Targeting Staphylococcus aureus α-toxin as a novel approach to reduce severity of recurrent skin and soft-tissue infections

Inhibitory Effect of Jingfang Mixture on Staphylococcus aureus α-Hemolysin

Staphylococcus aureus (S. aureus) is a kind of gram-positive bacteria, and its virulence factors can cause many kinds of infections. Traditional antibiotics can not only kill bacteria, but also easily lead to bacterial resistance. Jingfang Mixture (JFM) is commonly used in clinic to prevent and treat epidemic diseases and infectious diseases. The main purpose of this study is to explore the inhibitory effect of JFM on alpha-hemolysin (Hla) of S. aureus and to alleviate the damage caused by Hla. We found that JFM could inhibit the hemolytic activity, gene and protein level and neutralizing activity of Hla in a dose-dependent manner at the concentrations of 125, 250 and 500 μg/mL, without affecting the growth of bacteria. In addition, JFM reduced the damage of Hla to A549 cells and the release of lactate dehydrogenase (LDH). We also observed that in the S. aureus - induced pneumonia mouse model, JFM could significantly prolong the life of mice, reduce the bacterial load in the lungs, significantly improve the pathological state of the lungs and alleviate the damage caused by inflammatory factors, and the pathogenicity of gene deletion strain DU 1090 of S. aureus to pneumonia mice was also significantly reduced. In conclusion, this study proved that JFM is a potential drug against S. aureus infection, and this study provided a preliminary study for better guidance of clinical drug use.

α-Hemolysin-mediated endothelial injury contributes to the development of Staphylococcus aureus-induced dermonecrosis

Staphylococcus aureus α-hemolysin (Hla) is a pore-forming toxin critical for the pathogenesis of skin and soft tissue infections, which causes the pathognomonic lesion of cutaneous necrosis (dermonecrosis) in mouse models. To determine the mechanism by which dermonecrosis develops during S. aureus skin infection, mice were given control serum, Hla-neutralizing antiserum, or an inhibitor of Hla receptor [A-disintegrin and metalloprotease 10 (ADAM10) inhibitor] followed by subcutaneous infection by S. aureus, and the lesions were evaluated using immunohistochemistry and immunofluorescence. Hla induced apoptosis in the vascular endothelium at 6 hours post-infection (hpi), followed by apoptosis in keratinocytes at 24 hpi. The loss of vascular endothelial (VE)-cadherin expression preceded the loss of epithelial-cadherin expression. Hla also induced hypoxia in the keratinocytes at 24 hpi following vascular injury. Treatment with Hla-neutralizing antibody or ADAM10 inhibitor attenuated early cleavage of VE-cadherin, cutaneous hypoxia, and dermonecrosis. These findings suggest that Hla-mediated vascular injury with cutaneous hypoxia underlies the pathogenesis of S. aureus-induced dermonecrosis.

Inhibitory effect of Jingfang mixture on Staphylococcus aureus α-hemolysin

Staphylococcus aureus is a gram-positive bacteria, and its virulence factors can cause many kinds of infections, such as pneumonia, sepsis, enteritis and osteomyelitis. Traditional antibiotics can not only kill bacteria, but also easily lead to bacterial resistance. Jingfang Mixture (JFM) has the effects of inducing sweating and relieving the exterior, dispelling wind and eliminating dampness, and is commonly used in clinic to prevent and treat epidemic diseases and infectious diseases. The main purpose of this study is to explore the inhibitory effect of JFM on alpha-hemolysin (Hla) of S. aureus and to alleviate the damage caused by Hla. We found that JFM could inhibit the hemolytic activity, transcription level and neutralizing activity of Hla in a dose-dependent manner at the concentrations of 125, 250 and 500 µg/mL, without affecting the growth of bacteria. In addition, JFM reduced the damage of Hla to A549 cells and the release of lactate dehydrogenase (LDH). We also observed that in the S. aureus - induced pneumonia mouse model, JFM could significantly prolong the life of mice, reduce the bacterial load in the lungs, significantly improve the pathological state of the lungs and alleviate the damage caused by inflammatory factors, and the pathogenicity of gene deletion strain DU 1090 of S. aureus to pneumonia mice was also significantly reduced. In conclusion, this study proved that JFM is a potential drug against S. aureus infection, and this study provided a preliminary study for better guidance of clinical drug use.

Skin colonization by Staphylococcus aureus in hemodialysis patients with pruritus and the effect of Staphylococcus aureus-secreted α-toxin on filaggrin expression

Staphylococcus aureus (S. aureus) commonly reside on human skin in residents in long-term care facilities, yet its colonization and impact on the skin of hemodialysis (HD) patients have yet to be studied. The aim of the present study was to investigate the colonization of S. aureus on the skin of pruritic and non-pruritic HD patients, and the influence of S. aureus and S. aureus-secreted α-toxin on skin barrier function-related protein expression. In this study, a higher relative S. aureus count in pruritic HD patients compared to non-pruritic HD patients and healthy subjects were revealed by real-time polymerase chain reaction. S. aureus and α-toxin decreased mRNA and protein expression levels of aryl hydrocarbon receptor (AHR), ovo-like transcriptional repressor 1 (OVOL1), and filaggrin (FLG) in keratinocytes. In addition, anti-alpha-hemolysin (anti-hla) was used as an α-toxin neutralizer, and it successfully abrogated S. aureus-induced AHR, OVOL1, and FLG mRNA and protein expression downregulation. Mechanistically, α-toxin could decrease FLG activity by preventing the recruitment of AHR to the FLG promoter region. In conclusion, pruritic HD patients had higher S. aureus colonization, with S. aureus-secreted α-toxin suppressing FLG expression through the AHR-FLG axis.

LAIR1 prevents excess inflammatory tissue damage in S. aureus skin infection and Cutaneous T-cell Lymphoma

Patients with cutaneous T cell lymphoma (CTCL) experience high morbidity and mortality due to S. aureus skin infections and sepsis, but the causative immune defect is unclear. We previously identified high levels of LAIR2, a decoy protein for the inhibitory receptor LAIR1, in advanced CTCL. Mice do not have a LAIR2 homolog, so we used Lair1 knock-out (KO) mice to model LAIR2 overexpression. In a model of subcutaneous S. aureus skin infection, Lair1 KO mice had significantly larger abscesses and areas of dermonecrosis compared to WT. Lair1 KO exhibited a pattern of increased inflammatory responses in infection and sterile immune stimulation, including increased production of proinflammatory cytokines and myeloid chemokines, neutrophil ROS, and collagen/ECM remodeling pathways. Notably, Lair1 KO infected skin had a similar bacterial burden and neutrophils and monocytes had equivalent S. aureus phagocytosis compared to WT. These findings support a model in which lack of LAIR1 signaling causes an excessive inflammatory response that does not improve infection control. CTCL skin lesions harbored similar patterns of increased expression in cytokine and collagen/ECM remodeling pathways, suggesting that high levels of LAIR2 in CTCL recapitulates Lair1 KO, causing inflammatory tissue damage and compromising host defense against S. aureus infection.

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.

Vaccination with staphylococcal protein A protects mice against systemic complications of skin infection recurrences

Skin and soft tissue infections (SSTIs) are the most common diseases caused by Staphylococcus aureus (S. aureus), which can progress to threatening conditions due to recurrences and systemic complications. Staphylococcal protein A (SpA) is an immunomodulator antigen of S. aureus, which allows bacterial evasion from the immune system by interfering with different types of immune responses to pathogen antigens. Immunization with SpA could potentially unmask the pathogen to the immune system, leading to the production of antibodies that can protect from a second encounter with S. aureus, as it occurs in skin infection recurrences. Here, we describe a study in which mice are immunized with a mutated form of SpA mixed with the Adjuvant System 01 (SpAmut/AS01) before a primary S. aureus skin infection. Although mice are not protected from the infection under these conditions, they are able to mount a broader pathogen-specific functional immune response that results in protection against systemic dissemination of bacteria following an S. aureus second infection (recurrence). We show that this "hidden effect" of SpA can be partially explained by higher functionality of induced anti-SpA antibodies, which promotes better phagocytic activity. Moreover, a broader and stronger humoral response is elicited against several S. aureus antigens that during an infection are masked by SpA activity, which could prevent S. aureus spreading from the skin through the blood.

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.

The Staphylococcus aureus CamS lipoprotein is a repressor of toxin production that shapes host-pathogen interaction

Lipoproteins of the opportunistic pathogen Staphylococcus aureus play a crucial role in various cellular processes and host interactions. Consisting of a protein and a lipid moiety, they support nutrient acquisition and anchor the protein to the bacterial membrane. Recently, we identified several processed and secreted small linear peptides that derive from the secretion signal sequence of S. aureus lipoproteins. Here, we show, for the first time, that the protein moiety of the S. aureus lipoprotein CamS has a biological role that is distinct from its associated linear peptide staph-cAM373. The small peptide was shown to be involved in interspecies horizontal gene transfer, the primary mechanism for the dissemination of antibiotic resistance among bacteria. We provide evidence that the CamS protein moiety is a potent repressor of cytotoxins, such as α-toxin and leukocidins. The CamS-mediated suppression of toxin transcription was reflected by altered disease severity in in vivo infection models involving skin and soft tissue, as well as bloodstream infections. Collectively, we have uncovered the role of the protein moiety of the staphylococcal lipoprotein CamS as a previously uncharacterized repressor of S. aureus toxin production, which consequently regulates virulence and disease outcomes. Notably, the camS gene is conserved in S. aureus, and we also demonstrated the muted transcriptional response of cytotoxins in 2 different S. aureus lineages. Our findings provide the first evidence of distinct biological functions of the protein moiety and its associated linear peptide for a specific lipoprotein. Therefore, lipoproteins in S. aureus consist of 3 functional components: a lipid moiety, a protein moiety, and a small linear peptide, with putative different biological roles that might not only determine the outcome of host-pathogen interactions but also drive the acquisition of antibiotic resistance determinants.

Virulence attributes of successful methicillin-resistant Staphylococcus aureus lineages

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of severe and often fatal infections. MRSA epidemics have occurred in waves, whereby a previously successful lineage has been replaced by a more fit and better adapted lineage. Selection pressures in both hospital and community settings are not uniform across the globe, which has resulted in geographically distinct epidemiology. This review focuses on the mechanisms that trigger the establishment and maintenance of current, dominant MRSA lineages across the globe. While the important role of antibiotic resistance will be mentioned throughout, factors which influence the capacity of S. aureus to colonize and cause disease within a host will be the primary focus of this review. We show that while MRSA possesses a diverse arsenal of toxins including alpha-toxin, the success of a lineage involves more than just producing toxins that damage the host. Success is often attributed to the acquisition or loss of genetic elements involved in colonization and niche adaptation such as the arginine catabolic mobile element, as well as the activity of regulatory systems, and shift metabolism accordingly (e.g., the accessory genome regulator, agr). Understanding exactly how specific MRSA clones cause prolonged epidemics may reveal targets for therapies, whereby both core (e.g., the alpha toxin) and acquired virulence factors (e.g., the Panton-Valentine leukocidin) may be nullified using anti-virulence strategies.

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.

Inhibition of α-hemolysin activity of Staphylococcus aureus by theaflavin 3,3'-digallate

The ongoing rise in antibiotic resistance, and a waning of the introduction of new antibiotics, has resulted in limited treatment options for bacterial infections, including these caused by methicillin-resistant Staphylococcus aureus, leaving the world in a post-antibiotic era. Here, we set out to examine mechanisms by which theaflavin 3,3'-digallate (TF3) might act as an anti-hemolytic compound. In the presented study, we found that TF3 has weak bacteriostatic and bactericidal effects on Staphylococcus aureus, and strong inhibitory effect towards the hemolytic activity of its α-hemolysin (Hla) including its production and secretion. A supportive SPR assay reinforced these results and further revealed binding of TF3 to Hla with KD = 4.57×10-5 M. Interestingly, TF3 was also able to protect human primary keratinocytes from Hla-induced cell death, being at the same time non-toxic for them. Further analysis of TF3 properties revealed that TF3 blocked Hla-prompting immune reaction by inhibiting production and secretion of IL1β, IL6, and TNFα in vitro and in vivo, through affecting NFκB activity. Additionally, we observed that TF3 also markedly attenuated S. aureus-induced barrier disruption, by inhibiting Hla-triggered E-cadherin and ZO-1 impairment. Overall, by blocking activity of Hla, TF3 subsequently subdued the inflammation and protected the epithelial barrier, which is considered as beneficial to relieving skin injury.

Anti-Alpha-Toxin Antibody Responses and Clinical Outcomes of Staphylococcus aureus Bacteremia

BACKGROUND

Alpha-toxin (AT), a major virulence factor of Staphylococcus aureus, is an important immunotherapeutic target to prevent or treat invasive S. aureus infections. Previous studies have suggested that anti-AT antibodies (Abs) may have a protective role against S. aureus bacteremia (SAB), but their function remains unclear. Therefore, we aimed to investigate the association between serum anti-AT Ab levels and clinical outcomes of SAB.

METHODS

Patients from a prospective SAB cohort at a tertiary-care medical center (n = 51) were enrolled in the study from July 2016 to January 2019. Patients without symptoms or signs of infection were enrolled as controls (n = 100). Blood samples were collected before the onset of SAB and at 2- and 4-weeks post-bacteremia. Anti-AT immunoglobin G (IgG) levels were measured using an enzyme-linked immunosorbent assay. All clinical S. aureus isolates were tested for the presence of hla using polymerase chain reaction.

RESULTS

Anti-AT IgG levels in patients with SAB before the onset of bacteremia did not differ significantly from those in non-infectious controls. Pre-bacteremic anti-AT IgG levels tended to be lower in patients with worse clinical outcomes (7-day mortality, persistent bacteremia, metastatic infection, septic shock), although the differences were not statistically significant. Patients who needed intensive care unit care had significantly lower anti-AT IgG levels at 2 weeks post-bacteremia (P = 0.020).

CONCLUSION

The study findings suggest that lower anti-AT Ab responses before and during SAB, reflective of immune dysfunction, are associated with more severe clinical presentations of infection.

Toxin expression during Staphylococcus aureus infection imprints host immunity to inhibit vaccine efficacy

Staphylococcus aureus infections are a major public health issue, and a vaccine is urgently needed. Despite a considerable promise in preclinical models, all vaccines tested thus far have failed to protect humans against S. aureus. Unlike laboratory mice, humans are exposed to S. aureus throughout life. In the current study, we hypothesized that prior exposure to S. aureus "imprints" the immune response to inhibit vaccine-mediated protection. We established a mouse model in which S. aureus skin and soft tissue infection (SSTI) is followed by vaccination and secondary SSTI. Unlike naïve mice, S. aureus-sensitized mice were incompletely protected against secondary SSTI by vaccination with the inactivated α-hemolysin (Hla) mutant Hla_H35L. Inhibition of protection was specific for the Hla_H35L vaccine and required hla expression during primary SSTI. Surprisingly, inhibition occurred at the level of vaccine-elicited effector T cells; hla expression during primary infection limited the expansion of T cells and dendritic cells and impaired vaccine-specific T cell responses. Importantly, the T cell-stimulating adjuvant CAF01 rescued inhibition and restored vaccine-mediated protection. Together, these findings identify a potential mechanism for the failure of translation of promising S. aureus vaccines from mouse models to clinical practice and suggest a path forward to prevent these devastating infections.

Neutralization of Staphylococcus aureus Protein A Prevents Exacerbated Osteoclast Activity and Bone Loss during Osteomyelitis

Osteomyelitis caused by Staphylococcus aureus is an important and current health care problem worldwide. Treatment of this infection frequently fails not only due to the increasing incidence of antimicrobial-resistant isolates but also because of the ability of S. aureus to evade the immune system, adapt to the bone microenvironment, and persist within this tissue for decades. We have previously demonstrated the role of staphylococcal protein A (SpA) in the induction of exacerbated osteoclastogenesis and increased bone matrix degradation during osteomyelitis. The aim of this study was to evaluate the potential of using anti-SpA antibodies as an adjunctive therapy to control inflammation and bone damage. By using an experimental in vivo model of osteomyelitis, we demonstrated that the administration of an anti-SpA antibody by the intraperitoneal route prevented excessive inflammatory responses in the bone upon challenge with S. aureus. Ex vivo assays indicated that blocking SpA reduced the priming of osteoclast precursors and their response to RANKL. Moreover, the neutralization of SpA was able to prevent the differentiation and activation of osteoclasts in vivo, leading to reduced expression levels of cathepsin K, reduced expression of markers associated with abnormal bone formation, and decreased trabecular bone loss during osteomyelitis. Taken together, these results demonstrate the feasibility of using anti-SpA antibodies as an antivirulence adjunctive therapy that may prevent the development of pathological conditions that not only damage the bone but also favor bacterial escape from antimicrobials and the immune system.

Identification of two neutralizing human single-chain variable fragment antibodies targeting Staphylococcus aureus alpha-hemolysin

Objectives

The inability of the host immune system to defeat Staphylococcus aureus is due to various secreted virulent factors such as leukocidins, superantigens, and hemolysins, which interrupt the function of immune components. Alpha-hemolysin is one of the most studied cytolysins due to its pronounced effect on developing staphylococcal infections. Alpha-hemolysin-neutralizing antibodies are among the best candidates for blocking the toxin activity and preventing S. aureus pathogenesis.

Materials and Methods

A human single-chain variable fragment (scFv) phage display library was biopanned against alpha-hemolysin. The selected phage clones were assessed based on their binding ability to alpha-hemolysin. The binding specificity and affinity of two scFvs (designated SP192 and SP220) to alpha-hemolysin were determined by enzyme-linked immunosorbent assay. Furthermore, the neutralizing activity of SP192 and SP220 was examined by concurrent incubation of rabbit red blood cells (RBCs) with alpha-hemolysin and scFvs.

Results

SP192 and SP220 showed significant binding to alpha-hemolysin compared with the control proteins, including bovine serum albumin, human adiponectin, and toxic shock syndrome toxin-1. Besides, both scFvs showed high-affinity binding to alpha-hemolysin in the nanomolar range (Kaff: 0.9 and 0.7 nM-1, respectively), leading to marked inhibition of alpha-hemolysin-mediated lysis of rabbit RBCs (73% and 84% inhibition; respectively).

Conclusion

SP192 and SP220 scFvs can potentially be used as alpha-hemolysin-neutralizing agents in conjunction with conventional antibiotics to combat S. aureus infections.

Inhibitory Effect of Andrographis paniculata Lactone on Staphylococcus aureus α-Hemolysin

We investigated the effect of andrographolide (AP) on the hemolytic capacity of Staphylococcus aureus (S. aureus) isolated from our region. AP is a labdane diterpenoid isolated from the stem and leaves of Andrographis paniculata. The hla gene from 234 S. aureus strains and the quality control standard strain ATCC29213 in dairy cows in some areas of Ningxia was analyzed. Evolutionary analysis, homology modeling, and functional enrichment annotation of α-hemolysin Hla detected from our region were performed through bioinformatics. The hemolytic ability of S. aureus isolates from the region was examined using the hemolysis test, and the effect of AP on S. aureus was quantified. Moreover, the effect of AP on the transcript levels of hla and genes highly related to hla (i.e., clfA and fnbA) was examined through fluorescence quantitative PCR. The mode of action of AP on the detected Hla was analyzed through molecular docking and dynamic simulation. The results showed that S. aureus in our region has a high rate of hla carriage. The hemolytic activity of strains NM98 and XF10 was significant, and ATCC29213 also exhibited some hemolytic activity. AP could inhibit the expression of Hla and its related proteins by downregulating hla, clfA, and fnbA transcript levels, which in turn attenuated the S. aureus hemolytic activity. Meanwhile, the AP molecule can form three hydrogen bonds with residues ASN105, SER106, and THR155 of Hla protein; bind with PRO103 through alkyl intermolecular forces; and form carbon hydrogen bonds with LYS154, reflecting that the AP molecule has a comparatively ideal theoretical binding activity with Hla protein. Among them, PRO103 and LYS154 are highly conserved in Hla protein molecules and play pivotal roles in the biological functions of Hla, and their binding may affect these functions. Their binding may also prevent the conformational transition of Hla from a monomer to an oligomer, thus inhibiting Hla hemolytic activity. This study offers a molecular basis for use of AP as an antivirulence drug and new ideas for developing novel drugs against S. aureus infection.

Recent advances in metal-organic framework-based materials for anti-staphylococcus aureus infection

The rapid spread of staphylococcus aureus (S. aureus) causes an increased morbidity and mortality, as well as great economic losses in the world. Anti-S. aureus infection becomes a major challenge for clinicians and nursing professionals to address drug resistance. Hence, it is urgent to explore high efficiency, low toxicity, and environmental-friendly methods against S. aureus. Metal-organic frameworks (MOFs) represent great potential in treating S. aureus infection due to the unique features of MOFs including tunable chemical constitute, open crystalline structure, and high specific surface area. Especially, these properties endow MOF-based materials outstanding antibacterial effect, which can be mainly attributed to the continuously released active components and the exerted catalytic activity to fight bacterial infection. Herein, the structural characteristics of MOFs and evaluation method of antimicrobial activity are briefly summarized. Then we systematically give an overview on their recent progress on antibacterial mechanisms, metal ion sustained-release system, controlled delivery system, catalytic system, and energy conversion system based on MOF materials. Finally, suggestions and direction for future research to develop and mechanism understand MOF-based materials are discussed in antibacterial application.

Increased Risk of Thrombocytopenia and Death in Patients with Bacteremia Caused by High Alpha Toxin-Producing Methicillin-Resistant Staphylococcus aureus

Alpha toxin (Hla) is a major virulence factor of Staphylococcus aureus that targets platelets but clinical data on Hla pathogenesis in bacteremia (SAB) is limited. We examined the link between in vitro Hla activity and outcome. Study isolates obtained from 100 patients with SAB (50 survivors; 50 non-survivors) were assessed for in vitro Hla production by Western immunoblotting in a subset of isolates and Hla activity by hemolysis assay in all isolates. Relevant demographics, laboratory and clinical data were extracted from patients' medical records to correlate Hla activity of the infecting isolates with outcome. Hla production strongly correlated with hemolytic activity (r_s = 0.93) in vitro. A trend towards higher hemolytic activity was observed for MRSA compared to MSSA and with high-risk source infection. Significantly higher hemolytic activity was noted for MRSA strains isolated from patients who developed thrombocytopenia (median 52.48 vs. 16.55 HU/mL in normal platelet count, p = 0.012) and from non survivors (median 30.96 vs. 14.87 HU/mL in survivors, p = 0.014) but hemolytic activity of MSSA strains did not differ between patient groups. In vitro Hla activity of MRSA strains obtained from patients with bacteremia is significantly associated with increased risk for thrombocytopenia and death which supports future studies to evaluate feasibility of bedside phenotyping and therapeutic targeting.

Gram-Positive Pneumonia: Possibilities Offered by Phage Therapy

Pneumonia is an acute pulmonary infection whose high hospitalization and mortality rates can, on occasion, bring healthcare systems to the brink of collapse. Both viral and bacterial pneumonia are uncovering many gaps in our understanding of host–pathogen interactions, and are testing the effectiveness of the currently available antimicrobial strategies. In the case of bacterial pneumonia, the main challenge is antibiotic resistance, which is only expected to increase during the current pandemic due to the widespread use of antibiotics to prevent secondary infections in COVID-19 patients. As a result, alternative therapeutics will be necessary to keep this disease under control. This review evaluates the advantages of phage therapy to treat lung bacterial infections, in particular those caused by the Gram-positive bacteria Streptococcus pneumoniae and Staphylococcus aureus, while also highlighting the regulatory impediments that hamper its clinical use and the difficulties associated with phage research.

Repurposed drugs block toxin-driven platelet clearance by the hepatic Ashwell-Morell receptor to clear Staphylococcus aureus bacteremia

Staphylococcus aureus (SA) bloodstream infections cause high morbidity and mortality (20 to 30%) despite modern supportive care. In a human bacteremia cohort, we found that development of thrombocytopenia was correlated to increased mortality and increased α-toxin expression by the pathogen. Platelet-derived antibacterial peptides are important in bloodstream defense against SA, but α-toxin decreased platelet viability, induced platelet sialidase to cause desialylation of platelet glycoproteins, and accelerated platelet clearance by the hepatic Ashwell-Morell receptor (AMR). Ticagrelor (Brilinta), a commonly prescribed P2Y12 receptor inhibitor used after myocardial infarction, blocked α-toxin-mediated platelet injury and resulting thrombocytopenia, thereby providing protection from lethal SA infection in a murine intravenous challenge model. Genetic deletion or pharmacological inhibition of AMR stabilized platelet counts and enhanced resistance to SA infection, and the anti-influenza sialidase inhibitor oseltamivir (Tamiflu) provided similar therapeutic benefit. Thus, a "toxin-platelet-AMR" regulatory pathway plays a critical role in the pathogenesis of SA bloodstream infection, and its elucidation provides proof of concept for repurposing two commonly prescribed drugs as adjunctive therapies to improve patient outcomes.

Impaired T lymphocyte responses during childhood Staphylococcus aureus infection

BACKGROUND

Staphylococcus aureus infections are common throughout the lifespan, with recurrent infections occuring in nearly half of infected children. There is no licensed vaccine, underscoring the need to better understand how S. aureus evades protective immunity. Despite much study, the relative contributions of antibodies and T cells to protection against S. aureus infections in humans are not fully understood.

METHODS

We prospectively quantified S. aureus-specific antibody levels by ELISA and T cell responses by ELISpot in S. aureus-infected and healthy children.

RESULTS

S. aureus-specific antibody levels and T cell responses increased with age in healthy children, suggesting a coordinated development of anti-staphylococcal immunity. Antibody levels against leukotoxin E (LukE) and Panton-Valentine leukocidin (LukS-PV), but not α-hemolysin (Hla), were higher in younger infected children, compared with healthy children; these differences disappeared in older children. We observed a striking impairment of global and S. aureus-specific T cell function in children with invasive and non-invasive infection, suggesting that S. aureus-specific immune responses are dysregulated during childhood infection regardless of the infection phenotype.

CONCLUSIONS

These findings identify a potential mechanism by which S. aureus infection actively evades adaptive immune responses, thereby preventing the development of protective immunty and maintaining susceptibility to recurrent infection.

Evasion of Immunological Memory by S. aureus Infection: Implications for Vaccine Design

Recurrent S. aureus infections are common, suggesting that natural immune responses are not protective. All candidate vaccines tested thus far have failed to protect against S. aureus infections, highlighting an urgent need to better understand the mechanisms by which the bacterium interacts with the host immune system to evade or prevent protective immunity. Although there is evidence in murine models that both cellular and humoral immune responses are important for protection against S. aureus, human studies suggest that T cells are critical in determining susceptibility to infection. This review will use an “anatomic” approach to systematically outline the steps necessary in generating a T cell-mediated immune response against S. aureus. Through the processes of bacterial uptake by antigen presenting cells, processing and presentation of antigens to T cells, and differentiation and proliferation of memory and effector T cell subsets, the ability of S. aureus to evade or inhibit each step of the T-cell mediated response will be reviewed. We hypothesize that these interactions result in the redirection of immune responses away from protective antigens, thereby precluding the establishment of “natural” memory and potentially inhibiting the efficacy of vaccination. It is anticipated that this approach will reveal important implications for future design of vaccines to prevent these infections.

Staphylococcus aureus toxin suppresses antigen-specific T cell responses

Staphylococcus aureus remains a leading cause of human infection. These infections frequently recur when the skin is a primary site of infection, especially in infants and children. In contrast, invasive staphylococcal disease is less commonly associated with reinfection, suggesting that tissue-specific mechanisms govern the development of immunity. Knowledge of how S. aureus manipulates protective immunity has been hampered by a lack of antigen-specific models to interrogate the T cell response. Using a chicken egg OVA-expressing S. aureus strain to analyze OVA-specific T cell responses, we demonstrated that primary skin infection was associated with impaired development of T cell memory. Conversely, invasive infection induced antigen-specific memory and protected against reinfection. This defect in adaptive immunity following skin infection was associated with a loss of DCs, attributable to S. aureus α-toxin (Hla) expression. Gene- and immunization-based approaches to protect against Hla during skin infection restored the T cell response. Within the human population, exposure to α-toxin through skin infection may modulate the establishment of T cell-mediated immunity, adversely affecting long-term protection. These studies prompt consideration that vaccination targeting S. aureus may be most effective if delivered prior to initial contact with the organism.

A Natural Dietary Flavone Myricetin as an α-Hemolysin Inhibitor for Controlling Staphylococcus aureus Infection

Staphylococcus aureus, an important agent for lethal bacterial infections, can cause a broad spectrum of diseases in various host species. The emergence of multidrug-resistant and highly virulent strains has raised increasing concerns about the novel therapeutic strategies or agents available for treating S. aureus infection. The critical role of Hla, an essential virulence determinant, in the pathogenicity of S. aureus renders this toxin an attractive target for effective therapeutic applications. Here, we have identified myricetin as an effective inhibitor of Hla that simultaneously inhibits Hla production and neutralizes Hla activity without affecting bacterial growth. Myricetin treatment reduced the oligomerization of Hla and Hla-mediated biofilm formation. The addition of myricetin to the coinfection system of host cells and S. aureus significantly decreased cell injury and downregulated the inflammatory response in cells. Furthermore, S. aureus-infected mice that received myricetin showed alleviated tissue damage in the lung. Our results indicated that myricetin inhibits S. aureus virulence by targeting Hla and downregulates the inflammatory response in host cells. Overall, in addition to traditional antibiotics with antibacterial activity, myricetin may represent a potential candidate, and strategy for S. aureus infection.

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.

Research Techniques Made Simple: Mouse Bacterial Skin Infection Models for Immunity Research

Bacterial skin infections are a major societal health burden and are increasingly difficult to treat owing to the emergence of antibiotic-resistant strains such as community-acquired methicillin-resistant Staphylococcus aureus. Understanding the immunologic mechanisms that provide durable protection against skin infections has the potential to guide the development of immunotherapies and vaccines to engage the host immune response to combat these antibiotic-resistant strains. To this end, mouse skin infection models allow researchers to examine host immunity by investigating the timing, inoculum, route of infection and the causative bacterial species in different wild-type mouse backgrounds as well as in knockout, transgenic, and other types of genetically engineered mouse strains. To recapitulate the various types of human skin infections, many different mouse models have been developed. For example, four models frequently used in dermatological research are based on the route of infection, including (i) subcutaneous infection models, (ii) intradermal infection models, (iii) wound infection models, and (iv) epicutaneous infection models. In this article, we will describe these skin infection models in detail along with their advantages and limitations. In addition, we will discuss how humanized mouse models such as the human skin xenograft on immunocompromised mice might be used in bacterial skin infection research.

Inhibition of protective immunity against Staphylococcus aureus infection by MHC-restricted immunodominance is overcome by vaccination

Recurrent Staphylococcus aureus infections are common, despite robust immune responses. S. aureus infection elicited protective antibody and T cell responses in mice that expressed the Major Histocompatibility Complex (MHC) of the H-2^d haplotype, but not H-2^b, demonstrating that host genetics drives individual variability. Vaccination with a-toxin or leukotoxin E (LukE) elicited similar antibody and T cell responses in mice expressing H-2^d or H-2^b, but vaccine-elicited responses were inhibited by concomitant infection in H-2^d-expressing mice. These findings suggested that competitive binding of microbial peptides to host MHC proteins determines the specificity of the immunodominant response, which was confirmed using LukE-derived peptide-MHC tetramers. A vaccine that elicited T cell and antibody responses protected mice that expressed H-2^d or H-2^b, demonstrating that vaccination can overcome MHC-restricted immunodominance. Together, these results define how host genetics determine whether immunity elicted by S. aureus is protective and provide a mechanistic roadmap for future vaccine design.

Contribution of hla Regulation by SaeR to Staphylococcus aureus USA300 Pathogenesis

The SaeRS two-component system in Staphylococcus aureus is critical for regulation of many virulence genes, including hla, which encodes alpha-toxin. However, the impact of regulation of alpha-toxin by Sae on S. aureus pathogenesis has not been directly addressed. Here, we mutated the SaeR-binding sequences in the hla regulatory region and determined the contribution of this mutation to hla expression and pathogenesis in strain USA300 JE2. Western blot analyses revealed drastic reduction of alpha-toxin levels in the culture supernatants of SaeR-binding mutant in contrast to the marked alpha-toxin production in the wild type. The SaeR-binding mutation had no significant effect on alpha-toxin regulation by Agr, MgrA, and CcpA. In animal studies, we found that the SaeR-binding mutation did not contribute to USA300 JE2 pathogenesis using a rat infective endocarditis model. However, in a rat skin and soft tissue infection model, the abscesses on rats infected with the mutant were significantly smaller than the abscesses on those infected with the wild type but similar to the abscesses on those infected with a saeR mutant. These studies indicated that there is a direct effect of hla regulation by SaeR on pathogenesis but that the effect depends on the animal model used.

The good side of inflammation: Staphylococcus aureus proteins SpA and Sbi contribute to proper abscess formation and wound healing during skin and soft tissue infections

Staphylococcus aureus is the most prominent cause of skin and soft tissue infections (SSTI) worldwide. Mortality associated with invasive SSTI is a major threat to public health considering the incidence of antibiotic resistant isolates in particular methicillin resistant S. aureus both in the hospital (HA-MRSA) and in the community (CA-MRSA). To overcome the increasing difficulties in the clinical management of SSTI due to MRSA, new prophylactic and therapeutic approaches are urgently needed and a preventive vaccine would be welcome. The rational design of an anti-S. aureus vaccine requires a deep knowledge of the role that the different bacterial virulence factors play according to the type of infection. In the present study, using a set of isogenic deficient mutants and their complemented strains we determined that the staphylococcal surface proteins SpA and Sbi play an important role in the induction of inflammatory cytokines and chemokines in the skin during SSTI. SpA and Sbi initiate signaling cascades that lead to the early recruitment of neutrophils, modulate their lifespan in the skin milieu and contribute to proper abscess formation and bacterial eradication. Moreover, the expression of SpA and Sbi appear critical for skin repair and wound healing. Thus, these results indicate that SpA and Sbi can promote immune responses in the skin that are beneficial for the host and therefore, should not be neutralized with vaccine formulations designed to prevent SSTI.

Inactivation of farR Causes High Rhodomyrtone Resistance and Increased Pathogenicity in Staphylococcus aureus

Rhodomyrtone (Rom) is an acylphloroglucinol antibiotic originally isolated from leaves of Rhodomyrtus tomentosa. Rom targets the bacterial membrane and is active against a wide range of Gram-positive bacteria but the exact mode of action remains obscure. Here we isolated and characterized a spontaneous Rom-resistant mutant from the model strain Staphylococcus aureus HG001 (Rom^R) to learn more about the resistance mechanism. We showed that Rom-resistance is based on a single point mutation in the coding region of farR [regulator of fatty acid (FA) resistance] that causes an amino acid change from Cys to Arg at position 116 in FarR, that affects FarR activity. Comparative transcriptome analysis revealed that mutated farR affects transcription of many genes in distinct pathways. FarR represses for example the expression of its own gene (farR), its flanking gene farE (effector of FA resistance), and other global regulators such as agr and sarA. All these genes were consequently upregulated in the Rom^R clone. Particularly the upregulation of agr and sarA leads to increased expression of virulence genes rendering the Rom^R clone more cytotoxic and more pathogenic in a mouse infection model. The Rom-resistance is largely due to the de-repression of farE. FarE is described as an efflux pump for linoleic and arachidonic acids. We observed an increased release of lipids in the Rom^R clone compared to its parental strain HG001. If farE is deleted in the Rom^R clone, or, if native farR is expressed in the Rom^R strain, the corresponding strains become hypersensitive to Rom. Overall, we show here that the high Rom-resistance is mediated by overexpression of farE in the Rom^R clone, that FarR is an important regulator, and that the point mutation in farR (Rom^R clone) makes the clone hyper-virulent.

Comparison of livestock-associated and community-associated Staphylococcus aureus pathogenicity in a mouse model of skin and soft tissue infection

Industrial hog operation (IHO) workers are at increased risk of carrying Staphylococcus aureus in their nares, particularly strains that are livestock-associated (LA) and multidrug-resistant. The pathogenicity of LA-S. aureus strains remains unclear, with some prior studies suggesting reduced transmission and virulence in humans compared to community-associated methicillin-resistant (CA-MRSA) S. aureus. The objective of this study was to determine the degree to which LA-S. aureus strains contracted by IHO workers cause disease relative to a representative CA-MRSA strain in a mouse model of skin and soft tissue infection (SSTI). Mice infected with CC398 LA-S. aureus strains (IHW398-1 and IHW398-2) developed larger lesion sizes with higher bacterial burden than mice infected with CA-MRSA (SF8300) (p < 0.05). The greatest lesion size and bacterial burden was seen with a CC398 strain that produced a recurrent SSTI in an IHO worker. The LA-S. aureus infected mice had decreased IL-1β protein levels compared with CA-MRSA-infected mice (p < 0.05), suggesting a suboptimal host response to LA-S. aureus SSTIs. WGSA revealed heterogeneity in virulence factor and antimicrobial resistance genes carried by LA-S. aureus and CA-MRSA strains. The observed pathogenicity suggest that more attention should be placed on preventing the spread of LA-S. aureus into human populations.

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.

Sequential evolution of virulence and resistance during clonal spread of community-acquired methicillin-resistant Staphylococcus aureus

The past two decades have witnessed an alarming expansion of staphylococcal disease caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). The factors underlying the epidemic expansion of CA-MRSA lineages such as USA300, the predominant CA-MRSA clone in the United States, are largely unknown. Previously described virulence and antimicrobial resistance genes that promote the dissemination of CA-MRSA are carried by mobile genetic elements, including phages and plasmids. Here, we used high-resolution genomics and experimental infections to characterize the evolution of a USA300 variant plaguing a patient population at increased risk of infection to understand the mechanisms underlying the emergence of genetic elements that facilitate clonal spread of the pathogen. Genetic analyses provided conclusive evidence that fitness (manifest as emergence of a dominant clone) changed coincidently with the stepwise emergence of (i) a unique prophage and mutation of the regulator of the pyrimidine nucleotide biosynthetic operon that promoted abscess formation and colonization, respectively, thereby priming the clone for success; and (ii) a unique plasmid that conferred resistance to two topical microbiocides, mupirocin and chlorhexidine, frequently used for decolonization and infection prevention. The resistance plasmid evolved through successive incorporation of DNA elements from non-S. aureus spp. into an indigenous cryptic plasmid, suggesting a mechanism for interspecies genetic exchange that promotes antimicrobial resistance. Collectively, the data suggest that clonal spread in a vulnerable population resulted from extensive clinical intervention and intense selection pressure toward a pathogen lifestyle that involved the evolution of consequential mutations and mobile genetic elements.

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.

Alanine Scanning Mutagenesis of the MEDI4893 (Suvratoxumab) Epitope Reduces Alpha Toxin Lytic Activity In Vitro and Staphylococcus aureus Fitness in Infection Models

Alpha toxin (AT) is a cytolytic pore-forming toxin that plays a key role in Staphylococcus aureus pathogenesis; consequently, extensive research was undertaken to understand the AT mechanism of action and its utility as a target for novel prophylaxis and treatment strategies against S. aureus infections. MEDI4893 (suvratoxumab) is a human anti-AT IgG1 monoclonal antibody (MAb) that targets AT and is currently in phase 2 clinical development.

Alpha toxin (AT) is a cytolytic pore-forming toxin that plays a key role in Staphylococcus aureus pathogenesis; consequently, extensive research was undertaken to understand the AT mechanism of action and its utility as a target for novel prophylaxis and treatment strategies against S. aureus infections. MEDI4893 (suvratoxumab) is a human anti-AT IgG1 monoclonal antibody (MAb) that targets AT and is currently in phase 2 clinical development. As shown previously, the MEDI4893-binding epitope on AT is comprised of the highly conserved amino acid regions 177 to 200 and 261 to 271, suggesting these amino acids are important for AT function. To test this hypothesis and gain insight into the effect of mutations in the epitope on AT neutralization by MEDI4893, nine MEDI4893 contact residues in AT were individually mutated to alanine. Consistent with our hypothesis, 8 out of 9 mutants exhibited >2-fold loss in lytic activity resulting from a defect in cell binding and pore formation. MEDI4893 binding affinity was reduced >2-fold (2- to 27-fold) for 7 out of 9 mutants, and no binding was detected for the W187A mutant. MEDI4893 effectively neutralized all of the lytic mutants in vitro and in vivo. When the defective mutants were introduced into an S. aureus clinical isolate, the mutant-expressing strains exhibited less severe disease in mouse models and were effectively neutralized by MEDI4893. These results indicate the MEDI4893 epitope is highly conserved due in part to its role in AT pore formation and bacterial fitness, thereby decreasing the likelihood for the emergence of MAb-resistant variants.

α-Toxin Induces Platelet Aggregation and Liver Injury during Staphylococcus aureus Sepsis

During sepsis, small blood vessels can become occluded by large platelet aggregates of poorly understood etiology. During Staphylococcal aureus infection, sepsis severity is linked to the bacterial α-toxin (α-hemolysin, AT) through unclear mechanisms. In this study, we visualized intravascular events in the microcirculation and found that intravenous AT injection induces rapid platelet aggregation, forming dynamic micro-thrombi in the microcirculation. These aggregates are retained in the liver sinusoids and kidney glomeruli, causing multi-organ dysfunction. Acute staphylococcal infection results in sequestration of most bacteria by liver macrophages. Platelets are initially recruited to these macrophages and help eradicate S. aureus. However, at later time points, AT causes aberrant and damaging thrombosis throughout the liver. Treatment with an AT neutralizing antibody (MEDI4893^∗) prevents platelet aggregation and subsequent liver damage, without affecting the initial and beneficial platelet recruitment. Thus, AT neutralization may represent a promising approach to combat staphylococcal-induced intravascular coagulation and organ dysfunction.

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.

Neutralizing Alpha-Toxin Accelerates Healing of Staphylococcus aureus-Infected Wounds in Nondiabetic and Diabetic Mice

Staphylococcus aureus wound infections delay healing and result in invasive complications such as osteomyelitis, especially in the setting of diabetic foot ulcers. In preclinical animal models of S. aureus skin infection, antibody neutralization of alpha-toxin (AT), an S. aureus-secreted pore-forming cytolytic toxin, reduces disease severity by inhibiting skin necrosis and restoring effective host immune responses. However, whether therapeutic neutralization of alpha-toxin is effective against S. aureus-infected wounds is unclear. Herein, the efficacy of prophylactic treatment with a human neutralizing anti-AT monoclonal antibody (MAb) was evaluated in an S. aureus skin wound infection model in nondiabetic and diabetic mice. In both nondiabetic and diabetic mice, anti-AT MAb treatment decreased wound size and bacterial burden and enhanced reepithelialization and wound resolution compared to control MAb treatment. Anti-AT MAb had distinctive effects on the host immune response, including decreased neutrophil and increased monocyte and macrophage infiltrates in nondiabetic mice and decreased neutrophil extracellular traps (NETs) in diabetic mice. Similar therapeutic efficacy was achieved with an active vaccine targeting AT. Taken together, neutralization of AT had a therapeutic effect against S. aureus-infected wounds in both nondiabetic and diabetic mice that was associated with differential effects on the host immune response.

Staphylococcus aureus produces pain through pore-forming toxins and neuronal TRPV1 that is silenced by QX-314

The hallmark of many bacterial infections is pain. The underlying mechanisms of pain during live pathogen invasion are not well understood. Here, we elucidate key molecular mechanisms of pain produced during live methicillin-resistant Staphylococcus aureus (MRSA) infection. We show that spontaneous pain is dependent on the virulence determinant agr and bacterial pore-forming toxins (PFTs). The cation channel, TRPV1, mediated heat hyperalgesia as a distinct pain modality. Three classes of PFTs-alpha-hemolysin (Hla), phenol-soluble modulins (PSMs), and the leukocidin HlgAB-directly induced neuronal firing and produced spontaneous pain. From these mechanisms, we hypothesized that pores formed in neurons would allow entry of the membrane-impermeable sodium channel blocker QX-314 into nociceptors to silence pain during infection. QX-314 induced immediate and long-lasting blockade of pain caused by MRSA infection, significantly more than lidocaine or ibuprofen, two widely used clinical analgesic treatments.

Bacterial toxins: Offensive, defensive, or something else altogether?

The secretion of proteins that damage host tissue is well established as integral to the infectious processes of many bacterial pathogens. However, recent advances in our understanding of the activity of toxins suggest that the attributes we have assigned to them from early in vitro experimentation have misled us into thinking of them as merely destructive tools. Here, we will discuss the multifarious ways in which toxins contribute to the lifestyle of bacteria and, by considering their activity from an evolutionary perspective, demonstrate how this extends far beyond their ability to destroy host tissue.

α-Toxin Regulates Local Granulocyte Expansion from Hematopoietic Stem and Progenitor Cells in Staphylococcus aureus-Infected Wounds

The immune response to Staphylococcus aureus infection in skin involves the recruitment of polymorphonuclear neutrophils (PMNs) from the bone marrow via the circulation and local granulopoiesis from hematopoietic stem and progenitor cells (HSPCs) that also traffic to infected skin wounds. We focus on regulation of PMN number and function and the role of pore-forming α-toxin (AT), a virulence factor that causes host cell lysis and elicits inflammasome-mediated IL-1β secretion in wounds. Infection with wild-type S. aureus enriched in AT reduced PMN recruitment and resulted in sustained bacterial burden and delayed wound healing. In contrast, PMN recruitment to wounds infected with an isogenic AT-deficient S. aureus strain was unimpeded, exhibiting efficient bacterial clearance and hastened wound resolution. HSPCs recruited to infected wounds were unaffected by AT production and were activated to expand PMN numbers in proportion to S. aureus abundance in a manner regulated by TLR2 and IL-1R signaling. Immunodeficient MyD88-knockout mice infected with S. aureus experienced lethal sepsis that was reversed by PMN expansion mediated by injection of wild-type HSPCs directly into wounds. We conclude that AT-induced IL-1β promotes local granulopoiesis and effective resolution of S. aureus-infected wounds, revealing a potential antibiotic-free strategy for tuning the innate immune response to treat methicillin-resistant S. aureus infection in immunodeficient patients.

The S. aureus 4-oxalocrotonate tautomerase SAR1376 enhances immune responses when fused to several antigens

A persistent goal of vaccine development is the enhancement of the immunogenicity of antigens while maintaining safety. One strategy involves alteration of the presentation of the antigen by combining antigens with a multimeric scaffold. Multi-antigen vaccines are under development, and there are presently far more candidate antigens than antigen scaffolding strategies. This is potentially problematic, since prior immunity to a scaffold may inhibit immune responses to the antigen-scaffold combination. In this study, a series of domains from S. aureus which have been shown to crystallise into multimeric structures have been examined for their scaffolding potential. Of these domains, SAR1376, a 62 amino acid member of the 4-oxalocrotonate tautomerase (4-OT) family, was pro-immunogenic in mice when fused to a range of pathogen antigens from both S. aureus and P. falciparum, and delivered by either DNA vaccination, viral vector vaccines or as protein-in-adjuvant formulations. The adjuvant effect did not depend on enzymatic activity, but was abrogated by mutations disrupting the hexameric structure of the protein. We therefore propose that SAR1376, and perhaps other members of the 4-OT protein family, represent very small domains which can be fused to a wide range of antigens, enhancing immune responses against them.

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.

Simple Wound Irrigation in the Postoperative Treatment for Surgically Drained Spontaneous Soft Tissue Abscesses: Study Protocol for a Prospective, Single-Blinded, Randomized Controlled Trial

Background

Skin abscesses are a frequent encountered health care problem and lead to a significant source of morbidity. They consequently have an essential impact on the quality of life and work. To date, the type of aftercare for surgically drained abscesses remains under debate. This leads to undesirable practice variations. Many clinical standard protocols include sterile wound dressings twice a day by a home-care service to reduce the chance of a recurrent wound infection. It is unknown, however, whether reinfection rates are comparable to adequate wound irrigation with a nonsterile solution performed by the patient. Our hypothesis is that simple wound irrigation with nonsterile water for postoperative wound care after an abscess is surgically drained is feasible. We assume that in terms of reinfection and reintervention rates unsterile wound irrigation is equal to sterile wound irrigation.

Objective

The primary aim of this study is therefore to investigate if there is a need for sterile wound irrigation after surgically drained spontaneous skin abscesses.

Methods

In a prospective, randomized controlled, single-blinded, single-center trial based on a noninferiority design, we will enroll 128 patients randomized to either the control or the intervention group. The control group will be treated according to our current, standard protocol in which all patients receive a sterile wound irrigation performed by a home-care service twice a day. Patients randomized to the intervention group will be treated with a nonsterile wound irrigation (shower) twice a day. All patients will have a routine clinical control visit after 1, 3, 6, and 12 weeks in the outpatient clinic. Primary outcome is the reinfection and reoperation rate due to insufficient wound healing diagnosed either at the outpatient control visit or during general practitioner visits. Secondary outcome measures include a Short Form Health Survey, Visual Analog Scale, Patient and Observer Scar Assessment Scale, Vancouver Scar Scale, and the EurolQol 5-Dimension Questionnaire. Those questionnaires will be completed at the outpatient control visits.

Results

The trial was started in June 2016 and enrolled 50 patients by article publication. Regarding the adherence to our protocol, we found 10% of loss to follow-up until now. Only 2 patients needed reoperation and only 1 patient needed a change of treatment (antiseptic therapy). Most patients are happy with their randomized treatment but as expected some patients in the sterile group complained about timing problems with their working hours and home-care service appointments. Most patients in the nonsterile group are satisfied being able to take care of their wounds independently although some patients still depend on the home-care service for the wound dressing. We are hoping to have enrolled enough patients by summer 2017. The follow-up will take until autumn 2017, and study results are expected to be published by the end of 2017. This trial is solely supported by the cantonal hospital of Lucerne.

Conclusions

Nonsterile wound irrigation is more likely to be carried out independently by the patient than sterile wound irrigation. Therefore, if nonsterile wound care shows comparable results in terms of reinfection and reintervention rates, patient independence in the aftercare of surgically drained abscesses will increase, patients can return to work earlier, and health care costs can be reduced. In a preliminary, conservative estimation of health care costs, an annual savings of 300,000 CHF will be achieved in our hospital.

Trial Registration

German Clinical Trials Register DRKS00010418; https://drks-neu.uniklinik-freiburg.de/ drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00010418 (Archived by WebCite at http://www.webcitation.org/6q0AXp5EX)