measures should be recommended for individuals with recurrent SSTIs or whose household members have SSTIs. Targeted decolonization with topical antimicrobials should be prescribed to all affected individuals within the household.

IMPLICATIONS

S. aureus infections result in substantial mortality and morbidity because of the high incidence of recurrent skin infections. Although current decolonization strategies are beneficial, interventions are often costly to families and effectiveness wanes over time. Results from a recently completed trial evaluating integrated periodic decolonization and household environmental hygiene will further add to our understanding of what constitutes a sustainable decolonization approach. In addition, novel preventive strategies are being developed such as S. aureus vaccines, lytic agents, probiotics, microbiota transplants, and phage therapy.

Endothelial ADAM10 utilization defines a molecular pathway of vascular injury in mice with bacterial sepsis

The endothelium plays a critical role in the host response to infection and has been a focus of investigation in sepsis. While it is appreciated that intravascular thrombus formation, severe inflammation, and loss of endothelial integrity impair tissue oxygenation during sepsis, the precise molecular mechanisms that lead to endothelial injury remain poorly understood. We demonstrate here that endothelial ADAM10 was essential for the pathogenesis of Staphylococcus aureus sepsis, contributing to α-toxin-mediated (Hla-mediated) microvascular thrombus formation and lethality. As ADAM10 is essential for endothelial development and homeostasis, we examined whether other major human sepsis pathogens also rely on ADAM10-dependent pathways in pathogenesis. Mice harboring an endothelium-specific knockout of ADAM10 were protected against lethal Pseudomonas aeruginosa and Streptococcus pneumoniae sepsis, yet remained fully susceptible to group B streptococci and Candida albicans sepsis. These studies illustrate a previously unknown role for ADAM10 in sepsis-associated endothelial injury and suggest that understanding pathogen-specific divergent host pathways in sepsis may enable more precise targeting of disease.

Reverse vaccinology & immunoinformatics approach to design a multiepitope vaccine (CV3Ag-antiMRSA) against methicillin resistant Staphylococcus aureus (MRSA) - a pathogen affecting both human and animal health

Infections caused by drug resistant bacteria is a silent detrimental pandemic affecting the global health care profoundly. Methicillin resistant Staphylococcus aureus (MRSA) is a pathogen that causes serious infections in different settings (community, hospital & veterinary) whose treatment remains highly challenging due to its powerful characteristics (antibiotic resistance strategies, virulence factors). In this study, we used reverse vaccinology (RV) approach and designed an immunogenic multi epitope vaccine (CV3Ag-antiMRSA) targeting three potential antigen candidates viz., mecA encoding transpeptidase (PBP2a) protein responsible for conferring methicillin resistance and two virulence determinants - hlgA encoding gamma-hemolysin component A (a pore forming toxin) and isdB encoding iron regulated surface determinant B (heme transport component that allows S. aureus to scavenge iron from host hemoglobin and myoglobin). We employed an array of immunoinformatic tools/server to identify and use immunogenic epitopes (B cell and MHC class) to develop the chimeric subunit vaccine V4 (CV3Ag-antiMRSA) with immune modulating adjuvant and linkers. Based on different parameters, the vaccine construct V4 (CV3Ag-antiMRSA) was determined to be suitable vaccine (antigenic and non-allergen). Molecular docking and simulation of CV3Ag-antiMRSA with Toll Like Receptor (TLR2) predicted its immuno-stimulating potential. Finally, in silico cloning of CV3Ag-antiMRSA construct into pet28a and pet30 vector displayed its feasibility for the heterologous expression in the E. coli expression system. This vaccine candidate (CV3Ag-antiMRSA) designed based on the MRSA genomes obtained from both animal and human hosts can be experimentally validated and thereby contribute to vaccine development to impart protection to both animal and human health.Communicated by Ramaswamy H. Sarma.

MRSA compendium of epidemiology, transmission, pathophysiology, treatment, and prevention within one health framework

Staphylococcus aureus is recognized as commensal as well as opportunistic pathogen of humans and animals. Methicillin resistant strain of S. aureus (MRSA) has emerged as a major pathogen in hospitals, community and veterinary settings that compromises the public health and livestock production. MRSA basically emerged from MSSA after acquiring SCCmec element through gene transfer containing mecA gene responsible for encoding PBP-2α. This protein renders the MRSA resistant to most of the β-lactam antibiotics. Due to the continuous increasing prevalence and transmission of MRSA in hospitals, community and veterinary settings posing a major threat to public health. Furthermore, high pathogenicity of MRSA due to a number of virulence factors produced by S. aureus along with antibiotic resistance help to breach the immunity of host and responsible for causing severe infections in humans and animals. The clinical manifestations of MRSA consist of skin and soft tissues infection to bacteremia, septicemia, toxic shock, and scalded skin syndrome. Moreover, due to the increasing resistance of MRSA to number of antibiotics, there is need to approach alternatives ways to overcome economic as well as human losses. This review is going to discuss various aspects of MRSA starting from emergence, transmission, epidemiology, pathophysiology, disease patterns in hosts, novel treatment, and control strategies.

The natural product, echinatin, protects mice from methicillin-resistant Staphylococcus aureus pneumonia by inhibition of alpha-hemolysin expression

Antimicrobial resistance (AMR) is a global, multifaceted crisis that poses significant challenges to the successful eradication of devastating pathogens, particularly methicillin-resistant Staphylococcus aureus (MRSA), a persistent superbug that causes devastating infections. The scarcity of new antibacterial drugs is obvious, and antivirulence strategies that reduce the pathogenicity of bacteria by weakening their virulence have become the subject of intense investigation. Alpha-hemolysin (Hla), a cytolytic pore-forming toxin, has a pivotal role in S. aureus pathogenesis. Here, we demonstrated that echinatin, a natural compound isolated from licorice, effectively inhibited the hemolytic activity of MRSA at 32 μg/mL. In addition, echinatin did not interfere with bacterial growth and had no significant cytotoxicity at the inhibitory concentration of S. aureus hemolysis. Heptamer formation tightly correlated with Hla-mediated cell invasion, whereas echinatin did not affect deoxycholic acid-induced oligomerization of Hla. Echinatin affected hemolytic activity through indirect binding to Hla as confirmed by the neutralization assay and cellular thermal shift assay (CETSA). Furthermore, qRT-PCR and western blot analyses revealed that echinatin suppressed Hla expression at both the mRNA and protein levels as well as the transcript levels of Agr quorum-sensing system-related genes. Additionally, when echinatin was added to a coculture system of A549 cells and S. aureus, it significantly reduced cell damage. Importantly, echinatin exhibited a significant therapeutic effect in an MRSA-induced mouse pneumonia model. In conclusion, the present findings demonstrated that echinatin significantly inhibits the hemolysin effect and may be a potential candidate compound for combating drug-resistant MRSA infections.

Hyperimmune Targeting Staphylococcal Toxins Effectively Protect Against USA 300 MRSA Infection in Mouse Bacteremia and Pneumonia Models

Staphylococcus aureus has been acquiring multiple drug resistance and has evolved into superbugs such as Methicillin/Vancomycin-resistant S. aureus (MRSA/VRSA) and, consequently, is a major cause of nosocomial and community infections associated with high morbidity and mortality for which no FDA-approved vaccines or biotherapeutics are available. Previous efforts targeting the surface-associated antigens have failed in clinical testing. Here, we generated hyperimmune products from sera in rabbits against six major S. aureus toxins targeted by an experimental vaccine (IBT-V02) and demonstrated significant efficacy for an anti-virulence passive immunization strategy. Extensive in vitro binding and neutralizing titers were analyzed against six extracellular toxins from individual animal sera. All IBT-V02 immunized animals elicited the maximum immune response upon the first boost dose against all pore-forming vaccine components, while for superantigen (SAgs) components of the vaccine, second and third doses of a boost were needed to reach a plateau in binding and toxin neutralizing titers. Importantly, both anti-staphylococcus hyperimmune products consisting of full-length IgG (IBT-V02-IgG) purified from the pooled sera and de-speciated F(ab')₂ (IBT-V02-F(ab')2) retained the binding and neutralizing titers against IBT-V02 target toxins. F(ab')₂ also exhibited cross-neutralization titers against three leukotoxins (HlgAB, HlgCB, and LukED) and four SAgs (SEC1, SED, SEK, and SEQ) which were not part of IBT-V02. F(ab')₂ also neutralized toxins in bacterial culture supernatant from major clinical strains of S. aureus. In vivo efficacy data generated in bacteremia and pneumonia models using USA300 S. aureus strain demonstrated dose-dependent protection by F(ab')₂. These efficacy data confirmed the staphylococcal toxins as viable targets and support the further development effort of hyperimmune products as a potential adjunctive therapy for emergency uses against life-threatening S. aureus infections.

Antigenic landscapes on Staphylococcus aureus pore-forming toxins reveal insights into specificity and cross-neutralization

Staphylococcus aureus carries an exceptional repertoire of virulence factors that aid in immune evasion. Previous single-target approaches for S. aureus-specific vaccines and monoclonal antibodies (mAbs) have failed in clinical trials due to the multitude of virulence factors released during infection. Emergence of antibiotic-resistant strains demands a multi-target approach involving neutralization of different, non-overlapping pathogenic factors. Of the several pore-forming toxins that contribute to S. aureus pathogenesis, efforts have largely focused on mAbs that neutralize α-hemolysin (Hla) and target the receptor-binding site. Here, we isolated two anti-Hla and three anti-Panton-Valentine Leukocidin (LukSF-PV) mAbs, and used a combination of hydrogen deuterium exchange mass spectrometry (HDX-MS) and alanine scanning mutagenesis to delineate and validate the toxins’ epitope landscape. Our studies identified two novel, neutralizing epitopes targeted by 2B6 and CAN6 on Hla that provided protection from hemolytic activity in vitro and showed synergy in rodent pneumonia model against lethal challenge. Of the anti-LukF mAbs, SA02 and SA131 showed specific neutralization activity to LukSF-PV while SA185 showed cross-neutralization activity to LukSF-PV, γ-hemolysin HlgAB, and leukotoxin ED. We further compared these antigen-specific mAbs to two broadly neutralizing mAbs, H5 (targets Hla, LukSF-PV, HlgAB, HlgCB, and LukED) and SA185 (targeting LukSF-PV, HlgAB, and LukED), and identified molecular level markers for broad-spectrum reactivity among the pore-forming toxins by HDX-MS. To further underscore the need to target the cross-reactive epitopes on leukocidins for the development of broad-spectrum therapies, we annotated Hla sequences isolated from patients in multiple countries for genomic variations within the perspective of our defined epitopes.

Progress in the Development of Structure-Based Vaccines

The immune response elicited by vaccines against microorganisms makes it the most successful medical interventions against infectious diseases. Conventional vaccines have limitations in inducing immunity against many types of pathogenic microorganism. The genetic diversity of microorganisms, coupled with the high degree of sequence variability in antigenic proteins, presents a challenge to developing broadly effective conventional vaccines. Atomic-resolution structure determination is crucial for understanding antigenic protein function. Cryo-electron microscopy, nuclear magnetic resonance spectroscopy coupled with bioinformatics provide three-dimensional structure of the antigenic proteins and provide a wealth of information about the organization of individual atoms and their chemical makeup. The atomic detail information of proteins offers enormous potential to rationally engineer proteins to enhance their properties and act as effective immunogens to induce immunity. The observation that whole protein antigens are not necessarily essential for inducing immunity has led to the emergence "structural vaccinology." Structure-based vaccines are designed on the rationale that protective epitopes should be sufficient to induce immune responses and provide protection against pathogens. In 2013 we published a review on structure-based vaccines (Thomas and Luxon. Expert Rev Vaccines 12 1301-11, 2013). This review states the progress in development of structure-based vaccines since the first review.

Immunoinformatics analysis and evaluation of recombinant chimeric triple antigen toxoid (r-HAB) against Staphylococcus aureus toxaemia in mouse model

Abstract

Staphylococcus aureus is a serious pathogen unleashing its virulence through several classes of exotoxins such as hemolysins and enterotoxins. In this study, we designed a novel multi-antigen subunit vaccine which can induce innate, humoral and cellular immune responses. Alpha hemolysin, enterotoxins A and B were selected as protective antigens for combining into a triple antigen chimeric protein (HAB). Immunoinformatics analysis predicted HAB protein as a suitable vaccine candidate for inducing both humoral and cellular immune responses. Tertiary structure of the HAB protein was predicted and validated through computational approaches. Docking studies were performed between the HAB protein and mice TLR2 receptor. Furthermore, we constructed and generated recombinant HAB (r-HAB) protein in E. coli and studied its toxicity, immunogenicity and protective efficacy in a mouse model. Triple antigen chimeric protein (r-HAB) was found to be highly immunogenic in mouse as the anti-r-HAB hyperimmune serum was strongly reactive to all three native exotoxins on Western blot. In vitro toxin neutralization assay using anti-r-HAB antibodies demonstrated > 75% neutralization of toxins on RAW 264.7 cell line. Active immunization with r-HAB toxoid gave ~ 83% protection against 2 × lethal dosage of secreted exotoxins. The protection was mediated by induction of strong antibody responses that neutralized the toxins. Passive immunization with anti-r-HAB antibodies gave ~ 50% protection from lethal challenge. In conclusion, in vitro and in vivo testing of r-HAB found the molecule to be nontoxic, highly immunogenic and induced excellent protection towards native toxins in actively immunized and partial protection to passively immunized mice groups.

Key points

• HAB protein was computationally designed to induce humoral and cellular responses.

• r-HAB protein was found to be nontoxic, immunogenic and protective in mouse model.

• r-HAB conferred protection against lethal challenge in active and passive immunization.

Staphylococcus aureus Putative Vaccines Based on the Virulence Factors: A Mini-Review

Since the 1960s, the frequency of methicillin-resistant Staphylococcus aureus as a recurrent cause of nosocomial infections has increased. Since multidrug-resistant Staphylococcus has overcome antimicrobial treatment, the development of putative vaccines based on virulence factors could be a great help in controlling the infections caused by bacteria and are actively being pursued in healthcare settings. This mini-review provides an overview of the recent progress in vaccine development, immunogenicity, and therapeutic features of some S. aureus macromolecules as putative vaccine candidates and their implications against human S. aureus-related infections. Based on the reviewed experiments, multivalent vaccines could prevent the promotion of the diseases caused by this bacterium and enhance the prevention chance of S. aureus infections.

Identification and application of a neutralizing epitope within alpha-hemolysin using human serum antibodies elicited by vaccination

Staphylococcus aureus (SA), especially the methicillin-resistant variant (MRSA), is becoming a serious threat to human health in hospitals and communities, making the development of an effective vaccine urgent. Alpha-hemolysin (Hla) is a key virulence factor and also a good target for the development of SA vaccines. However, the epitopes in Hla recognized by human immunity are not characterized in detail, which hinders the design of epitope-based human vaccines against SA. In this study, we collected sera from volunteers in a phase 1b clinical trial of a novel recombinant five-antigen SA vaccine (NCT03966040). Using a Luminex-based assay, we characterized the human serologic response against Hla, and identified Hla_121-138 as a neutralizing epitope. In addition, we successfully produced ferritin nanoparticles carrying the neutralizing Hla_121-138 epitope (EpNP) in E. coli. EpNP presented as homogenous nanoparticles in aqueous solution. Immunization with EpNP elicited potent hemolysis-neutralizing antibodies and conferred significant protection in a mouse model of SA skin infection. Our data suggest that EpNP, carrying the neutralizing epitope Hla_121-138, is a good candidate for a vaccine against SA.

Designing multi-epitope vaccine against Staphylococcus aureus by employing subtractive proteomics, reverse vaccinology and immuno-informatics approaches

Staphylococcus aureus is a deadly human bacterial pathogen that causes a wide variety of clinical manifestations. Invasive S. aureus infections in hospitals and the community are one of the main causes of mortality and morbidity, as virulent and multi-drug-resistant strains have evolved. There is an unmet and urgent clinical need for immune-based non-antibiotic approaches to treat these infections as the growing antibiotic resistance poses a significant public health danger. Subtractive proteomics assisted reverse vaccinology-based immunoinformatics pipeline was used in this study to target the suitable antigenic proteins for the development of multi-epitope vaccine (MEV). Three essential virulent and antigenic proteins were identified including Glycosyltransferase, Elastin Binding Protein, and Staphylococcal secretory antigen. A variety of immunoinformatics tools have been used to forecast T-cell and B-cell epitopes from target proteins. Seven CTL, five HTL, and eight LBL epitopes, connected through suitable linkers and adjuvant, were employed to design 444 amino acids long MEV construct. The vaccine was paired with the TLR4 agonist 50S ribosomal protein L7/L12 adjuvant to enhance the immune response towards the vaccine. The predicted MEV structure was assessed to be highly antigenic, non-toxic, non-allergenic, flexible, stable, and soluble. Molecular docking simulation of the MEV with the human TLR4 (toll-like receptor 4) and major histocompatibility complex molecules (MHCI and MHCII) was performed to validate the interactions with the receptors. Molecular dynamics (MD) simulation and MMGBSA binding free energy analyses were carried out for the stability evaluation and binding of the MEV docked complexes with TLR4, MHCI and MHCII. To achieve maximal vaccine protein expression with optimal post-translational modifications, MEV was reverse translated, its mRNA structure was analyzed, and finally in silico cloning was performed into E. coli expression host. These rigorous computational analyses supported the effectivity of proposed MEV in protection against infections associated with S. aureus. However, further experimental validations are required to fully evaluate the potential of proposed vaccine candidate.

PIA and rSesC Mixture Arisen Antibodies Could Inhibit the Biofilm-Formation in Staphylococcus aureus

BACKGROUND

Staphylococcus aureus as a causative agent of hospital-acquired infections has been considered as the primary concern in biomaterial-related infections (BAIs).

METHODS

Following the purification of polysaccharide intercellular adhesion (PIA) as an efficient macromolecule in biofilm formation in the native condition, recombinant S. epidermidis surface-exposed rSesC protein, with the most homology to clumping factor A (ClfA) in S. aureus was cloned and expressed in a prokaryotic host as well. Fourier transform infrared spectrometry (FTIR) and Western blotting procedure analyzed purified PIA and protein, respectively. Then, the immune response was evaluated by measuring total IgG titers. Moreover, the capacity of Anti-biofilm forming activity of arisen antibodies to a biofilm-forming S. aureus strains was assessed by the semi-quantitative micro-plate procedure.

RESULTS

Data showed that the total IgGs were boosted in mice immunized sera. By performing an inhibition assay, the biofilm inhibitory effect of secreted antibodies to test strain was observed. Arisen antibodies against the mixture significantly were more potent than PIA and rSesC, when comparing individual antigens in a biofilm inhibition assay.

CONCLUSION

immunization of mice with mentioned antigens especially a mixture of them, could eliminate the biofilm formation process in S. aureus. Hopefully, this study corresponds to the suggestion that the immunization of mice with PIA and rSesC candidate vaccines could protect against S. aureus infection.

IBT-V02: A Multicomponent Toxoid Vaccine Protects Against Primary and Secondary Skin Infections Caused by Staphylococcus aureus

Staphylococcus aureus causes a wide range of diseases from skin infections to life threatening invasive diseases such as bacteremia, endocarditis, pneumonia, surgical site infections, and osteomyelitis. Skin infections such as furuncles, carbuncles, folliculitis, erysipelas, and cellulitis constitute a large majority of infections caused by S. aureus (SA). These infections cause significant morbidity, healthcare costs, and represent a breeding ground for antimicrobial resistance. Furthermore, skin infection with SA is a major risk factor for invasive disease. Here we describe the pre-clinical efficacy of a multicomponent toxoid vaccine (IBT-V02) for prevention of S. aureus acute skin infections and recurrence. IBT-V02 targets six SA toxins including the pore-forming toxins alpha hemolysin (Hla), Panton-Valentine leukocidin (PVL), leukocidin AB (LukAB), and the superantigens toxic shock syndrome toxin-1 and staphylococcal enterotoxins A and B. Immunization of mice and rabbits with IBT-V02 generated antibodies with strong neutralizing activity against toxins included in the vaccine, as well as cross-neutralizing activity against multiple related toxins, and protected against skin infections by several clinically relevant SA strains of USA100, USA300, and USA1000 clones. Efficacy of the vaccine was also shown in non-naïve mice pre-exposed to S. aureus. Furthermore, vaccination with IBT-V02 not only protected mice from a primary infection but also demonstrated lasting efficacy against a secondary infection, while prior challenge with the bacteria alone was unable to protect against recurrence. Serum transfer studies in a primary infection model showed that antibodies are primarily responsible for the protective response.

Safety and Immunogenicity of a 4-Component Toxoid-Based Staphylococcus aureus Vaccine in Rhesus Macaques

Staphylococcus aureus is a leading cause of significant morbidity and mortality and an enormous economic burden to public health worldwide. Infections caused by methicillin-resistant S. aureus (MRSA) pose a major threat as MRSA strains are becoming increasingly prevalent and multi-drug resistant. To this date, vaccines targeting surface-bound antigens demonstrated promising results in preclinical testing but have failed in clinical trials. S. aureus pathogenesis is in large part driven by immune destructive and immune modulating toxins and thus represent promising vaccine targets. Hence, the objective of this study was to evaluate the safety and immunogenicity of a staphylococcal 4-component vaccine targeting secreted bi-component pore-forming toxins (BCPFTs) and superantigens (SAgs) in non-human primates (NHPs). The 4-component vaccine proved to be safe, even when repeated vaccinations were given at a dose that is 5 to 10- fold higher than the proposed human dose. Vaccinated rhesus macaques did not exhibit clinical signs, weight loss, or changes in hematology or serum chemistry parameters related to the administration of the vaccine. No acute, vaccine-related elevation of serum cytokine levels was observed after vaccine administration, confirming the toxoid components lacked superantigenicity. Immunized animals demonstrated high level of toxin-specific total and neutralizing antibodies toward target antigens of the 4-component vaccine as well as cross-neutralizing activity toward staphylococcal BCPFTs and SAgs that are not direct targets of the vaccine. Cross-neutralization was also observed toward the heterologous streptococcal pyogenic exotoxin B. Ex vivo stimulation of PBMCs with individual vaccine components demonstrated an overall increase in several T cell cytokines measured in supernatants. Immunophenotyping of CD4 T cells ex vivo showed an increase in Ag-specific polyfunctional CD4 T cells in response to antigen stimulation. Taken together, we demonstrate that the 4-component vaccine is well-tolerated and immunogenic in NHPs generating both humoral and cellular immune responses. Targeting secreted toxin antigens could be the next-generation vaccine approach for staphylococcal vaccines if also proven to provide efficacy in humans.

Novel Treatments and Preventative Strategies Against Food-Poisoning Caused by Staphylococcal Species

Staphylococcal infections are a widespread cause of disease in humans. In particular, S. aureus is a major causative agent of infection in clinical medicine. In addition, these bacteria can produce a high number of staphylococcal enterotoxins (SE) that may cause food intoxications. Apart from S. aureus, many coagulase-negative Staphylococcus spp. could be the source of food contamination. Thus, there is an active research work focused on developing novel preventative interventions based on food supplements to reduce the impact of staphylococcal food poisoning. Interestingly, many plant-derived compounds, such as polyphenols, flavonoids, or terpenoids, show significant antimicrobial activity against staphylococci, and therefore these compounds could be crucial to reduce the incidence of food intoxication in humans. Here, we reviewed the most promising strategies developed to prevent staphylococcal food poisoning.

Exploring Virulence Factors and Alternative Therapies against Staphylococcus aureus Pneumonia

Pneumonia is an acute pulmonary infection associated with high mortality and an immense financial burden on healthcare systems. Staphylococcus aureus is an opportunistic pathogen capable of inducing S. aureus pneumonia (SAP), with some lineages also showing multidrug resistance. Given the high level of antibiotic resistance, much research has been focused on targeting S. aureus virulence factors, including toxins and biofilm-associated proteins, in an attempt to develop effective SAP therapeutics. Despite several promising leads, many hurdles still remain for S. aureus vaccine research. Here, we review the state-of-the-art SAP therapeutics, highlight their pitfalls, and discuss alternative approaches of potential significance and future perspectives.

Efficacy of Active Immunization With Attenuated α-Hemolysin and Panton-Valentine Leukocidin in a Rabbit Model of Staphylococcus aureus Necrotizing Pneumonia

Staphylococcus aureus is a common pathogen causing infections in humans with various degrees of severity, with pneumonia being one of the most severe infections. In as much as staphylococcal pneumonia is a disease driven in large part by α-hemolysin (Hla) and Panton-Valentine leukocidin (PVL), we evaluated whether active immunization with attenuated forms of Hla (HlaH35L/H48L) alone, PVL components (LukS-PVT28F/K97A/S209A and LukF-PVK102A) alone, or combination of all 3 toxoids could prevent lethal challenge in a rabbit model of necrotizing pneumonia caused by the USA300 community-associated methicillin-resistant S. aureus (MRSA). Rabbits vaccinated with Hla toxoid alone or PVL components alone were only partially protected against lethal pneumonia, whereas those vaccinated with all 3 toxoids had 100% protection against lethality. Vaccine-mediated protection correlated with induction of polyclonal antibody response that neutralized not only α-hemolysin and PVL, but also other related toxins, produced by USA300 and other epidemic MRSA clones.

Vaccination with VLPs Presenting a Linear Neutralizing Domain of S. aureus Hla Elicits Protective Immunity

The pore-forming cytotoxin α-hemolysin, or Hla, is a critical Staphylococcus aureus virulence factor that promotes infection by causing tissue damage, excessive inflammation, and lysis of both innate and adaptive immune cells, among other cellular targets. In this study, we asked whether a virus-like particle (VLP)-based vaccine targeting Hla could attenuate S. aureus Hla-mediated pathogenesis. VLPs are versatile vaccine platforms that can be used to display target antigens in a multivalent array, typically resulting in the induction of high titer, long-lasting antibody responses. In the present study, we describe the first VLP-based vaccines that target Hla. Vaccination with either of two VLPs displaying a 21 amino-acid linear neutralizing domain (LND) of Hla protected both male and female mice from subcutaneous Hla challenge, evident by reduction in lesion size and neutrophil influx to the site of intoxication. Antibodies elicited by VLP-LND vaccination bound both the LND peptide and the native toxin, effectively neutralizing Hla and preventing toxin-mediated lysis of target cells. We anticipate these novel and promising vaccines being part of a multi-component S. aureus vaccine to reduce severity of S. aureus infection.

Vaccine display on artificial bacterial spores enhances protective efficacy against Staphylococcus aureus infection

Spores of Bacillus subtilis are encased in a protein coat composed of ∼80 different proteins. Recently, we reconstituted the basement layer of the coat, composed of two structural proteins (SpoVM and SpoIVA) around spore-sized silica beads encased in a lipid bilayer, to create synthetic spore-like particles termed 'SSHELs'. We demonstrated that SSHELs could display thousands of copies of proteins and small molecules of interest covalently linked to SpoIVA. In this study, we investigated the efficacy of SSHELs in delivering vaccines. We show that intramuscular vaccination of mice with undecorated one micron-diameter SSHELs elicited an antibody response against SpoIVA. We further demonstrate that SSHELs covalently modified with a catalytically inactivated staphylococcal alpha toxin variant (HlaH35L), without an adjuvant, resulted in improved protection against Staphylococcus aureus infection in a bacteremia model as compared to vaccination with the antigen alone. Although vaccination with either HlaH35L or HlaH35L conjugated to SSHELs similarly elicited the production of neutralizing antibodies to Hla, we found that a subset of memory T cells was differentially activated when the antigen was delivered on SSHELs. We propose that the particulate nature of SSHELs elicits a more robust immune response to the vaccine that results in superior protection against subsequent S. aureus infection.

Using SimulATe to model the effects of antibiotic selective pressure on the dynamics of pathogenic bacterial populations

Antibiotics are notable weapons in fighting bacteria. Nowadays, however, the effectiveness of antibiotics is severely hindered by the increasing levels of antibiotic resistances in pathogenic bacterial populations, which can persist due to the selective pressure caused by antibiotic exposure. Arguably, the main cause of antibiotic resistances endurance in nature is antibiotic misuse, such as via overusing, inappropriate prescribing as well as the uncontrolled use in agriculture and livestock. There is also a lack of knowledge on appropriate antibiotic usage by the general public. Public scientific literacy and more research on therapeutic practices are fundamental to tackle this problem. Here, we present SimulATe a software which allows the simulation of the effects of antibiotic therapies on bacterial populations during human infections. This software can be used to develop students’ scientific literacy, using infections and antibiotic treatments as context to engage students in scientific practices, and discussions on antibiotic treatment onset and duration or on its use in immunosuppressed or critically ill individuals. SimulATe’s features also allow it to be used for research purposes allowing the simulation of real scenarios and exploration of their outcomes across the parameters’ landscape.

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.

GPER activation protects against epithelial barrier disruption by Staphylococcus aureus α-toxin

Sex bias in innate defense against Staphylococcus aureus skin and soft tissue infection (SSTI) is dependent on both estrogen production by the host and S. aureus secretion of the virulence factor, α-hemolysin (Hla). The impact of estrogen signaling on the immune system is most often studied in terms of the nuclear estrogen receptors ERα and ERβ. However, the potential contribution of the G protein-coupled estrogen receptor (GPER) to innate defense against infectious disease, particularly with respect to skin infection, has not been addressed. Using a murine model of SSTI, we found that GPER activation with the highly selective agonist G-1 limits S. aureus SSTI and Hla-mediated pathogenesis, effects that were absent in GPER knockout mice. Specifically, G-1 reduced Hla-mediated skin lesion formation and pro-inflammatory cytokine production, while increasing bacterial clearance. In vitro, G-1 reduced surface expression of the Hla receptor, ADAM10, in a human keratinocyte cell line and increased resistance to Hla-mediated permeability barrier disruption. This novel role for GPER activation in skin innate defense against infectious disease suggests that G-1 may have clinical utility in patients with epithelial permeability barrier dysfunction or who are otherwise at increased risk of S. aureus infection, including those with atopic dermatitis or cancer.

Subinhibitory concentrations of tedizolid potently inhibit extracellular toxin production by methicillin-sensitive and methicillin-resistant Staphylococcus aureus

PURPOSE

Potent extracellular toxins including alpha-haemolysin, Panton-Valentine leukocidin (PVL) and toxic-shock syndrome toxin 1 (TSST-1) significantly contribute to Staphylococcus aureus pathogenesis, thus, toxin suppression is a primary focus in treatment of staphylococcal disease. S. aureus maintains complex strategies to regulate toxin expression and previous data have demonstrated that subinhibitory concentrations of beta-lactam antibiotics can adversely increase S. aureus exotoxin production. The current study evaluates the effects of subinhibitory concentrations of tedizolid, a second-generation oxazolidinone derivative, on expression of staphylococcal exotoxins in both methicillin-resistant and methicillin-sensitive S. aureus.

METHODOLOGY

S. aureus exotoxin expression levels were compared at 12 and 24 h following treatment with tedizolid, linezolid, nafcillin or vehicle control.

RESULTS

Our findings show that the level of antibiotic required to alter toxin production was strain-dependent and corresponds with the quantity of toxin produced, but both tedizolid and linezolid could effectively reduce expression of alpha-haemolysin, PVL and TSST-1 toxin at subinhibitory concentrations. In contrast, nafcillin showed less attenuation and, in some S. aureus strains, led to an increase in toxin expression. Tedizolid consistently inhibited toxin production at a lower overall drug concentration than comparator agents.

CONCLUSION

Together, our data support that tedizolid has the potential to improve outcomes of infection due to its superior ability to inhibit S. aureus growth and attenuate exotoxin production.

Pharmacological Targeting of Pore-Forming Toxins as Adjunctive Therapy for Invasive Bacterial Infection

For many of the most important human bacterial infections, invasive disease severity is fueled by the cell damaging and pro-inflammatory effects of secreted pore-forming toxins (PFTs). Isogenic PFT-knockout mutants, e.g., Staphylococcus aureus lacking α-toxin or Streptococcus pneumoniae deficient in pneumolysin, show attenuation in animal infection models. This knowledge has inspired multi-model investigations of strategies to neutralize PFTs or counteract their toxicity as a novel pharmacological approach to ameliorate disease pathogenesis in clinical disease. Promising examples of small molecule, antibody or nanotherapeutic drug candidates that directly bind and neutralize PFTs, block their oligomerization or membrane receptor interactions, plug establishment membrane pores, or boost host cell resiliency to withstand PFT action have emerged. The present review highlights these new concepts, with a special focus on β-PFTs produced by leading invasive human Gram-positive bacterial pathogens. Such anti-virulence therapies could be applied as an adjunctive therapy to antibiotic-sensitive and -resistant strains alike, and further could be free of deleterious effects that deplete the normal microflora.

A Critical Role for HlgA in Staphylococcus aureus Pathogenesis Revealed by A Switch in the SaeRS Two-Component Regulatory System

Cytolytic pore-forming toxins including alpha hemolysin (Hla) and bicomponent leukotoxins play an important role in the pathogenesis of Staphylococcus aureus. These toxins kill the polymorphonuclear phagocytes (PMNs), disrupt epithelial and endothelial barriers, and lyse erythrocytes to provide iron for bacterial growth. The expression of these toxins is regulated by the two-component sensing systems Sae and Agr. Here, we report that a point mutation (L18P) in SaeS, the histidine kinase sensor of the Sae system, renders the S. aureus Newman hemolytic activity fully independent of Hla and drastically increases the PMN lytic activity. Furthermore, this Hla-independent activity, unlike Hla itself, can lyse human erythrocytes. The Hla-independent activity towards human erythrocytes was also evident in USA300, however, under strict agr control. Gene knockout studies revealed that this Hla-independent Sae-regulated activity was entirely dependent on gamma hemolysin A subunit (HlgA). In contrast, hemolytic activity of Newman towards human erythrocytes from HlgAB resistant donors was completely dependent on agr. The culture supernatant from Newman S. aureus could be neutralized by antisera against two vaccine candidates based on LukS and LukF subunits of Panton-Valentine leukocidin but not by an anti-Hla neutralizing antibody. These findings display the complex involvement of Sae and Agr systems in regulating the virulence of S. aureus and have important implications for vaccine and immunotherapeutics development for S. aureus disease in humans.

A D-Alanine auxotrophic live vaccine is effective against lethal infection caused by Staphylococcus aureus

Staphylococcus aureus infections are becoming a major global health issue due to the rapid emergence of multidrug-resistant strains. Therefore, there is an urgent need to develop an effective vaccine to prevent and control these infections. In order to develop a universal immunization strategy, we constructed a mutant derivative of S. aureus 132 which lacks the genes involved in D-alanine biosynthesis, a structural component of cell wall peptidoglycan. This unmarked deletion mutant requires the exogenous addition of D-alanine for in vitro growth. The aim of this study was to examine the ability of this D-alanine auxotroph to induce protective immunity against staphylococcal infection. Our findings demonstrate that this deletion mutant is highly attenuated, elicits a protective immune response in mice and generates cross-reactive antibodies. Moreover, the D-alanine auxotroph was completely eliminated from the blood of mice after its intravenous or intraperitoneal injection. We determined that the protective effect was dependent on antibody production since the adoptive transfer of immune serum into naïve mice resulted in effective protection against S. aureus bacteremia. In addition, splenocytes from mice immunized with the D-alanine auxotroph vaccine showed specific production of IL-17A after ex vivo stimulation. We conclude that this D-alanine auxotroph protects mice efficiently against virulent staphylococcal strains through the combined action of antibodies and IL-17A, and therefore constitutes a promising vaccine candidate against staphylococcal disease, for which no licensed vaccine is available yet.

Effect of 2 Emulsion-Based Adjuvants on the Structure and Thermal Stability of Staphylococcus aureus Alpha-Toxin

The effects of 2 squalene-based emulsion adjuvant systems (MedImmune emulsion 0 [ME.0] and Stable Emulsion [SE]) on the structure and stability of the recombinant protein antigen alpha-toxin (AT), a potential vaccine candidate for Staphylococcus aureus infection, were investigated using Fourier-transform infrared spectroscopy and both steady-state and time-resolved intrinsic fluorescence spectroscopy as well as differential scanning calorimetry (DSC). A component study, performed to identify the effects of the individual emulsion's components, showed negligible interactions between AT and ME.0. DSC analysis showed the ME.0 emulsion thermally destabilized AT, probably because of changes in the buffer composition of AT upon mixing. The SE emulsion caused increased alpha-helix and decreased beta-sheet content in AT, and a significant blue shift in the fluorescence spectra relative to that of AT in solution. DSC analysis showed SE exerted a dramatic thermal stabilization effect on AT, probably attributable to an interaction between AT and SE. Size exclusion chromatography showed a complete loss in the recovery of AT when mixed with SE, but not ME.0, indicating a high degree of interaction with SE. This work successfully characterized the biophysical properties of AT in the presence of 2 emulsion adjuvants including a component study to rationalize how emulsion components affect protein antigen stability.

Staphylococcus Aureus Surface Protein G is An Immunodominant Protein and a Possible Target in An Anti-Biofilm Drug Development

Background

Staphylococcus aureus is a Gram-positive bacterium that causes severe illnesses in the human population. The capacity of S. aureus strains to form biofilms on biotic and abiotic surfaces creates serious problems for treatment of hospital infections and has stimulated efforts to develop new means of specific protection or immunotherapy.

Material and Methods

We found that rabbit serum raised against crude concentrated S. aureus liquid culture significantly decreased the development of staphylococcal biofilm in vitro. To discover the corresponding staphylococcal antigen, we used mass-spectrometry and molecular cloning and identified three major immunodominant proteins. They included α-haemolysin, serine proteinase SplB and S. aureus surface protein G, known as adhesin SasG.

Results

Although according to literature data, all these proteins represent virulence factors of S. aureus and play diverse and important roles in the pathogenesis of staphylococcal diseases, only SasG can be directly implicated into the biofilm formation because of its surface location on a staphylococcal cell. Indeed, rabbit serum directed against purified recombinant SasG, similar to serum against crude staphylococcal liquid culture, prevented the formation of a biofilm.

Conclusion

SasG can be considered as a target in an anti-biofilm drug development and a component of the vaccine or immunotherapeutic preparations directed against staphylococcal infections in humans.

Protective humoral and CD4+ T cellular immune responses of Staphylococcus aureus vaccine MntC in a murine peritonitis model

Staphylococcus aureus can cause different types of diseases from mild skin infections to life-threatening sepsis worldwide. Owing to the emergence and transmission of multidrug-resistant strains, developing an impactful immunotherapy especially vaccine control approach against S. aureus infections is increasingly encouraged and supported. S. aureus manganese transport protein C (MntC), which is a highly-conserved cell surface protein, can elicit protective immunity against S. aureus and Staphylococcus epidermidis. In this study, we evaluated the humoral immune response and CD4⁺ T cell-mediated immune responses in a mouse peritonitis model. The results showed that MntC-specific antibodies conferred an essential protection for mice to reduce invasion of S. aureus, which was corroborated via the opsonophagocytic killing assay and passive immunization experiment in mice, and moreover MntC-induced Th17 played a remarkable part in preventing S. aureus infection since the MntC-induced protective immunity decreased after neutralization of IL-17 by antibody in vivo and the Th17 adoptive transferred-mice could partly resist S. aureus challenge. In conclusion, we considered that the MntC-specific antibodies and MntC-specific Th17 cells play cooperative roles in the prevention of S. aureus infection.

Characterisation of anti-alpha toxin antibody levels and colonisation status after administration of an investigational human monoclonal antibody, MEDI4893, against Staphylococcus aureus alpha toxin

Objectives

MEDI4893 is a novel, long‐acting human monoclonal antibody targeting Staphylococcus aureus (SA) alpha toxin (AT). This report presents the results of the exploratory analyses from a randomised phase 1 dose‐escalation study in healthy human subjects receiving single intravenous MEDI4893 doses or placebo.

Methods

Anti‐AT antibodies and AT expression were measured as described previously. Nasal swabs were analysed by culture and PCR. Data were summarised by treatment groups and visits by using SAS System Version 9.3.

Results

Subjects receiving 2250 or 5000 mg of MEDI4893 had the highest serum anti‐AT neutralising antibody (NAb) levels: approximately 180‐ to 240‐, 70‐ to 100‐ and sevenfold to 10‐fold higher than respective baseline levels at peak, 30 and 360 days, respectively. In these subjects, levels of serum anti‐AT NAbs were >3.2 International Units (IU) mL⁻¹ for at least 211 days. In the upper respiratory tract, anti‐AT NAb levels increased with MEDI4893 dose. No apparent effect of MEDI4893 on SA nasal colonisation, hla gene sequence or AT expression was observed. Five AT variants were detected, their lytic activity was fully neutralised by MEDI4893.

Discussion

Our results indicate that (1) MEDI4893 administration at 2250 and 5000 mg would provide effective immunoprophylaxis against systemic SA disease; (2) MEDI4983 distributes to the upper respiratory tract and retains neutralising activity against AT; and (3) potential for emergence of MEDI4893 resistance is low.

Conclusion

Intravenous administration of MEDI4893 maintained levels of anti‐AT NAbs in serum and nasal mucosa that may provide effective immunoprophylaxis against SA disease and support continued clinical development of MEDI4893.

Subinhibitory Dalbavancin Attenuates Exotoxin Production from Methicillin-Sensitive and Methicillin-Resistant Staphylococcus aureus In Vitro

This study investigated the effects of subinhibitory doses of the lipoglycopeptide antibiotic dalbavancin on Staphylococcus aureus toxin production in vitroS. aureus toxin production levels were compared to those seen with the natural glycopeptide antibiotic vancomycin and with representative beta-lactam and oxazolidinone antibiotics. While neither dalbavancin nor vancomycin adversely affected toxin production, of these glycopeptide antibiotics, only dalbavancin significantly attenuated toxin production at subinhibitory concentrations. These findings support the recent success of dalbavancin for treatment of staphylococcal infections.

VLP-based vaccine induces immune control of Staphylococcus aureus virulence regulation

Staphylococcus aureus is the leading cause of skin and soft tissue infections (SSTIs) and mounting antibiotic resistance requires innovative treatment strategies. S. aureus uses secreted cyclic autoinducing peptides (AIPs) and the accessory gene regulator (agr) operon to coordinate expression of virulence factors required for invasive infection. Of the four agr alleles (agr types I-IV and corresponding AIPs1-4), agr type I isolates are most frequently associated with invasive infection. Cyclization via a thiolactone bond is essential for AIP function; therefore, recognition of the cyclic form of AIP1 may be necessary for antibody-mediated neutralization. However, the small sizes of AIPs and labile thiolactone bond have hindered vaccine development. To overcome this, we used a virus-like particle (VLP) vaccine platform (PP7) for conformationally-restricted presentation of a modified AIP1 amino acid sequence (AIP1S). Vaccination with PP7-AIP1S elicited AIP1-specific antibodies and limited agr-activation in vivo. Importantly, in a murine SSTI challenge model with a highly virulent agr type I S. aureus isolate, PP7-AIP1S vaccination reduced pathogenesis and increased bacterial clearance compared to controls, demonstrating vaccine efficacy. Given the contribution of MRSA agr type I isolates to human disease, vaccine targeting of AIP1-regulated virulence could have a major clinical impact in the fight against antibiotic resistance.

Pediatric Multiple Organ Dysfunction Syndrome: Promising Therapies

OBJECTIVE

To describe the state of the science, identify knowledge gaps, and offer potential future research questions regarding promising therapies for children with multiple organ dysfunction syndrome presented during the Eunice Kennedy Shriver National Institute of Child Health and Human Development Workshop on Pediatric Multiple Organ Dysfunction Syndrome (March 26-27, 2015).

DATA SOURCES

Literature review, research data, and expert opinion.

STUDY SELECTION

Not applicable.

DATA EXTRACTION

Moderated by an expert from the field, issues relevant to the association of multiple organ dysfunction syndrome with a variety of conditions were presented, discussed, and debated with a focus on identifying knowledge gaps and research priorities.

DATA SYNTHESIS

Summary of presentations and discussion supported and supplemented by relevant literature.

CONCLUSIONS

Among critically ill children, multiple organ dysfunction syndrome is relatively common and associated with significant morbidity and mortality. For outcomes to improve, effective therapies aimed at preventing and treating this condition must be discovered and rigorously evaluated. In this article, a number of potential opportunities to enhance current care are highlighted including the need for a better understanding of the pharmacokinetics and pharmacodynamics of medications, the effect of early and optimized nutrition, and the impact of effective glucose control in the setting of multiple organ dysfunction syndrome. Additionally, a handful of the promising therapies either currently being implemented or developed are described. These include extracorporeal therapies, anticytokine therapies, antitoxin treatments, antioxidant approaches, and multiple forms of exogenous steroids. For the field to advance, promising therapies and other therapies must be assessed in rigorous manner and implemented accordingly.

Safety and Immunogenicity of a Parenterally Administered, Structure-Based Rationally Modified Recombinant Staphylococcal Enterotoxin B Protein Vaccine, STEBVax

Staphylococcus aureus produces several enterotoxins and superantigens, exposure to which can elicit profound toxic shock. A recombinant staphylococcal enterotoxin B (rSEB) containing 3 distinct mutations in the major histocompatibility complex class II binding site was combined with an alum adjuvant (Alhydrogel) and used as a potential parenteral vaccine named STEBVax. Consenting healthy adult volunteers (age range, 23 to 38 years) participated in a first-in-human open-label dose escalation study of parenteral doses of STEBVax ranging from 0.01 μg up to 20 μg. Safety was assessed by determination of the frequency of adverse events and reactogenicity. Immune responses to the vaccination were determined by measurement of anti-staphylococcal enterotoxin B (anti-SEB) IgG by enzyme-linked immunosorbent assay and a toxin neutralization assay (TNA). Twenty-eight participants were enrolled in 7 dosing cohorts. All doses were well tolerated. The participants exhibited heterogeneous baseline antibody titers. More seroconversions and a faster onset of serum anti-SEB IgG toxin-neutralizing antibodies were observed by TNA with increasing doses of STEBVax. There was a trend for a plateau in antibody responses with doses of STEBVax of between 2.5 and 20 μg. Among the participants vaccinated with 2.5 μg to 20 μg of STEBVax, ∼93% seroconverted for SEB toxin-neutralizing antibody. A strong correlation between individual SEB-specific serum IgG antibody titers and the neutralization of gamma interferon production was found in vitro STEBvax appeared to be safe and immunogenic, inducing functional toxin-neutralizing antibodies. These data support its continued clinical development. (This study has been registered at ClinicalTrials.gov under registration no. NCT00974935.).

Protective efficacy of a novel alpha hemolysin subunit vaccine (AT62) against Staphylococcus aureus skin and soft tissue infections

Alpha hemolysin (Hla) is a pore-forming toxin produced by most Staphylococcus aureus isolates. Hla is reported to play a key role in the pathogenesis of staphylococcal infections, such as skin and soft tissue infection, pneumonia, and lethal peritonitis. This study makes use of a novel recombinant subunit vaccine candidate (AT62) that was rationally designed based on the Hla heptameric crystal structure. AT62 comprises a critical structural domain at the N terminus of Hla, and it has no inherent toxic properties. We evaluated the efficacy of AT62 in protection against surgical wound infection and skin and soft tissue infection. Mice were vaccinated on days 0, 14, and 28 with 20μg AT62 or bovine serum albumin (BSA) mixed with Sigma adjuvant system®. Mice immunized with AT62 produced a robust antibody response against native Hla. In the surgical wound infection model, mice immunized with AT62 and challenged with a USA300 S. aureus strain showed a significantly reduced bacterial burden in the infected tissue compared to animals given BSA. Similarly, mice passively immunized with rabbit IgG to AT62 showed reduced wound infection and tissue damage. Subcutaneous abscess formation was not prevented by immunization with AT62. However, in a skin necrosis infection model, immunization with the AT62 vaccine resulted in smaller lesions and reduced mouse weight loss compared to controls. Although AT62 immunization reduced tissue necrosis, it did not reduce the bacterial burdens in the lesions compared to controls. Our data indicate that AT62 may be a valuable component of a multivalent vaccine against S. aureus.

Targeting Alpha Toxin and ClfA with a Multimechanistic Monoclonal-Antibody-Based Approach for Prophylaxis of Serious Staphylococcus aureus Disease

Staphylococcus aureus produces numerous virulence factors, each contributing different mechanisms to bacterial pathogenesis in a spectrum of diseases. Alpha toxin (AT), a cytolytic pore-forming toxin, plays a key role in skin and soft tissue infections and pneumonia, and a human anti-AT monoclonal antibody (MAb), MEDI4893*, has been shown to reduce disease severity in dermonecrosis and pneumonia infection models. However, interstrain diversity and the complex pathogenesis of S. aureus bloodstream infections suggests that MEDI4893* alone may not provide adequate protection against S. aureus sepsis. Clumping factor A (ClfA), a fibrinogen binding protein, is an important virulence factor facilitating S. aureus bloodstream infections. Herein, we report on the identification of a high-affinity anti-ClfA MAb, 11H10, that inhibits ClfA binding to fibrinogen, prevents bacterial agglutination in human plasma, and promotes opsonophagocytic bacterial killing (OPK). 11H10 prophylaxis reduced disease severity in a mouse bacteremia model and was dependent on Fc effector function and OPK. Additionally, prophylaxis with 11H10 in combination with MEDI4893* provided enhanced strain coverage in this model and increased survival compared to that obtained with the individual MAbs. The MAb combination also reduced disease severity in murine dermonecrosis and pneumonia models, with activity similar to that of MEDI4893* alone. These results indicate that an MAb combination targeting multiple virulence factors provides benefit over a single MAb neutralizing one virulence mechanism by providing improved efficacy, broader strain coverage, and protection against multiple infection pathologies.

Alternative strategies to broad-spectrum antibiotics are required to combat the antibiotic resistance epidemic. Previous attempts at active or passive immunization against Staphylococcus aureus targeting single antigens have failed in clinical trials despite positive preclinical data. To provide broad disease and isolate coverage, an effective immunization strategy likely must target multiple virulence mechanisms of the pathogen. Herein, we tested a multimechanistic MAb combination targeting alpha toxin (AT) and clumping factor A (ClfA) that neutralizes AT-mediated cytotoxicity, blocks fibrinogen binding by ClfA, prevents bacterial agglutination, targets the bacteria for opsonophagocytic killing, and provides broad isolate coverage in a lethal-bacteremia model. Although each MAb alone was effective in bacteremia against some individual isolates, the MAb combination provided improved protection against other isolates. These results illustrate the importance of targeting multiple virulence mechanisms and highlight the potential for an MAb combination targeting AT and ClfA to effectively prevent S. aureus disease.

Auto-Assembling Detoxified Staphylococcus aureus Alpha-Hemolysin Mimicking the Wild-Type Cytolytic Toxin

Staphylococcus aureus alpha-hemolysin (Hla) assembles into heptameric pores on the host cell membrane, causing lysis, apoptosis, and junction disruption. Herein, we present the design of a newly engineered S. aureus alpha-toxin, HlaPSGS, which lacks the predicted membrane-spanning stem domain. This protein is able to form heptamers in aqueous solution in the absence of lipophilic substrata, and its structure, obtained by transmission electron microscopy and single-particle reconstruction analysis, resembles the cap of the wild-type cytolytic Hla pore. HlaPSGS was found to be impaired in binding to host cells and to its receptor ADAM10 and to lack hemolytic and cytotoxic activity. Immunological studies using human sera as well as sera from mice convalescent from S. aureus infection suggested that the heptameric conformation of HlaPSGS mimics epitopes exposed by the cytolytic Hla pore during infection. Finally, immunization with this newly engineered Hla generated high protective immunity against staphylococcal infection in mice. Overall, this study provides unprecedented data on the natural immune response against Hla and suggests that the heptameric HlaPSGS is a highly valuable vaccine candidate against S. aureus.

The promise and challenge of epitope-focused vaccines

Traditional vaccination with whole pathogens or pathogen-derived subunits has completely eliminated diseases like smallpox, and has greatly limited the incidence, morbidity and mortality associated with many other infectious diseases. Unfortunately, a large burden of infectious disease remains that may be preventable through vaccination. For many of these, more focused and innovative approaches may be essential for the development of effective vaccines.

Nanoparticle-Based Antivirulence Vaccine for the Management of Methicillin-Resistant Staphylococcus aureus Skin Infection

With the rising threat of antibiotic-resistant bacteria, vaccination is becoming an increasingly important strategy to prevent and manage bacterial infections. Made from deactivated bacterial toxins, toxoid vaccines are widely used in the clinic as they help to combat the virulence mechanisms employed by different pathogens. Herein, the efficacy of a biomimetic nanoparticle-based anti-virulence vaccine is examined in a mouse model of methicillin-resistant Staphylococcus aureus (MRSA) skin infection. Vaccination with nanoparticle-detained staphylococcal α-hemolysin (Hla) effectively triggers the formation of germinal centers and induces high anti-Hla titers. Compared to mice vaccinated with control samples, those vaccinated with the nanoparticle toxoid show superior protective immunity against MRSA skin infection. The vaccination not only inhibits lesion formation at the site of bacterial challenge, but also reduces the invasiveness of MRSA, preventing dissemination into other organs. Overall, this biomimetic nanoparticle-based toxin detainment strategy is a promising method for the design of potent anti-virulence vaccines for managing bacterial infections.

Innate Immune Signaling Activated by MDR Bacteria in the Airway

Health care-associated bacterial pneumonias due to multiple-drug resistant (MDR) pathogens are an important public health problem and are major causes of morbidity and mortality worldwide. In addition to antimicrobial resistance, these organisms have adapted to the milieu of the human airway and have acquired resistance to the innate immune clearance mechanisms that normally prevent pneumonia. Given the limited efficacy of antibiotics, bacterial clearance from the airway requires an effective immune response. Understanding how specific airway pathogens initiate and regulate innate immune signaling, and whether this response is excessive, leading to host-induced pathology may guide future immunomodulatory therapy. We will focus on three of the most important causes of health care-associated pneumonia, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, and review the mechanisms through which an inappropriate or damaging innate immune response is stimulated, as well as describe how airway pathogens cause persistent infection by evading immune activation.

Protective efficacy of the chimeric Staphylococcus aureus vaccine candidate IC in sepsis and pneumonia models

Staphylococcus aureus causes serious sepsis and necrotic pneumonia worldwide. Due to the spread of multidrug-resistant strains, developing an effective vaccine is the most promising method for combating S. aureus infection. In this study, based on the immune-dominant areas of the iron surface determinant B (IsdB) and clumping factor A (ClfA), we designed the novel chimeric vaccine IsdB_151-277ClfA_33-213 (IC). IC formulated with the AlPO₄ adjuvant induced higher protection in an S. aureus sepsis model compared with the single components alone and showed broad immune protection against several clinical S. aureus isolates. Immunisation with IC induced strong antibody responses. The protective effect of antibodies was demonstrated through the opsonophagocytic assay (OPA) and passive immunisation experiment. Moreover, this new chimeric vaccine induced Th1/Th17-skewed cellular immune responses based on cytokine profiles and CD4⁺ T cell stimulation tests. Neutralisation of IL-17A alone (but not IFN-γ) resulted in a significant decrease in vaccine immune protection. Finally, we found that IC showed protective efficacy in a pneumonia model. Taken together, these data provide evidence that IC is a potentially promising vaccine candidate for combating S. aureus sepsis and pneumonia.