Staphylococcus aureus induces caspase-independent cell death in human peritoneal mesothelial cells

Rescue plan for CAPD peritonitis: Using ultrasonography as a guide on when to remove the catheter

INTRODUCTION

Ultrasound has been found to facilitate early identification of peritonitis in patients undergoing continuous ambulatory peritoneal dialysis (CAPD).

METHODS

A retrospective analysis was carried out to evaluate the effectiveness of ultrasonography-guided removal of the Tenckhoff catheter in reducing complications like a shift to hemodialysis or death in CAPD patients.

RESULTS

The "peritonitis rescue plan" supported timely decision-making for the removal of the infected catheter and resulted in a lower peritonitis episode per patient per month ratio (from 1:36 to 1:122) in 2021, a lower death rate (from 19% to 6.6%) and lower incidences of shifts to hemodialysis (from 2%-9% to 0%) as compared to that before the implementation of the plan in 2019.

CONCLUSION

The implementation of the "peritonitis rescue plan" and the removal of the infected catheter within 3 days of peritonitis being detected was successful in improving the standard of care for patients undergoing CAPD.

The Gut-Peritoneum Axis in Peritoneal Dialysis and Peritoneal Fibrosis

Peritoneal fibrosis is an important cause of peritoneal dialysis (PD) discontinuation worldwide and is associated with high morbidity and mortality rate. Although the era of metagenomics has provided new insights into the interactions between the gut microbiota and fibrosis in various organs and tissues, its role in peritoneal fibrosis has rarely been discussed. This review provides a scientific rationale and points out the potential role of gut microbiota in peritoneal fibrosis. In addition, the interaction between the gut, circulatory, and peritoneal microbiota is highlighted, with an emphasis on the relationship to PD outcomes. More research is needed to elucidate the mechanisms underlying the role of gut microbiota in peritoneal fibrosis and potentially unveil new target options for the management of PD technique failure.

Metastatic Voyage of Ovarian Cancer Cells in Ascites with the Assistance of Various Cellular Components

Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy and has a unique metastatic route using ascites, known as the transcoelomic root. However, studies on ascites and contained cellular components have not yet been sufficiently clarified. In this review, we focus on the significance of accumulating ascites, contained EOC cells in the form of spheroids, and interaction with non-malignant host cells. To become resistant against anoikis, EOC cells form spheroids in ascites, where epithelial-to-mesenchymal transition stimulated by transforming growth factor-β can be a key pathway. As spheroids form, EOC cells are also gaining the ability to attach and invade the peritoneum to induce intraperitoneal metastasis, as well as resistance to conventional chemotherapy. Recently, accumulating evidence suggests that EOC spheroids in ascites are composed of not only cancer cells, but also non-malignant cells existing with higher abundance than EOC cells in ascites, including macrophages, mesothelial cells, and lymphocytes. Moreover, hetero-cellular spheroids are demonstrated to form more aggregated spheroids and have higher adhesion ability for the mesothelial layer. To improve the poor prognosis, we need to elucidate the mechanisms of spheroid formation and interactions with non-malignant cells in ascites that are a unique tumor microenvironment for EOC.

Gut microbial metabolite TMAO increases peritoneal inflammation and peritonitis risk in peritoneal dialysis patients

Trimethylamine-N-oxide (TMAO), a gut microbiota-produced metabolite, is accumulated in chronic kidney disease (CKD) patients. It is well known to contribute to CKD-related cardiovascular complications. However, the effect of TMAO on peritoneal dialysis (PD)-related peritonitis remains largely unknown. Here, we demonstrate that serum concentrations of TMAO were positively correlated with C-reactive protein levels, and the appearance rate of dialysate IL-6 and PAI-1, in PD patients. During the follow-up period of 28.3 ± 8.0 months, patients with higher TMAO levels (≥50 μM) had a higher risk of new-onset peritonitis (HR, 3.60; 95%CI, 1.18-10.99; P=0.025) after adjusting for sex, age, diabetes, PD duration, BUN, rGFR, C-reactive protein, BMI and β2-M. In CKD rat models, TMAO significantly promoted peritoneal dialysate-induced inflammatory cell infiltration, inflammatory cytokines production in the peritoneum. In vitro study revealed that TMAO directly induced primary peritoneal mesothelial cell necrosis, together with increased production of pro-inflammatory cytokines including CCL2, TNF-α, IL-6, and IL-1β. In addition, TMAO significantly increased TNF-α-induced P-selectin production in mesothelial cells, as well as high glucose-induced TNF-α and CCL2 expression in endothelial cells. In conclusion, our data demonstrate that higher levels of TMAO exacerbate peritoneal inflammation and might be a risk factor of incidence of peritonitis in PD patients.

Pleiotropic Effects of Statins: New Therapeutic Approaches to Chronic, Recurrent Infection by Staphylococcus aureus

An emergent approach to bacterial infection is the use of host rather than bacterial-directed strategies. This approach has the potential to improve efficacy in especially challenging infection settings, including chronic, recurrent infection due to intracellular pathogens. For nearly two decades, the pleiotropic effects of statin drugs have been examined for therapeutic usefulness beyond the treatment of hypercholesterolemia. Interest originated after retrospective studies reported decreases in the risk of death due to bacteremia or sepsis for those on a statin regimen. Although subsequent clinical trials have yielded mixed results and earlier findings have been questioned for biased study design, in vitro and in vivo studies have provided clear evidence of protective mechanisms that include immunomodulatory effects and the inhibition of host cell invasion. Ultimately, the benefits of statins in an infection setting appear to require attention to the underlying host response and to the timing of the dosage. From this examination of statin efficacy, additional novel host-directed strategies may produce adjunctive therapeutic approaches for the treatment of infection where traditional antimicrobial therapy continues to yield poor outcomes. This review focuses on the opportunistic pathogen, Staphylococcus aureus, as a proof of principle in examining the promise and limitations of statins in recalcitrant infection.

Intracellular Staphylococcus aureus employs the cysteine protease staphopain A to induce host cell death in epithelial cells

Staphylococcus aureus is a major human pathogen, which can invade and survive in non-professional and professional phagocytes. Uptake by host cells is thought to contribute to pathogenicity and persistence of the bacterium. Upon internalization by epithelial cells, cytotoxic S. aureus strains can escape from the phagosome, replicate in the cytosol and induce host cell death. Here, we identified a staphylococcal cysteine protease to induce cell death after translocation of intracellular S. aureus into the host cell cytoplasm. We demonstrated that loss of staphopain A function leads to delayed onset of host cell death and prolonged intracellular replication of S. aureus in epithelial cells. Overexpression of staphopain A in a non-cytotoxic strain facilitated intracellular killing of the host cell even in the absence of detectable intracellular replication. Moreover, staphopain A contributed to efficient colonization of the lung in a mouse pneumonia model. In phagocytic cells, where intracellular S. aureus is exclusively localized in the phagosome, staphopain A did not contribute to cytotoxicity. Our study suggests that staphopain A is utilized by S. aureus to exit the epithelial host cell and thus contributes to tissue destruction and dissemination of infection.

Staphylococcus aureus is an antibiotic-resistant pathogen that emerges in hospital and community settings and can cause a variety of diseases ranging from skin abscesses to lung inflammation and blood poisoning. The bacterium can asymptomatically colonize the upper respiratory tract and skin of humans and take advantage of opportune conditions, like immunodeficiency or breached barriers, to cause infection. Although S. aureus was not regarded as intracellular bacterium, it can be internalized by human cells and subsequently exit the host cells by induction of cell death, which is considered to cause tissue destruction and spread of infection. The bacterial virulence factors and underlying molecular mechanisms involved in the intracellular lifestyle of S. aureus remain largely unknown. We identified a bacterial cysteine protease to contribute to host cell death of epithelial cells mediated by intracellular S. aureus. Staphopain A induced killing of the host cell after translocation of the pathogen into the cell cytosol, while bacterial proliferation was not required. Further, the protease enhanced survival of the pathogen during lung infection. These findings reveal a novel, intracellular role for the bacterial protease staphopain A.

Staphylococcus aureus Toxins: Promoter or Handicap during Infection?

Staphylococcus aureus is an opportunistic and versatile pathogen that can cause several diseases, which range from acute and destructive, to chronic and difficult-to-treat infections [...].

Manipulation of Autophagy and Apoptosis Facilitates Intracellular Survival of Staphylococcus aureus in Human Neutrophils

Polymorphonuclear neutrophils (PMN) are critical for first line innate immune defence against Staphylococcus aureus. Mature circulating PMN maintain a short half-life ending in constitutive apoptotic cell death. This makes them unlikely candidates as a bacterial intracellular niche. However, there is significant evidence to suggest that S. aureus can survive intracellularly within PMN and this contributes to persistence and dissemination during infection. The precise mechanism by which S. aureus parasitizes these cells remains to be established. Herein we propose a novel mechanism by which S. aureus subverts both autophagy and apoptosis in PMN in order to maintain an intracellular survival niche during infection. Intracellular survival of S. aureus within primary human PMN was associated with an accumulation of the autophagic flux markers LC3-II and p62, while inhibition of the autophagy pathway led to a significant reduction in intracellular survival of bacteria. This intracellular survival of S. aureus was coupled with a delay in neutrophil apoptosis as well as increased expression of several anti-apoptotic factors. Importantly, blocking autophagy in infected PMN partially restored levels of apoptosis to that of uninfected PMN, suggesting a connection between the autophagic and apoptotic pathways during intracellular survival. These results provide a novel mechanism for S. aureus intracellular survival and suggest that S. aureus may be subverting crosstalk between the autophagic and apoptosis pathways in order to maintain an intracellular niche within human PMN.

Intracellular Environment and agr System Affect Colony Size Heterogeneity of Staphylococcus aureus

Staphylococcus aureus causes chronic and relapsing infections, which may be difficult to treat. So-called small colony variants (SCVs) have been associated with chronic infections and their occurrence has been shown to increase under antibiotic pressure, low pH and intracellular localization. In clinics, S. aureus isolated from invasive infections often show a dysfunction in the accessory gene regulator (agr), a major virulence regulatory system in S. aureus. To assess whether intracellular environment and agr function influence SCV formation, an infection model was established using lung epithelial cells and skin fibroblasts. This allowed analyzing intracellular survival and localization of a panel of S. aureus wild type strains and their isogenic agr knock out mutants as well as a natural dysfunctional agr strain by confocal laser scanning microscopy (CLSM). Furthermore, bacterial colonies were quantified after 1, 3, and 5 days of intracellular survival by time-lapse analysis to determine kinetics of colony appearance and SCV formation. Here, we show that S. aureus strains with an agr knock out predominantly resided in a neutral environment, whereas wild type strains and an agr complemented strain resided in an acidic environment. S. aureus agr mutants derived from an intracellular environment showed a higher percentage of SCVs as compared to their corresponding wild type strains. Neutralizing acidic phagolysosomes with chloroquine resulted in a significant reduction of SCVs in S. aureus wild type strain 6850, but not in its agr mutant indicating a pH dependent formation of SCVs in the wild type strain. The in-depth understanding of the interplay between intracellular persistence, agr function and pH should help to identify new therapeutic options facilitating the treatment of chronic S. aureus infections in the future.

Isolating Crucial Steps in Induction of Infective Endocarditis With Preclinical Modeling of Host Pathogen Interaction

Animal models of Staphylococcus aureus infective endocarditis (IE), especially in rodents, are commonly used to investigate the underlying pathogenesis, disease progression, potential diagnostic approaches, and therapeutic treatment. All these models are based on surgical interventions, and imply valve trauma by placing a polyurethane catheter at the aortic root. While the influence of endothelial damage and inflammation on the induction of IE has been studied intensively, the role of the catheter, as permanent source of bacteremia, and the interplay with bacterial virulence factors during the formation of IE is poorly understood. In our study, we aimed at identifying which set of preconditions is required for induction and formation of IE: (1) tissue injury, (2) permanent presence of bacteria, and (3) presence of the full bacterial repertoire of adhesion proteins. We investigated the manifestation of the disease in different modifications of the animal model, considering different degrees of endothelial damage and the presence or absence of the catheter. In four infection models the induction of IE was assessed by using two bacterial strains with different expression patterns of virulence factors – S. aureus 6850 and Newman. In vivo magnetic resonance imaging showed conspicuous morphological structures on the aortic valves, when an endothelial damage and a continuous bacterial source were present simultaneously. Cellular and inflammatory pathophysiology were characterized additionally by histology, real-time quantitative polymerase chain reaction analysis, and bacterial counts, revealing strain-specific pathogenesis and manifestation of IE, crucially influenced by bacterial adherence and toxicity. The severity of IE was dependent on the degree of endothelial irritation. However, even severe endothelial damage in the absence of a permanent bacterial source resulted in reduced valve infection. The spread of bacteria to other organs was also dependent on the pathogenic profile of the infectious agent.

Evasion of host defenses by intracellular Staphylococcus aureus

Staphylococcus aureus is one of the leading causes of hospital and community-acquired infections worldwide. The increasing occurrence of antibiotic resistant strains and the high rates of recurrent staphylococcal infections have placed several treatment challenges on healthcare systems. In recent years, it has become evident that S. aureus is a facultative intracellular pathogen, able to invade and survive in a range of cell types. The ability to survive intracellularly provides this pathogen with yet another way to evade antibiotics and immune responses during infection. Intracellular S. aureus have been strongly linked to several recurrent infections, including severe bone infections and septicemias. S. aureus is armed with an array of virulence factors as well as an intricate network of regulators that enable it to survive, replicate and escape from a number of immune and nonimmune host cells. It is able to successfully manipulate host cell pathways and use it as a niche to multiply, disseminate, as well as persist during an infection. This bacterium is also known to adapt to the intracellular environment by forming small colony variants, which are metabolically inactive. In this review we will discuss the clinical evidence, the molecular pathways involved in S. aureus intracellular persistence, and new treatment strategies for targeting intracellular S. aureus.

Respiration and Small Colony Variants of Staphylococcus aureus

Respiratory mutants, both naturally occurring and genetically constructed, have taught us about the importance of metabolism in influencing virulence factor production, persistence, and antibiotic resistance. As we learn more about small colony variants, we find that Staphylococcus aureus has many pathways to produce small colony variants, although the respiratory variants are the best described clinically and in the laboratory.

Peritoneal Microbiome in End-Stage Renal Disease Patients and the Impact of Peritoneal Dialysis Therapy

Factors influencing the occurrence of peritoneal dialysis (PD)-related infections are still far from fully understood. Recent studies described the existence of specific microbiomes in body sites previously considered microbiome-free, unravelling new microbial pathways in the human body. In the present study, we analyzed the peritoneum of end-stage kidney disease (ESKD) patients to determine if they harbored a specific microbiome and if it is altered in patients on PD therapy. We conducted a cross-sectional study where the peritoneal microbiomes from ESKD patients with intact peritoneal cavities (ESKD non-PD, n = 11) and ESKD patients undergoing PD therapy (ESKD PD, n = 9) were analyzed with a 16S rRNA approach. Peritoneal tissue of ESKD patients contained characteristically low-abundance microbiomes dominated by Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes. Patients undergoing PD therapy presented lower species richness, with dominance by the Pseudomonadaceae and Prevotelaceae families. This study provides the first characterization of the peritoneal microbiome in ESKD patients, bringing new insight to the human microbiome. Additionally, PD therapy may induce changes in this unique microbiome. The clinical relevance of these observations should be further explored to uncover the role of the peritoneal microbiome as a key element in the onset or aggravation of infection in ESKD patients, especially those undergoing PD.

Standardized irrigation technique reduces intraabdominal abscess after appendectomy

PURPOSE

The utility of irrigation at the time of appendectomy for acute appendicitis has been debated, with recent studies showing no benefit to irrigation. In our practice, two techniques have been used; one in which irrigation was at the discretion of the surgeon, and one in which irrigation was standardized. The standardized irrigation technique involved large volume (3-12 l) irrigation in small, focused, directed aliquots to achieve optimal dilution. We sought to retrospectively assess whether the standardized large volume irrigation technique was associated with measurably reduced intraabdominal infection. We hypothesized that there would be no difference in intraabdominal infection rate.

METHODS

Medical records for cases of appendectomies performed for acute appendicitis, years 2007 through 2017, were reviewed (n = 432). Rate of subsequent abdominal infection was compared between patients who underwent the standardized large volume irrigation technique compared to those who did not using Fisher's exact test; p < 0.05 was considered significant.

RESULTS

For patients that underwent the standardized large volume irrigation technique there were no (0/140) subsequent abdominal infections within the study period, compared with a rate of 6.2% (18/292) for all other patients (p value 0.001). Among cases that had a perforated appendix (n = 105), the rates were 0% (0/31) compared to 18.9% (14/74; p value 0.009).

CONCLUSIONS

Utilization of a standardized large volume irrigation technique with the objective of serial dilution is associated with a significantly lower rate of subsequent abdominal infection, even among cases with a perforated appendix. Prospective studies are needed to evaluate this technique.

LEVEL OF EVIDENCE

Level III.

TYPE OF STUDY

Treatment study.

Streptococcus pneumoniae potently induces cell death in mesothelial cells

Pleural infection/empyema is common and its incidence continues to rise. Streptococcus pneumoniae is the commonest bacterial cause of empyema in children and among the commonest in adults. The mesothelium represents the first line of defense against invading microorganisms, but mesothelial cell responses to common empyema pathogens, including S. pneumoniae, have seldom been studied. We assessed mesothelial cell viability in vitro following exposure to common empyema pathogens. Clinical isolates of S. pneumoniae from 25 patients with invasive pneumococcal disease and three reference strains were tested. All potently induced death of cultured mesothelial cells (MeT-5A) in a dose- and time-dependent manner (>90% at 10⁷ CFU/mL after 24 hours). No significant mesothelial cell killing was observed when cells were co-cultured with Staphylococcus aureus, Streptococcus sanguinis and Streptococcus milleri group bacteria. S. pneumoniae induced mesothelial cell death via secretory product(s) as cytotoxicity could be: i) reproduced using conditioned media derived from S. pneumoniae and ii) in transwell studies when the bacteria and mesothelial cells were separated. No excess cell death was seen when heat-killed S. pneumoniae were used. Pneumolysin, a cytolytic S. pneumoniae toxin, induced cell death in a time- and dose-dependent manner. S. pneumoniae lacking the pneumolysin gene (D39 ΔPLY strain) failed to kill mesothelial cells compared to wild type (D39) controls, confirming the necessity of pneumolysin in D39-induced mesothelial cell death. However, pneumolysin gene mutation in other S. pneumoniae strains (TIGR4, ST3 and ST23F) only partly abolished their cytotoxic effects, suggesting different strains may induce cell death via different mechanisms.

Inside job: Staphylococcus aureus host-pathogen interactions

Staphylococcus aureus is a notorious opportunistic pathogen causing a plethora of diseases. Recent research established that once phagocytosed by neutrophils and macrophages, a certain percentage of S. aureus is able to survive within these phagocytes which thereby even may contribute to dissemination of the pathogen. S. aureus further induces its uptake by otherwise non-phagocytic cells and the ensuing intracellular cytotoxicity is suggested to lead to tissue destruction, whereas bacterial persistence within cells is thought to lead to immune evasion and chronicity of infections. We here review recent work on the S. aureus host pathogen interactions with a focus on the intracellular survival of the pathogen.

Activation of salt-inducible kinase 2 promotes the viability of peritoneal mesothelial cells exposed to stress of peritoneal dialysis

Maintaining mesothelial cell viability is critical to long-term successful peritoneal dialysis (PD) treatment. To clarify the viability mechanism of peritoneal mesothelial cells under PD solutions exposure, we examined the mechanisms of cellular response to this stress conditions. Here we report that the proteasome activity is inhibited when treated with PD solutions. Proteasome inhibition-mediated activation of salt-inducible kinase 2 (SIK2), an endoplasmic reticulum-resident protein, is important for mesothelial cell viability. SIK2 is mobilized to promote autophagy and protect the cells from apoptosis under PD solution or MG132 treatment. Immunofluorescence staining showed that SIK2 is colocalized with LC3B in the autophagosomes of mesothelial cells treated with PD solution or derived from patients undergoing PD treatment. SIK2 activation is likely via a two-step mechanism, upstream kinases relieving the autoinhibitory conformation of SIK2 molecule followed by autophosphorylation of Thr175 and activation of kinase activity. These results suggest that activation of SIK2 is required for the cell viability when proteasome activity is inhibited by PD solutions. Maintaining or boosting the activity of SIK2 may promote peritoneal mesothelial cell viability and evolve as a potential therapeutic target for maintaining or restoring peritoneal membrane integrity in PD therapy.

New developments in peritoneal fibroblast biology: implications for inflammation and fibrosis in peritoneal dialysis

Uraemia and long-term peritoneal dialysis (PD) can lead to fibrotic thickening of the peritoneal membrane, which may limit its dialytic function. Peritoneal fibrosis is associated with the appearance of myofibroblasts and expansion of extracellular matrix. The extent of contribution of resident peritoneal fibroblasts to these changes is a matter of debate. Recent studies point to a significant heterogeneity and complexity of the peritoneal fibroblast population. Here, we review recent developments in peritoneal fibroblast biology and summarize the current knowledge on the involvement of peritoneal fibroblasts in peritoneal inflammation and fibrosis.

Comparative proteome analysis reveals conserved and specific adaptation patterns of Staphylococcus aureus after internalization by different types of human non-professional phagocytic host cells

Staphylococcus aureus is a human pathogen that can cause a wide range of diseases. Although formerly regarded as extracellular pathogen, it has been shown that S. aureus can also be internalized by host cells and persist within these cells. In the present study, we comparatively analyzed survival and physiological adaptation of S. aureus HG001 after internalization by two human lung epithelial cell lines (S9 and A549), and human embryonic kidney cells (HEK 293). Combining enrichment of bacteria from host-pathogen assays by cell sorting and quantitation of the pathogen's proteome by mass spectrometry we characterized S. aureus adaptation during the initial phase between 2.5 h and 6.5 h post-infection. Starting with about 2 × 10⁶ bacteria, roughly 1450 S. aureus proteins, including virulence factors and metabolic enzymes were identified by spectral comparison and classical database searches. Most of the bacterial adaptation reactions, such as decreased levels of ribosomal proteins and metabolic enzymes or increased amounts of proteins involved in arginine and lysine biosynthesis, enzymes coding for terminal oxidases and stress responsive proteins or activation of the sigma factor SigB were observed after internalization into any of the three cell lines studied. However, differences were noted in central carbon metabolism including regulation of fermentation and threonine degradation. Since these differences coincided with different intracellular growth behavior, complementary profiling of the metabolome of the different non-infected host cell types was performed. This revealed similar levels of intracellular glucose but host cell specific differences in the amounts of amino acids such as glycine, threonine or glutamate. With this comparative study we provide an impression of the common and specific features of the adaptation of S. aureus HG001 to specific host cell environments as a starting point for follow-up studies with different strain isolates and regulatory mutants.

Regulation of chemokine CCL5 synthesis in human peritoneal fibroblasts: a key role of IFN-γ

Peritonitis is characterized by a coordinated influx of various leukocyte subpopulations. The pattern of leukocyte recruitment is controlled by chemokines secreted primarily by peritoneal mesothelial cells and macrophages. We have previously demonstrated that some chemokines may be also produced by human peritoneal fibroblasts (HPFB). Aim of our study was to assess the potential of HPFB in culture to release CCL5, a potent chemoattractant for mononuclear leukocytes. Quiescent HPFB released constitutively no or trace amounts of CCL5. Stimulation of HPFB with IL-1β and TNF-α resulted in a time- (up to 96 h) and dose-dependent increase in CCL5 expression and release. IFN-γ alone did not induce CCL5 secretion over a wide range of concentrations (0.01–100 U/mL). However, it synergistically amplified the effects of TNF-α and IL-1β through upregulation of CCL5 mRNA. Moreover, pretreatment of cells with IFN-γ upregulated CD40 receptor, which enabled HPFB to respond to a recombinant ligand of CD40 (CD40L). Exposure of IFN-γ-treated HPFB, but not of control cells, to CD40L resulted in a dose-dependent induction of CCL5. These data demonstrate that HPFB synthesise CCL5 in response to inflammatory mediators present in the inflamed peritoneal cavity. HPFB-derived CCL5 may thus contribute to the intraperitoneal recruitment of mononuclear leukocytes during peritonitis.

Stimulation of platelet apoptosis by peptidoglycan from Staphylococcus aureus 113

Peptidoglycan (PGN), a component of bacterial cell wall and belonging to "Microbe-Associated Molecular Patterns" (MAMP) triggers host reactions contributing to the pathophysiology of infectious disease. Host cell responses to PGN exposure include apoptosis. Bacterial infections may result in activation of blood platelets and thrombocytopenia. The present study explored, whether HPLC-purified fractions of PGNs from Staphylococcus aureus 113 triggers apoptosis of platelets. To this end platelets were exposed to PGN fractions and annexin-V binding determined to depict cell membrane scrambling, DiOC6 fluorescence to estimate depolarization of mitochondrial potential, Fluo-3AM staining for intracellular Ca(2+) activity ([Ca(2+)](i)) and immunofluorescence to quantify protein abundance of active caspase-3. As a result, a 30 min exposure to monomeric fraction (mPGN) (≥50 ng/ml) was followed by annexin-V binding, paralleled by increase of [Ca(2+)](i), mitochondrial depolarization, caspase-3 activation and integrin α(IIb)β(3) upregulation. The annexin-V binding was significantly blunted by anti-TLR-2 antibodies, in absence of extracellular Ca(2+), and by pancaspase inhibitor zVAD-FMK (1 μM). In conclusion, PGN triggers apoptosis of platelets in activation-dependent manner, characterized by mitochondrial depolarization, caspase-3 activation and cell membrane scrambling.

Bacteria-derived DNA fragment in peritoneal dialysis effluent as a predictor of relapsing peritonitis

BACKGROUND AND OBJECTIVES

Relapsing and recurrent peritonitis episodes are important causes of treatment failure in patients undergoing peritoneal dialysis (PD). This study explored whether the level of bacteria-derived DNA fragment in PD effluent predicts the development of relapsing or recurrent peritonitis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The study included 143 patients with PD peritonitis in a dialysis unit between September 2010 and December 2011. Every 5 days until antibiotic treatment ended, PD effluent was collected to determine bacteria-derived DNA fragment level, which is represented by the number of PCR cycles at which bacterial DNA could be detected. Patients were followed for the development of relapsing or recurrent peritonitis.

RESULTS

Thirty-nine patients were excluded because of immediate treatment failure or incorrect diagnosis. Of the other 104 patients, 15 (14.4%) developed relapsing peritonitis, 3 (2.9%) had recurrent peritonitis, and 5 (4.8%) had repeat episodes. Patients with relapsing or recurrent peritonitis episodes had significantly higher levels of bacterial DNA fragment in PD effluent than those without relapsing or recurrence, both 5 days before (31.9 ± 3.4 versus 34.3 ± 3.0 cycles; P=0.002) and on the day of (32.3 ± 2.6 versus 34.1 ± 1.7 cycles; P<0.001) completion of antibiotics. When bacterial DNA fragment detectable by 34 PCR cycles 5 days before the completion of antibiotics is used as the cutoff, it has a sensitivity of 88.9% and specificity of 60.5% for the prediction of relapsing or recurrent peritonitis.

CONCLUSIONS

Bacterial DNA fragment levels in PD effluent are significantly higher, both 5 days before and on the date of completion of antibiotics, among patients who subsequently develop relapsing or recurrent peritonitis than among those cured by antibiotics. Further studies are needed to validate these results and confirm the clinical utility of dialysate bacterial DNA fragment level.

Complete Genome Sequence of Staphylococcus aureus 6850, a Highly Cytotoxic and Clinically Virulent Methicillin-Sensitive Strain with Distant Relatedness to Prototype Strains

Staphylococcus aureus is a frequent human commensal bacterium and pathogen. Here we report the complete genome sequence of strain 6850 (spa type t185; sequence type 50 [ST50]), a highly cytotoxic and clinically virulent methicillin-sensitive strain from a patient with complicated S. aureus bacteremia associated with osteomyelitis and septic arthritis.

Update on the challenging role of biofilms in peritoneal dialysis

Biofilms are commonly associated with an increased risk of patient infection. In peritoneal dialysis (PD), catheter associated infection, especially peritonitis, remains a clinically relevant problem. Although the presence of a biofilm is recognized in relapsing, repeat, and catheter-related peritonitis, it remains poorly characterized. In this review, an update on the role of biofilms in PD infections is presented. The emerging concept that host cells and tissue associated biofilms, in addition to the biofilms on the catheters themselves, contribute to the recalcitrance of infections is discussed. Furthermore, the evidence of biofilms on PD catheters, their developmental stages, and the possible influence of the PD environment are reviewed. The focus is given to ex vivo and in vitro studies that contribute to the elucidation of the interplay between host, microbial, and dialysis factors. The key issues that are still to be answered and the challenges to clinical practice are discussed.

Effect of bacterial peptidoglycan on erythrocyte death and adhesion to endothelial cells

Peptidoglycans, bacterial wall components, have previously been shown to trigger eryptosis, the suicidal erythrocyte death, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the cell surface. Phosphatidylserine exposing erythrocytes adhere to the vascular wall at least partially by interaction of erythrocytic phosphatidylserine with endothelial CXC chemokine ligand 16 (CXCL16). The present study explored whether peptidoglycan exposure fosters the adhesion of erythrocytes to human umbilical vein endothelial cells (HUVEC). To this end, HUVEC were treated for 48 h with peptidoglycan (10 μg/ml) and CXCL16 abundance determined by confocal microscopy and FACS analysis. Moreover, human erythrocytes were exposed for 48 h to peptidoglycan (10 μg/ml) and phosphatidylserine exposure estimated from binding of fluorescent annexin-V, cell volume from forward scatter in FACS analysis and erythrocyte adhesion to human umbilical vein endothelial cells (HUVEC) from trapping of labeled erythrocytes in a flow chamber. As a result, bacterial peptidoglycan exposure was followed by increased CXCL16 expression in HUVEC as well as erythrocyte shrinkage, phosphatidylserine exposure and adhesion to HUVEC under flow conditions at arterial shear rates. The adhesion was significantly attenuated but not abrogated in the presence of either, erythrocyte phosphatidylserine-coating annexin-V (5 μl/ml) or CXCL16 neutralizing antibody directed against endothelial CXCL16 (4 μg/ml). In conclusion, exposure to peptidoglycan increases endothelial CXCL16 expression and leads to eryptosis followed by phosphatidylserine- and CXCL16-mediated adhesion of eryptotic erythrocytes to vascular endothelial cells.

Pathophysiological changes to the peritoneal membrane during PD-related peritonitis: the role of mesothelial cells

The success of peritoneal dialysis (PD) is dependent on the structural and functional integrity of the peritoneal membrane. The mesothelium lines the peritoneal membrane and is the first line of defense against chemical and/or bacterial insult. Peritonitis remains a major complication of PD and is a predominant cause of technique failure, morbidity and mortality amongst PD patients. With appropriate antibiotic treatment, peritonitis resolves without further complications, but in some PD patients excessive peritoneal inflammatory responses lead to mesothelial cell exfoliation and thickening of the submesothelium, resulting in peritoneal fibrosis and sclerosis. The detrimental changes in the peritoneal membrane structure and function correlate with the number and severity of peritonitis episodes and the need for catheter removal. There is evidence that despite clinical resolution of peritonitis, increased levels of inflammatory and fibrotic mediators may persist in the peritoneal cavity, signifying persistent injury to the mesothelial cells. This review will describe the structural and functional changes that occur in the peritoneal membrane during peritonitis and how mesothelial cells contribute to these changes and respond to infection. The latter part of the review discusses the potential of mesothelial cell transplantation and genetic manipulation in the preservation of the peritoneal membrane.

The effect of Staphylococcus aureus on apoptosis of cultured human osteoblasts

OBJECTIVE

To investigate the effect of Staphylococcus aureus (S. aureus) on cultured human osteoblast apoptosis and the corresponding mode of action.

METHODS

Transmission electron microscopy (TEM), assessment of DNA laddering, and flow cytometry assays were used to investigate human osteoblast apoptosis following infection with S. aureus.

RESULTS

TEM examination and DNA laddering assessment indicated that S. aureus can induce cultured human osteoblast apoptosis. Flow cytometry assays showed that human osteoblast apoptosis occurs in a dose-dependent manner following infection with S. aureus. In addition, compared with under co-culture conditions, inhibition of invasion by S. aureus resulted in a 64.62% reduction in the percentage of early apoptotic cells (P < 0.01); 7.09% ± 1.21% of human osteoblasts under indirect co-culture with S. aureus at a multiplicity of infection of 250 showed an early apoptotic profile compared with uninfected controls(P < 0.01).

CONCLUSIONS

S. aureus induces cultured human osteoblast apoptosis in a dose-dependent manner. Intracellular S. aureus is mainly responsible for cultured human osteoblast apoptosis following infection; secreted soluble factor(s) of S. aureus playing a minor role in this process.

Peritoneal dialysis-related peritonitis due to Staphylococcus aureus: a single-center experience over 15 years

Peritonitis caused by Staphylococcus aureus is a serious complication of peritoneal dialysis (PD), which is associated with poor outcome and high PD failure rates. We reviewed the records of 62 S. aureus peritonitis episodes that occurred between 1996 and 2010 in the dialysis unit of a single university hospital and evaluated the host and bacterial factors influencing peritonitis outcome. Peritonitis incidence was calculated for three subsequent 5-year periods and compared using a Poisson regression model. The production of biofilm, enzymes, and toxins was evaluated. Oxacillin resistance was evaluated based on minimum inhibitory concentration and presence of the mecA gene. Logistic regression was used for the analysis of demographic, clinical, and microbiological factors influencing peritonitis outcome. Resolution and death rates were compared with 117 contemporary coagulase-negative staphylococcus (CoNS) episodes. The incidence of S. aureus peritonitis declined significantly over time from 0.13 in 1996–2000 to 0.04 episodes/patient/year in 2006–2010 (p = 0.03). The oxacillin resistance rate was 11.3%. Toxin and enzyme production was expressive, except for enterotoxin D. Biofilm production was positive in 88.7% of strains. The presence of the mecA gene was associated with a higher frequency of fever and abdominal pain. The logistic regression model showed that diabetes mellitus (p = 0.009) and β-hemolysin production (p = 0.006) were independent predictors of non-resolution of infection. The probability of resolution was higher among patients aged 41 to 60 years than among those >60 years (p = 0.02). A trend to higher death rate was observed for S. aureus episodes (9.7%) compared to CoNS episodes (2.5%), (p = 0.08), whereas resolution rates were similar. Despite the decline in incidence, S. aureus peritonitis remains a serious complication of PD that is associated with a high death rate. The outcome of this infection is negatively influenced by host factors such as age and diabetes mellitus. In addition, β-hemolysin production is predictive of non-resolution of infection, suggesting a pathogenic role of this factor in PD-related S. aureus peritonitis.

Phagocytosis of dying tumor cells by human peritoneal mesothelial cells

Peritoneal carcinomatosis is an advanced form of metastatic disease characterized by cancer cell dissemination onto the peritoneum. It is commonly observed in ovarian and colorectal cancers and is associated with poor patient survival. Novel therapies consist of cytoreductive surgery in combination with intraperitoneal chemotherapy, aiming at tumor cell death induction. The resulting dying tumor cells are considered to be eliminated by professional as well as semi-professional phagocytes. In the present study, we have identified a hitherto unknown type of 'amateur' phagocyte in this environment: human peritoneal mesothelial cells (HMCs). We demonstrate that HMCs engulf corpses of dying ovarian and colorectal cancer cells, as well as other types of apoptotic cells. Flow cytometric, confocal and electron microscopical analyses revealed that HMCs ingest dying cell fragments in a dose- and time-dependent manner and the internalized material subsequently traffics into late phagolysosomes. Regarding the mechanisms of prey cell recognition, our results show that HMCs engulf apoptotic corpses in a serum-dependent and -independent fashion and quantitative real-time PCR (qRT-PCR) analyses revealed that diverse opsonin receptor systems orchestrating dying cell clearance are expressed in HMCs at high levels. Our data strongly suggest that HMCs contribute to dying cell removal in the peritoneum, and future studies will elucidate in what manner this influences tumor cell dissemination and the antitumor immune response.

Staphylococcus aureus phenotype switching: an effective bacterial strategy to escape host immune response and establish a chronic infection

Staphylococcus aureus is a frequent cause for serious, chronic and therapy-refractive infections in spite of susceptibility to antibiotics in vitro. In chronic infections, altered bacterial phenotypes, such as small colony variants (SCVs), have been found. Yet, it is largely unclear whether the ability to interconvert from the wild-type to the SCV phenotype is only a rare clinical and/or just laboratory phenomenon or is essential to sustain an infection. Here, we performed different long-term in vitro and in vivo infection models with S. aureus and we show that viable bacteria can persist within host cells and/or tissues for several weeks. Persistence induced bacterial phenotypic diversity, including SCV phenotypes, accompanied by changes in virulence factor expression and auxotrophism. However, the recovered SCV phenotypes were highly dynamic and rapidly reverted to the fully virulent wild-type form when leaving the intracellular location and infecting new cells. Our findings demonstrate that bacterial phenotype switching is an integral part of the infection process that enables the bacteria to hide inside host cells, which can be a reservoir for chronic and therapy-refractive infections.

Bacterial pore-forming cytolysins induce neuronal damage in a rat model of neonatal meningitis

BACKGROUND

Group B Streptococcus (GBS) and Streptococcus pneumoniae (SP) are leading causes of bacterial meningitis in neonates and children. Each pathogen produces a pore-forming cytolytic toxin, β-hemolysin/cytolysin (β-h/c) by GBS and pneumolysin by SP. The aim of this study was to understand the role of these pore-forming cytotoxins, in particular of the GBS β-h/c, as potential neurotoxins in experimental neonatal meningitis.

METHODS

Meningitis was induced in 7- and 11-day-old rats by intracisternal injection of wild type (WT) GBS or SP and compared with isogenic β-h/c- or pneumolysin-deficient mutants, or a double mutant of SP deficient in pneumolysin and hydrogen peroxide production.

RESULTS

GBS β-h/c and SP pneumolysin contributed to neuronal damage, worsened clinical outcome and weight loss, but had no influence on the early kinetics of leukocyte influx and bacterial growth in the cerebrospinal fluid. In vitro, β-h/c-induced neuronal apoptosis occurred independently of caspase-activation and was not preventable by the broad spectrum caspase-inhibitor z-VAD-fmk.

CONCLUSIONS

These data suggest that both cytolytic toxins, the GBS β-h/c and SP pneumolysin, contribute to neuronal damage in meningitis and extend the concept of a key role for bacterial pore-forming cytolysins in the pathogenesis and sequelae of neonatal meningitis.

Staphylococcus aureus adaptation to the host and persistence: role of loss of capsular polysaccharide expression

A vast array of virulence factors enable Staphylococcus aureus to readily adapt to different environmental niches in diverse hosts. The cap gene cluster is present in almost all relevant clinical S. aureus isolates and capsular polysaccharide expression is apparent in isolates from patients with acute infection. The number of S. aureus isolates from patients with chronic infections that do not express capsular polysaccharide, however, is significantly high, indicating that loss of capsular polysaccharide expression may be a key S. aureus feature associated with persistence. The role of the loss of capsular polysaccharide expression as well as the emergence of other defined phenotypes and their relevance to persistence of S. aureus and chronicity of the infection is discussed in this article.

Phagolysosomal integrity is generally maintained after Staphylococcus aureus invasion of nonprofessional phagocytes but is modulated by strain 6850

Staphylococcus aureus is a major cause of a variety of both local and systemic infections. It can invade human host cells, a process that may account for disseminated and recurrent infections. S. aureus postinvasion events in nonprofessional phagocytes are only partially understood. While morphological data suggest a phagosomal escape, there is a lack of corroborating functional data. Using a combination of pH determination and morphological techniques, we have tested the integrity of Staphylococcus-containing phagosomes in 293 (HEK-293), HeLa, and EA.hy926 cells over time. Rapid acidification of S. aureus-containing phagosomes occurred and was sustained for up to 24 h. All S. aureus strains tested displayed equally sustained intraphagosomal pH levels without exhibiting any correlation with pH level and hemolytic activity. The membrane morphology of the phagosomal compartment was heterogeneous, even under conditions where acidic pH was fully maintained, an observation incompatible with phagolysosomal membrane destruction. As an exception, S. aureus strain 6850 showed a reduced phagosomal acidification signal 6 h after invasion. Additionally, only strain 6850 failed to localize to LAMP-1-positive vesicles in HeLa cells, although this was observed only rarely. Several other strongly beta-hemolytic strains did not modulate phagolysosomal pH, suggesting that S. aureus alpha-toxin and beta-toxin are not sufficient for this process. Taken together, our data suggest that S. aureus-containing phagolysosomes generally remain functionally intact in nonprofessional phagocytes, thereby contrasting with transmission electron micrographic results.

The role of virulence factors in the outcome of staphylococcal peritonitis in CAPD patients

Background

Peritonitis continues to be the most frequent cause of peritoneal dialysis (PD) failure, with an important impact on patient mortality. Gram-positive cocci such as Staphylococcus epidermidis, other coagulase-negative staphylococci (CoNS), and Staphylococcus aureus are the most frequent etiological agents of PD-associated peritonitis worldwide. The objective of the present study was to compare peritonitis caused by S. aureus and CoNS and to evaluate the factors influencing outcome.

Methods

Records of 86 new episodes of staphylococcal peritonitis that occurred between 1996 and 2000 in the Dialysis unit of a single university hospital were studied (35 due to S. aureus, 24 to S. epidermidis and 27 to other CoNS). The production of slime, lipase, lecithinase, nuclease (DNAse), thermonuclease (TNAse), α- and β-hemolysin, enterotoxins (SEA, SEB, SEC, SED) and toxic shock syndrome toxin-1 (TSST-1) was studied in S. aureus and CoNS. Antimicrobial susceptibility was evaluated based on the minimal inhibitory concentration determined by the E-test. Outcome predictors were evaluated by two logistic regression models.

Results

The oxacillin susceptibility rate was 85.7% for S. aureus, 41.6% for S. epidermidis, and 51.8% for other CoNS (p = 0.001). Production of toxins and enzymes, except for enterotoxin A and α-hemolysin, was associated with S. aureus episodes (p < 0.001), whereas slime production was positive in 23.5% of CoNS and 8.6% of S. aureus strains (p = 0.0047). The first model did not include enzymes and toxins due to their association with S. aureus. The odds of resolution were 9.5 times higher for S. epidermidis than for S. aureus (p = 0.02) episodes, and were similar for S. epidermidis and other CoNS (p = 0.8). The resolution odds were 68 times higher for non-slime producers (p = 0.001) and were not influenced by oxacillin resistance among vancomycin-treated cases (p = 0.89). In the second model, the resolution rate was similar for S. aureus and S. epidermidis (p = 0.70), and slime (p = 0.001) and α-hemolysin (p = 0.04) production were independent predictors of non-resolution.

Conclusion

Bacterial species and virulence factors rather than antibiotic resistance influence the outcome of staphylococcal peritonitis.

Staphylococcus aureus host cell invasion and post-invasion events

Staphylococcus aureus is now recognized as a facultative intracellular pathogen. The aim of this review is to discuss novel data regarding the invasion mechanism and post-invasion events with a focus on the fate of the infected phagosome in non-professional phagocytes and the role of S. aureus alpha-toxin.

A nanoconjugate Apaf-1 inhibitor protects mesothelial cells from cytokine-induced injury

Background

Inflammation may lead to tissue injury. We have studied the modulation of inflammatory milieu-induced tissue injury, as exemplified by the mesothelium. Peritoneal dialysis is complicated by peritonitis episodes that cause loss of mesothelium. Proinflammatory cytokines are increased in the peritoneal cavity during peritonitis episodes. However there is scarce information on the modulation of cell death by combinations of cytokines and on the therapeutic targets to prevent desmesothelization.

Methodology

Human mesothelial cells were cultured from effluents of stable peritoneal dialysis patients and from omentum of non-dialysis patients. Mesothelial cell death was studied in mice with S. aureus peritonitis and in mice injected with tumor necrosis factor alpha and interferon gamma.

Tumor necrosis factor alpha and interferon gamma alone do not induce apoptosis in cultured mesothelial cells. By contrast, the cytokine combination increased the rate of apoptosis 2 to 3-fold over control. Cell death was associated with the activation of caspases and a pancaspase inhibitor prevented apoptosis. Specific caspase-8 and caspase-3 inhibitors were similarly effective. Co-incubation with both cytokines also impaired mesothelial wound healing in an in vitro model. However, inhibition of caspases did not improve wound healing and even impaired the long-term recovery from injury. By contrast, a polymeric nanoconjugate Apaf-1 inhibitor protected from apoptosis and allowed wound healing and long-term recovery. The Apaf-1 inhibitor also protected mesothelial cells from inflammation-induced injury in vivo in mice.

Conclusion

Cooperation between tumor necrosis factor alpha and interferon gamma contributes to mesothelial injury and impairs the regenerative capacity of the monolayer. Caspase inhibition attenuates mesothelial cell apoptosis but does not facilitate regeneration. A drug targeting Apaf-1 allows protection from apoptosis as well as regeneration in the course of inflammation-induced tissue injury.

Toll-like receptor 2 ligands on the staphylococcal cell wall downregulate superantigen-induced T cell activation and prevent toxic shock syndrome

Staphylococcal superantigens are pyrogenic exotoxins that cause massive T cell activation leading to toxic shock syndrome and death. Despite the strong adaptive immune response induced by these toxins, infections by superantigen-producing staphylococci are very common clinical events. We hypothesized that this may be partly a result of staphylococcal strains having developed strategies that downregulate the T cell response to these toxins. Here we show that the human interleukin-2 response to staphylococcal superantigens is inhibited by the simultaneous presence of bacteria. Such a downregulatory effect is the result of peptidoglycan-embedded molecules binding to Toll-like receptor 2 and inducing interleukin-10 production and apoptosis of antigen-presenting cells. We corroborated these findings in vivo by showing substantial prevention of mortality after simultaneous administration of staphylococcal enterotoxin B with either heat-killed staphylococci or Staphylococcus aureus peptidoglycan in mouse models of superantigen-induced toxic shock syndrome.

Staphylococcal alpha-toxin is not sufficient to mediate escape from phagolysosomes in upper-airway epithelial cells

Intracellular Staphylococcus aureus has been implicated in the establishment of chronic infections. It is therefore imperative to understand by what means S. aureus is able to survive within cells. Here we use two expression systems with a fluorescent readout to assay alpha-toxin expression and function within phagolysosomes of infected upper-airway epithelial cells: avirulent Staphylococcus carnosus TM300 and phenotypically alpha-toxin-negative S. aureus laboratory strains. Data from CFU recovery assays suggest that the presence of alpha-toxin is not beneficial for the intracellular survival of recombinant Staphylococcus strains. This finding was corroborated by immunofluorescence studies: whereas S. carnosus and S. aureus are able to deliver S. aureus alpha-toxin to lumina of host cell phagolysosomes, the membrane integrity of these organelles was not affected. Alpha-toxin-expressing strains were detected exclusively within lysosome-associated membrane protein 1 (LAMP1)-yellow fluorescent protein (YFP)-positive vesicles. Measurements of intraphagosomal pH illustrated that all infected phagolysosomes acidified regardless of alpha-toxin expression. In contrast, S. aureus expressing Listeria monocytogenes listeriolysin O leads to the breakdown of the phagolysosomal membrane, as indicated by staphylococci that are not associated with LAMP1-YFP-decorated vesicles and that do not reside within an acidic cellular environment. Thus, our results suggest that staphylococcal alpha-toxin is not sufficient to mediate phagolysosomal escape in upper-airway epithelial cells.

Receptor-interacting protein-2 deficiency delays macrophage migration and increases intracellular infection during peritoneal dialysis-associated peritonitis

BACKGROUND

Early upregulation of receptor-interacting protein-2 (RIP2) expression during peritoneal dialysis (PD)-associated peritonitis correlates with a favorable clinical outcome, while failure to upregulate RIP2 correlates with a protracted course. We noticed that patients who do not upregulate RIP2 during PD-associated peritonitis have more peritoneal macrophages during the early phase of infection.

METHODS

To study the mechanism behind this observation, we examined the role of RIP2 in the immune response to bacterial challenge in a mouse model of acute peritonitis. We injected RIP2(+/+) and RIP2(-/-) mice intraperitoneally with a Staphylococcus epidermidis cell free-preparation, and peritoneal cells were isolated 3, 6 and 24 h after challenge.

RESULTS

Surprisingly, RIP2(-/-) mice had a comparable influx of inflammatory leukocytes, but had a significantly higher number of peritoneal macrophages at 3 h, indicating delayed emigration of these cells. No significant differences were seen at later times suggesting that migration was delayed but not inhibited. In addition, RIP2(-/-) macrophages were more permissive to intracellular infection by Staphylococcus aureus, indicating that, in the absence of RIP2, resident peritoneal macrophages could become reservoirs of bacteria.

CONCLUSION

These findings provide a mechanism for the observation that upregulation of RIP2 expression is required for rapid resolution of peritonitis, by decreasing intracellular infection and by regulating the migration of antigen-presenting cells in the early stages of an inflammatory response.

CD47 deficiency protects mice from lipopolysaccharide-induced acute lung injury and Escherichia coli pneumonia

CD47 modulates neutrophil transmigration toward the sites of infection or injury. Mice lacking CD47 are susceptible to Escherichia coli (E. coli) peritonitis. However, less is known concerning the role of CD47 in the development of acute lung inflammation and injury. In this study, we show that mice lacking CD47 are protected from LPS-induced acute lung injury and E. coli pneumonia with a significant reduction in pulmonary edema, lung vascular permeability, and bacteremia. Reconstitution of CD47(+/-) mice with CD47(-/-) neutrophils significantly reduced lung edema and neutrophil infiltration, thus demonstrating that CD47(+) neutrophils are required for the development of lung injury from E. coli pneumonia. Importantly, CD47-deficient mice with E. coli pneumonia had an improved survival rate. Taken together, deficiency of CD47 protects mice from LPS-induced acute lung injury and E. coli pneumonia. Targeting CD47 may be a novel pathway for treatment of acute lung injury.

A potential new pathway for Staphylococcus aureus dissemination: the silent survival of S. aureus phagocytosed by human monocyte-derived macrophages

Although considered to be an extracellular pathogen, Staphylococcus aureus is able to invade a variety of mammalian, non-professional phagocytes and can also survive engulfment by professional phagocytes such as neutrophils and monocytes. In both of these cell types S. aureus promptly escapes from the endosomes/phagosomes and proliferates within the cytoplasm, which quickly leads to host cell death. In this report we show that S. aureus interacted with human monocyte-derived macrophages in a very different way to those of other mammalian cells. Upon phagocytosis by macrophages, S. aureus persisted intracellularly in vacuoles for 3-4 days before escaping into the cytoplasm and causing host cell lysis. Until the point of host cell lysis the infected macrophages showed no signs of apoptosis or necrosis and were functional. They were able to eliminate intracellular staphylococci if prestimulated with interferon-gamma at concentrations equivalent to human therapeutic doses. S. aureus survival was dependent on the alternative sigma factor B as well as the global regulator agr, but not SarA. Furthermore, isogenic mutants deficient in alpha-toxin, the metalloprotease aureolysin, protein A, and sortase A were efficiently killed by macrophages upon phagocytosis, although with different kinetics. In particular alpha-toxin was a key effector molecule that was essential for S. aureus intracellular survival in macrophages. Together, our data indicate that the ability of S. aureus to survive phagocytosis by macrophages is determined by multiple virulence factors in a way that differs considerably from its interactions with other cell types. S. aureus persists inside macrophages for several days without affecting the viability of these mobile cells which may serve as vehicles for the dissemination of infection.

Bacterial induction of early response genes and activation of proapoptotic factors in pleural mesothelial cells

In bacterial empyema the pleural mesothelium is constantly exposed to microorganisms. Staphylococcus aureus (S. aureus) is one of the most frequent pathogens associated with empyema. In an earlier study we demonstrated that S. aureus induced barrier dysfunction in pleural mesothelial cell monolayers. In the present study we report that S. aureus activates the early response genes c-fos and c-jun and activator protein-1 (AP-1), and induces proapoptosis genes Bad and Bak in primary mouse pleural mesothelial cells (PMCs). Our data indicate that in PMCs S. aureus induces apoptosis in a time- and multiplicity of infection (MOI)-dependent manner. Staphylococcus aureus induced Bcl (2), Bcl-X (L), c-fos, c-jun, and AP-1 expression in PMCs during the initial phase of infection. In S. aureus-infected PMCs, Bad and Bak gene expression was increased and correlated with DNA fragmentation and cytochrome-c release. Bcl (2) and Bcl-X (L) gene expression was significantly lower in S. aureus-infected PMCs than in uninfected PMCs 12 h postinfection. We conclude that at the initial stage of infection S. aureus modulates expression of early response genes c-fos and c-jun, and in the late phase of infection S. aureus induces expression of proapoptotic genes Bak and Bad in PMCs. Silencing AP-1 significantly inhibited S. aureus-induced Bak and Bad expression in PMCs. The upregulation of early response genes during the early phase of infection may contribute to the activation of proapoptotic genes Bak and Bad and release of cytochrome-c, caspase-3 thereby resulting in apoptosis in PMCs.

Staphylococcus aureusPeritonitis Complicates Peritoneal Dialysis: Review of 245 Consecutive Cases

Peritonitis that is caused by Staphylococcus aureus is a serious complication in peritoneal dialysis (PD), but the clinical course of PD-related S. aureus peritonitis remains unclear. All of the S. aureus peritonitis in a dialysis unit from 1994 to 2005 were reviewed. During this period, 2065 episodes of peritonitis were recorded; 245 (11.9%) episodes in 152 patients were caused by S. aureus and 45 (18.4%) episodes were caused by methicillin-resistant S. aureus (MRSA). Patients with a history of recent hospitalization had a higher risk for isolation of MRSA than the others (30.6 versus 14.2%; P = 0.004). The overall primary response rate was 87.8%; the complete cure rate was 74.3%. However, 21 (8.6%) episodes developed relapse and 59 (24.1%) developed repeat S. aureus peritonitis. Episodes that were caused by MRSA had a lower primary response rate (64.4 versus 93.0%; P < 0.001) and complete cure rate (60.0 versus 77.5%; P = 0.023) than the others. Episodes that were treated initially with vancomycin had better primary response rate than those that were treated with cefazolin (98.0 versus 85.2%; P = 0.001), but the complete cure rate was similar. Adjuvant rifampicin treatment was associated with a significantly lower risk for relapse or repeat S. aureus peritonitis than was treatment without rifampicin (21.4 versus 42.8%; P = 0.004). In contrast, initial antibiotic regimen (cefazolin versus vancomycin) and concomitant exit-site infection did not have any effect on the risk for relapse or repeat peritonitis. S. aureus peritonitis is a serious complication of PD. Recent hospitalization is a major risk factor of methicillin resistance in the bacterial isolate. Rifampicin is a valuable adjunct in preventing relapse and repeat S. aureus peritonitis after the index episode.

Host-Cell Survival and Death During Chlamydia Infection

Different Chlamydia trachomatis strains are responsible for prevalent bacterial sexually-transmitted disease and represent the leading cause of preventable blindness worldwide. Factors that predispose individuals to disease and mechanisms by which chlamydiae cause inflammation and tissue damage remain unclear. Results from recent studies indicate that prolonged survival and subsequent death of infected cells and their effect on immune effector cells during chlamydial infection may be important in determining the outcome. Survival of infected cells is favored at early times of infection through inhibition of the mitochondrial pathway of apoptosis. Death at later times displays features of both apoptosis and necrosis, but pro-apoptotic caspases are not involved. Most studies on chlamydial modulation of host-cell death until now have been performed in cell lines. The consequences for pathogenesis and the immune response will require animal models of chlamydial infection, preferably mice with targeted deletions of genes that play a role in cell survival and death.