Towards the immune proteome of Staphylococcus aureus – The anti-S. aureus antibody response

Vaccines: Do they have a role in orthopedic trauma?

Although vaccines have been hailed as one of the greatest advances in medicine based on their unparalleled cost-effectiveness in eradicating life-threatening infectious diseases, their role in orthopedic trauma-related infections is unclear. This is largely because vaccines are primarily made against pathogens that cause communicable diseases rather than opportunistic infections secondary to trauma, and most successful vaccines are against viruses rather than biofilm forming bacteria. Nonetheless, the tremendous costs to patients and healthcare systems warrant orthopedic trauma vaccine research, which has been a focal topic in recent international consensus meetings on musculoskeletal infection. This subject was also covered at the 2023 Osteosynthesis and Trauma Care Foundation (OTCF) meeting in Rome, Italy, and the purpose of this supplement article is to (1) highlight the osteoimmunology, animal models, translational research and clinical pilots that were discussed, (2) the proposed future directions that could lead to diagnostics and prognostics that are critically needed for evidence-based decision making, and (3) vaccines and passive-immunization strategies that could potentially be utilized to treat patients with orthopedic infections.

Host-induced cell wall remodeling impairs opsonophagocytosis of Staphylococcus aureus by neutrophils

The bacterial pathogen Staphylococcus aureus responds to the host environment by increasing the thickness of its cell wall. However, the impact of cell wall thickening on susceptibility to host defenses is unclear. Using bacteria incubated in human serum, we show that host-induced increases in cell wall thickness led to a reduction in the exposure of bound antibody and complement and a corresponding reduction in phagocytosis and killing by neutrophils. The exposure of opsonins bound to protein antigens or lipoteichoic acid (LTA) was most significantly reduced, while opsonization by IgG against wall teichoic acid or peptidoglycan was largely unaffected. Partial digestion of accumulated cell wall using the enzyme lysostaphin restored opsonin exposure and promoted phagocytosis and killing. Concordantly, the antibiotic fosfomycin inhibited cell wall remodeling and maintained the full susceptibility of S. aureus to opsonophagocytic killing by neutrophils. These findings reveal that host-induced changes to the S. aureus cell wall reduce the ability of the immune system to detect and kill this pathogen through reduced exposure of protein- and LTA-bound opsonins.

IMPORTANCE

Understanding how bacteria adapt to the host environment is critical in determining fundamental mechanisms of immune evasion, pathogenesis, and the identification of targets for new therapeutic approaches. Previous work demonstrated that Staphylococcus aureus remodels its cell envelope in response to host factors and we hypothesized that this may affect recognition by antibodies and thus killing by immune cells. As expected, incubation of S. aureus in human serum resulted in rapid binding of antibodies. However, as bacteria adapted to the serum, the increase in cell wall thickness resulted in a significant reduction in exposure of bound antibodies. This reduced antibody exposure, in turn, led to reduced killing by human neutrophils. Importantly, while antibodies bound to some cell surface structures became obscured, this was not the case for those bound to wall teichoic acid, which may have important implications for vaccine design.

The Cell Wall, Cell Membrane and Virulence Factors of Staphylococcus aureus and Their Role in Antibiotic Resistance

Antibiotic resistant strains of bacteria are a serious threat to human health. With increasing antibiotic resistance in common human pathogens, fewer antibiotics remain effective against infectious diseases. Staphylococcus aureus is a pathogenic bacterium of particular concern to human health as it has developed resistance to many of the currently used antibiotics leaving very few remaining as effective treatment. Alternatives to conventional antibiotics are needed for treating resistant bacterial infections. A deeper understanding of the cellular characteristics of resistant bacteria beyond well characterized resistance mechanisms can allow for increased ability to properly treat them and to potentially identify targetable changes. This review looks at antibiotic resistance in S aureus in relation to its cellular components, the cell wall, cell membrane and virulence factors. Methicillin resistant S aureus bacteria are resistant to most antibiotics and some strains have even developed resistance to the last resort antibiotics vancomycin and daptomycin. Modifications in cell wall peptidoglycan and teichoic acids are noted in antibiotic resistant bacteria. Alterations in cell membrane lipids affect susceptibility to antibiotics through surface charge, permeability, fluidity, and stability of the bacterial membrane. Virulence factors such as adhesins, toxins and immunomodulators serve versatile pathogenic functions in S aureus. New antimicrobial strategies can target cell membrane lipids and virulence factors including anti-virulence treatment as an adjuvant to traditional antibiotic therapy.

Fracture-related infection

Musculoskeletal trauma leading to broken and damaged bones and soft tissues can be a life-threating event. Modern orthopaedic trauma surgery, combined with innovation in medical devices, allows many severe injuries to be rapidly repaired and to eventually heal. Unfortunately, one of the persisting complications is fracture-related infection (FRI). In these cases, pathogenic bacteria enter the wound and divert the host responses from a bone-healing course to an inflammatory and antibacterial course that can prevent the bone from healing. FRI can lead to permanent disability, or long courses of therapy lasting from months to years. In the past 5 years, international consensus on a definition of these infections has focused greater attention on FRI, and new guidelines are available for prevention, diagnosis and treatment. Further improvements in understanding the role of perioperative antibiotic prophylaxis and the optimal treatment approach would be transformative for the field. Basic science and engineering innovations will be required to reduce infection rates, with interventions such as more efficient delivery of antibiotics, new antimicrobials, and optimizing host defences among the most likely to improve the care of patients with FRI.

Evidence of Neutralizing and Non-Neutralizing Anti-Glucosaminidase Antibodies in Patients With S. Aureus Osteomyelitis and Their Association With Clinical Outcome Following Surgery in a Clinical Pilot

Staphylococcus aureus osteomyelitis remains a very challenging condition; recent clinical studies have shown infection control rates following surgery/antibiotics to be ~60%. Additionally, prior efforts to produce an effective S. aureus vaccine have failed, in part due to lack of knowledge of protective immunity. Previously, we demonstrated that anti-glucosaminidase (Gmd) antibodies are protective in animal models but found that only 6.7% of culture-confirmed S. aureus osteomyelitis patients in the AO Clinical Priority Program (AO-CPP) Registry had basal serum levels (>10 ng/ml) of anti-Gmd at the time of surgery (baseline). We identified a small subset of patients with high levels of anti-Gmd antibodies and adverse outcomes following surgery, not explained by Ig class switching to non-functional isotypes. Here, we aimed to test the hypothesis that clinical cure following surgery is associated with anti-Gmd neutralizing antibodies in serum. Therefore, we first optimized an in vitro assay that quantifies recombinant Gmd lysis of the M. luteus cell wall and used it to demonstrate the 50% neutralizing concentration (NC50) of a humanized anti-Gmd mAb (TPH-101) to be ~15.6 μg/ml. We also demonstrated that human serum deficient in anti-Gmd antibodies can be complemented by TPH-101 to achieve the same dose-dependent Gmd neutralizing activity as purified TPH-101. Finally, we assessed the anti-Gmd physical titer and neutralizing activity in sera from 11 patients in the AO-CPP Registry, who were characterized into four groups post-hoc. Group 1 patients (n=3) had high anti-Gmd physical and neutralizing titers at baseline that decreased with clinical cure of the infection over time. Group 2 patients (n=3) had undetectable anti-Gmd antibodies throughout the study and adverse outcomes. Group 3 (n=3) had high titers +/- neutralizing anti-Gmd at baseline with adverse outcomes. Group 4 (n=2) had low titers of non-neutralizing anti-Gmd at baseline with delayed high titers and adverse outcomes. Collectively, these findings demonstrate that both neutralizing and non-neutralizing anti-Gmd antibodies exist in S. aureus osteomyelitis patients and that screening for these antibodies could have a value for identifying patients in need of passive immunization prior to surgery. Future prospective studies to test the prognostic value of anti-Gmd antibodies to assess the potential of passive immunization with TPH-101 are warranted.

Dissecting the Human Response to Staphylococcus aureus Systemic Infections

Staphylococcus aureus is a common human commensal and the leading cause of diverse infections. To identify distinctive parameters associated with infection and colonization, we compared the immune and inflammatory responses of patients with a diagnosis of invasive S. aureus disease to healthy donors. We analyzed the inflammatory responses founding a pattern of distinctive cytokines significantly higher in the patients with invasive disease. The measure of antibody levels revealed a wide antibody responsiveness from all subjects to most of the antigens, with significantly higher response for some antigens in the invasive patients compared to control. Moreover, functional antibodies against toxins distinctively associated with the invasive disease. Finally, we examined the genomic variability of isolates, showing no major differences in genetic distribution compared to a panel of representative strains. Overall, our study shows specific signatures of cytokines and functional antibodies in patients with different primary invasive diseases caused by S. aureus. These data provide insight into human responses towards invasive staphylococcal infections and are important for guiding the identification of novel preventive and therapeutic interventions against S. aureus.

A Comprehensive View on the Human Antibody Repertoire Against Staphylococcus aureus Antigens in the General Population

Our goal was to provide a comprehensive overview of the antibody response to Staphylococcus aureus antigens in the general population as a basis for defining disease-specific profiles and diagnostic signatures. We tested the specific IgG and IgA responses to 79 staphylococcal antigens in 996 individuals from the population-based Study of Health in Pomerania. Using a dilution-based multiplex suspension array, we extended the dynamic range of specific antibody detection to seven orders of magnitude, allowing the precise quantification of high and low abundant antibody specificities in the same sample. The observed IgG and IgA antibody responses were highly heterogeneous with differences between individuals as well as between bacterial antigens that spanned several orders of magnitude. Some antigens elicited significantly more IgG than IgA and vice versa. We confirmed a strong influence of colonization on the antibody response and quantified the influence of sex, smoking, age, body mass index, and serum glucose on anti-staphylococcal IgG and IgA. However, all host parameters tested explain only a small part of the extensive variability in individual response to the different antigens of S. aureus.

Long-Term Sinonasal Carriage of Staphylococcus aureus and Anti-Staphylococcal Humoral Immune Response in Patients with Chronic Rhinosinusitis

We investigated Staphylococcus aureus diversity, genetic factors, and humoral immune responses against antigens via genome analysis of S. aureus isolates from chronic rhinosinusitis (CRS) patients in a long-term follow-up. Of the 42 patients who provided S. aureus isolates and serum for a previous study, 34 could be included for follow-up after a decade. Clinical examinations were performed and bacterial samples were collected from the maxillary sinus and nares. S. aureus isolates were characterized by whole-genome sequencing, and specific anti-staphylococcal IgG in serum was determined using protein arrays. S. aureus was detected in the nares and/or maxillary sinus at both initial inclusion and follow-up in 15 of the 34 respondents (44%). Three of these (20%) had S. aureus isolates from the same genetic lineage as at inclusion. A low number of single-nucleotide polymorphisms (SNPs) were identified when comparing isolates from nares and maxillary sinus collected at the same time point. The overall change of antibody responses to staphylococcal antigens over time showed great variability, and no correlation was found between the presence of genes encoding antigens and the corresponding anti-staphylococcal IgG in serum; thus our findings did not support a role, in CRS, of the specific S. aureus antigens investigated.

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.

Lack of Humoral Immunity Against Glucosaminidase Is Associated with Postoperative Complications in Staphylococcus aureus Osteomyelitis

BACKGROUND

Glucosaminidase (Gmd) is known to be a protective antigen in animal models of Staphylococcus aureus osteomyelitis. We compared the endogenous anti-Gmd antibody levels in sera of patients with culture-confirmed S. aureus bone infections to their sera at 1 year after operative treatment of the infection.

METHODS

A novel global biospecimen registry of 297 patients with deep-wound culture-confirmed S. aureus osteomyelitis was analyzed to assess relationships between baseline anti-Gmd serum titers (via custom Luminex assay), known host risk factors for infection, and 1-year postoperative clinical outcomes (e.g., infection control, inconclusive, refracture, persistent infection, septic nonunion, amputation, and septic death).

RESULTS

All patients had measurable humoral immunity against some S. aureus antigens, but only 20 patients (6.7%; p < 0.0001) had high levels of anti-Gmd antibodies (>10 ng/mL) in serum at baseline. A subset of 194 patients (65.3%) who completed 1 year of follow-up was divided into groups based on anti-Gmd level: low (<1 ng/mL, 54 patients; 27.8%), intermediate (<10 ng/mL, 122 patients; 62.9%), and high (>10 ng/mL, 18 patients; 9.3%), and infection control rates were 40.7%, 50.0%, and 66.7%, respectively. The incidence of adverse outcomes in these groups was 33.3%, 16.4%, and 11.1%, respectively. Assessing anti-Gmd level as a continuous variable showed a 60% reduction in adverse-event odds (p = 0.04) for every tenfold increase in concentration. No differences in patient demographics, body mass index of >40 kg/m, diabetes status, age of ≥70 years, male sex, Charlson Comorbidity Index of >1, or Cierny-Mader host type were observed between groups, and these risk factors were not associated with adverse events. Patients with low anti-Gmd titer demonstrated a significant 2.68-fold increased odds of adverse outcomes (p = 0.008).

CONCLUSIONS

Deficiency in circulating anti-Gmd antibodies was associated serious adverse outcomes following operative treatment of S. aureus osteomyelitis. At 1 year, high levels of anti-Gmd antibodies were associated with a nearly 3-fold increase in infection-control odds. Additional prospective studies clarifying Gmd immunization for osteomyelitis are needed.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Development of a vaccine against Staphylococcus aureus invasive infections: Evidence based on human immunity, genetics and bacterial evasion mechanisms

Invasive Staphylococcus aureus infections are a leading cause of morbidity and mortality in both hospital and community settings, especially with the widespread emergence of virulent and multi-drug resistant methicillin-resistant S. aureus strains. There is an urgent and unmet clinical need for non-antibiotic immune-based approaches to treat these infections as the increasing antibiotic resistance is creating a serious threat to public health. However, all vaccination attempts aimed at preventing S. aureus invasive infections have failed in human trials, especially all vaccines aimed at generating high titers of opsonic antibodies against S. aureus surface antigens to facilitate antibody-mediated bacterial clearance. In this review, we summarize the data from humans regarding the immune responses that protect against invasive S. aureus infections as well as host genetic factors and bacterial evasion mechanisms, which are important to consider for the future development of effective and successful vaccines and immunotherapies against invasive S. aureus infections in humans. The evidence presented form the basis for a hypothesis that staphylococcal toxins (including superantigens and pore-forming toxins) are important virulence factors, and targeting the neutralization of these toxins are more likely to provide a therapeutic benefit in contrast to prior vaccine attempts to generate antibodies to facilitate opsonophagocytosis.

Virulence factors and clonal diversity of Staphylococcus aureus in colonization and wound infection with emphasis on diabetic foot infection

Foot ulcer is a common complication in diabetic subjects and infection of these wounds contributes to increased rates of morbidity and mortality. Diabetic foot infections are caused by a multitude of microbes and Staphylococcus aureus, a major nosocomial and community-associated pathogen, significantly contributes to wound infections as well. Staphylococcus aureus is also the primary pathogen commonly associated with diabetic foot osteomyelitis and can cause chronic and recurrent bone infections. The virulence capability of the pathogen and host immune factors can determine the occurrence and progression of S. aureus infection. Pathogen-related factors include complexity of bacterial structure and functional characteristics that provide metabolic and adhesive properties to overcome host immune response. Even though, virulence markers and toxins of S. aureus are broadly similar in different wound models, certain distinguishing features can be observed in diabetic foot infection. Specific clonal lineages and virulence factors such as TSST-1, leukocidins, enterotoxins, and exfoliatins play a significant role in determining wound outcomes. In this review, we describe the role of specific virulence determinants and clonal lineages of S. aureus that influence wound colonization and infection with special reference to diabetic foot infections.

A Bioinformatic Approach to Utilize a Patient's Antibody-Secreting Cells against Staphylococcus aureus to Detect Challenging Musculoskeletal Infections

Noninvasive diagnostics for Staphylococcus aureus musculoskeletal infections (MSKI) remain challenging. Abs from newly activated, pathogen-specific plasmablasts in human blood, which emerge during an ongoing infection, can be used for diagnosing and tracking treatment response in diabetic foot infections. Using multianalyte immunoassays on medium enriched for newly synthesized Abs (MENSA) from Ab-secreting cells, we assessed anti-S. aureus IgG responses in 101 MSKI patients (63 culture-confirmed S. aureus, 38 S. aureus-negative) and 52 healthy controls. MENSA IgG levels were assessed for their ability to identify the presence and type of S. aureus MSKI using machine learning and multivariate receiver operating characteristic curves. Eleven S. aureus-infected patients were presented with prosthetic joint infections, 15 with fracture-related infections, 5 with native joint septic arthritis, 15 with diabetic foot infections, and 17 with suspected orthopedic infections in the soft tissue. Anti-S. aureus MENSA IgG levels in patients with non-S. aureus infections and healthy controls were 4-fold (***p = 0.0002) and 8-fold (****p < 0.0001) lower, respectively, compared with those with culture-confirmed S. aureus infections. Comparison of MENSA IgG responses among S. aureus culture-positive patients revealed Ags predictive of active MSKI (IsdB, SCIN, Gmd) and Ags predictive of MSKI type (IsdB, IsdH, Amd, Hla). When combined, IsdB, IsdH, Gmd, Amd, SCIN, and Hla were highly discriminatory of S. aureus MSKI (area under the ROC curve = 0.89 [95% confidence interval 0.82-0.93, p < 0.01]). Collectively, these results demonstrate the feasibility of a bioinformatic approach to use a patient's active immune proteome against S. aureus to diagnose challenging MSKI.

Staphylococcus aureus and its IgE-inducing enterotoxins in asthma: current knowledge

While immunoglobulin (Ig) E is a prominent biomarker for early-onset, its levels are often elevated in non-allergic late-onset asthma. However, the pattern of IgE expression in the latter is mostly polyclonal, with specific IgEs low or below detection level albeit with an increased total IgE. In late-onset severe asthma patients, specific IgE to Staphylococcal enterotoxins (se-IgE) can frequently be detected in serum, and has been associated with asthma, with severe asthma defined by hospitalisations, oral steroid use and decrease in lung function. Recently, se-IgE was demonstrated to even predict the development into severe asthma with exacerbations over the next decade. Staphylococcus aureus manipulates the airway mucosal immunology at various levels via its proteins, including superantigens, serine-protease-like proteins (Spls), or protein A (SpA) and possibly others. Release of IL-33 from respiratory epithelium and activation of innate lymphoid cells (ILCs) via its receptor ST2, type 2 cytokine release from those ILCs and T helper (Th) 2 cells, mast cell degranulation, massive local B-cell activation and IgE formation, and finally eosinophil attraction with consequent release of extracellular traps, adding to the epithelial damage and contributing to disease persistence via formation of Charcot-Leyden crystals are the most prominent hallmarks of the manipulation of the mucosal immunity by S. aureus In summary, S. aureus claims a prominent role in the orchestration of severe airway inflammation and in current and future disease severity. In this review, we discuss current knowledge in this field and outline the needs for future research to fully understand the impact of S. aureus and its proteins on asthma.

Comparison of antibody repertories against Staphylococcus aureus in healthy and infected dairy cows with a distinct mastitis history and vaccinated with a polyvalent mastitis vaccine

Staphylococcus aureus is one of the pathogens most frequently isolated from cases of mastitis worldwide. To decrease the effect of S. aureus mastitis in dairy farming, alternative strategies for controlling mastitis are needed that depend on a better knowledge of cow-to-cow variations in S. aureus antibody production. The present study sought to explore the diversity of S. aureus antibodies produced by dairy cows with a distinct mastitis history and vaccinated with a polyvalent mastitis vaccine. We obtained protein extracts from S. aureus isolates derived from persistent subclinical mastitis. Proteins were fractionated using 2-dimensional gel electrophoresis and Western blotting. Then, Western blotting membranes were exposed to sera from 24 dairy cows that had been divided into the following groups: vaccinated dairy cows that were infected with S. aureus, further subdivided according to whether they (a) remained infected by S. aureus or (b) recovered from the intramammary infection; unvaccinated dairy cows infected with S. aureus; and vaccinated healthy dairy cows with no history of S. aureus mastitis. Proteins found to be reactive by Western blot were identified by mass spectrometry (MALDI/TOF-TOF). Our most important finding was that F₀F₁ ATP synthase subunit α, succinyl-diaminopimelate desuccinylase, and cysteinyl-tRNA synthetase were potential candidate proteins for the prevention of S. aureus mastitis. This study strengthens the notion that variations among animals should not be ignored and shows that the heterogeneity of antibody production against anti-staphylococcal antigens in animals may enable the identification of new immunotherapy targets.

Deriving a dose and regimen for anti-glucosaminidase antibody passive-immunisation for patients with Staphylococcus aureus osteomyelitis

Staphylococcus aureus (S. aureus) osteomyelitis remains a major clinical problem. Anti-glucosaminidase (Gmd) antibodies (1C11) are efficacious in prophylactic and therapeutic murine models. Feasibility, safety and pharmacokinetics of 1C11 passive immunisation in sheep and endogenous anti-Gmd levels were quantified in osteomyelitis patients. 3 sheep received a 500 mg intravenous (i.v.) bolus of 1C11 and its levels in sera were determined by enzyme-linked immunosorbent assay (ELISA) over 52 d. A humanised anti-Gmd monoclonal antibody, made by grafting the antigen-binding fragment (Fab) portion of 1C11 onto the fragment crystallisable region (Fc) of human IgG1, was used to make a standard curve of mean fluorescent intensity versus concentration of anti-Gmd. Anti-Gmd serum levels were determined in 297 patients with culture-confirmed S. aureus osteomyelitis and 40 healthy controls. No complications or adverse events were associated with the sheep 1C11 i.v. infusion and the estimated circulating half-life of 1C11 was 23.7 d. Endogenous anti-Gmd antibody levels in sera of osteomyelitis patients ranged from < 1 ng/mL to 300 µg/mL, with a mean concentration of 21.7 µg/mL. The estimated circulating half-life of endogenous anti-Gmd antibodies in sera of 12 patients with cured osteomyelitis was 120.4 d. A clinically relevant administration of anti-Gmd (500 mg i.v. = 7 mg/kg/70 kg human) was safe in sheep. This dose was 8 times more than the endogenous anti-Gmd levels observed in osteomyelitis patients and was predicted to have a half-life of > 3 weeks. Anti-Gmd passive immunisation has potential to prevent and treat S. aureus osteomyelitis. Further clinical development is warranted.

Identification of Key Determinants of Staphylococcus aureus Vaginal Colonization

Staphylococcus aureus is an important pathogen responsible for nosocomial and community-acquired infections in humans, and methicillin-resistant S. aureus (MRSA) infections have continued to increase despite widespread preventative measures. S. aureus can colonize the female vaginal tract, and reports have suggested an increase in MRSA infections in pregnant and postpartum women as well as outbreaks in newborn nurseries. Currently, little is known about specific factors that promote MRSA vaginal colonization and subsequent infection. To study S. aureus colonization of the female reproductive tract in a mammalian system, we developed a mouse model of S. aureus vaginal carriage and demonstrated that both hospital-associated and community-associated MRSA isolates can colonize the murine vaginal tract. Immunohistochemical analysis revealed an increase in neutrophils in the vaginal lumen during MRSA colonization. Additionally, we observed that a mutant lacking fibrinogen binding adhesins exhibited decreased persistence within the mouse vagina. To further identify novel factors that promote vaginal colonization, we performed RNA sequencing to determine the transcriptome of MRSA growing in vivo during vaginal carriage at 5 h, 1 day, and 3 days postinoculation. Over 25% of the bacterial genes were differentially regulated at all time points during colonization compared to laboratory cultures. The most highly induced genes were those involved in iron acquisition, including the Isd system and siderophore transport systems. Mutants deficient in these pathways did not persist as well during in vivo colonization. These results reveal that fibrinogen binding and the capacity to overcome host nutritional limitation are important determinants of MRSA vaginal colonization.IMPORTANCE Staphylococcus aureus is an opportunistic pathogen able to cause a wide variety of infections in humans. Recent reports have suggested an increasing prevalence of MRSA in pregnant and postpartum women, coinciding with the increased incidence of MRSA infections in neonatal intensive care units (NICUs) and newborn nurseries. Vertical transmission from mothers to infants at delivery is a likely route of MRSA acquisition by the newborn; however, essentially nothing is known about host and bacterial factors that influence MRSA carriage in the vagina. Here, we established a mouse model of vaginal colonization and observed that multiple MRSA strains can persist in the vaginal tract. Additionally, we determined that MRSA interactions with fibrinogen and iron uptake can promote vaginal persistence. This study is the first to identify molecular mechanisms which govern vaginal colonization by MRSA, the critical initial step preceding infection and neonatal transmission.

Mechanisms of Immune Evasion and Bone Tissue Colonization That Make Staphylococcus aureus the Primary Pathogen in Osteomyelitis

PURPOSE OF REVIEW

Staphylococcus aureus is the primary pathogen responsible for osteomyelitis, which remains a major healthcare burden. To understand its dominance, here we review the unique pathogenic mechanisms utilized by S. aureus that enable it to cause incurable osteomyelitis.

RECENT FINDINGS

Using an arsenal of toxins and virulence proteins, S. aureus kills and usurps immune cells during infection, to produce non-neutralizing pathogenic antibodies that thwart adaptive immunity. S. aureus also has specific mechanisms for distinct biofilm formation on implants, necrotic bone tissue, bone marrow, and within the osteocyte lacuno-canicular networks (OLCN) of live bone. In vitro studies have also demonstrated potential for intracellular colonization of osteocytes, osteoblasts, and osteoclasts. S. aureus has evolved a multitude of virulence mechanisms to achieve life-long infection of the bone, most notably colonization of OLCN. Targeting S. aureus proteins involved in these pathways could provide new targets for antibiotics and immunotherapies.

Organization of the Skin Immune System and Compartmentalized Immune Responses in Infectious Diseases

The skin is an organ harboring several types of immune cells that participate in innate and adaptive immune responses. The immune system of the skin comprises both skin cells and professional immune cells that together constitute what is designated skin-associated lymphoid tissue (SALT). In this review, I extensively discuss the organization of SALT and the mechanisms involved in its responses to infectious diseases of the skin and mucosa. The nature of these SALT responses, and the cellular mediators involved, often determines the clinical course of such infections. I list and describe the components of innate immunity, such as the roles of the keratinocyte barrier and of inflammatory and natural killer cells. I also examine the mechanisms involved in adaptive immune responses, with emphasis on new cytokine profiles, and the role of cell death phenomena in host-pathogen interactions and control of the immune responses to infectious agents. Finally, I highlight the importance of studying SALT in order to better understand host-pathogen relationships involving the skin and detail future directions in the immunological investigation of this organ, especially in light of recent findings regarding the skin immune system.

Comparative genomics of Staphylococcus aureus associated with subclinical and clinical bovine mastitis

Many efforts have been made to understand the pathogenesis of bovine mastitis to reduce losses and promote animal welfare. Staphylococcus aureus may cause bovine clinical mastitis, but it is mainly associated with subclinical infection, which is usually persistent and can easily reoccur. Here, we conducted a comparative genomic analysis between strains of S. aureus causing subclinical infection (Sau170, 302, 1269, 1364), previously sequenced by our group, and two well-characterized strains causing clinical mastitis (N305 and RF122) to find differences that could be linked to mastitis outcome. A total of 146 virulence-associated genes were compared and no appreciable differences were found between the bacteria. However, several nonsynonymous single nucleotide polymorphisms (SNPs) were identified in genes present in the subclinical strains when compared to RF122 and N305, especially in genes encoding host immune evasion and surface proteins. The secreted and surface proteins predicted by in silico tools were compared through multidimensional scaling analysis (MDS), revealing a high degree of similarity among the strains. The comparison of orthologous genes by OrthoMCL identified a membrane transporter and a lipoprotein as exclusive of bacteria belonging to the subclinical and clinical groups, respectively. No hit was found in RF122 and N305 for the membrane transporter using BLAST algorithm. For the lipoprotein, sequences of Sau170, 302, 1269, and 1364 with identities between 68–73% were found in the MDS dataset. A conserved region found only in the lipoprotein genes of RF122 and N305 was used for primer design. Although the polymerase chain reaction (PCR) on field isolates of S. aureus did not validate the findings for the transporter, the lipoprotein was able to separate the clinical from the subclinical isolates. These results show that sequence variation among bovine S. aureus, and not only the presence/absence of virulence factors, is an important aspect to consider when comparing isolates causing different mastitis outcomes.

Evolving concepts in bone infection: redefining "biofilm", "acute vs. chronic osteomyelitis", "the immune proteome" and "local antibiotic therapy"

Osteomyelitis is a devastating disease caused by microbial infection of bone. While the frequency of infection following elective orthopedic surgery is low, rates of reinfection are disturbingly high. Staphylococcus aureus is responsible for the majority of chronic osteomyelitis cases and is often considered to be incurable due to bacterial persistence deep within bone. Unfortunately, there is no consensus on clinical classifications of osteomyelitis and the ensuing treatment algorithm. Given the high patient morbidity, mortality, and economic burden caused by osteomyelitis, it is important to elucidate mechanisms of bone infection to inform novel strategies for prevention and curative treatment. Recent discoveries in this field have identified three distinct reservoirs of bacterial biofilm including: Staphylococcal abscess communities in the local soft tissue and bone marrow, glycocalyx formation on implant hardware and necrotic tissue, and colonization of the osteocyte-lacuno canalicular network (OLCN) of cortical bone. In contrast, S. aureus intracellular persistence in bone cells has not been substantiated in vivo, which challenges this mode of chronic osteomyelitis. There have also been major advances in our understanding of the immune proteome against S. aureus, from clinical studies of serum antibodies and media enriched for newly synthesized antibodies (MENSA), which may provide new opportunities for osteomyelitis diagnosis, prognosis, and vaccine development. Finally, novel therapies such as antimicrobial implant coatings and antibiotic impregnated 3D-printed scaffolds represent promising strategies for preventing and managing this devastating disease. Here, we review these recent advances and highlight translational opportunities towards a cure.

Staphylococcus aureus Impairs the Function of and Kills Human Dendritic Cells via the LukAB Toxin

Antigen-presenting cells such as dendritic cells (DCs) fulfill an indispensable role in the development of adaptive immunity by producing proinflammatory cytokines and presenting microbial antigens to lymphocytes to trigger a faster, specific, and long-lasting immune response. Here, we studied the effect of Staphylococcus aureus toxins on human DCs. We discovered that the leukocidin LukAB hinders the development of adaptive immunity by targeting human DCs. The ability of S. aureus to blunt the function of DCs could help explain the high frequency of recurrent S. aureus infections. Taken together, the results from this study suggest that therapeutically targeting the S. aureus leukocidins may boost effective innate and adaptive immune responses by protecting innate leukocytes, enabling proper antigen presentation and T cell activation.

Staphylococcus aureus is a human pathogen responsible for high morbidity and mortality worldwide. Recurrent infections with this bacterium are common, suggesting that S. aureus thwarts the development of sterilizing immunity. S. aureus strains that cause disease in humans produce up to five different bicomponent toxins (leukocidins) that target and lyse neutrophils, innate immune cells that represent the first line of defense against S. aureus infections. However, little is known about the role of leukocidins in blunting adaptive immunity. Here, we explored the effects of leukocidins on human dendritic cells (DCs), antigen-presenting cells required for the development of adaptive immunity. Using an ex vivo infection model of primary human monocyte-derived dendritic cells, we found that S. aureus, including strains from different clonal complexes and drug resistance profiles, effectively kills DCs despite efficient phagocytosis. Although all purified leukocidins could kill DCs, infections with live bacteria revealed that S. aureus targets and kills DCs primarily via the activity of leukocidin LukAB. Moreover, using coculture experiments performed with DCs and autologous CD4⁺ T lymphocytes, we found that LukAB inhibits DC-mediated activation and proliferation of primary human T cells. Taken together, the data determined in the study reveal a novel immunosuppressive strategy of S. aureus whereby the bacterium blunts the development of adaptive immunity via LukAB-mediated injury of DCs.

Hierarchy of human IgG recognition within the Staphylococcus aureus immunome

Staphylococcus aureus is an opportunistic pathogen that causes a range of serious infections associated with significant morbidity, by strains increasingly resistant to antibiotics. However, to date all candidate vaccines have failed to induce protective immune responses in humans. We need a more comprehensive understanding of the antigenic targets important in the context of human infection. To investigate infection-associated immune responses, patients were sampled at initial presentation and during convalescence from three types of clinical infection; skin and soft tissue infection (SSTI), prosthetic joint infection (PJI) and pediatric hematogenous osteomyelitis (PHO). Reactivity of serum IgG was tested with an array of recombinant proteins, representing over 2,652 in-vitro-translated open reading frames (ORFs) from a community-acquired methicillin-resistant S. aureus USA300 strain. High-level reactivity was demonstrated for 104 proteins with serum IgG in all patient samples. Overall, high-level IgG-reactivity was most commonly directed against a subset of secreted proteins. Although based on limited surveys, we found subsets of S. aureus proteins with differential reactivity with serum samples from patients with different clinical syndromes. Together, our studies have revealed a hierarchy within the diverse proteins of the S. aureus “immunome”, which will help to advance efforts to develop protective immunotherapeutic agents.

Messing with the Sentinels-The Interaction of Staphylococcus aureus with Dendritic Cells

Staphylococcus aureus (S. aureus) is a dangerous pathogen as well as a frequent colonizer, threatening human health worldwide. Protection against S. aureus infection is challenging, as the bacteria have sophisticated strategies to escape the host immune response. To maintain equilibrium with S. aureus, both innate and adaptive immune effector mechanisms are required. Dendritic cells (DCs) are critical players at the interface between the two arms of the immune system, indispensable for inducing specific T cell responses. In this review, we highlight the importance of DCs in mounting innate as well as adaptive immune responses against S. aureus with emphasis on their role in S. aureus-induced respiratory diseases. We also review what is known about mechanisms that S. aureus has adopted to evade DCs or manipulate these cells to its advantage.

Staphylococcus aureus Evasion of Host Immunity in the Setting of Prosthetic Joint Infection: Biofilm and Beyond

PURPOSE OF REVIEW

The incidence of complications from prosthetic joint infection (PJI) is increasing, and treatment failure remains high. We review the current literature with a focus on Staphylococcus aureus pathogenesis and biofilm, as well as treatment challenges, and novel therapeutic strategies.

RECENT FINDINGS

S. aureus biofilm creates a favorable environment that increases antibiotic resistance, impairs host immunity, and increases tolerance to nutritional deprivation. Secreted proteins from bacterial cells within the biofilm and the quorum-sensing agr system contribute to immune evasion. Additional immunoevasive properties of S. aureus include the formation of staphylococcal abscess communities (SACs) and canalicular invasion. Novel approaches to target biofilm and increase resistance to implant colonization include novel antibiotic therapy, immunotherapy, and local implant treatments. Challenges remain given the diverse mechanisms developed by S. aureus to alter the host immune responses. Further understanding of these processes should provide novel therapeutic mechanisms to enhance eradication after PJI.

Immunotherapy synergizes with debridement and antibiotic therapy in a murine 1-stage exchange model of MRSA implant-associated osteomyelitis

Methicillin-resistant Staphylococcus aureus (MRSA) reinfection following revision surgery remains a major orthopaedic problem. Toward the development of immunotherapy with anti-glucosaminidase monoclonal antibodies (anti-Gmd), we aimed to: (i) develop a murine 1-stage exchange model of bioluminescent MRSA (USA300LAC::lux) contaminated femoral implants; and (ii) utilize this model to demonstrate the synergistic effects of combination vancomycin and anti-Gmd therapy on reinfection and bone healing. Following an infection surgery, the original plate and two screws were removed on day 7, and exchanged with sterile implants. Mice were randomized to five groups: (i) no infection control; (ii) infected placebo; (iii) anti-Gmd; (iv) vancomycin; and (v) combination therapy. Bioluminescent imaging (BLI) was performed on days 0, 1, 3, 5, 7, 8, 10, 12, and 14. Mice were euthanized on day 14 (day 7 post-revision), and efficacy was assessed via colony forming units (CFU) on explanted hardware, micro-CT, and histology. As monotherapies, anti-Gmd inhibited Staphylococcus abscess communities, and vancomycin reduced CFU on the implants. However, only combination therapy prevented increased BLI post-revision surgery, with a significant 6.5-fold reduction on day 10 (p < 0.05 vs. placebo), and achieved sterile implant levels by day 12. Synergistic effects were also apparent from reduced osteolysis and increased new bone formation around the screws only observed following combination therapy. Taken together, we find that: (i) this murine femoral plate 1-stage revision model can efficiently evaluate therapies to prevent reinfection; and (ii) immunotherapy plays a distinct role from antibiotics to reduce reinfection following revision surgery, such that synergy to achieve osseointegration is possible. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1590-1598, 2018.

Clonally expanded γδ T cells protect against Staphylococcus aureus skin reinfection

The mechanisms that mediate durable protection against Staphylococcus aureus skin reinfections are unclear, as recurrences are common despite high antibody titers and memory T cells. Here, we developed a mouse model of S. aureus skin reinfection to investigate protective memory responses. In contrast with WT mice, IL-1β-deficient mice exhibited poor neutrophil recruitment and bacterial clearance during primary infection that was rescued during secondary S. aureus challenge. The γδ T cells from skin-draining LNs utilized compensatory T cell-intrinsic TLR2/MyD88 signaling to mediate rescue by trafficking and producing TNF and IFN-γ, which restored neutrophil recruitment and promoted bacterial clearance. RNA-sequencing (RNA-seq) of the LNs revealed a clonotypic S. aureus-induced γδ T cell expansion with a complementarity-determining region 3 (CDR3) aa sequence identical to that of invariant Vγ5+ dendritic epidermal T cells. However, this T cell receptor γ (TRG) aa sequence of the dominant CDR3 sequence was generated from multiple gene rearrangements of TRGV5 and TRGV6, indicating clonotypic expansion. TNF- and IFN-γ-producing γδ T cells were also expanded in peripheral blood of IRAK4-deficient humans no longer predisposed to S. aureus skin infections. Thus, clonally expanded γδ T cells represent a mechanism for long-lasting immunity against recurrent S. aureus skin infections.

Human antibody responses against non-covalently cell wall-bound Staphylococcus aureus proteins

Human antibody responses to pathogens, like Staphylococcus aureus, are important indicators for in vivo expression and immunogenicity of particular bacterial components. Accordingly, comparing the antibody responses to S. aureus components may serve to predict their potential applicability as antigens for vaccination. The present study was aimed at assessing immunoglobulin G (IgG) responses elicited by non-covalently cell surface-bound proteins of S. aureus, which thus far received relatively little attention. To this end, we applied plasma samples from patients with the genetic blistering disease epidermolysis bullosa (EB) and healthy S. aureus carriers. Of note, wounds of EB patients are highly colonized with S. aureus and accordingly these patients are more seriously exposed to staphylococcal antigens than healthy individuals. Ten non-covalently cell surface-bound proteins of S. aureus, namely Atl, Eap, Efb, EMP, IsaA, LukG, LukH, SA0710, Sle1 and SsaA2, were selected by bioinformatics and biochemical approaches. These antigens were recombinantly expressed, purified and tested for specific IgG responses using human plasma. We show that high exposure of EB patients to S. aureus is mirrored by elevated IgG levels against all tested non-covalently cell wall-bound staphylococcal antigens. This implies that these S. aureus cell surface proteins are prime targets for the human immune system.

Analysis of colostrum IgA against bacteria involved in neonatal infections

OBJECTIVE

To describe e compare the specificity of IgA antibodies against bacteria extract of Klebsiella pneumoniae , Staphylococcus aureus , Escherichia coli , and Salmonella enteritidis .

METHODS

Colostrum samples were aseptically collected in the first 12 hours after C-section delivery. The specificity of IgA against bacteria extracts was analyzed by the Western blot.

RESULTS

The findings showed proteins of high molecular weight frequently detectable in the samples. S. aureus was the most frequently found bacterium in the samples (p<0.05). Approximately 93.8, 56.3, 62.5 and 60.4% of samples presented IgA reactive to S. aureus , K. pneumoniae , S. enteritidis, and E. coli, respectively. Roughly 40% of samples showed no IgA reactive to K. pneumoniae, S. enteritidis and E. coli .

CONCLUSION

Clinical evidence of the importance of breastfeeding for the immune protection of neonates was consistent with the observed immunological findings, since most samples showed IgA reactive against the species tested. The application and development of immunotherapies during pregnancy, focused on frequently detected antigens, could be an important tool to enhance the presence of IgA in colostrum.

The Staphylococcal Biofilm: Adhesins, Regulation, and Host Response

The staphylococci comprise a diverse genus of Gram-positive, nonmotile commensal organisms that inhabit the skin and mucous membranes of humans and other mammals. In general, staphylococci are benign members of the natural flora, but many species have the capacity to be opportunistic pathogens, mainly infecting individuals who have medical device implants or are otherwise immunocompromised. Staphylococcus aureus and Staphylococcus epidermidis are major sources of hospital-acquired infections and are the most common causes of surgical site infections and medical device-associated bloodstream infections. The ability of staphylococci to form biofilms in vivo makes them highly resistant to chemotherapeutics and leads to chronic diseases. These biofilm infections include osteomyelitis, endocarditis, medical device infections, and persistence in the cystic fibrosis lung. Here, we provide a comprehensive analysis of our current understanding of staphylococcal biofilm formation, with an emphasis on adhesins and regulation, while also addressing how staphylococcal biofilms interact with the immune system. On the whole, this review will provide a thorough picture of biofilm formation of the staphylococcus genus and how this mode of growth impacts the host.

Staphylococcus aureus in the Intensive Care Unit: Are These Golden Grapes Ripe for a New Approach?

Staphylococcus aureus is the leading cause of infection in the setting of critical illness and injury. This pathogen causes life-threatening infection in otherwise healthy individuals and also complicates the clinical course of patients requiring intensive care as a result of their primary medical or surgical disease processes. S. aureus infection in the intensive care unit (ICU) most commonly manifests as sepsis, ventilator-associated pneumonia, and infection of surgical sites and indwelling medical devices. With the epidemic spread of methicillin-resistant S. aureus, many cases of staphylococcal infection in the ICU are now classified as drug resistant, prompting hospital-based screening for methicillin-resistant S. aureus and implementation of both isolation practices and decolonization strategies in ICU patients. The genetic adaptability of S. aureus, heterogeneity of disease presentation, clinical course, and outcome between individual S. aureus-infected ICU patients remains enigmatic, suggesting a need to define disease classification subtypes that inform disease progression and therapy. We propose that S. aureus infection in the ICU now presents a unique opportunity for individualized risk stratification coupled with the investigation of novel approaches to mitigate disease. Given our increasing knowledge of the molecular pathogenesis of S. aureus disease, we suggest that the application of molecular pathological epidemiology to S. aureus infection can usher in a new era of highly focused personalized therapy that may be particularly beneficial in the setting of critical illness and injury.

Safety and immunogenicity of a recombinant Staphylococcus aureus α-toxoid and a recombinant Panton-Valentine leukocidin subunit, in healthy adults

We conducted a randomized, double-blind, placebo-controlled dose-escalation study in healthy adults to evaluate the safety and immunogenicity of recombinant Staphylococcus aureus candidate vaccine antigens, recombinant α-toxoid (rAT) and a sub-unit of Panton-Valentine leukocidin (rLukS-PV). 176 subjects were enrolled and randomized within 1 of 11 treatment cohorts: monovalent rAT or rLukS-PV dosages of 10, 25, 50, and 100 μg; bivalent rAT:rLukS dosages of 10:10, 25:25, and 50:50 μg; and alum or saline placebo. All subjects were assessed at Days 0, 7, 14, 28, and 84. Subjects in the 50:50 μg bivalent cohort received a second injection on Day 84 and were assessed on Days 98 and 112. Incidence and severity of reactogenicity and adverse events (AEs) were compared. Geometric mean serum concentrations (GMC) and neutralizing activity of anti-rAT and anti-rLukS-PV IgG were assessed. Reactogenicity incidence was significantly higher in vaccine than placebo recipients (77% versus 55%, respectively; p = 0.006). However, 77% of reactogenicity events were mild and 19% were moderate in severity. The AE incidence and severity were similar between the cohorts. All monovalent and bivalent rAT dosages resulted in a significant increase in the anti-rAT IgG and anti- rLukS-PV GMCs between day 0 and 28 compared with placebo, and persisted through Day 84. Exploratory subgroup analyses suggested a higher GMC and neutralizing antibody titers for the 50 μg monovalent or bivalent rAT and rLukS-PV dose as compared to the other doses. No booster effect was observed after administration of the second dose. We conclude that the rAT and rLukS-PV vaccine formulations were well-tolerated and had a favorable immunogenicity profile, producing antibody with neutralizing activity through day 84. There was no benefit observed with a booster dose of the vaccine.

Proteomic profile of susceptible and multidrug-resistant clinical isolates of Escherichia coli and Klebsiella pneumoniae using label-free and immunoproteomic strategies

Infectious diseases caused by multidrug-resistant (MDR) Enterobacteriaceae have exponentially increased in the past decade, and are a major concern in hospitals. In the first part of the work, we compared the proteome profile of MDR and susceptible clinical isolates of Escherichia coli and Klebsiella pneumoniae in order to identify possible biological processes associated with drug resistance and susceptible phenotypes, using a label-free approach. In the second part, we used an immunoproteomics approach to identify immunoreactive proteins in the same isolates. A total of 388 and 377 proteins were identified in MDR and susceptible E. coli, respectively, evidencing that biological processes related to translation are upregulated in E. coli MDR, while there is an upregulation of processes related to catalytic activity in K. pneumoniae MDR. Both MDR strains show downregulation of processes related to amino acid activation and tRNA amino-acylation. Our data also suggest that MDR strains have higher immunoreactivity than the susceptible strains. The application of high-throughput mass spectrometry (MS) and bioinformatics to the study of modulation of biological processes might shed light on the characterization of multidrug resistance in bacteria.

Combining in vitro protein detection and in vivo antibody detection identifies potential vaccine targets against Staphylococcus aureus during osteomyelitis

Currently, little is known about the in vivo human immune response against Staphylococcus aureus during a biofilm-associated infection, such as osteomyelitis, and how this relates to protein production in biofilms in vitro. Therefore, we characterized IgG responses in 10 patients with chronic osteomyelitis against 50 proteins of S. aureus, analyzed the presence of these proteins in biofilms of the infecting isolates on polystyrene (PS) and human bone in vitro, and explored the relation between in vivo and in vitro data. IgG levels against 15 different proteins were significantly increased in patients compared to healthy controls. Using a novel competitive Luminex-based assay, eight of these proteins [alpha toxin, Staphylococcus aureus formyl peptide receptor-like 1 inhibitor (FlipR), glucosaminidase, iron-responsive surface determinants A and H, the putative ABC transporter SACOL0688, staphylococcal complement inhibitor (SCIN), and serine-aspartate repeat-containing protein E (SdrE)] were also detected in a majority of the infecting isolates during biofilm formation in vitro. However, 4 other proteins were detected in only a minority of isolates in vitro while, vice versa, 7 proteins were detected in multiple isolates in vitro but not associated with significantly increased IgG levels in patients. Detection of proteins was largely confirmed using a transcriptomic approach. Our data provide further insights into potential therapeutic targets, such as for vaccination, to reduce S. aureus virulence and biofilm formation. At the same time, our data suggest that either in vitro or immunological in vivo data alone should be interpreted cautiously and that combined studies are necessary to identify potential targets.

The immunopathogenesis of staphylococcal skin infections - A review

Staphylococcus aureus and S. pseudintermedius are the major causes of bacterial skin disease in humans and dogs. These organisms can exist as commensals on the skin, but they can also cause severe or even devastating infections. The immune system has evolved mechanisms to deal with pathogenic microorganisms and has strategies to combat bacteria of this type. What emerges is a delicate "peace" between the opposing sides, but this balance can be disrupted leading to a full blown "war". In the ferocious battle that ensues, both sides attempt to get the upper hand, using strategies that are comparable to those used by modern day armies. In this review article, the complex interactions between the immune system and the organisms are described using such military analogies. The process is described in a sequential manner, starting with the invasion itself, and progressing to the eventual battlezone in which there are heavy casualties on both sides. By the end, the appearance of a simple pustule on the skin surface will take on a whole new meaning.

Adaptive immune response to lipoproteins of Staphylococcus aureus in healthy subjects

Staphylococcus aureus is a frequent commensal but also a dangerous pathogen, causing many forms of infection ranging from mild to life‐threatening conditions. Among its virulence factors are lipoproteins, which are anchored in the bacterial cell membrane. Lipoproteins perform various functions in colonization, immune evasion, and immunomodulation. These proteins are potent activators of innate immune receptors termed Toll‐like receptors 2 and 6. This study addressed the specific B‐cell and T‐cell responses directed to lipoproteins in human S. aureus carriers and non‐carriers. 2D immune proteomics and ELISA approaches revealed that titers of antibodies (IgG) binding to S. aureus lipoproteins were very low. Proliferation assays and cytokine profiling data showed only subtle responses of T cells; some lipoproteins did not elicit proliferation. Hence, the robust activation of the innate immune system by S. aureus lipoproteins does not translate into a strong adaptive immune response. Reasons for this may include inaccessibility of lipoproteins for B cells as well as ineffective processing and presentation of the antigens to T cells.

Global antibody response to Staphylococcus aureus live-cell vaccination

The pathogen Staphylococcus aureus causes a broad range of severe diseases and is feared for its ability to rapidly develop resistance to antibiotic substances. The increasing number of highly resistant S. aureus infections has accelerated the search for alternative treatment options to close the widening gap in anti-S. aureus therapy. This study analyses the humoral immune response to vaccination of Balb/c mice with sublethal doses of live S. aureus. The elicited antibody pattern in the sera of intravenously and intramuscularly vaccinated mice was determined using of a recently developed protein array. We observed a specific antibody response against a broad set of S. aureus antigens which was stronger following i.v. than i.m. vaccination. Intravenous but not intramuscular vaccination protected mice against an intramuscular challenge infection with a high bacterial dose. Vaccine protection was correlated with the strength of the anti-S. aureus antibody response. This study identified novel vaccine candidates by using protein microarrays as an effective tool and showed that successful vaccination against S. aureus relies on the optimal route of administration.

Orthopaedic device-related infection: current and future interventions for improved prevention and treatment

Orthopaedic and trauma device-related infection (ODRI) remains one of the major complications in modern trauma and orthopaedic surgery.Despite best practice in medical and surgical management, neither prophylaxis nor treatment of ODRI is effective in all cases, leading to infections that negatively impact clinical outcome and significantly increase healthcare expenditure.The following review summarises the microbiological profile of modern ODRI, the impact antibiotic resistance has on treatment outcomes, and some of the principles and weaknesses of the current systemic and local antibiotic delivery strategies.The emerging novel strategies aimed at preventing or treating ODRI will be reviewed. Particular attention will be paid to the potential for clinical impact in the coming decades, when such interventions are likely to be critically important.The review focuses on this problem from an interdisciplinary perspective, including basic science innovations and best practice in infectious disease. Cite this article: Moriarty TF, Kuehl R, Coenye T, et al. Orthopaedic device related infection: current and future interventions for improved prevention and treatment. EFORT Open Rev 2016;1:89-99. DOI: 10.1302/2058-5241.1.000037.

Omics Approaches for the Study of Adaptive Immunity to Staphylococcus aureus and the Selection of Vaccine Candidates

Staphylococcus aureus is a dangerous pathogen both in hospitals and in the community. Due to the crisis of antibiotic resistance, there is an urgent need for new strategies to combat S. aureus infections, such as vaccination. Increasing our knowledge about the mechanisms of protection will be key for the successful prevention or treatment of S. aureus invasion. Omics technologies generate a comprehensive picture of the physiological and pathophysiological processes within cells, tissues, organs, organisms and even populations. This review provides an overview of the contribution of genomics, transcriptomics, proteomics, metabolomics and immunoproteomics to the current understanding of S. aureus‑host interaction, with a focus on the adaptive immune response to the microorganism. While antibody responses during colonization and infection have been analyzed in detail using immunoproteomics, the full potential of omics technologies has not been tapped yet in terms of T-cells. Omics technologies promise to speed up vaccine development by enabling reverse vaccinology approaches. In consequence, omics technologies are powerful tools for deepening our understanding of the “superbug” S. aureus and for improving its control.

Development of a novel multiplex electrochemiluminescent-based immunoassay for quantification of human serum IgG against 10 Staphylococcus aureus toxins

An electrochemiluminescent (ECL)-based multiplex immunoassay using Meso-Scale Discovery (MSD) technology was developed for detecting antibody response toward 10 Staphylococcus aureus (S. aureus) exotoxins. These 10 antigens included three different groups of toxins: 1) single component pore-forming toxins such as alpha- and delta-hemolysins, 2) the bicomponent pore-forming toxin Panton-Valentine leukocidin (PVL), comprised of LukS-PV and LukF-PV subunits, and 3) enterotoxin/superantigens - Staphylococcal enterotoxins A (SEA), B (SEB), C1 (SEC1), D (SED), K (SEK) and Toxic shock syndrome toxin-1 (TSST-1). Assay development included optimization steps with a conventional SEB ELISA-based serological assay and then optimized parameters were transferred and re-optimized in a singleplex ECL format. Finally, two pentaplex solid-phase ECL formats were developed. As proof of concept, one set of pentaplex ECL data was compared with conventional ELISA results. During the assay development controls were screened and developed for both the singleplex and multiplex assays. ECL-based multiplex assays were more sensitive with a wide dynamic range and proved more time-efficient than conventional ELISAs. Using the newly developed ECL method we showed, for the first time, that delta-hemolysin toxin can induce an immune response as antibody titers could be detected.

Immunization with heat-inactivated Staphylococcus aureus induced an antibody response mediated by IgG1 and IgG2 in patients with recurrent tonsillitis

Currently Staphylococcus aureus is the predominant pathogen isolated from the respiratory tract of patients with recurrent tonsillitis. Because of an increase in multi-drug resistant strains of S. aureus, there is a pressing need for effective treatments and preventive approaches to reduce the risk of invasive and life-threatening infections. A preventive vaccine against S. aureus would have a tremendous clinical impact. However, multiple clinical trials have failed to identify an agent that can induce protective responses. Most trials have been based on subunit vaccines using one or a few purified antigens, which may not be enough to confer protection. Here, the impact of a whole-cell vaccine comprised of heat-inactivated S. aureus was investigated in patients with RT. The vaccine was well tolerated and had no significant local or systemic reactions. Immunization with heat-inactivated S. aureus elicited a significant antibody response characterized by production of IgG1 and IgG2 antibodies and, to a lesser extent, of IgA antibodies. Notably, this response was associated with an important decrease in the incidence of tonsillitis and bacterial colonization of the oropharyngeal mucosa. Our results show that whole-cell inactivated S. aureus is safe and capable of evoking specific antibody responses in patients with recurrent tonsillitis.

Investigational drugs to treat methicillin-resistant Staphylococcus aureus

INTRODUCTION

Staphylococcus aureus remains one of the leading causes of morbidity and mortality worldwide. This is to a large extent due to antibiotic-resistant strains, in particular methicillin-resistant S. aureus (MRSA). While the toll of invasive MRSA infections appears to decrease in U.S. hospitals, the rate of community-associated MRSA infections remains constant and there is a surge of MRSA in many other countries, a situation that calls for continuing if not increased efforts to find novel strategies to combat MRSA infections.

AREAS COVERED

This review provides an overview of current investigational drugs and therapeutic antibodies against S. aureus in early clinical development (up to phase II clinical development). It includes a short description of the mechanism of action and a presentation of microbiological and clinical data.

EXPERT OPINION

Increased recent antibiotic development efforts and results from pathogenesis research have led to several new antibiotics and therapies, such as anti-virulence drugs, as well as a more informed selection of targets for vaccination efforts against MRSA. This developing portfolio of novel anti-staphylococcal drugs will hopefully provide us with additional and more efficient ways to combat MRSA infections in the near future and prevent us from running out of treatment options, even if new resistances arise.

A Diagnostic Serum Antibody Test for Patients With Staphylococcus aureus Osteomyelitis

BACKGROUND

Because immunity against Staphylococcus aureus has not been fully elucidated, there is no diagnostic test to gauge how robust a patient's host response is likely to be. Therefore, we aimed to develop a test for specific antibodies in serum with diagnostic and prognostic potential.

QUESTIONS/PURPOSES

We describe the development and validation of a multiplex immunoassay for characterizing a patient's immune response against 14 known S aureus antigens, which we then used to answer four questions: (1) Do certain antigens predominate in the immune response against S aureus? (2) Is there a predominant pattern of antigens recognized by patients and mice with infections? (3) Is the immunoglobulin G (IgG) response to any single antigen a useful predictor of ongoing S aureus infection? (4) Does measurement of the combined response against all 14 antigens provide a better predictor of ongoing infection?

METHODS

A case-control study was performed. Sera were collected from 35 consecutive patients with S aureus culture-confirmed (methicillin-sensitive S aureus or methicillin-resistant S aureus) musculoskeletal infections (deep implant-associated, osteomyelitis, and cases of established septic arthritis). Patients were excluded only if they did not give informed consent for participation. Twenty-four patients had implant infections after total joint replacements, five had fracture implant infections, four had native knee infections, and two had chronic osteomyelitis without an implant. Control patients were chosen from a group of healthy, medically optimized patients scheduled to undergo elective arthroplasty. Control patients were matched for age (± 3 years), BMI (± 3 kg/m(2)), and sex as closely as possible to patients with infections. Sera from patients with S aureus infections and murine S aureus tibial implant infections were used to evaluate a multiplex immunoassay for immunoglobulin titers against 14 recombinant S aureus antigens. All patients were treated with organism-targeted antibiotic therapy and appropriate, timely surgery. Treatment response was monitored with clinical examination, erythrocyte sedimentation rate, C-reactive protein, and resampling of the infection site for the pathogen as needed. Elevated inflammatory markers or persistent positive culture results were considered evidence of ongoing infection. Treatment provided was considered standard-of-care therapy in our medical center and all patients were treated jointly with a board-certified infectious disease specialist.

RESULTS

Four antigens elicited more than 65% of the measurable IgG, the most dominant being against iron-regulated surface determinant protein B (IsdB). Patients with infections had different patterns of elevated IgG titers, so that no single titer was elevated in more than 50% of patients with infections (area under the curve [AUC] ≤ 0.80). Multivariate analysis of IgG titers yielded greater predictive power of S aureus infection (AUC = 0.896). Patients with infections who had high titers against IsdB (median of survivors, 7.28 [25%-75% range, 2.22-21.26] vs median of patients with infection-related death, 40.41 [25%-75% range, 23.57-51.37], difference of medians, 33.13; p = 0.043) and iron-regulated surface determinant protein A (IsdA) median of survivors, 2.21 [25%-75% range, 0.79-9.11] vs median of patients with infection-related death, 12.24 [25%-75% range, 8.85-15.95], difference of medians, 10.03; p = 0.043) were more likely to die from infections than those who did not have high titers of IsdB.

CONCLUSIONS

Measurement of the host antibody response is a predictor of ongoing infection that may prove to have prognostic value. Future studies will seek to enlarge the patient population with infections to allow us to reduce the number of antigens required to achieve a stronger predictive power.

CLINICAL RELEVANCE

Measurement of the immune response against S aureus with this diagnostic tool may help guide future studies on prophylaxis and therapy in an era of personalized medicine and pathogen-specific therapies.

Prevalence of enterotoxin genes in Staphylococcus aureus colonising food handlers: does nasal carriage status matter?

This study investigated the association between the presence of staphylococcal enterotoxin (SE) genes and nasal carriage status, and determined temporal changes in the prevalence of these genes in Staphylococcus aureus strains isolated from healthy carriers between 2002 and 2011. Three large samples of food handlers recruited in 2002, 2003 and 2011 were nasally sampled on two occasions to determine S. aureus colonisation status. Those carrying the same spa type on both occasions were defined as persistent carriers. Genes for SEs SEA-SEU were amplified and associations between carriage status and presence of SE genes were investigated. Although 80 % of nasal isolates harboured at least one SE gene over the sampling period, persistent carriers were significantly more likely to harbour enterotoxigenic S. aureus than transiently colonised subjects [odds ratio (OR) 2.52-3.06]. Strains from persistent carriers more commonly harboured sea, seb and sem. The prevalence of classical SE genes and sej, sem, sen, seo, seq and ses was stable over time, but seh, sel, sep, ser, set and selu increased significantly. Increased toxigenicity of isolates from persistent carriers is consistent with the elevated antibody levels to classical SEs previously reported in persistent carriers, supporting the hypothesis that superantigen production in the nasal cavity may enhance colonisation.

Surface Glycopolymers Are Crucial for In Vitro Anti-Wall Teichoic Acid IgG-Mediated Complement Activation and Opsonophagocytosis of Staphylococcus aureus

The cell envelopes of many Gram-positive bacteria contain wall teichoic acids (WTAs). Staphylococcus aureus WTAs are composed of ribitol phosphate (RboP) or glycerol phosphate (GroP) backbones substituted with D-alanine and N-acetyl-D-glucosamine (GlcNAc) or N-acetyl-D-galactosamine (GalNAc). Two WTA glycosyltransferases, TarM and TarS, are responsible for modifying the RboP WTA with α-GlcNAc and β-GlcNAc, respectively. We recently reported that purified human serum anti-WTA IgG specifically recognizes β-GlcNAc of the staphylococcal RboP WTA and then facilitates complement C3 deposition and opsonophagocytosis of S. aureus laboratory strains. This prompted us to examine whether anti-WTA IgG can induce C3 deposition on a diverse set of clinical S. aureus isolates. To this end, we compared anti-WTA IgG-mediated C3 deposition and opsonophagocytosis abilities using 13 different staphylococcal strains. Of note, the majority of S. aureus strains tested was recognized by anti-WTA IgG, resulting in C3 deposition and opsonophagocytosis. A minority of strains was not recognized by anti-WTA IgG, which correlated with either extensive capsule production or an alteration in the WTA glycosylation pattern. Our results demonstrate that the presence of WTAs with TarS-mediated glycosylation with β-GlcNAc in clinically isolated S. aureus strains is an important factor for induction of anti-WTA IgG-mediated C3 deposition and opsonophagocytosis.

Adjuvant-dependent immunogenicity of Staphylococcus aureus Efb and Map proteins in chickens

The avian IgY antibodies generated in hens and isolated from egg yolk have gained in popularity as they present an alternative source of antibodies for diagnostic as well as therapeutic applications. One of the advantages of IgY technology are the large amounts of produced antibodies from a single animal combined with their high reactivity representing an attractive alternative for mammalian antibodies. Despite many known protocols for the immunization of chickens, the administration of new antigens often requires additional modification such as antigen dose or use of an adjuvant in order to elicit a significant immune response. We investigated the immunogenicity of three Staphylococcus aureus antigens including two extracellular proteins Map and Efb and one selected Efb105-124 epitope conjugated to KLH that were administered to the animals. Additionally, the immunization protocol included two adjuvant systems: Freund's complete adjuvant and Emulsigen-D. The results demonstrated a high immunostimulatory potency of Freund's complete adjuvant, especially in case of Efb compared to the immune response elicited by Emulsigen-D. However, after immunization with the KLH-Efb105-124 conjugate, the obtained antibodies showed similar reactivity regardless of adjuvant system used with the only exception being their avidity.

Four-component Staphylococcus aureus vaccine 4C-staph enhances Fcγ receptor expression in neutrophils and monocytes and mitigates S. aureus infection in neutropenic mice

Staphylococcus aureus is a human bacterial pathogen causing a variety of diseases. The occurrence of multidrug-resistant strains of Staphylococcus aureus underlines the need for a vaccine. Defining immune correlates of protection may support the design of an effective vaccine. We used a murine Staphylococcus aureus infection model, in which bacteria were inoculated in an air pouch generated on the back of the animal. Analysis of the air-pouch content in mice immunized or not with an adjuvanted multiantigen vaccine formulation, four-component S. aureus vaccine (4C-Staph), prior to infection allowed us to measure bacteria, cytokines, and 4C-Staph-specific antibodies and to analyze host immune cells recruited to the infection site. Immunization with 4C-Staph resulted in accumulation of antigen-specific antibodies in the pouch and mitigated the infection. Neutrophils were the most abundant cells in the pouch, and they showed the upregulation of Fcγ receptor (FcγR) following immunization with 4C-Staph. Reduction of the infection was also obtained in mice immunized with 4C-Staph and depleted of neutrophils; these mice showed an increase in monocytes and macrophages. Upregulation of the FcγR and the presence of antigen-specific antibodies induced by immunization with 4C-Staph may contribute to increase bacterial opsonophagocytosis. Protection in neutropenic mice indicated that an effective vaccine could activate alternative protection mechanisms compensating for neutropenia, a condition often occurring in S. aureus-infected patients.

Microarray-based identification of human antibodies against Staphylococcus aureus antigens

PURPOSE

The mortality rate of patients with Staphylococcus aureus infections is alarming and urgently demands new strategies to attenuate the course of these infections or to detect them at earlier stages.

EXPERIMENTAL DESIGN

To study the adaptive immune response to S. aureus antigens in healthy human volunteers, a protein microarray containing 44 S. aureus proteins was developed using the ArrayStrip platform technology.

RESULTS

Testing plasma samples from 15 S. aureus carriers and 15 noncarriers 21 immunogenic S. aureus antigens have been identified. Seven antigens were recognized by antibodies present in at least 60% of the samples, representing the core S. aureus immunome of healthy individuals. S. aureus-specific serum immunoglobulin G (IgG) levels were significantly lower in noncarriers than in carriers specifically anti-IsaA, anti-SACOL0479, and anti-SACOL0480 IgGs were found at lower frequencies and quantities. Twenty-two antigens present on the microarray were encoded by all S. aureus carrier isolates. Nevertheless, the immune system of the carriers was responsive to only eight of them and with different intensities.

CONCLUSION AND CLINICAL RELEVANCE

The established protein microarray allows a broad profiling of the S. aureus-specific antibody response and can be used to identify S. aureus antigens that might serve as vaccines or diagnostic markers.

A multi-omics approach identifies key hubs associated with cell type-specific responses of airway epithelial cells to staphylococcal alpha-toxin

Responsiveness of cells to alpha-toxin (Hla) from Staphylococcus aureus appears to occur in a cell-type dependent manner. Here, we compare two human bronchial epithelial cell lines, i.e. Hla-susceptible 16HBE14o- and Hla-resistant S9 cells, by a quantitative multi-omics strategy for a better understanding of Hla-induced cellular programs. Phosphoproteomics revealed a substantial impact on phosphorylation-dependent signaling in both cell models and highlights alterations in signaling pathways associated with cell-cell and cell-matrix contacts as well as the actin cytoskeleton as key features of early rHla-induced effects. Along comparable changes in down-stream activity of major protein kinases significant differences between both models were found upon rHla-treatment including activation of the epidermal growth factor receptor EGFR and mitogen-activated protein kinases MAPK1/3 signaling in S9 and repression in 16HBE14o- cells. System-wide transcript and protein expression profiling indicate induction of an immediate early response in either model. In addition, EGFR and MAPK1/3-mediated changes in gene expression suggest cellular recovery and survival in S9 cells but cell death in 16HBE14o- cells. Strikingly, inhibition of the EGFR sensitized S9 cells to Hla indicating that the cellular capacity of activation of the EGFR is a major protective determinant against Hla-mediated cytotoxic effects.