Inhibition of endothelial interleukin-8 production and neutrophil transmigration by Staphylococcus aureus beta-hemolysin

Contribution of staphylococcal virulence factors in the pathogenesis of thrombosis

Staphylococci are responsible for many infections in humans, starting with skin and soft tissue infections and finishing with invasive diseases such as endocarditis, sepsis and pneumonia, which lead to high mortality. Patients with sepsis often demonstrate activated clotting pathways, decreased levels of anticoagulants, decreased fibrinolysis, activated endothelial surfaces and activated platelets. This results in disseminated intravascular coagulation and formation of a microthrombus, which can lead to a multiorgan failure. This review describes various staphylococcal virulence factors that contribute to vascular thrombosis, including deep vein thrombosis in infected patients. The article presents mechanisms of action of different factors released by bacteria in various host defense lines, which in turn can lead to formation of blood clots in the vessels.

Molecular Characteristics and Pathogenicity of Staphylococcus aureus Exotoxins

Staphylococcus aureus stands as one of the most pervasive pathogens given its morbidity and mortality worldwide due to its roles as an infectious agent that causes a wide variety of diseases ranging from moderately severe skin infections to fatal pneumonia and sepsis. S. aureus produces a variety of exotoxins that serve as important virulence factors in S. aureus-related infectious diseases and food poisoning in both humans and animals. For example, staphylococcal enterotoxins (SEs) produced by S. aureus induce staphylococcal foodborne poisoning; toxic shock syndrome toxin-1 (TSST-1), as a typical superantigen, induces toxic shock syndrome; hemolysins induce cell damage in erythrocytes and leukocytes; and exfoliative toxin induces staphylococcal skin scalded syndrome. Recently, Panton-Valentine leucocidin, a cytotoxin produced by community-associated methicillin-resistant S. aureus (CA-MRSA), has been reported, and new types of SEs and staphylococcal enterotoxin-like toxins (SEls) were discovered and reported successively. This review addresses the progress of and novel insights into the molecular structure, biological activities, and pathogenicity of both the classic and the newly identified exotoxins produced by S. aureus.

Research progress of nanoparticle targeting delivery systems in bacterial infections

Bacterial infection is a huge threat to the health of human beings and animals. The abuse of antibiotics have led to the occurrence of bacterial multidrug resistance, which have become a difficult problem in the treatment of clinical infections. Given the outstanding advantages of nanodrug delivery systems in cancer treatment, many scholars have begun to pay attention to their application in bacterial infections. However, due to the similarity of the microenvironment between bacterial infection lesions and cancer sites, the targeting and accuracy of traditional microenvironment-responsive nanocarriers are questionable. Therefore, finding new specific targets has become a new development direction of nanocarriers in bacterial prevention and treatment. This article reviews the infectious microenvironment induced by bacteria and a series of virulence factors of common pathogenic bacteria and their physiological functions, which may be used as potential targets to improve the targeting accuracy of nanocarriers in lesions.

Ciprofloxacin-Loaded Polyvinylpyrrolidone Foils for the Topical Treatment of Wound Infections with Methicillin-Resistant Staphylococcus aureus (MRSA)

Bacterial infections are a constant challenge in the management of acute and chronic wounds. Chronic wounds, such as diabetic foot ulcers, have increased significantly in the last few years due to the rise of an aging population. A better understanding of the infectious pathophysiological mechanisms is urgently needed along with new options for the treatment of wound infections and wound-healing disorders. New advances in the preparation of biocompatible dressing materials that can be loaded with antimicrobial drugs may improve the topical treatment of infected wounds. In this study, we investigated the antimicrobial activity of polyvinylpyrrolidone (PVP) foils loaded with ciprofloxacin (Cipro-foils) in the presence of acetic acid as a co-solvent. We used ex vivo human wounds that were infected with two bacterial strains: methicillin-resistant Staphylococcus aureus (MRSA) or Pseudomonas aeruginosa (PAO1). The effectiveness of the treatment was demonstrated by the quantification of the living bacteria extracted from the wound and the detection of released immunological mediators in skin extracts and in the skin culture media. We found that Cipro-foils effectively treated the infection with both PAO1 and MRSA. Other than PAO1, MRSA had no lytic activity toward skin proteins. MRSA infections increased cytokines' expression and release. Interestingly, treatment with Cipro-foils could partially counteract these effects.

How Staphylococcus aureus and Pseudomonas aeruginosa Hijack the Host Immune Response in the Context of Cystic Fibrosis

Cystic fibrosis (CF) is a serious genetic disease that leads to premature death, mainly due to impaired lung function. CF lungs are characterized by ongoing inflammation, impaired immune response, and chronic bacterial colonization. Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) are the two most predominant bacterial agents of these chronic infections. Both can colonize the lungs for years by developing host adaptation strategies. In this review, we examined the mechanisms by which SA and PA adapt to the host immune response. They are able to bypass the physical integrity of airway epithelia, evade recognition, and then modulate host immune cell proliferation. They also modulate the immune response by regulating cytokine production and by counteracting the activity of neutrophils and other immune cells. Inhibition of the immune response benefits not only the species that implements them but also other species present, and we therefore discuss how these mechanisms can promote the establishment of coinfections in CF lungs.

In Silico Genome-Scale Analysis of Molecular Mechanisms Contributing to the Development of a Persistent Infection with Methicillin-Resistant Staphylococcus aureus (MRSA) ST239

The increasing frequency of isolation of methicillin-resistant Staphylococcus aureus (MRSA) limits the chances for the effective antibacterial therapy of staphylococcal diseases and results in the development of persistent infection such as bacteremia and osteomyelitis. The aim of this study was to identify features of the MRSA_ST239 0943-1505-2016 (SA943) genome that contribute to the formation of both acute and chronic musculoskeletal infections. The analysis was performed using comparative genomics data of the dominant epidemic S. aureus lineages, namely ST1, ST8, ST30, ST36, and ST239. The SA943 genome encodes proteins that provide resistance to the host's immune system, suppress immunological memory, and form biofilms. The molecular mechanisms of adaptation responsible for the development of persistent infection were as follows: amino acid substitution in PBP2 and PBP2a, providing resistance to ceftaroline; loss of a large part of prophage DNA and restoration of the nucleotide sequence of beta-hemolysin, that greatly facilitates the escape of phagocytosed bacteria from the phagosome and formation of biofilms; dysfunction of the AgrA system due to the presence of psm-mec and several amino acid substitutions in the AgrC; partial deletion of the nucleotide sequence in genomic island vSAβ resulting in the loss of two proteases of Spl-operon; and deletion of SD repeats in the SdrE amino acid sequence.

Chronic Rhinosinusitis, S. aureus Biofilm and Secreted Products, Inflammatory Responses, and Disease Severity

Chronic rhinosinusitis (CRS) is a persistent inflammation of the nasal cavity and paranasal sinuses associated with tissue remodelling, dysfunction of the sinuses' natural defence mechanisms, and induction of different inflammatory clusters. The etiopathogenesis of CRS remains elusive, and both environmental factors, such as bacterial biofilms and the host's general condition, are thought to play a role. Bacterial biofilms have significant clinical relevance due to their potential to cause resistance to antimicrobial therapy and host defenses. Despite substantial medical advances, some CRS patients suffer from recalcitrant disease that is unresponsive to medical and surgical treatments. Those patients often have nasal polyps with tissue eosinophilia, S. aureus-dominant mucosal biofilm, comorbid asthma, and a severely compromised quality of life. This review aims to summarise the contemporary knowledge of inflammatory cells/pathways in CRS, the role of bacterial biofilm, and their impact on the severity of the disease. Here, an emphasis is placed on S. aureus biofilm and its secreted products. A better understanding of these factors might offer important diagnostic and therapeutic perceptions for recalcitrant disease.

Endothelial inflammation and neutrophil transmigration are modulated by extracellular matrix composition in an inflammation-on-a-chip model

Inflammatory diseases are often characterised by excessive neutrophil infiltration from the blood stream to the site of inflammation, which damages healthy tissue and prevents resolution of inflammation. Development of anti-inflammatory drugs is hindered by lack of in vitro and in vivo models which accurately represent the disease microenvironment. In this study, we used the OrganoPlate to develop a humanized 3D in vitro inflammation-on-a-chip model to recapitulate neutrophil transmigration across the endothelium and subsequent migration through the extracellular matrix (ECM). Human umbilical vein endothelial cells formed confluent vessels against collagen I and geltrex mix, a mix of basement membrane extract and collagen I. TNF-α-stimulation of vessels upregulated inflammatory cytokine expression and promoted neutrophil transmigration. Intriguingly, major differences were found depending on the composition of the ECM. Neutrophils transmigrated in higher number and further in geltrex mix than collagen I, and did not require an N-formyl-methionyl-leucyl-phenylalanine (fMLP) gradient for transmigration. Inhibition of neutrophil proteases inhibited neutrophil transmigration on geltrex mix, but not collagen I. These findings highlight the important role of the ECM in determining cell phenotype and response to inhibitors. Future work could adapt the ECM composition for individual diseases, producing accurate models for drug development.

Staphylococcus aureus β-Toxin Exerts Anti-angiogenic Effects by Inhibiting Re-endothelialization and Neovessel Formation

Staphylococcus aureus causes severe, life-threatening infections that often are complicated by severe local and systemic pathologies with non-healing lesions. A classic example is S. aureus infective endocarditis (IE), where the secreted hemolysin β-toxin potentiates the disease via its sphingomyelinase and biofilm ligase activities. Although these activities dysregulate human aortic endothelial cell activation, β-toxin effect on endothelial cell function in wound healing has not been addressed. With the use of the ex vivo rabbit aortic ring model, we provide evidence that β-toxin prevents branching microvessel formation, highlighting its ability to interfere with tissue re-vascularization and vascular repair. We show that β-toxin specifically targets both human aortic endothelial cell proliferation and cell migration and inhibits human umbilical vein endothelial cell rearrangement into capillary-like networks in vitro. Proteome arrays specific for angiogenesis-related molecules provided evidence that β-toxin promotes an inhibitory profile in endothelial cell monolayers, specifically targeting production of TIMP-1, TIMP-4, and IGFBP-3 to counter the effect of a pro-angiogenic environment. Dysregulation in the production of these molecules is known to result in sprouting defects (including deficient cell proliferation, migration, and survival), vessel instability and/or vascular regression. When endothelial cells are grown under re-endothelialization/wound healing conditions, β-toxin decreases the pro-angiogenic molecule MMP-8 and increases the anti-angiogenic molecule endostatin. Altogether, the data indicate that β-toxin is an anti-angiogenic virulence factor and highlight a mechanism where β-toxin exacerbates S. aureus invasive infections by interfering with tissue re-vascularization and vascular repair.

Differences in the sequence of PlcR transcriptional regulator binding site affect sphingomyelinase production in Bacillus cereus

Bacillus cereus is an opportunistic pathogen that often causes severe infections such as bacteremia, with sphingomyelinase (SMase) being a crucial virulence factor. Although many strains of B. cereus carry the SMase gene, they are classified as SMase-producing and non-producing strains. The reason for different SMase production among B. cereus strains remains unknown. In this study, we investigated the relationship between SMase and the PlcR transcriptional regulation system to clarify the mechanism leading to varied SMase production among B. cereus strains. We analyzed the sequence of the PlcR box, which is a transcriptional regulator binding site, located at the promoter region of SMase and phosphatidylcholine-specific phospholipase C. Based on differences in the PlcR box sequences, we classified the B. cereus strains into three groups (I, II, and III). SMase expression and activity were hardly detected in Group III strains. In Group I strains, SMase activity and its expression were maximal at the onset of the stationary phase and decreased during the stationary phase, whereas those were maintained during the stationary phase in Group II stains. On injection of B. cereus strains into mice or incubation with macrophages for phagocytosis assay, the SMase-producing Group I and II strains showed higher pathogenicity than Group III strains. These findings suggest that PlcR box sequence in B. cereus affects the production of SMase, which may provide important clinical information for the detection of highly pathogenic B. cereus strains. This article is protected by copyright. All rights reserved.

The Role of hlb-Converting Bacteriophages in Staphylococcus aureus Host Adaption

As an opportunistic pathogen of humans and animals, Staphylococcus aureus asymptomatically colonizes the nasal cavity but is also a leading cause of life-threatening acute and chronic infections. The evolution of S. aureus resulting from short- and long-term adaptation to diverse hosts is tightly associated with mobile genetic elements. S. aureus strains can carry up to four temperate phages, many of which possess accessory genes encoding staphylococcal virulence factors. More than 90% of human nasal isolates of S. aureus have been shown to carry Sa3int phages, whereas invasive S. aureus isolates tend to lose these phages. Sa3int phages integrate as prophages into the bacterial hlb gene, disrupting the expression of the sphingomyelinase Hlb, an important virulence factor under specific infection conditions. Virulence factors encoded by genes carried by Sa3int phages include staphylokinase, enterotoxins, chemotaxis-inhibitory protein, and staphylococcal complement inhibitor, all of which are highly human specific and probably essential for bacterial survival in the human host. The transmission of S. aureus from humans to animals is strongly correlated with the loss of Sa3int phages, whereas phages are regained once a strain is transmitted from animals to humans. Thus, both the insertion and excision of prophages may confer a fitness advantage to this bacterium. There is also growing evidence that Sa3int phages may perform "active lysogeny," a process during which prophages are temporally excised from the chromosome without forming intact phage particles. The molecular mechanisms controlling the peculiar life cycle of Sa3int phages remain largely unclear. Nevertheless, their regulation is likely fine-tuned to ensure bacterial survival within different hosts.

Staphylococcus aureus ST228 and ST239 as models for expression studies of diverse markers during osteoblast infection and persistence

The ability of S. aureus to infect bone and osteoblasts is correlated with its incredible virulence armamentarium that can mediate the invasion/internalization process, cytotoxicity, membrane damage, and intracellular persistence. We comparatively analyzed the interaction, persistence, and modulation of expression of selected genes and cell viability in an ex vivo model using human MG‐63 osteoblasts of two previously studied and well‐characterized S. aureus clinical strains belonging to the ST239‐SCCmecIII‐t037 and ST228‐SCCmecI‐t041 clones at 3 h and 24 h post‐infection (p.i). S. aureus ATCC12598 ST30‐t076 was used as a control strain. Using imaging flow cytometry (IFC), we found that these strains invaded and persisted in MG‐63 osteoblasts to different extents. The invasion was evaluated at 3 h p.i and persistence at 24 h p.i., in particular: ATCC12598 internalized in 70% and persisted in 50% of MG‐63 cells; ST239‐SCCmecIII internalized in 50% and persisted in 45% of MG‐63 cells; and ST228‐SCCmecI internalized in 30% and persisted in 20% of MG‐63 cells. During the infection period, ST239‐III exerted significant cytotoxic activity resulting from overexpression of hla and psmA and increased expression of the genes involved in adhesion, probably due to the release and re‐entry of bacteria inside MG‐63 cells at 24 h p.i. The lower invasiveness of ST228‐I was also associated with non‐cytotoxic activity inside osteoblasts. This clone was unable to activate sufficient cellular reaction and succumbed inside MG‐63 cells. Our findings support the idea of considering new strategies, based on a translational approach—eukaryotic host–pathogen interaction (EHPI)—and to be applied on a large scale, to predict S. aureus /osteoblast interaction and treat bone infections. Such strategies rely on the study of the genetic and biochemical basis of both pathogen and host.

Microfluidics in Sickle Cell Disease Research: State of the Art and a Perspective Beyond the Flow Problem

Sickle cell disease (SCD) is the monogenic hemoglobinopathy where mutated sickle hemoglobin molecules polymerize to form long fibers under deoxygenated state and deform red blood cells (RBCs) into predominantly sickle form. Sickled RBCs stick to the vascular bed and obstruct blood flow in extreme conditions, leading to acute painful vaso-occlusion crises (VOCs) – the leading cause of mortality in SCD. Being a blood disorder of deformed RBCs, SCD manifests a wide-range of organ-specific clinical complications of life (in addition to chronic pain) such as stroke, acute chest syndrome (ACS) and pulmonary hypertension in the lung, nephropathy, auto-splenectomy, and splenomegaly, hand-foot syndrome, leg ulcer, stress erythropoiesis, osteonecrosis and osteoporosis. The physiological inception for VOC was initially thought to be only a fluid flow problem in microvascular space originated from increased viscosity due to aggregates of sickled RBCs; however, over the last three decades, multiple molecular and cellular mechanisms have been identified that aid the VOC in vivo. Activation of adhesion molecules in vascular endothelium and on RBC membranes, activated neutrophils and platelets, increased viscosity of the blood, and fluid physics driving sickled and deformed RBCs to the vascular wall (known as margination of flow) – all of these come together to orchestrate VOC. Microfluidic technology in sickle research was primarily adopted to benefit from mimicking the microvascular network to observe RBC flow under low oxygen conditions as models of VOC. However, over the last decade, microfluidics has evolved as a valuable tool to extract biophysical characteristics of sickle red cells, measure deformability of sickle red cells under simulated oxygen gradient and shear, drug testing, in vitro models of intercellular interaction on endothelialized or adhesion molecule-functionalized channels to understand adhesion in sickle microenvironment, characterizing biomechanics and microrheology, biomarker identification, and last but not least, for developing point-of-care diagnostic technologies for low resource setting. Several of these platforms have already demonstrated true potential to be translated from bench to bedside. Emerging microfluidics-based technologies for studying heterotypic cell–cell interactions, organ-on-chip application and drug dosage screening can be employed to sickle research field due to their wide-ranging advantages.

Investigation of a Staphylococcus argenteus Strain Involved in a Chronic Prosthetic-Joint Infection

Staphylococcus argenteus is an emerging species responsible for infections comparable to those induced by Staphylococcus aureus. It has been involved in few chronic or persistent infections so far. In this study, we described a case of a persistent prosthetic-joint infection (PJI) affecting a young woman. We investigated in vitro the virulence traits of the incriminated S. argenteus strain (bone cell invasion, biofilm formation and induction of inflammation) and analyzed its genome, in comparison with two other strains of S. argenteus and two S. aureus isolates. It appeared that this S. argenteus PJI strain combined biofilm formation, osteoblast invasion and intracellular persistence abilities together with genes potentially involved in the escape of the host immune defenses, which might explain the chronicization of the infection.

Sub-Inhibitory Clindamycin and Azithromycin reduce S. aureus Exoprotein Induced Toxicity, Inflammation, Barrier Disruption and Invasion

Background: Chronic rhinosinusitis (CRS) is defined as a chronic inflammation of the nose and paranasal sinus mucosa associated with relapsing infections—particularly with S. aureus. Long-term treatments with protein synthesis inhibitor antibiotics have been proposed to reduce inflammation in the context chronic severe inflammatory airway pathologies, including CRS. This study assessed the effect of subinhibitory clindamycin and azithromycin on S. aureus exoprotein induced inflammation, toxicity and invasiveness. Methods: S. aureus ATCC51650 and two clinical isolates grown in planktonic and biofilm form were treated with subinhibitory clindamycin and azithromycin. Exoproteins were collected and applied to primary human nasal epithelial cells (HNECs) in monolayers and at air-liquid interface. This was followed by lactate dehydrogenase (LDH), enzyme-linked immunosorbent assay (ELISA), Transepithelial Electrical Resistance (TEER) and paracellular permeability assays to assess the effect on cell toxicity, inflammatory cytokine production and mucosal barrier structure and function, respectively. The effect of these treatments was tested as well on the S. aureus invasiveness of HNECs. Results: Subinhibitory clindamycin reduced S. aureus exoprotein production in planktonic and biofilm form, thereby blocking exoprotein-induced toxicity, reversing its detrimental effects on mucosal barrier structure and function and modulating its inflammatory properties. Sub-inhibitory azithromycin had similar effects—albeit to a lesser extent. Furthermore, clindamycin—but not azithromycin—treated S. aureus lost its invasive capacity of HNECs. Conclusion: Subinhibitory clindamycin and azithromycin reduce S. aureus exoprotein production, thereby modulating the inflammatory cascade by reducing exoprotein-induced toxicity, inflammation, mucosal barrier disruption and invasiveness.

LIPUS inhibited the expression of inflammatory factors and promoted the osteogenic differentiation capacity of hPDLCs by inhibiting the NF-κB signaling pathway

BACKGROUND AND OBJECTIVES

As a chronic infectious disease, periodontitis could lead to tooth and bone loss. Low-intensity pulsed ultrasound (LIPUS) is a safe, noninvasive treatment method to effectively inhibit inflammation and promote bone differentiation. However, the application of LIPUS in curing periodontitis is still rare. Our study aimed to explore the ability of LIPUS to inhibit inflammatory factors and promote the osteogenic differentiation capacity of human periodontal ligament cells (hPDLCs), and its underlying mechanism.

MATERIAL AND METHODS

Human periodontal ligament cells were obtained and cultured from the premolar tissue samples for experiments. First, hPDLCs were treated for 24 hours using lipopolysaccharide (LPS) and then exposed to LIPUS (10 mW/cm² , 30 mW/cm² , 60 mW/cm² , and 90 mW/cm² ) to determine the appropriate intensity to inhibit expression of the inflammatory factors interleukin-6 (IL-6) and interleukin-8 (IL-8) expression. The expression of IL-6 and IL-8 was detected by real-time PCR and enzyme-linked immunosorbent assay. The safety of the most appropriate intensity of LIPUS was tested by a cell counting kit 8 test and an apoptosis assay. Then, LPS-induced hPDLCs were treated in osteogenic medium for 7-21 days with or without LIPUS (90 mW/cm² , 30 min/d) stimulation. The osteogenic genes RUNX2, OPN, OSX, and OCN were measured by real-time PCR. Additionally, osteogenic differentiation capacity was determined using alkaline phosphatase (ALP) staining, ALP activity analysis, and Alizarin red staining. The activity of the nuclear factor-kappa B (NF-κB) signaling pathway was determined by western blotting, real-time PCR, immunofluorescence, and pathway blockade assays.

RESULTS

Lipopolysaccharide significantly upregulated the production and gene expression of IL-6 and IL-8, while LIPUS stimulation significantly inhibited IL-6 and IL-8 expression in an intensity-dependent manner. LIPUS (90 mW/cm² ) was chosen as the most appropriate intensity, and there was no detrimental influence on cell proliferation and status with or without osteogenic medium. In addition, consecutive stimulation with LIPUS (90 mW/cm² ) for 30 min/d for 7 days could also inhibit IL-6 and IL-8 gene expression, upregulate the expression of the osteogenesis-related genes RUNX2, OPN, OSX, and OCN, and promote osteogenic differentiation capacity in osteogenic medium in inflamed hPDLCs. The NF-κB signaling pathway was inhibited with LIPUS (90 mW/cm² ) via inhibition of the phosphorylation of IκBα and the translocation of p65 into the nucleus in inflamed hPDLCs. Additional investigations of the NF-κB inhibitor, BAY 11-7082, revealed that LIPUS (90 mW/cm² ) acted similarly to BAY 11-7802 to inhibit the NF-κB signaling pathway and increase osteogenesis-related genes and promote the osteogenic differentiation capacity of inflamed hPDLCs.

CONCLUSION

Low-intensity pulsed ultrasound (90 mW/cm² ) stimulation could be a safe method to inhibit IL-6 and IL-8 in hPDLCs by inhibiting the NF-κB signaling pathway. The effect of LIPUS (90 mW/cm² ) and BAY 11-7082 on LPS-induced inflammation demonstrated that both of these agents were capable of promoting osteogenesis-related gene expression and osteogenic differentiation in hPDLCs, suggesting that the effect of LIPUS on the promotion of osteogenic activity could be mediated in part through its ability to inhibit the NF-κB signal pathway. Hence, LIPUS could be a potential therapeutic method to cure periodontitis.

Mycobacterium tuberculosis Primary Infection and Dissemination: A Critical Role for Alveolar Epithelial Cells

Globally, tuberculosis (TB) has reemerged as a major cause of morbidity and mortality, despite the use of the Mycobacterium bovis BCG vaccine and intensive attempts to improve upon BCG or develop new vaccines. Two lacunae in our understanding of the Mycobacterium tuberculosis (M. tb)-host pathogenesis have mitigated the vaccine efforts; the bacterial-host interaction that enables successful establishment of primary infection and the correlates of protection against TB. The vast majority of vaccine efforts are based on the premise that cell-mediated immunity (CMI) is the predominating mode of protection against TB. However, studies in animal models and in humans demonstrate that post-infection, a period of several weeks precedes the initiation of CMI during which the few inhaled bacteria replicate dramatically and disseminate systemically. The “Trojan Horse” mechanism, wherein M. tb is phagocytosed and transported across the alveolar barrier by infected alveolar macrophages has been long postulated as the sole, primary M. tb:host interaction. In the current review, we present evidence from our studies of transcriptional profiles of M. tb in sputum as it emerges from infectious patients where the bacteria are in a quiescent state, to its adaptations in alveolar epithelial cells where the bacteria transform to a highly replicative and invasive phenotype, to its maintenance of the invasive phenotype in whole blood to the downregulation of invasiveness upon infection of epithelial cells at an extrapulmonary site. Evidence for this alternative mode of infection and dissemination during primary infection is supported by in vivo, in vitro cell-based, and transcriptional studies from multiple investigators in recent years. The proposed alternative mechanism of primary infection and dissemination across the alveolar barrier parallels our understanding of infection and dissemination of other Gram-positive pathogens across their relevant mucosal barriers in that barrier-specific adhesins, toxins, and enzymes synergize to facilitate systemic establishment of infection prior to the emergence of CMI. Further exploration of this M. tb:non-phagocytic cell interaction can provide alternative approaches to vaccine design to prevent infection with M. tb and not only decrease clinical disease but also decrease the overwhelming reservoir of latent TB infection.

ϕSa3mw Prophage as a Molecular Regulatory Switch of Staphylococcus aureus β-Toxin Production

Phage regulatory switches (phage-RSs) are a newly described form of active lysogeny where prophages function as regulatory mechanisms for expression of chromosomal bacterial genes. In Staphylococcus aureus, ϕSa3int is a widely distributed family of prophages that integrate into the β-toxin structural gene hlb, effectively inactivating it. However, β-toxin-producing strains often arise during infections and are more virulent in experimental infective endocarditis and pneumonia infections. We present evidence that in S. aureus MW2, ϕSa3mw excision is temporally and differentially responsive to growth conditions relevant to S. aureus pathogenesis. PCR analyses of ϕSa3mw (integrated and excised) and of intact hlb showed that ϕSa3mw preferentially excises in response to hydrogen peroxide-induced oxidative stress and during biofilm growth. ϕSa3mw remains as a prophage when in contact with human aortic endothelial cells in culture. A criterion for a prophage to be considered a phage-RS is the inability to lyse host cells. MW2 grown under phage-inducing conditions did not release infectious phage particles by plaque assay or transmission electron microscopy, indicating that ϕSa3mw does not carry out a productive lytic cycle. These studies highlight a dynamic, and perhaps more sophisticated, S. aureus-prophage interaction where ϕSa3int prophages provide a novel regulatory mechanism for the conditional expression of virulence factors.IMPORTANCE β-Toxin is a sphingomyelinase hemolysin that significantly contributes to Staphylococcus aureus pathogenesis. In most S. aureus isolates the prophage ϕSa3int inserts into the β-toxin gene hlb, inactivating it, but human and experimental infections give rise to β-toxin-producing variants. However, it remained to be established whether ϕSa3mw excises in response to specific environmental cues, restoring the β-toxin gene sequence. This is not only of fundamental interest but also critical when designing intervention strategies and therapeutics. We provide evidence that ϕSa3mw actively excises, allowing the conditional expression of β-toxin. ϕSa3int prophages may play a novel and largely uncharacterized role in S. aureus pathogenesis as molecular regulatory switches that promote bacterial fitness and adaptation to the challenges presented by the mammalian host.

Staphylococcus aureus Secreted Toxins and Extracellular Enzymes

Staphylococcus aureus is a formidable pathogen capable of causing infections in different sites of the body in a variety of vertebrate animals, including humans and livestock. A major contribution to the success of S. aureus as a pathogen is the plethora of virulence factors that manipulate the host's innate and adaptive immune responses. Many of these immune modulating virulence factors are secreted toxins, cofactors for activating host zymogens, and exoenzymes. Secreted toxins such as pore-forming toxins and superantigens are highly inflammatory and can cause leukocyte cell death by cytolysis and clonal deletion, respectively. Coagulases and staphylokinases are cofactors that hijack the host's coagulation system. Exoenzymes, including nucleases and proteases, cleave and inactivate various immune defense and surveillance molecules, such as complement factors, antimicrobial peptides, and surface receptors that are important for leukocyte chemotaxis. Additionally, some of these secreted toxins and exoenzymes can cause disruption of endothelial and epithelial barriers through cell lysis and cleavage of junction proteins. A unique feature when examining the repertoire of S. aureus secreted virulence factors is the apparent functional redundancy exhibited by the majority of the toxins and exoenzymes. However, closer examination of each virulence factor revealed that each has unique properties that have important functional consequences. This chapter provides a brief overview of our current understanding of the major secreted virulence factors critical for S. aureus pathogenesis.

The effects of Lawsonia intracellularis, Salmonella enterica serovar Typhimurium and co-infection on IL-8 and TNFα expression in IPEC-J2 cells

Lawsonia intracellularis is among the most important enteric pathogens of swine and has been shown to be a risk factor for increased Salmonella enterica shedding. S. enterica serovar Typhimurium, in addition to being a significant pathogen of swine, also remains one of the most common causes of foodborne illness worldwide. Inflammation and the expression of IL8 and TNFα are an important process in the establishment of S. Typhimurium infection. Yet the effect of L. intracellularis on the expression of these cytokines by enterocytes, the niche both pathogens occupy during infection, is poorly understood. In this study we compared cytokine gene expression between singly and dually infected IPEC-J2 cells, a non-transformed porcine enterocyte cell line. Our results show that L. intracellularis leads to increased expression of IL8 and TNFα and has an additive effect on their expression in co-infection. The increase in expression of inflammatory cytokines may be one mechanism by which L. intracellularis favors S. Typhimurium infection.

Protective vascular coagulation in response to bacterial infection of the kidney is regulated by bacterial lipid A and host CD147

Bacterial infection of the kidney leads to a rapid cascade of host protective responses, many of which are still poorly understood. We have previously shown that following kidney infection with uropathogenic Escherichia coli (UPEC), vascular coagulation is quickly initiated in local perivascular capillaries that protects the host from progressing from a local infection to systemic sepsis. The signaling mechanisms behind this response have not however been described. In this study, we use a number of in vitro and in vivo techniques, including intravital microscopy, to identify two previously unrecognized components influencing this protective coagulation response. The acylation state of the Lipid A of UPEC lipopolysaccharide (LPS) is shown to alter the kinetics of local coagulation onset in vivo. We also identify epithelial CD147 as a potential host factor influencing infection-mediated coagulation. CD147 is expressed by renal proximal epithelial cells infected with UPEC, contingent to bacterial expression of the α-hemolysin toxin. The epithelial CD147 subsequently can activate tissue factor on endothelial cells, a primary step in the coagulation cascade. This study emphasizes the rapid, multifaceted response of the kidney tissue to bacterial infection and the interplay between host and pathogen during the early hours of renal infection.

Metabolism of Caprine Milk Carbohydrates by Probiotic Bacteria and Caco-2:HT29⁻MTX Epithelial Co-Cultures and Their Impact on Intestinal Barrier Integrity

The development and maturation of the neonatal intestine is generally influenced by diet and commensal bacteria, the composition of which, in turn, can be influenced by the diet. Colonisation of the neonatal intestine by probiotic Lactobacillus strains can strengthen, preserve, and improve barrier integrity, and adherence of probiotics to the intestinal epithelium can be influenced by the available carbon sources. The goal of the present study was to examine the role of probiotic lactobacilli strains alone or together with a carbohydrate fraction (CF) from caprine milk on barrier integrity of a co-culture model of the small intestinal epithelium. Barrier integrity (as measured by trans epithelial electrical resistance (TEER)), was enhanced by three bacteria/CF combinations (Lactobacillus rhamnosus HN001, L. plantarum 299v, and L. casei Shirota) to a greater extent than CF or bacteria alone. Levels of occludin mRNA were increased for all treatments compared to untreated co-cultures, and L. plantarum 299v in combination with CF had increased mRNA levels of MUC4, MUC2 and MUC5AC mucins and MUC4 protein abundance. These results indicate that three out of the four probiotic bacteria tested, in combination with CF, were able to elicit a greater increase in barrier integrity of a co-culture model of the small intestinal epithelium compared to that for either component alone. This study provides additional insight into the individual or combined roles of microbe–diet interactions in the small intestine and their beneficial contribution to the intestinal barrier.

Staphylococcus aureus Toxins and Their Molecular Activity in Infectious Diseases

Staphylococcus aureus is a microorganism resident in the skin and nasal membranes with a dreadful pathogenic potential to cause a variety of community and hospital-acquired infections. The frequency of these infections is increasing and their treatment is becoming more difficult. The ability of S. aureus to form biofilms and the emergence of multidrug-resistant strains are the main reasons determining the challenge in dealing with these infections. S. aureus' infectious capacity and its success as a pathogen is related to the expression of virulence factors, among which the production of a wide variety of toxins is highlighted. For this reason, a better understanding of S. aureus toxins is needed to enable the development of new strategies to reduce their production and consequently improve therapeutic approaches. This review focuses on understanding the toxin-based pathogenesis of S. aureus and their role on infectious diseases.

Glycogen Synthase Kinase 3α Is the Main Isoform That Regulates the Transcription Factors Nuclear Factor-Kappa B and cAMP Response Element Binding in Bovine Endothelial Cells Infected with Staphylococcus aureus

Glycogen synthase kinase 3 (GSK3) is a constitutive enzyme implicated in the regulation of cytokine expression and the inflammatory response during bacterial infections. Mammals have two GSK3 isoforms named GSK3α and GSK3β that plays different but often overlapping functions. Although the role of GSK3β in cytokine regulation during the inflammatory response caused by bacteria is well described, GSK3α has not been found to participate in this process. Therefore, we tested if GSK3α may act as a regulatory isoform in the cytokine expression by bovine endothelial cells infected with Staphylococcus aureus because this bacterium is one of the major pathogens that cause tissue damage associated with inflammatory dysfunction. Interestingly, although both isoforms were phosphorylated–inactivated, we consistently observed a higher phosphorylation of GSK3α at Ser21 than that of GSK3β at Ser9 after bacterial challenge. During a temporal course of infection, we characterized a molecular switch from pro-inflammatory cytokine expression (IL-8), promoted by nuclear factor-kappa B (NF-κB), at an early stage (2 h) to an anti-inflammatory cytokine expression (IL-10), promoted by cAMP response element binding (CREB), at a later stage (6 h). We observed an indirect effect of GSK3α activity on NF-κB activation that resulted in a low phosphorylation of CREB at Ser133, a decreased interaction between CREB and the co-activator CREB-binding protein (CBP), and a lower expression level of IL-10. Gene silencing of GSK3α and GSK3β with siRNA indicated that GSK3α knockout promoted the interaction between CREB and CBP that, in turn, increased the expression of IL-10, reduced the interaction of NF-κB with CBP, and reduced the expression of IL-8. These results indicate that GSK3α functions as the primary isoform that regulates the expression of IL-10 in endothelial cells infected with S. aureus.

Extracellular sphingomyelinase activity impairs TNF-α-induced endothelial cell death via ADAM17 activation and TNF receptor 1 shedding

ADAM17, a prominent member of the “Disintegrin and Metalloproteinase” (ADAM) family, is an important regulator of endothelial cell proliferation and cell survival. The protease controls vital cellular functions through cleavage of growth factors, cytokines and their receptors including transforming growth factor-alpha (TGF-α), tumor necrosis factor-alpha (TNF-α) and TNF-α receptor 1 (TNFR1). TNF-α is the major inducer of endothelial cell death in cardiovascular diseases. The latter are also characterized by elevated plasma and tissue levels of extracellular sphingomyelinase (SMase). Whether the SMase affects ADAM activity and thus endothelial cell function has not been addressed to date. Here, we analyzed the effect of SMase on ADAM17-mediated shedding in COS7 cells and in human umbilical vein endothelial cells (HUVECs). Exposure to SMase significantly increased ADAM17-mediated release of alkaline-phosphatase (AP)-tagged TGF-α in COS7 cells and shedding of endogenously expressed TNFR1 in HUVECs. We previously presented evidence that surface exposure of phosphatidylserine (PS) is pivotal for ADAM17 to exert sheddase function. We found that SMase treatment led to PS externalization in both cell types. Transient non-apoptotic PS exposure is often mediated by Ca²⁺-dependent phospholipid scramblases. Accordingly, the Ca²⁺-chelator EGTA markedly reduced the breakdown of phospholipid asymmetry and shedding of TGF-α and TNFR1. Moreover, sheddase activity was significantly diminished in the presence of the competing PS-headgroup OPLS. SMase-stimulated TNFR1 shedding strikingly diminished TNF-α-induced signalling cascades and endothelial cell death. Taken together, our data suggest that SMase activity might act as protective factor for endothelial cells in cardiovascular diseases.

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

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

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

Bacterial Sphingomyelinases and Phospholipases as Virulence Factors

Bacterial sphingomyelinases and phospholipases are a heterogeneous group of esterases which are usually surface associated or secreted by a wide variety of Gram-positive and Gram-negative bacteria. These enzymes hydrolyze sphingomyelin and glycerophospholipids, respectively, generating products identical to the ones produced by eukaryotic enzymes which play crucial roles in distinct physiological processes, including membrane dynamics, cellular signaling, migration, growth, and death. Several bacterial sphingomyelinases and phospholipases are essential for virulence of extracellular, facultative, or obligate intracellular pathogens, as these enzymes contribute to phagosomal escape or phagosomal maturation avoidance, favoring tissue colonization, infection establishment and progression, or immune response evasion. This work presents a classification proposal for bacterial sphingomyelinases and phospholipases that considers not only their enzymatic activities but also their structural aspects. An overview of the main physiopathological activities is provided for each enzyme type, as are examples in which inactivation of a sphingomyelinase- or a phospholipase-encoding gene impairs the virulence of a pathogen. The identification of sphingomyelinases and phospholipases important for bacterial pathogenesis and the development of inhibitors for these enzymes could generate candidate vaccines and therapeutic agents, which will diminish the impacts of the associated human and animal diseases.

Effect of a Semi-Purified Oligosaccharide-Enriched Fraction from Caprine Milk on Barrier Integrity and Mucin Production of Co-Culture Models of the Small and Large Intestinal Epithelium

Caprine milk contains the highest amount of oligosaccharides among domestic animals, which are structurally similar to human milk oligosaccharides (HMOs). This suggests caprine milk oligosaccharides may offer similar protective and developmental effects to that of HMOs. However, to date, studies using oligosaccharides from caprine milk have been limited. Thus, this study aimed to examine the impact of a caprine milk oligosaccharide-enriched fraction (CMOF) on barrier function of epithelial cell co-cultures of absorptive enterocytes (Caco-2 cells) and mucus-secreting goblet cells (HT29-MTX cells), that more closely simulate the cell proportions found in the small (90:10) and large intestine (75:25). Treatment of epithelial co-cultures with 0.4, 1.0, 2.0 and 4.0 mg/mL of CMOF was shown to have no effect on metabolic activity but did enhance cell epithelial barrier integrity as measured by trans-epithelial electrical resistance (TEER), in a dose-dependent manner. The CMOF at the maximum concentration tested (4.0 mg/mL) enhanced TEER, mucin gene expression and mucin protein abundance of epithelial co-cultures, all of which are essential components of intestinal barrier function.

Searching for Beta-Haemolysin hlb Gene in Staphylococcus pseudintermedius with Species-Specific Primers

The paper presents an analysis of 51 Staphylococcus pseudintermedius clinically isolated strains from humans and from animals. Staphylococcus pseudintermedius strains’ ability to produce β-haemolysin was evaluated with phenotypic methods (hot–cold effect, reverse CAMP test). In order to determine the hlb gene presence (coding for β-haemolysin) in a genomic DNA, PCR reactions were conducted with two different pairs of primers: one described in the literature for Staphylococcus aureus and recommended for analysing SIG group staphylococci and newly designed one in CLC Main Workbench software. Only reactions with newly designed primers resulted in product amplification, the presence of which was fully compatible with the results of phenotypic β-haemolysin test. Negative results for S. aureus and S. intermedius reference ATCC strains suggest that after further analysis the fragment of hlb gene amplified with primers described in this study might be included in the process of S. pseudintermedius strains identification.

Inflammasome Activation Can Mediate Tissue-Specific Pathogenesis or Protection in Staphylococcus aureus Infection

Staphylococcus aureus is a Gram-positive coccus that interacts with human hosts on a spectrum from quiet commensal to deadly pathogen. S. aureus is capable of infecting nearly every tissue in the body resulting in cellulitis, pneumonia, osteomyelitis, endocarditis, brain abscesses, bacteremia, and more. S. aureus has a wide range of factors that promote infection, and each site of infection triggers a different response in the human host. In particular, the different patterns of inflammasome activation mediate tissue-specific pathogenesis or protection in S. aureus infection. Although still a nascent field, understanding the unique host-pathogen interactions in each infection and the role of inflammasomes in mediating pathogenesis may lead to novel strategies for treating S. aureus infections. Reviews addressing S. aureus virulence and pathogenesis (Thammavongsa et al. 2015), as well as epidemiology and pathophysiology (Tong et al. 2015), have recently been published. This review will focus on S. aureus factors that activate inflammasomes and their impact on innate immune signaling and bacterial survival.

Staphylococcus aureus: Immunopathogenesis and Human Immunity

Considering a large number of pathogen factors that enable high virulence of a microorganism such as Staphylococcus aureus (S. aureus), it is essential to see them through the continuous adaptation to the newly acquired mechanisms of the host immune response and efforts to overcome these, allowing the bacteria a perfect ecological niche for growth, reproduction, and location of new hosts. Past efforts to create a vaccine that would provide effective protection against infections caused by S. aureus remained without success. The reasons for this stem from the outstanding adaptability skills of this microorganism to almost all environmental conditions, the existence of a numerous virulence factors whose mechanisms of action are not well known, as well as insufficient knowledge of the immune response to S. aureus infections. This review article deals with this issue from another perspective and emphasizes actual knowledge on virulence factors and immune response to S. aureus.

Staphylococcus aureus Inhibits IL-8 Responses Induced by Pseudomonas aeruginosa in Airway Epithelial Cells

Pseudomonas aeruginosa (PA) and Staphylococcus aureus (SA) are major respiratory pathogens and can concurrently colonize the airways of patients with chronic obstructive diseases, such as cystic fibrosis (CF). Airway epithelial cell signalling is critical to the activation of innate immune responses. In the setting of polymicrobial colonization or infection of the respiratory tract, how epithelial cells integrate different bacterial stimuli remains unknown. Our study examined the inflammatory responses to PA and SA co-stimulations. Immortalised airway epithelial cells (Beas-2B) exposed to bacteria-free filtrates from PA (PAF) induced a robust production of the neutrophil chemoattractant IL-8 while bacteria-free filtrates from SA (SAF) had a minimal effect. Surprisingly, co-stimulation with PAF+SAF demonstrated that SAF strongly inhibited the PAF-driven IL-8 production, showing that SAF has potent anti-inflammatory effects. Similarly SAF decreased IL-8 production induced by the TLR1/TLR2 ligand Pam₃CysSK₄ but not the TLR4 ligand LPS nor TLR5 ligand flagellin in Beas-2B cells. Moreover, SAF greatly dampened TLR1/TLR2-mediated activation of the NF-κB pathway, but not the p38 MAPK pathway. We observed this SAF-dependent anti-inflammatory activity in several SA clinical strains, as well as in the CF epithelial cell line CFBE41o-. These findings show a novel direct anti-inflammatory effect of SA on airway epithelial cells, highlighting its potential to modulate inflammatory responses in the setting of polymicrobial infections.

Tormentic acid inhibits LPS-induced inflammatory response in human gingival fibroblasts via inhibition of TLR4-mediated NF-κB and MAPK signalling pathway

OBJECTIVE

Periodontal disease is one of the most prevalent oral diseases, which is associated with inflammation of the tooth-supporting tissues. Tormentic acid (TA), a triterpene isolated from Rosa rugosa, has been reported to exert anti-inflammatory effects. The aim of this study was to investigate the anti-inflammatory effects of TA on lipopolysaccharide (LPS)-stimulated human gingival fibroblasts (HGFs).

METHODS

The levels of inflammatory cytokines such as interleukin (IL)-6 and chemokines such as IL-8 were detected by enzyme-linked immunosorbent assay (ELISA). The expression of Toll-like receptor 4 (TLR4), nuclear factor kappa B (NF-κB), IκBα, p38, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) was determined by Western blotting.

RESULTS

The results showed that Porphyromonas gingivalis LPS significantly upregulated the expression of IL-6 and IL-8. TA inhibited the LPS-induced production of IL-6 and IL-8 in a dose-dependent manner. Furthermore, TA inhibited LPS-induced TLR4 expression; NF-κB activation; IκBα degradation; and phosphorylation of ERK, JNK, and P38.

CONCLUSION

TA inhibits the LPS-induced inflammatory response in HGFs by suppressing the TLR4-mediated NF-κB and mitogen-activated protein kinase (MAPK) signalling pathway.

Production and applications of an N-terminally-truncated recombinant beta-haemolysin from Staphylococcus aureus

The beta-haemolysin of Staphylococcus aureus (SA-hlb) is a secreted neutral sphingomyelinase (nSMase) implicated in the pathogenesis of infection and responsible for the characteristic in vitro 'hot-cold' haemolytic ability of the bacterium. Here, we describe the production of a biologically active N-terminally-truncated recombinant SA-hlb protein for use in in vitro assays and as a research tool. Using local isolates of S. aureus, we PCR-amplified an SA-hlb DNA sequence of 891 nucleotides, 99 nucleotides shorter than the full-length molecule, before cloning and sequencing (GenBank accession no. JN580071). The pQE.TriSystem vector (Qiagen, Germany) was used to express recombinant SA-hlb (r-SA-hlb) with a C-terminal 8xHis tag in Escherichia coli JM107 cells. Both JM107 lysate and the purified r-SA-hlb possessed hot-cold lytic activity against sheep and buffalo erythrocytes, which was abolished by incubation at ≥90 °C for 30 min or exposure to dithiothreitol, and could be neutralized by bovine immune sera. Purified r-SA-hlb was also cytotoxic to buffalo mononuclear cells and was effective as a coating antigen for indirect ELISA to screen for reactive sera. Importantly, the r-SA-hlb was suitable for use as a β-toxin in the modified CAMP test. We conclude that the r-SA-hlb protein produced was functionally active and has numerous potential applications.

New insights into the prevention of staphylococcal infections and toxic shock syndrome

Staphylococcus aureus is a major human pathogen capable of causing various diseases, from skin infections to life-threatening pneumonia and toxic shock syndrome. S. aureus exoproteins, including superantigens, contribute significantly to the pathogenesis of this organism. Antibiotics inhibit growth, but often provide no protection from S. aureus exoproteins. With the emergence of antibiotic-resistant S. aureus, new therapeutic options to treat or prevent S. aureus-associated diseases are critical. Most S. aureus infections begin on the skin or mucosal surfaces from direct inflammatory or cytotoxic effects of exotoxins. Therefore, antitoxin therapies that prevent toxin production and prevent their effects on host cells are being researched. Current treatments for staphylococcal diseases and recent developments in antitoxin therapeutic agents and vaccines are reviewed.

Staphylococcus aureus innate immune evasion is lineage-specific: a bioinfomatics study

Staphylococcus aureus is a major human pathogen, and is targeted by the host innate immune system. In response, S. aureus genomes encode dozens of secreted proteins that inhibit complement, chemotaxis and neutrophil activation resulting in successful evasion of innate immune responses. These proteins include immune evasion cluster proteins (IEC; Chp, Sak, Scn), staphylococcal superantigen-like proteins (SSLs), phenol soluble modulins (PSMs) and several leukocidins. Biochemical studies have indicated that genetic variants of these proteins can have unique functions. To ascertain the scale of genetic variation in secreted immune evasion proteins, whole genome sequences of 88 S. aureus isolates, representing 25 clonal complex (CC) lineages, in the public domain were analysed across 43 genes encoding 38 secreted innate immune evasion protein complexes. Twenty-three genes were variable, with between 2 and 15 variants, and the variants had lineage-specific distributions. They include genes encoding Eap, Ecb, Efb, Flipr/Flipr-like, Hla, Hld, Hlg, Sbi, Scin-B/C and 13 SSLs. Most of these protein complexes inhibit complement, chemotaxis and neutrophil activation suggesting that isolates from each S. aureus lineage respond to the innate immune system differently. In contrast, protein complexes that lyse neutrophils (LukSF-PVL, LukMF, LukED and PSMs) were highly conserved, but can be carried on mobile genetic elements (MGEs). MGEs also encode proteins with narrow host-specificities arguing that their acquisition has important roles in host/environmental adaptation. In conclusion, this data suggests that each lineage of S. aureus evades host immune responses differently, and that isolates can adapt to new host environments by acquiring MGEs and the immune evasion protein complexes that they encode. Cocktail therapeutics that targets multiple variant proteins may be the most appropriate strategy for controlling S. aureus infections.

Divergent responses of different endothelial cell types to infection with Candida albicans and Staphylococcus aureus

Endothelial cells are important in the pathogenesis of bloodstream infections caused by Candida albicans and Staphylococcus aureus. Numerous investigations have used human umbilical vein endothelial cells (HUVECs) to study microbial-endothelial cell interactions in vitro. However, the use of HUVECs requires a constant supply of umbilical cords, and there are significant donor-to-donor variations in these endothelial cells. The use of an immortalized endothelial cell line would obviate such difficulties. One candidate in this regard is HMEC-1, an immortalized human dermal microvascular endothelial cell line. To determine if HMEC-1 cells are suitable for studying the interactions of C. albicans and S. aureus with endothelial cells in vitro, we compared the interactions of these organisms with HMEC-1 cells and HUVECs. We found that wild-type C. albicans had significantly reduced adherence to and invasion of HMEC-1 cells as compared to HUVECs. Although wild-type S. aureus adhered to and invaded HMEC-1 cells similarly to HUVECs, an agr mutant strain had significantly reduced invasion of HMEC-1 cells, but not HUVECs. Furthermore, HMEC-1 cells were less susceptible to damage induced by C. albicans, but more susceptible to damage caused by S. aureus. In addition, HMEC-1 cells secreted very little IL-8 in response to infection with either organism, whereas infection of HUVECs induced substantial IL-8 secretion. This weak IL-8 response was likely due to the anatomic site from which HMEC-1 cells were obtained because infection of primary human dermal microvascular endothelial cells with C. albicans and S. aureus also induced little increase in IL-8 production above basal levels. Thus, C. albicans and S. aureus interact with HMEC-1 cells in a substantially different manner than with HUVECs, and data obtained with one type of endothelial cell cannot necessarily be extrapolated to other types.

Host- and microbe determinants that may influence the success of S. aureus colonization

Staphylococcus aureus may cause serious skin and soft tissue infections, deep abscesses, endocarditis, osteomyelitis, pneumonia, and sepsis. S. aureus persistently colonizes 25–30% of the adult human population, and S. aureus carriers have an increased risk for infections caused by the bacterium. The major site of colonization is the nose, i.e., the vestibulum nasi, which is covered with ordinary skin and hair follicles. Several host and microbe determinants are assumed to be associated with colonization. These include the presence and expression level of bacterial adhesins, which can adhere to various proteins in the extracellular matrix or on the cellular surface of human skin. The host expresses several antimicrobial peptides and lipids. The level of β-defensin 3, free sphingosine, and cis-6-hexadecenoic acid are found to be associated with nasal carriage of S. aureus. Other host factors are certain polymorphisms in Toll-like receptor 2, mannose-binding lectin, C-reactive protein, glucocorticoid-, and vitamin D receptor. Additional putative determinants for carriage include genetic variation and expression of microbial surface components recognizing adhesive matrix molecules and their interaction partners, as well as variation among humans in the ability of recognizing and responding appropriately to the bacteria. Moreover, the available microflora may influence the success of S. aureus colonization. In conclusion, colonization is a complex interplay between the bacteria and its host. Several bacterial and host factors are involved, and an increased molecular understanding of these are needed.

Staphylococcus aureus hemolysins, bi-component leukocidins, and cytolytic peptides: a redundant arsenal of membrane-damaging virulence factors?

One key aspect of the virulence of Staphylococcus aureus lies in its ability to target the host cell membrane with a large number of membrane-damaging toxins and peptides. In this review, we describe the hemolysins, the bi-component leukocidins (which include the Panton Valentine leukocidin, LukAB/GH, and LukED), and the cytolytic peptides (phenol soluble modulins). While at first glance, all of these factors might appear redundant, it is now clear that some of these factors play specific roles in certain S. aureus life stages and diseases or target specific cell types or species. In this review, we present an update of the literature on toxin receptors and their cell type and species specificities. Furthermore, we review epidemiological studies and animal models illustrating the role of these membrane-damaging factors in various diseases. Finally, we emphasize the interplay of these factors with the host immune system and highlight all their non-lytic functions.

Francisella tularensis suppresses the proinflammatory response of endothelial cells via the endothelial protein C receptor

Various bacterial pathogens activate the endothelium to secrete proinflammatory cytokines and recruit circulating leukocytes. In contrast, there is a distinct lack of activation of these cells by Francisella tularensis, the causative agent of tularemia. Given the importance of endothelial cells in facilitating innate immunity, we investigated the ability of the attenuated live vaccine strain and virulent Schu S4 strain of F. tularensis to inhibit the proinflammatory response of HUVECs. Living F. tularensis live vaccine strain and Schu S4 did not stimulate secretion of the chemokine CCL2 by HUVECs, whereas material released from heat-killed bacteria did. Furthermore, the living bacteria suppressed secretion in response to heat-killed F. tularensis. This phenomenon was dose and contact dependent, and it occurred rapidly upon infection. The living bacteria did not inhibit the activation of HUVECs by Escherichia coli LPS, highlighting the specificity of this suppression. The endothelial protein C receptor (EPCR) confers anti-inflammatory properties when bound by activated protein C. When the EPCR was blocked, F. tularensis lost the ability to suppress activation of HUVECs. To our knowledge, this is the first report that a bacterial pathogen inhibits the host immune response via the EPCR. Endothelial cells are a critical component of the innate immune response to infection, and suppression of their activation by F. tularensis is likely a mechanism that aids in bacterial dissemination and evasion of host defenses.

Sphingomyelin metabolism at the plasma membrane: implications for bioactive sphingolipids

The plasma membrane (PM) is a major resource for production of bioactive lipids and contains a large proportion of the cellular sphingomyelin (SM) content. Consequently, the regulation of SM levels at the PM by enzymes such as sphingomyelinase (SMase) and SM synthase 2 (SMS2) can have profound effects - both on biophysical properties of the membrane, but also on cellular signaling. Over the past 20 years, there has been considerable research into the physiological and cellular functions associated with regulation of SM levels, notably with regards to the production of ceramide. In this review, we will summarize this research with particular focus on the SMases and SMS2. We will outline what biological functions are associated with SM metabolism/production at the PM, and discuss what we believe are major challenges that need to be addressed in future studies.

Francisella tularensis directly interacts with the endothelium and recruits neutrophils with a blunted inflammatory phenotype

Francisella tularensis, the causative agent of tularemia, is a highly virulent organism, especially when exposure occurs by inhalation. Recent data suggest that Francisella interacts directly with alveolar epithelial cells. Although F. tularensis causes septicemia and can live extracellularly in a murine infection model, there is little information about the role of the vascular endothelium in the host response. We hypothesized that F. tularensis would interact with pulmonary endothelial cells as a prerequisite to the clinically observed recruitment of neutrophils to the lung. Using an in vitro Transwell model system, we studied interactions between F. tularensis live vaccine strain (Ft LVS) and a pulmonary microvascular endothelial cell (PMVEC) monolayer. Organisms invaded the endothelium and were visualized within individual endothelial cells by confocal microscopy. Although these bacteria-endothelial cell interactions did not elicit production of the proinflammatory chemokines, polymorphonuclear leukocytes (PMN) were stimulated to transmigrate across the endothelium in response to Ft LVS. Moreover, transendothelial migration altered the phenotype of recruited PMN; i.e., the capacity of these PMN to activate NADPH oxidase and release elastase in response to subsequent stimulation was reduced compared with PMN that traversed PMVEC in response to Streptococcus pneumoniae. The blunting of PMN responsiveness required PMN transendothelial migration but did not require PMN uptake of Ft LVS, was not dependent on the presence of serum-derived factors, and was not reproduced by Ft LVS-conditioned medium. We speculate that the capacity of Ft LVS-stimulated PMVEC to support transendothelial migration of PMN without triggering release of IL-8 and monocyte chemotactic protein-1 and to suppress the responsiveness of transmigrated PMN to subsequent stimulation could contribute to the dramatic virulence during inhalational challenge with Francisella.