Staphylococcus epidermidis polysaccharide intercellular adhesin induces IL-8 expression in human astrocytes via a mechanism involving TLR2

Using the Traditional Ex Vivo Whole Blood Model to Discriminate Bacteria by Their Inducible Host Responses

Whole blood models are rapid and versatile for determining immune responses to inflammatory and infectious stimuli, but they have not been used for bacterial discrimination. Staphylococcus aureus, S. epidermidis and Escherichia coli are the most common causes of invasive disease, and rapid testing strategies utilising host responses remain elusive. Currently, immune responses can only discriminate between bacterial 'domains' (fungi, bacteria and viruses), and very few studies can use immune responses to discriminate bacteria at the species and strain level. Here, whole blood was used to investigate the relationship between host responses and bacterial strains. Results confirmed unique temporal profiles for the 10 parameters studied: IL-6, MIP-1α, MIP-3α, IL-10, resistin, phagocytosis, S100A8, S100A8/A9, C5a and TF3. Pairwise analysis confirmed that IL-6, resistin, phagocytosis, C5a and S100A8/A9 could be used in a discrimination scheme to identify to the strain level. Linear discriminant analysis (LDA) confirmed that (i) IL-6, MIP-3α and TF3 could predict genera with 95% accuracy; (ii) IL-6, phagocytosis, resistin and TF3 could predict species at 90% accuracy and (iii) phagocytosis, S100A8 and IL-10 predicted strain at 40% accuracy. These data are important because they confirm the proof of concept that host biomarker panels could be used to identify bacterial pathogens.

Skin Commensal Bacteria Modulates the Immune Balance of Mice to Alleviate Atopic Dermatitis-Induced Damage

Objective

Although studies indicate that Staphylococcus epidermidis (S. epidermidis) can regulate inflammation and anti-inflammatory cytokines, there is limited evidence supporting their effects on atopic dermatitis (AD). Here, we aimed to investigate the effects and potential mechanism of skin commensal bacteria on the immunity of mice with AD.

Methods

Twenty-four female BALB/C mice were selected and divided randomly into 4 groups: normal group, atopic dermatitis model group (AD), atopic dermatitis/substrate group (AD/substrates), and atopic dermatitis/substrates/epidermidis group (AD/S. epidermidis). All the mice were given different ways. After 14 days, their skin conditions were scored, and the serum, ear tissue, and inguinal lymph node tissue were collected and analyzed. Furthermore, the flow cytometry was used to analyze the number of CD4°+°CD25°+°Foxp3°+°Treg in the mouse lymph node tissue.

Results

Compared with the AD/substrate group, the mice ear thickness and dermatitis score were significantly reduced in the AD/S. epidermidis group; skin epidermis, acanthosis, the degree of keratinization, inflammatory cell infiltration in the dermis, and the number of mast cells were declined. The serum levels of IgE, IgG1, IgG2a, and TNF-α, IFN-γ, IL-4, and Eotaxin were significantly declined in the AD/S. epidermidis compared with the AD/substrate group. The proportion of CD4°+°CD25°+°Foxp3°+°Treg cells in the lymph node tissue was significantly increased in the AD/S. epidermidis group compared with the AD/substrate group.

Conclusion

Staphylococcus epidermidis can regulate mice's immune balance to alleviate AD-induced skin damage.

Presence of Candida tropicalis on Staphylococcus epidermidis Biofilms Facilitated Biofilm Production and Candida Dissemination: An Impact of Fungi on Bacterial Biofilms

While Staphylococcus epidermidis (SE) is a common cause of infections in implanted prostheses and other indwelling devices, partly due to the biofilm formation, Candida tropicalis (CT) is an emerging Candida spp. with a potent biofilm-producing property. Due to the possible coexistence between SE and CT infection in the same patient, characteristics of the polymicrobial biofilms from both organisms might be different from those of the biofilms of each organism. Then, the exploration on biofilms, from SE with or without CT, and an evaluation on l-cysteine (an antibiofilm against both bacteria and fungi) were performed. As such, Candida incubation in preformed SE biofilms (SE > CT) produced higher biofilms than the single- (SE or CT) or mixed-organism (SE + CT) biofilms as determined by crystal violet staining and fluorescent confocal images with z-stack thickness analysis. In parallel, SE > CT biofilms demonstrated higher expression of icaB and icaC than other groups at 20 and 24 h of incubation, suggesting an enhanced matrix polymerization and transportation, respectively. Although organism burdens (culture method) from single-microbial biofilms (SE or CT) were higher than multi-organism biofilms (SE + CT and SE > CT), macrophage cytokine responses (TNF-α and IL-6) against SE > CT biofilms were higher than those in other groups in parallel to the profound biofilms in SE > CT. Additionally, sepsis severity in mice with subcutaneously implanted SE > CT catheters was more severe than in other groups as indicated by mortality rate, fungemia, serum cytokines (TNF-α and IL-6), and kidney and liver injury. Although CT grows upon preformed SE-biofilm production, the biofilm structures interfered during CT morphogenesis leading to the frailty of biofilm structure and resulting in the prominent candidemia. However, l-cysteine incubation together with the organisms in catheters reduced biofilms, microbial burdens, macrophage responses, and sepsis severity. In conclusion, SE > CT biofilms prominently induced biofilm matrix, fungemia, macrophage responses, and sepsis severity, whereas the microbial burdens were lower than in the single-organism biofilms. All biofilms were attenuated by l-cysteine.

TLR2 signaling contributes to the angiogenesis of oxygen-induced retinopathy

PURPOSE

To evaluate the role of Toll-like receptor 2 (TLR2) signaling in retinal neovascularization in a mouse model of oxygen-induced retinopathy (OIR).

MATERIALS AND METHODS

The OIR model was established in C57BL/6J wild type (WT) mice and TLR2^-/- mice. Retinal neovascularization in the OIR model was measured by counting new vascular cell nuclei above the internal limiting membrane and analyzing flat-mounted retinas perfused with fluorescein dextran and immunostained with Griffonia Simplicifolia (GS) isolectin. The expression of TLR2 and VEGF in the retina was detected by immunofluorescence. Expression of TGF- β1, b-FGF, and IL-6 mRNA in the retina was measured by quantitative real-time PCR.

RESULTS

Compared to WT OIR mice, retinal neovascularization was attenuated in TLR2^-/- OIR mice. The co-expressions of TLR2 and VEGF were remarkably and consistently increased in WT OIR mice; however, there was no expression of TLR2 and a significant decrease in VEGF expression in TLR2^-/- OIR mice. These results suggest that TLR2 plays a central role in OIR model angiogenesis. Expression of TGF- β1, b-FGF, and IL-6 mRNA were reduced in the TLR2^-/- OIR mice, suggesting that the inflammatory response induced by TLR2 relates to angiogenesis.

CONCLUSION

TLR2 signaling in the retina is associated with neovascularization in mice. Inflammation contributes to the activation of angiogenesis and is partially mediated through the TLR2-VEGF retinal signaling pathway.

The staphylococcal exopolysaccharide PIA - Biosynthesis and role in biofilm formation, colonization, and infection

•

PIA is a key extracellular matrix component in staphylococci and other bacteria.

•

PIA is a cationic, partially deacetylated N-acetylglucosamine polymer.

•

PIA has a major role in bacterial biofilms and biofilm-associated infection.

Exopolysaccharide is a key part of the extracellular matrix that contributes to important mechanisms of bacterial pathogenicity, most notably biofilm formation and immune evasion. In the human pathogens Staphylococcus aureus and S. epidermidis, as well as in many other staphylococcal species, the only exopolysaccharide is polysaccharide intercellular adhesin (PIA), a cationic, partially deacetylated homopolymer of N-acetylglucosamine, whose biosynthetic machinery is encoded in the ica locus. PIA production is strongly dependent on environmental conditions and controlled by many regulatory systems. PIA contributes significantly to staphylococcal biofilm formation and immune evasion mechanisms, such as resistance to antimicrobial peptides and ingestion and killing by phagocytes, and presence of the ica genes is associated with infectivity. Due to its role in pathogenesis, PIA has raised considerable interest as a potential vaccine component or target.

Biofilm Produced In Vitro by Piscirickettsia salmonis Generates Differential Cytotoxicity Levels and Expression Patterns of Immune Genes in the Atlantic Salmon Cell Line SHK-1

Piscirickettsia salmonis is the causative agent of Piscirickettsiosis, an infectious disease with a high economic impact on the Chilean salmonid aquaculture industry. This bacterium produces biofilm as a potential resistance and persistence strategy against stressful environmental stimuli. However, the in vitro culture conditions that modulate biofilm formation as well as the effect of sessile bacteria on virulence and immune gene expression in host cells have not been described for P. salmonis. Therefore, this study aimed to analyze the biofilm formation by P. salmonis isolates under several NaCl and iron concentrations and to evaluate the virulence of planktonic and sessile bacteria, together with the immune gene expression induced by these bacterial conditions in an Atlantic salmon macrophage cell line. Our results showed that NaCl and Fe significantly increased biofilm production in the LF-89 type strain and EM-90-like isolates. Additionally, the planktonic EM-90 isolate and sessile LF-89 generated the highest virulence levels, associated with differential expression of il-1β, il-8, nf-κb, and iκb-α genes in SHK-1 cells. These results suggest that there is no single virulence pattern or gene expression profile induced by the planktonic or sessile condition of P. salmonis, which are dependent on each strain and bacterial condition used.

Hijacking of immune defences by biofilms: a multifront strategy

Biofilm formation by pathogens and opportunistic bacteria is the basis of persistent or recurrent infections. Up to 80% of bacterial infections in humans are associated with biofilms. Despite the efficiency of the evolved and complex human defence system against planktonic bacteria, biofilms are capable of subverting host defences. The immune system is not completely effective in opposing bacteria and preventing infection. Increasing attention is being focussed on the mechanisms enabling bacterial biofilms to skew the coordinate action of humoral and cell mediated responses. Knowledge of the interactions between biofilm bacteria and the immune system is critical to effectively address biofilm infections, which have multiplied over the years with the spread of biomaterials in medicine. In this article, the latest information on the interactions between bacterial biofilms and immune cells is examined and the areas where of information is still lacking are explored.

An underestimated pathogen: Staphylococcus epidermidis induces pro-inflammatory responses in human alveolar epithelial cells

OBJECTIVES

Conventionally regarded as a harmless skin commensal, Staphylococcus epidermidis accounts for the majority of neonatal late-onset sepsis and is shown to be associated with neonatal inflammatory morbidities, especially bronchopulmonary dysplasia. This study addressed the pro-inflammatory capacity of different S. epidermidis strains on human alveolar epithelial cells.

METHODS

A549 cell monolayers were stimulated by live bacteria of S. epidermidis RP62A strain (biofilm-positive) and ATCC 12228 strain (biofilm-negative) at a multiplicity of infection ratio of 10 for 24 h. LPS (100 ng/ml) and Pam3CSK4 (1 µg/ml) were used for comparisons. Cell viability was measured by MTT method. The mRNA and protein expression of inflammatory mediators and toll-like receptor (TLR)-2 were assessed using RT-PCR, immunoassays and immunofluorescence.

RESULTS

Both S. epidermidis strains induced expression of tumor necrosis factor (TNF)-α, IL-1β, interleukin (IL)-6, IL-8, monocyte chemoattractant protein (MCP)-1, interferon γ-induced protein 10 (IP-10) and intercellular adhesion molecule (ICAM)-1, but not IL-10. The stimulatory effect of RP62A exceeded that of LPS (p < 0.05). RP62A strain showed a trend towards higher induction of pro-inflammatory mediators than ATCC 12228 strain. The co-stimulation with RP62A strain decreased cell viability compared to control and TLR agonists (p < 0.05). RP62A but not ATCC 12228 stimulated mRNA and protein expression of TLR2.

CONCLUSIONS

S. epidermidis drives pro-inflammatory responses in lung epithelial cells in vitro. The pro-inflammatory capacity of S. epidermidis may differ between strains. Biofilm-positive S. epidermidis strain seems to induce more potent pulmonary pro-inflammation than biofilm-negative S. epidermidis strain.

Disease-associated genotypes of the commensal skin bacterium Staphylococcus epidermidis

Some of the most common infectious diseases are caused by bacteria that naturally colonise humans asymptomatically. Combating these opportunistic pathogens requires an understanding of the traits that differentiate infecting strains from harmless relatives. Staphylococcus epidermidis is carried asymptomatically on the skin and mucous membranes of virtually all humans but is a major cause of nosocomial infection associated with invasive procedures. Here we address the underlying evolutionary mechanisms of opportunistic pathogenicity by combining pangenome-wide association studies and laboratory microbiology to compare S. epidermidis from bloodstream and wound infections and asymptomatic carriage. We identify 61 genes containing infection-associated genetic elements (k-mers) that correlate with in vitro variation in known pathogenicity traits (biofilm formation, cell toxicity, interleukin-8 production, methicillin resistance). Horizontal gene transfer spreads these elements, allowing divergent clones to cause infection. Finally, Random Forest model prediction of disease status (carriage vs. infection) identifies pathogenicity elements in 415 S. epidermidis isolates with 80% accuracy, demonstrating the potential for identifying risk genotypes pre-operatively.

Beyond sepsis: Staphylococcus epidermidis is an underestimated but significant contributor to neonatal morbidity

Staphylococcus epidermidis accounts for the majority of cases of neonatal sepsis. Moreover, it has been demonstrated to be associated with neonatal morbidities, such as bronchopulmonary dysplasia (BPD), white matter injury (WMI), necrotizing enterocolitis (NEC) and retinopathy of prematurity (ROP), which affect short-term and long-term neonatal outcome. Imbalanced inflammation has been considered to be a major underlying mechanism of each entity. Conventionally regarded as a harmless commensal on human skin, S. epidermidis has received less attention than its more virulent relative Staphylococcus aureus. Particularities of neonatal innate immunity and nosocomial environmental factors, however, may contribute to the emergence of S. epidermidis as a significant nosocomial pathogen. Neonatal host response to S. epidermidis sepsis has not been fully elucidated. Evidence is emerging regarding the implication of S. epidermidis sepsis in the pathogenesis of neonatal inflammatory diseases. This review focuses on the interplay among S. epidermidis, neonatal innate immunity and inflammation-driven organ injury.

Novel anti-staphylococcal and anti-biofilm properties of two anti-malarial compounds: MMV665953 {1-(3-chloro-4-fluorophenyl)-3-(3,4-dichlorophenyl)urea} and MMV665807 {5-chloro-2-hydroxy-N-[3-(trifluoromethyl)phenyl]benzamide}

PURPOSE

The treatment of device-related infections is challenging and current anti-microbial compounds have poor anti-biofilm activity. We aimed to identify and characterize novel compounds effective in the eradication of Staphylococcus aureus biofilms.

METHODOLOGY

Two novel compounds, MMV665953 {1-(3-chloro-4-fluorophenyl)-3-(3,4-dichlorophenyl)urea} and MMV665807{5-chloro-2-hydroxy-N-[3-(trifluoromethyl)phenyl]benzamide}, effective in killing S. aureus biofilms, were identified by screening of the open access 'malaria box' chemical library. The minimum bactericidal concentrations, half-maximal inhibition concentration (IC50) values and minimal biofilm killing concentrations effective in the killing of biofilm were determined against meticillin-resistant S. aureus and meticillin-sensitive S. aureus. Fibrin-embedded biofilms were grown under in vivo-relevant conditions, and viability was measured using a resazurin-conversion assay and confocal microscopy. The potential for the development of resistance and cytotoxicity was also assessed.

RESULTS

MMV665953 and MMV665807 were bactericidal against S. aureus isolates. The IC50 against S. aureus biofilms was at 0.15-0.58 mg l-1 after 24 h treatment, whereas the concentration required to eradicate all tested biofilms was 4 mg l-1, making the compounds more bactericidal than conventional antibiotics. The cytotoxicity against human keratinocytes and primary endothelial cells was determined as IC50 7.47 and 0.18 mg l-1 for MMV665953, and as 1.895 and 0.076 mg l-1 for MMV665807. Neither compound was haemolytic nor caused platelet activation. MMV665953 and MMV665807 derivatives with reduced cytotoxicity exhibited a concomitant loss in anti-staphylococcal activity.

CONCLUSION

MMV665953 and MMV665807 are more bactericidal against S. aureus biofilms than currently used anti-staphylococcal antibiotics and represent a valuable structural basis for further investigation in the treatment of staphylococcal biofilm-related infections.

Host Response to Staphylococcus epidermidis Colonization and Infections

The majority of research in the Staphylococcus field has been dedicated to the understanding of Staphylococcus aureus infections. In contrast, there is limited information on infections by coagulase-negative Staphylococci (CoNS) and how the host responds to them. S. epidermidis, a member of the coagulase-negative Staphylococci, is an important commensal organism of the human skin and mucous membranes; and there is emerging evidence of its benefit for human health in fighting off harmful microorganisms. However, S. epidermidis can cause opportunistic infections, which include particularly biofilm-associated infections on indwelling medical devices. These often can disseminate into the bloodstream; and in fact, S. epidermidis is the most frequent cause of nosocomial sepsis. The increasing use of medical implants and the dramatic shift in the patient demographic population in recent years have contributed significantly to the rise of S. epidermidis infections. Furthermore, treatment has been complicated by the emergence of antibiotic-resistant strains. Today, S. epidermidis is a major nosocomial pathogen posing significant medical and economic burdens. In this review, we present the current understanding of mechanisms of host defense against the prototypical CoNS species S. epidermidis as a commensal of the skin and mucous membranes, and during biofilm-associated infection and sepsis.

Characteristics of resistance and virulence factors in different species of coagulase-negative staphylococci isolated from milk of healthy sheep and animals with subclinical mastitis

Coagulase-negative staphylococci (CNS) are among the main responsible agents for mastitis in sheep. Cure rates can be reduced due to several causes, such as those related to virulence factors presented by microorganisms. This study aims at characterizing the virulence and resistance factors to antimicrobial agents in different CNS species isolated from sheep milk. After collecting milk samples, the samples were analyzed and the CNS species were identified. After identification, the susceptibility-sensitivity profile was examined using the disk diffusion technique for 10 antimicrobial agents. The DNA was extracted to detect the presence of the mecA gene, biofilm (icaADBC, bap, and bhp) and toxin genes (sea, seb, sec, sed, tst, and luk-PV) by PCR. Samples carrying toxin genes had their expression assessed using the reverse-transcription PCR technique. The biofilm production was assessed using the adherence method on a polystyrene plate. One hundred twelve CNS samples were isolated, 53 (47.3%) from animals with subclinical mastitis and 59 (52.7%) from healthy animals. Drugs tested have shown to be efficient for most CNS samples. The largest resistance percentage of CNS was found for the penicillin (17.0%) and tetracycline (10.7%) and 4 samples carried the mecA gene. As for the biofilm genes, the icaADBC operon was found in 10 (8.9%) samples, the bap gene was found in 16 (14.3%), and the bhp gene was found in 3 (2.7%). In addition, 69 (61.6%) samples produced biofilm. The survey of toxin genes has shown that 70 (62.5%) samples showed some toxin-encoding gene. However, none of the samples has expressed any of the genes from those toxins studied.

Novel bioactive from Lactobacillus brevis DSM17250 to stimulate the growth of Staphylococcus epidermidis: a pilot study

Commensal skin microbiota plays an important role in both influencing the immune response of the skin and acting as a barrier against colonisation of potentially pathogenic microorganisms and overgrowth of opportunistic pathogens. Staphylococcus epidermidis is a key constituent of the normal microbiota on human skin. It balances the inflammatory response after skin injury and produces antimicrobial molecules that selectively inhibit skin pathogens. Here we describe Lactobacillus brevis DSM17250 that was identified among hundreds of Lactobacillus strains to exhibit an anti-inflammatory effect in human keratinocytes in vitro and specific stimulatory impact on the growth of S. epidermidis. The aqueous cell-free extract of L. brevis DSM17250 was used in an ointment formulation and tested in a randomized placebo-controlled double blinded human pilot study. Healthy volunteers with diagnosed dry skin were treated for four weeks. The study data shows that L. brevis DSM17250 extract induces re-colonisation of the skin by protective commensal microorganisms as judged from selective bacterial cultivation of surface-associated skin microorganism of the lower leg. Furthermore, the 4 week administration of the L. brevis DSM17250 extract significantly improved the transepidermal water loss value (TEWL), reduced the xerosis cutis symptoms and stinging. The data shows that daily application of L. brevis DSM17250 extract in a topical product significantly improves the microbial skin microbiota by promoting the growth of species which possess beneficial regulatory and protective properties such as S. epidermidis. Restoring the natural skin microbiota leads to significantly improved skin barrier function (as transepidermal water loss) and decrease of xeroderma (xerosis cutis) symptoms (as measured by dry skin area and severity index, DASI). We propose that improving and stabilizing the natural skin microbiota by specifically stimulating the growth of S. epidermidis is an important and novel concept to manage skin diseases associated with microbiota dysbiosis.

Poly-N-Acetylglucosamine Production by Staphylococcus epidermidis Cells Increases Their In Vivo Proinflammatory Effect

Poly-N-acetylglucosamine (PNAG) is a major component of the Staphylococcus epidermidis biofilm extracellular matrix. However, it is not yet clear how this polysaccharide impacts the host immune response and infection-associated pathology. Faster neutrophil recruitment and bacterial clearance were observed in mice challenged intraperitoneally with S. epidermidis biofilm cells of the PNAG-producing 9142 strain than in mice similarly challenged with the isogenic PNAG-defective M10 mutant. Moreover, intraperitoneal priming with 9142 cells exacerbated liver inflammatory pathology induced by a subsequent intravenous S. epidermidis challenge, compared to priming with M10 cells. The 9142-primed mice had elevated splenic CD4(+) T cells producing gamma interferon and interleukin-17A, indicating that PNAG promoted cell-mediated immunity. Curiously, despite having more marked liver tissue pathology, 9142-primed mice also had splenic T regulatory cells with greater suppressive activity than those of their M10-primed counterparts. By showing that PNAG production by S. epidermidis biofilm cells exacerbates host inflammatory pathology, these results together suggest that this polysaccharide contributes to the clinical features associated with biofilm-derived infections.

Effects of polysaccharide intercellular adhesin (PIA) in an ex vivo model of whole blood killing and in prosthetic joint infection (PJI): A role for C5a

BACKGROUND

A major complication of using medical devices is the development of biofilm-associated infection caused by Staphylococcus epidermidis where polysaccharide intercellular adhesin (PIA) is a major mechanism of biofilm accumulation. PIA affects innate and humoral immunity in isolated cells and animal models. Few studies have examined these effects in prosthetic joint infection (PJI).

METHODS

This study used ex vivo whole blood modelling in controls together with matched-serum and staphylococcal isolates from patients with PJI.

RESULTS

Whole blood killing of PIA positive S. epidermidis and its isogenic negative mutant was identical. Differences were unmasked in immunosuppressed whole blood pre-treated with dexamethasone where PIA positive bacteria showed a more resistant phenotype. PIA expression was identified in three unique patterns associated with bacteria and leukocytes, implicating a soluble form of PIA. Purified PIA reduced whole blood killing while increasing C5a levels. In clinically relevant staphylococcal isolates and serum samples from PJI patients; firstly complement C5a was increased 3-fold compared to controls; secondly, the C5a levels were significantly higher in serum from PJI patients whose isolates preferentially formed PIA-associated biofilms.

CONCLUSIONS

These data demonstrate for the first time that the biological effects of PIA are mediated through C5a in patients with PJI.

Bacterial skin commensals and their role as host guardians

Recent years' investigations of the co-evolution and functional integration of the human body and its commensal microbiota have disclosed that the microbiome has a major impact on physiological functions including protection against infections, reaction patterns in the immune system, and disposition for inflammation-mediated diseases. Two ubiquitous members of the skin microbiota, the Gram-positive bacteria Staphylococcus epidermidis and Propionibacterium acnes, are predominant on human epithelia and in sebaceous follicles, respectively. Their successful colonisation is a result of a commensal or even mutualistic lifestyle, favouring traits conferring persistency over aggressive host-damaging properties. Some bacterial properties suggest an alliance with the host to keep transient, potential pathogens at bay, such as the ability of S. epidermidis to produce antimicrobials, or the production of short-chain fatty acids by P. acnes. These features can function together with host-derived components of the innate host defence to establish and maintain the composition of a health-associated skin microbiota. However, depending largely on the host status, the relationship between the human host and S. epidermidis/P. acnes can also have parasitic features. Both microorganisms are frequently isolated from opportunistic infections. S. epidermidis is a causative agent of hospital-acquired infections, mostly associated with the use of medical devices. P. acnes is suspected to be of major importance in the pathogenesis of acne and also in a number of other opportunistic infections. In this review we will present bacterial factors and traits of these two key members of our skin microbiota and discuss how they contribute to mutualistic and parasitic properties. The elucidation of their roles in health-promoting or disease-causing processes could lead to new prophylactic and therapeutic strategies against skin disorders and other S. epidermidis/P. acnes-associated diseases, and increase our understanding of the delicate interplay of the skin microbiota with the human host.

Ventricular shunt infections: immunopathogenesis and clinical management

Ventricular shunts are the most common neurosurgical procedure performed in the United States. This hydrocephalus treatment is often complicated by infection of the device with biofilm-forming bacteria. In this review, we discuss the pathogenesis of shunt infection, as well as the implications of the biofilm formation on treatment and prevention of these infections. Many questions remain, including the contribution of glia and the impact of inflammation on developmental outcomes following infection. Immune responses within the CNS must be carefully regulated to contain infection while minimizing bystander damage; further study is needed to design optimal treatment strategies for these patients.

The diagnostic value of cytokine and nitric oxide concentrations in cerebrospinal fluid for the differential diagnosis of meningitis

PURPOSE

In several cases of meningitis routinely used diagnostic procedures are unable to identify the cause of this disease. The objective of the present study was to determine whether proinflammatory cytokine (tumour necrosis factor (TNF-α), interleukin-1β (IL-1β), interleukin-8 (IL-8)) and nitric oxide (NO) concentrations in the CSF are useful markers for the differential diagnosis of meningitis.

MATERIAL AND METHODS

Sixty-seven patients (42 patients with bacterial meningitis and 25 patients with viral meningitis) were included in the present study. In the investigated group, the TNF-α, IL-1β and IL-8 concentrations in the CSF samples collected on the day of admission were assessed. Furthermore, the NO concentrations were assessed in 23 patients.

RESULTS

The results revealed that the measurement of proinflammatory cytokines in CSF can aid in a differential diagnosis. In particular, a high concentration of TNF-α may be a sensitive and specific marker of a bacterial aetiology of the neuroinfection. In the present study, TNF-α concentrations greater than 75.8 pg/ml differentiated between bacterial and viral meningitis with 100% sensitivity and specificity. The NO concentration in the CSF was also significantly greater in patients with bacterial meningitis than in those with viral meningitis.

CONCLUSIONS

The assessment of TNF-α, IL-1β and IL-8 concentrations in the CSF is useful in the differential diagnosis of neuroinfection. Because many factors may influence NO production in the central nervous system (CNS), it is not clear whether NO values can be used for the differential diagnosis of meningitis, and further studies are required.

Deciphering mechanisms of staphylococcal biofilm evasion of host immunity

Biofilms are adherent communities of bacteria contained within a complex matrix. Although host immune responses to planktonic staphylococcal species have been relatively well-characterized, less is known regarding immunity to staphylococcal biofilms and how they modulate anti-bacterial effector mechanisms when organized in this protective milieu. Previously, staphylococcal biofilms were thought to escape immune recognition on the basis of their chronic and indolent nature. Instead, we have proposed that staphylococcal biofilms skew the host immune response away from a proinflammatory bactericidal phenotype toward an anti-inflammatory, pro-fibrotic response that favors bacterial persistence. This possibility is supported by recent studies from our laboratory using a mouse model of catheter-associated biofilm infection, where S. aureus biofilms led to the accumulation of alternatively activated M2 macrophages that exhibit anti-inflammatory and pro-fibrotic properties. In addition, relatively few neutrophils were recruited into S. aureus biofilms, representing another mechanism that deviates from planktonic infections. However, it is important to recognize the diversity of biofilm infections, in that studies by others have demonstrated the induction of distinct immune responses during staphylococcal biofilm growth in other models, suggesting influences from the local tissue microenvironment. This review will discuss the immune defenses that staphylococcal biofilms evade as well as conceptual issues that remain to be resolved. An improved understanding of why the host immune response is unable to clear biofilm infections could lead to targeted therapies to reverse these defects and expedite biofilm clearance.

Toll-like receptors (TLRs) in innate immune defense against Staphylococcus aureus

Toll-like receptors (TLRs) are the most important class of innate pattern recognition receptors (PRRs) by which host immune and non-immune cells are able to recognize pathogen-associated molecular patterns (PAMPs). Most mammalian species have 10 to 15 types of TLRs. TLRs are believed to function as homo- or hetero-dimers. TLR2, which plays a crucial role in recognizing PAMPs from Staphylococcus aureus, forms heterodimers with TLR1 or TLR6 and each dimer has a different ligand specificity. Staphylococcal lipoproteins, Panton-Valentine toxin and Phenol Soluble Modulins have been identified as potent TLR2 ligands. Conversely, the ligand function attributed to peptidoglycan and LTA remains controversial. TLR2 uses a MyD88-dependent signaling pathway that results in NF-kB translocation into the nucleus and activation of the expression of pro-inflammatory cytokine genes. Recognition rouses both an inflammatory response, culminating in the phagocytosis of bacteria, and an adaptive immune response, with the presentation of resulting bacterial compounds to T cells. Here, recent advances on the recognition of S. aureus by TLRs are presented and discussed, as well as the new therapeutic opportunities deriving from this new knowledge.

Bacterial adhesion, intracellular survival and cytokine induction upon stimulation of mononuclear cells with planktonic or biofilm phase Staphylococcus epidermidis

Staphylococcus epidermidis is a leading cause of hospital-acquired and biofilm-associated infections. Interactions of peripheral blood mononuclear cells (PBMCs) and monocyte-derived macrophages with planktonic or biofilm phase S. epidermidis cells were studied. Biofilm phase bacteria exhibited higher attachment, as well as, a 10-fold higher intracellular survival in monocyte-derived macrophages than their planktonic counterparts. Stimulation of PBMCs and monocyte-derived macrophages was performed with live or formalin-fixed bacterial cells. Supernatant concentration of selected cytokines was measured by Luminex(®) xMAP(™) technology at different time points. As compared to planktonic phase, biofilm phase bacteria elicited lower amounts of proinflammatory cytokines and Th1 response cytokines, such as TNFα, IL-12p40, IL-12p70 and IFN-γ, whereas they enhanced production of IL-8, GM-CSF and IL-13. This phenomenon was independent of formalin pretreatment. Taken together, these results may contribute to interpretation of observed silent course of biofilm-associated infections.

Staphylococcus epidermidis polysaccharide intercellular adhesin activates complement

Staphylococcus epidermidis is a frequent cause of nosocomial infections. The central virulence factor of S. epidermidis is biofilm formation. Polysaccharide intercellular adhesin (PIA) constitutes the major biofilm matrix-component. PIA and biofilm have been implicated in S. epidermidis evasion of host immune defence. We examined the effects of S. epidermidis PIA on the inflammatory response with focus on complement activation. We used a human whole-blood ex vivo model of infection and compared the effects of a PIA-positive S. epidermidis strain (SE1457) and its PIA-negative isogenic mutant (M10). The independent effect of purified PIA on complement activation was investigated. In glucose-rich media, the mutant formed a proteinacious DNA-rich biofilm, whereas SE1457 formed a thick PIA-biofilm. In biofilm growth, SE1457 induced a stronger activation of the complement system compared with M10. We verified that purified PIA was independently responsible for a strong activation of the complement system. In contrast, M10 induced higher granulocyte activation by expression of CD11b and higher secretion of cytokines. We conclude that PIA has potent pro-inflammatory properties by activating the complement system. However, in a complex balance of the immune response, the decreased activation of granulocytes and cytokines by a PIA biofilm may limit host eradication of S. epidermidis.

Molecular basis of Staphylococcus epidermidis infections

Staphylococcus epidermidis is the most important member of the coagulase-negative staphylococci and one of the most abundant colonizers of human skin. While for a long time regarded as innocuous, it has been identified as the most frequent cause of device-related infections occurring in the hospital setting and is therefore now recognized as an important opportunistic pathogen. S. epidermidis produces a series of molecules that provide protection from host defenses. Specifically, many proteins and exopolymers, such as the exopolysaccharide PIA, contribute to biofilm formation and inhibit phagocytosis and the activity of human antimicrobial peptides. Furthermore, recent research has identified a family of pro-inflammatory peptides in S. epidermidis, the phenol-soluble modulins (PSMs), which have multiple functions in immune evasion and biofilm development, and may be cytolytic. However, in accordance with the relatively benign relationship that S. epidermidis has with its host, production of aggressive members of the PSM family is kept at a low level. Interestingly, in contrast to S. aureus with its large arsenal of toxins developed for causing infection in the human host, most if not all "virulence factors" of S. epidermidis appear to have original functions in the commensal lifestyle of this bacterium.

MyD88 is pivotal for immune recognition of Citrobacter koseri and astrocyte activation during CNS infection

Citrobacter koseri (C. koseri) is a Gram-negative bacterium that can cause a highly aggressive form of neonatal meningitis, which often progresses to establish multi-focal brain abscesses. The roles of Toll-like receptor 4 (TLR4) and its signaling adaptor MyD88 during CNS C. koseri infection have not yet been examined, which is important since recent evidence indicates that innate immune responses are tailored towards specific pathogen classes. Here TLR4 WT (C3H/FeJ) and TLR4 mutant (C3H/HeJ) mice as well as MyD88 KO animals were infected intracerebrally with live C. koseri, resulting in meningitis and ventriculitis with accompanying brain abscess formation. MyD88 KO mice were exquisitely sensitive to C. koseri, demonstrating enhanced mortality rates and significantly elevated bacterial burdens compared to WT animals. Interestingly, although early proinflammatory mediator release (i.e. 12 h) was MyD88-dependent, a role for MyD88-independent signaling was evident at 24 h, revealing a compensatory response to CNS C. koseri infection. In contrast, TLR4 did not significantly impact bacterial burdens or proinflammatory mediator production in response to C. koseri. Similar findings were obtained with primary astrocytes, where MyD88-dependent pathways were essential for chemokine release in response to intact C. koseri, whereas TLR4 was dispensable; implicating the involvement of alternative TLRs since highly enriched astrocytes did not produce IL-1 upon bacterial exposure, which also signals via MyD88. Collectively, these findings demonstrate the importance of MyD88-dependent mechanisms in eliciting maximal proinflammatory responses, astrocyte activation, and bacterial containment during CNS C. koseri infection, as well as a late-phase MyD88-independent signaling pathway for cytokine/chemokine production.

Staphylococcus epidermidis uses distinct mechanisms of biofilm formation to interfere with phagocytosis and activation of mouse macrophage-like cells 774A.1

Assembly of adherent biofilms is the key mechanism involved in Staphylococcus epidermidis virulence during device-associated infections. Aside from polysaccharide intercellular adhesin (PIA), the accumulation-associated protein Aap and the extracellular matrix binding protein Embp act as intercellular adhesins, mediating S. epidermidis cell aggregation and biofilm accumulation. The aim of this study was to investigate structural features of PIA-, Aap-, and Embp-mediated S. epidermidis biofilms in more detail and to evaluate their specific contributions to biofilm-related S. epidermidis immune escape. PIA-, Embp-, and Aap-mediated biofilms exhibited substantial morphological differences. Basically, PIA synthesis induced formation of macroscopically visible, rough cell clusters, whereas Aap- and Embp-dependent biofilms preferentially displayed a smooth layer of aggregated bacteria. On the microscopic level, PIA was found to form a string-like organized extracellular matrix connecting the bacteria, while Embp produced small deposits of intercellular matrix and Aap was strictly localized to the bacterial surface. Despite marked differences, S. epidermidis strains using PIA, Aap, or Embp for biofilm formation were protected from uptake by J774A.1 macrophages, with similarly efficiencies. In addition, compared to biofilm-negative S. epidermidis strains, isogenic biofilm-forming S. epidermidis induced only a diminished inflammatory J774A.1 macrophage response, leading to significantly (88.2 to 88.7%) reduced NF-κB activation and 68.8 to 83% reduced interleukin-1β (IL-1β) production. Mechanical biofilm dispersal partially restored induction of NF-κB activation, although bacterial cell surfaces remained decorated with the respective intercellular adhesins. Our results demonstrate that distinct S. epidermidis biofilm morphotypes are similarly effective at protecting S. epidermidis from phagocytic uptake and at counteracting macrophage activation, providing novel insights into mechanisms that could contribute to the chronic and persistent course of biofilm-related S. epidermidis foreign material infections.

Rifampicin enhances activity of daptomycin and vancomycin against both a polysaccharide intercellular adhesin (PIA)-dependent and -independent Staphylococcus epidermidis biofilm

Objectives and methods

This study addressed the efficacy of daptomycin, vancomycin, rifampicin, daptomycin/rifampicin and vancomycin/rifampicin against a polysaccharide intercellular adhesin (PIA)-dependent and -independent Staphylococcus epidermidis biofilm using flow cell and guinea pig tissue cage models.

Results

The flow cell model of both PIA-dependent and -independent biofilms demonstrated that the viable cell count after treatment with daptomycin/rifampicin was significantly lower (P < 0.05) than after treatment with vancomycin, vancomycin/rifampicin, daptomycin or rifampicin alone. To validate these observations, a guinea pig tissue cage model was used. The results demonstrated that the addition of rifampicin to daptomycin or vancomycin sterilized 5/6 tissues cages colonized with S. epidermidis 1457 (PIA producing). Similar results were noted with S. epidermidis 1457 icaADBC::dhfr (non-PIA producing), where daptomycin/rifampicin and vancomycin/rifampicin sterilized 5/6 and 6/6 tissue cages, respectively. There was no statistical difference in comparison with the no-treatment control when both 1457 and 1457 icaADBC::dhfr were treated with vancomycin and daptomycin alone. Furthermore, treatment with rifampicin alone sterilized 5/6 and 3/6 1457 and 1457 icaADBC::dhfr tissue cages, respectively.

Conclusions

Interpretation of these data suggests that rifampicin is highly active against S. epidermidis biofilms and both vancomycin and daptomycin are effective at reducing the subpopulation of bacteria that develop rifampicin resistance.

Understanding the significance of Staphylococcus epidermidis bacteremia in babies and children

PURPOSE OF REVIEW

This article provides an overview of Staphylococcus epidermidis bacteremia/sepsis and coagulase-negative staphylococci (CoNS) infections in neonates and children.

RECENT FINDINGS

The incidence of S. epidermidis and CoNS sepsis in neonates is still very high and preventing and treating disease remains difficult. There has been recent progress in understanding the pathogenesis of S. epidermidis infection, interaction of S. epidermidis with host defenses, and risk factors for the development of S. epidermidis disease. For example, we have gained more insight into the development of biofilm-associated catheter infections, which are responsible for recurrent CoNS infections in hospitalized premature neonates and are especially difficult to treat owing to intrinsic resistance of biofilms to antibiotics.

SUMMARY

Biofilm-associated catheter infections by S. epidermidis occur frequently in neonates and adults. S. epidermidis bloodstream infections are particularly problematic in neonates. Prophylaxis in the form of eradicating colonizing S. epidermidis may be a double-edged sword, as S. epidermidis colonization may be beneficial to the host. New drugs may arise from a better understanding of S. epidermidis virulence and analysis of risk factors may help identify neonates susceptible to bacterial sepsis. However, reducing morbidity should always begin by increasing hygiene in hospital settings to reduce the introduction of potentially harmful opportunistic pathogens such as S. epidermidis on indwelling medical devices or during surgery.

TLR2 mediates recognition of live Staphylococcus epidermidis and clearance of bacteremia

Background

Staphylococcus epidermidis (SE) is a nosocomial pathogen that causes catheter-associated bacteremia in the immunocompromised, including those at the extremes of age, motivating study of host clearance mechanisms. SE-derived soluble components engage TLR2; but additional signaling pathways have also been implicated, and TLR2 can play complex, at times detrimental, roles in host defense against other Staphylococcal spp. The role of TLR2 in responses of primary blood leukocytes to live SE and in clearance of SE bacteremia, the most common clinical manifestation of SE infection, is unknown.

Methodology/Principal Findings

We studied TLR2-mediated recognition of live clinical SE strain 1457 employing TLR2-transfected cells, neutralizing anti-TLR antibodies and TLR2-deficient mice. TLR2 mediated SE-induced cytokine production in human embryonic kidney cells, human whole blood and murine primary macrophages, in part via recognition of a soluble TLR2 agonist. After i.v. challenge with SE, early (1 h) cytokine/chemokine production and subsequent clearance of bacteremia (24–48 h) were markedly impaired in TLR2-deficient mice.

Conclusions/Significance

TLR2 mediates recognition of live SE and clearance of SE bacteremia in vivo.

Alcohol-induced interactive phosphorylation of Src and toll-like receptor regulates the secretion of inflammatory mediators by human astrocytes

Secretion of pro-inflammatory molecules by astrocytes after alcohol treatment was shown to be associated with neuroinflammation. We hypothesized that activation of cytosolic phospholipase A2 (cPLA2) and cyclooxygenase (COX-2) by ethanol in astrocytes enhanced the secretion of inflammatory agents via the interactive tyrosine phosphorylation of toll-like receptor 4 (TLR4) and Src kinase. To test this hypothesis, we treated primary human astrocytes with 20 mM ethanol for 48 h at 37°C. Ethanol exposure elevated cytochrome P450-2E1 activity, reactive oxygen species levels, and secretion of prostaglandin E2 (PGE2) in these cells. Secretion of PGE2 was associated with induction of cPLA2 activity and protein content as well as COX-2 protein level in a Src phosphorylation-dependent manner that occurred by enhanced transcription. Immunoprecipitation and Western blot analyses indicated that the interactive tyrosine phosphorylation of TLR4-Src complex at the cell membrane triggered the activation of cPLA2 and COX-2 in the cytoplasm through a Src signaling intermediate. Inhibition of ethanol metabolism, blockage of Src activity, or inactivation of TLR4 prevented the activation of cPLA2 and COX-2 as well as diminished PGE2 production, suggesting that interactive phosphorylation of TLR4-Src regulated the pro-inflammatory response in astrocytes. Experiments with small interfering RNA knockdown of TLR4 in human astrocytes confirmed that silencing expression also abolished the interactive phosphorylation of both TLR4 and Src in the presence of ethanol.

Inhibition of Toll-like receptor 2-mediated interleukin-8 production in Cystic Fibrosis airway epithelial cells via the alpha7-nicotinic acetylcholine receptor

Cystic Fibrosis (CF) is an inherited disorder characterised by chronic inflammation of the airways. The lung manifestations of CF include colonization with Pseudomonas aeruginosa and Staphylococcus aureus leading to neutrophil-dominated airway inflammation and tissue damage. Inflammation in the CF lung is initiated by microbial components which activate the innate immune response via Toll-like receptors (TLRs), increasing airway epithelial cell production of proinflammatory mediators such as the neutrophil chemokine interleukin-8 (IL-8). Thus modulation of TLR function represents a therapeutic approach for CF. Nicotine is a naturally occurring plant alkaloid. Although it is negatively associated with cigarette smoking and cardiovascular damage, nicotine also has anti-inflammatory properties. Here we investigate the inhibitory capacity of nicotine against TLR2- and TLR4-induced IL-8 production by CFTE29o- airway epithelial cells, determine the role of α7-nAChR (nicotinic acetylcholine receptor) in these events, and provide data to support the potential use of safe nicotine analogues as anti-inflammatories for CF.

Staphylococcus epidermidis--the 'accidental' pathogen

Although nosocomial infections by Staphylococcus epidermidis have gained much attention, this skin-colonizing bacterium has apparently evolved not to cause disease, but to maintain the commonly benign relationship with its host. Accordingly, S. epidermidis does not produce aggressive virulence determinants. Rather, factors that normally sustain the commensal lifestyle of S. epidermidis seem to give rise to additional benefits during infection. Furthermore, we are beginning to comprehend the roles of S. epidermidis in balancing the epithelial microflora and serving as a reservoir of resistance genes. In this Review, I discuss the molecular basis of the commensal and infectious lifestyles of S. epidermidis.