Bacterial Cell Wall Components Research Articles

Circulating LPS and (1→3)-β-D-Glucan: A Folie à Deux Contributing to HIV-Associated Immune Activation.

Immune activation is the driving force behind the occurrence of AIDS and non-AIDS events, and is only partially reduced by antiretroviral therapy (ART). Soon after HIV infection, intestinal CD4+ T cells are depleted leading to epithelial gut damage and subsequent translocation of microbes and/or their products into systemic circulation. Bacteria and fungi are the two most abundant populations of the gut microbiome. Circulating lipopolysaccharide (LPS) and (1→3)-β-D-Glucan (βDG), major components of bacterial and fungal cell walls respectively, are measured as markers of microbial translocation in the context of compromised gut barriers. While LPS is a well-known inducer of innate immune activation, βDG is emerging as a significant source of monocyte and NK cell activation that contributes to immune dysfunction. Herein, we critically evaluated recent literature to untangle the respective roles of LPS and βDG in HIV-associated immune dysfunction. Furthermore, we appraised the relevance of LPS and βDG as biomarkers of disease progression and immune activation on ART. Understanding the consequences of elevated LPS and βDG on immune activation will provide insight into novel therapeutic strategies against the occurrence of AIDS and non-AIDS events.

Elucidating Peptidoglycan Structure: An Analytical Toolset.

Peptidoglycan (PG) is a ubiquitous structural polysaccharide of the bacterial cell wall, essential in preserving cell integrity by withstanding turgor pressure. Any change that affects its biosynthesis or degradation will disturb cell viability, therefore PG is one of the main targets of antimicrobial drugs. Considering its major role in cell structure and integrity, the study of PG is of utmost relevance, with prospective ramifications to several disciplines such as microbiology, pharmacology, agriculture, and pathogenesis. Traditionally, high-performance liquid chromatography (HPLC) has been the workhorse of PG analysis. In recent years, technological and bioinformatic developments have upgraded this seminal technique, making analysis more sensitive and efficient than ever before. Here we describe a set of analytical tools for the study of PG structure (from composition to 3D architecture), identify the most recent trends, and discuss future challenges in the field.

Human Anti-Lipopolysaccharid (LPS) antibodies against Legionella with high species specificity.

Legionella are Gram-negative bacteria that are ubiquitously present in natural and man-made water reservoirs. When humans inhale aerosolized water contaminated with Legionella, alveolar macrophages can be infected, which may lead to a life-threatening pneumonia called Legionnaires' disease. Due to the universal distribution of Legionella in water and their potential threat to human health, the Legionella concentration in water for human use must be strictly monitored, which is difficult since the standard detection still relies on lengthy cultivation and analysis of bacterial morphology. In this study, an antibody against L. pneumophila has been generated from the naïve human HAL antibody libraries by phage-display for the first time. The panning was performed on whole bacterial cells in order to select antibodies that bind specifically to the cell surface of untreated Legionella. The bacterial cell wall component lipopolysaccharide (LPS) was identified as the target structure. Specific binding to the important pathogenic L. pneumophila strains Corby, Philadelphia-1 and Knoxville was observed, while no binding was detected to seven members of the families Enterobacteriaceae, Pseudomonadaceae or Clostridiaceae. Production of this antibody in the recombinant scFv-Fc format using either a murine or a human Fc part allowed the set-up of a sandwich-ELISA for detection of Legionella cells. The scFv-Fc construct proved to be very stable, even when stored for several weeks at elevated temperatures. A sensitivity limit of 4,000 cells was achieved. The scFv-Fc antibody pair was integrated on a biosensor, demonstrating the specific and fast detection of L. pneumophila on a portable device. With this system, 10,000 Legionella cells were detected within 35 min. Combined with a water filtration/concentration system, this antibody may be developed into a promising reagent for rapid on-site Legionella monitoring.

Inhibition of inflammatory response in human keratinocytes by magnetic nanoparticles functionalized with PBP10 peptide derived from the PIP2-binding site of human plasma gelsolin

BackgroundHuman plasma gelsolin (pGSN) is a multifunctional actin-binding protein involved in a variety of biological processes, including neutralization of pro-inflammatory molecules such as lipopolysaccharide (LPS) and lipoteichoic acid (LTA) and modulation of host inflammatory response. It was found that PBP10, a synthetic rhodamine B-conjugated peptide, based on the phosphoinositide-binding site of pGSN, exerts bactericidal activity against Gram-positive and Gram-negative bacteria, interacts specifically with LPS and LTA, and limits microbial-induced inflammatory effects. The therapeutic efficiency of PBP10 when immobilized on the surface of iron oxide-based magnetic nanoparticles was not evaluated, to date.ResultsUsing the human keratinocyte cell line HaCaT stimulated by bacterially-derived LPS and LTA as an in vitro model of bacterial infection, we examined the anti-inflammatory effects of nanosystems consisting of iron oxide-based magnetic nanoparticles with aminosilane (MNP@NH2) or gold shells (MNP@Au) functionalized by a set of peptides, derived from the phosphatidylinositol 4,5-bisphosphate (PIP2)-binding site of the human plasma protein gelsolin, which also binds LPS and LTA. Our results indicate that these nanosystems can kill both Gram-positive and Gram-negative bacteria and limit the production of inflammatory mediators, including nitric oxide (NO), reactive oxygen species (ROS), and interleukin-8 (IL-8) in the response to heat-killed microbes or extracted bacterial cell wall components. The nanoparticles possess the potential to improve therapeutic efficacy and are characterized by lower toxicity and improved hemocompatibility when compared to free peptides. Atomic force microscopy (AFM) showed that these PBP10-based nanosystems prevented changes in nanomechanical properties of cells that were otherwise stimulated by LPS.ConclusionsNeutralization of endotoxemia-mediated cellular effects by gelsolin-derived peptides and PBP10-containing nanosystems might be considered as potent therapeutic agents in the improved therapy of bacterial infections and microbial-induced inflammation.

Lipopolysaccharide-Induced Increase in Intestinal Permeability Is Mediated by TAK-1 Activation of IKK and MLCK/MYLK Gene

Lipopolysaccharides (LPSs) are a major component of Gram-negative bacterial cell wall and play an important role in promoting intestinal inflammatory responses. Recent studies have shown that physiologically relevant concentrations of LPS (0 to 2000 pg/mL) cause an increase in intestinal epithelial tight junction (TJ) permeability without causing cell death. However, the intracellular pathways and the mechanisms that mediate LPS-induced increase in intestinal TJ permeability remain unclear. The aim was to delineate the intracellular pathways that mediate the LPS-induced increase in intestinal permeability using invitro and invivo intestinal epithelial models. LPS-induced increase in intestinal epithelial TJ permeability was preceded by an activation of transforming growth factor-β-activating kinase-1 (TAK-1) and canonical NF-κB (p50/p65) pathways. The siRNA silencing of TAK-1 inhibited the activation of NF-κB p50/p65. The siRNA silencing of TAK-1 and p65/p50 subunit inhibited the LPS-induced increase in intestinal TJ permeability and the increase in myosin light chain kinase (MLCK) expression, confirming the regulatory role of TAK-1 and NF-κB p65/p50 in up-regulating MLCK expression and the subsequent increase in TJ permeability. The data also showed that toll-like receptor (TLR)-4/myeloid differentiation primary response (MyD)88 pathway was crucial upstream regulator of TAK-1 and NF-κB p50/p65 activation. In conclusion, activation of TAK-1 by the TLR-4/MyD88 signal transduction pathway and MLCK by NF-κB p65/p50 regulates the LPS-induced increase in intestinal epithelial TJ permeability.

Detection of Endotoxin in Nano-formulations Using Limulus Amoebocyte Lysate (LAL) Assays.

When present in pharmaceutical products, a Gram-negative bacterial cell wall component endotoxin (often also called lipopolysaccharide) can cause inflammation, fever, hypo- or hypertension, and, in extreme cases, can lead to tissue and organ damage that may become fatal. The amounts of endotoxin in pharmaceutical products, therefore, are strictly regulated. Among the methods available for endotoxin detection and quantification, the Limulus Amoebocyte Lysate (LAL) assay is commonly used worldwide. While any pharmaceutical product can interfere with the LAL assay, nano-formulations represent a particular challenge due to their complexity. The purpose of this paper is to provide a practical guide to researchers inexperienced in estimating endotoxins in engineered nanomaterials and nanoparticle-formulated drugs. Herein, practical recommendations for performing three LAL formats including turbidity, chromogenic and gel-clot assays are discussed. These assays can be used to determine endotoxin contamination in nanotechnology-based drug products, vaccines, and adjuvants.

The Biophysical Interaction of the Danger-Associated Molecular Pattern (DAMP) Calreticulin with the Pattern-Associated Molecular Pattern (PAMP) Lipopolysaccharide.

The endoplasmic reticulum (ER) chaperone protein, calreticulin (CRT), is essential for proper glycoprotein folding and maintaining cellular calcium homeostasis. During ER stress, CRT is overexpressed as part of the unfolded protein response (UPR). In addition, CRT can be released as a damage-associated molecular pattern (DAMP) molecule that may interact with pathogen-associated molecular patterns (PAMPs) during the innate immune response. One such PAMP is lipopolysaccharide (LPS), a component of the gram-negative bacterial cell wall. In this report, we show that recombinant and native human placental CRT strongly interacts with LPS in solution, solid phase, and the surface of gram-negative and gram-positive bacteria. Furthermore, LPS induces oilgomerization of CRT with a disappearance of the monomeric form. The application of recombinant CRT (rCRT) to size exclusion and anion exchange chromatography shows an atypical heterogeneous elution profile, indicating that LPS affects the conformation and ionic charge of CRT. Interestingly, LPS bound to CRT is detected in sera of bronchiectasis patients with chronic bacterial infections. By ELISA, rCRT dose-dependently bound to solid phase LPS via the N- and C-domain globular head region of CRT and the C-domain alone. The specific interaction of CRT with LPS may be important in PAMP innate immunity.

Btk inhibitor ibrutinib reduces inflammatory myeloid cell responses in the lung during murine pneumococcal pneumonia

BackgroundStreptococcus pneumoniae is a major causative agent in community-acquired pneumonia and sepsis. Overwhelming lung inflammation during pneumococcal pneumonia may hamper lung function. Ibrutinib is an irreversible inhibitor of Bruton’s tyrosine kinase (Btk), a key signaling protein controlling the activation of various immune cells, including macrophages and neutrophils. The aim of this study was to determine whether ibrutinib treatment ameliorates acute lung inflammation during pneumococcal pneumonia.MethodsMice were treated orally with ibrutinib and the effect on acute pulmonary inflammation elicited by the gram-positive bacterial cell wall component lipoteichoic acid (LTA) and during ceftriaxone-treated pneumococcal pneumonia was assessed.ResultsTreatment with ibrutinib prior to and after intranasal LTA instillation reduced alveolar macrophage activation, neutrophil influx, cytokine release and plasma leakage into the lung. Postponed treatment with ibrutinib supplementing antibiotic therapy during ongoing pneumococcal pneumonia did not impair bacterial killing in lung, blood and spleen. In this setting, ibrutinib reduced alveolar macrophage and systemic neutrophil activation and substantially diminished further monocyte and neutrophil influx in the lung. In vitro, ibrutinib inhibited macrophage TNF secretion and neutrophil activation upon LTA and pneumococcal stimulation.ConclusionsTaken together, these data indicate that the Btk inhibitor ibrutinib reduces inflammatory myeloid cell responses during acute pulmonary inflammation evoked by LTA and antibiotic-treated pneumococcal pneumonia and suggest that ibrutinib has the potential to inhibit ongoing lung inflammation in an acute infectious setting.

Surface-enhanced Raman scattering method for the identification of methicillin-resistant Staphylococcus aureus using positively charged silver nanoparticles.

The article describes a SERS-based method for diagnosis of bacterial infections. Positively charged silver nanoparticles (AgNPs+) were employed for identification of methicillin-resistant Staphylococcus aureus (MRSA). It is found that AgNPs+ undergo self-assembly on the surface of bacteria via electrostatic aggregation. The assembled AgNPs+ are excellent SERS substrates. To prove the capability of SERS to differentiate between S. aureus and other microorganisms, six standard strains including S. aureus 29213, S. aureus 25923, C. albicans, B. cereus, E. coli, and P. aeruginosa were tested. To further demonstrate its applicability for the identification of MRSA in clinical samples, 52 methicillin-sensitive S. aureus (MSSA) isolates and 215 MRSA isolates were detected by SERS. The total measurement time (include incubation) is 45min when using a 3μL sample. The method gives a strongly enhanced Raman signal (at 730cm-1 and 1325cm-1) with good reproducibility and repeatability. It was successfully applied to the discrimination of the six strain microorganisms. The typical Raman peaks of S. aureus at 730, 1154, 1325, and 1457cm-1 were observed, which were assigned to the bacterial cell wall components (730cm-1- adenine, glycosidic ring mode, 1154cm-1- unsaturated fattyacid, 1325cm-1- adenine, polyadenine, and 1457cm-1 for-COO- stretching). S. aureus was completely separated from other species by partial least squares discriminant analysis (PLS-DA). Moreover, 52 MSSA isolates and 215 MRSA isolates from clinical samples were identified by PLS-DA. The accuracy was almost 100% when compared to the standard broth microdilution method. A classification based on latent structure discriminant analysis provided spectral variability directly. Conceivably, the method offers a potent tool for the identification of bacteria and antibiotics resistance, andfor studies onantibiotic-resistance in general. Graphical abstract Schematic of the surface-enhanced Raman scattering (SERS) measurements on Staphylococcus aureus (S. aureus) using positively charged silver nanoparticles (AgNPs+). AgNPs+ are adsorbed on the bacterial cell wall by electrostatic attraction. SERS spectra were analyzed by PLS-DA for the identification of Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus aureus (MSSA). MRSA isolates were divided into four groups, including R1, R2, R3, and R4. MSSA just includes group S.

Surface Imprinted Ag Decorated MnO2 Thin Film Electrodes for the Synergic Electrochemical Detection of Bacterial Pathogens

Pathogenic bacterial detection is needful in disease diagnosis as well as in the prevention of bacterial infections. This work proposes the electrochemical detection of pathogenic bacterial cells of Staphylococcus aureus (S. aureus) in a simple and cost-effective manner. We have developed a surface imprinted matrix on silver (Ag) decorated Manganese dioxide (MnO2) thin film coated Fluorine doped Tin oxide (FTO) electrode. The pulsed electrodeposition technique has been employed to develop the Ag decorated MnO2 thin films. The surface imprintation was done by using S. aureus as a model bacterial template, Polyethyleneimine (PEI) as a molecular recognizer and nafion as an additive to stick the imprinted PEI to the surface of the film. In order to find the binding probabilities, docking studies were done between PEI with the bacterial cell wall components. From cyclic voltammetry (CV) analysis, we found the presence and absence of the bacterial cells lead to the variability in the redox peaks corresponds to the redox activity of [Fe(CN)6]3–/[Fe(CN)6]4– has been found. Based on this, Differential Pulse Voltammetry (DPV) analysis was performed with different bacterial concentrations resulted in the detection range of 103 to 107 CFU/ml.

Effect of Inflammatory Mediators Lipopolysaccharide and Lipoteichoic Acid on Iron Metabolism of Differentiated SH-SY5Y Cells Alters in the Presence of BV-2 Microglia.

Lipopolysaccharide (LPS) and lipoteichoic acid (LTA), the Gram-negative and the Gram-positive bacterial cell wall components are important mediators of neuroinflammation in sepsis. LPS and LTA are potent activators of microglial cells which induce the production of various pro-inflammatory cytokines. It has been demonstrated that disturbance of iron homeostasis of the brain is one of the underlying causes of neuronal cell death but the mechanisms contributing to this process are still questionable. In the present study, we established monocultures of differentiated SH-SY5Y cells and co-cultures of differentiated SH-SY5Y cells and BV-2 microglia as neuronal model systems to selectively examine the effect of inflammatory mediators LPS and LTA on iron homeostasis of SH-SY5Y cells both in mono- and co-cultures. We monitored the IL-6 and TNFα secretions of the treated cells and determined the mRNA and protein levels of iron importers (transferrin receptor-1 and divalent metal transporter-1), and iron storing genes (ferritin heavy chain and mitochondrial ferritin). Moreover, we examined the relation between hepcidin secretion and intracellular iron content. Our data revealed that LPS and LTA triggered distinct responses in SH-SY5Y cells by differently changing the expressions of iron uptake, as well as cytosolic and mitochondrial iron storage proteins. Moreover, they increased the total iron contents of the cells but at different rates. The presence of BV-2 microglial cells influenced the reactions of SH-SY5Y cells on both LPS and LTA treatments: iron uptake and iron storage, as well as the neuronal cytokine production have been modulated. Our results demonstrate that BV-2 cells alter the iron metabolism of SH-SY5Y cells, they contribute to the iron accumulation of SH-SY5Y cells by manipulating the effects of LTA and LPS proving that microglia are important regulators of neuronal iron metabolism at neuroinflammation.

Neutrophils mitigate the systemic host response during endotoxemia in mice

SummaryRecent studies have suggested that neutrophils can exert anti‐inflammatory effects. To determine the role of neutrophils in the acute response to lipopolysaccharide (LPS), a component of the Gram‐negative bacterial cell wall, we challenged neutrophil‐depleted and control mice with LPS and analyzed the plasma concentrations of biomarkers indicative of the cytokine and chemokine network, activation of coagulation and the vascular endothelium, and cellular injury. We here show that neutrophils serve an anti‐inflammatory role upon LPS administration, as reflected by sustained elevations of multiple cytokines and chemokines, and enhanced release of nucleosomes in mice depleted of neutrophils, compared with control mice.

Neuroprotective Effect of Quercetin Against the Detrimental Effects of LPS in the Adult Mouse Brain.

Chronic neuroinflammation is responsible for multiple neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. Lipopolysaccharide (LPS) is an essential component of the gram-negative bacterial cell wall and acts as a potent stimulator of neuroinflammation that mediates neurodegeneration. Quercetin is a natural flavonoid that is abundantly found in fruits and vegetables and has been shown to possess multiple forms of desirable biological activity including anti-inflammatory and antioxidant properties. This study aimed to evaluate the neuroprotective effect of quercetin against the detrimental effects of LPS, such as neuroinflammation-mediated neurodegeneration and synaptic/memory dysfunction, in adult mice. LPS [0.25 mg/kg/day, intraperitoneally (I.P.) injections for 1 week]-induced glial activation causes the secretion of cytokines/chemokines and other inflammatory mediators, which further activate the mitochondrial apoptotic pathway and neuronal degeneration. Compared to LPS alone, quercetin (30 mg/kg/day, I.P.) for 2 weeks (1 week prior to the LPS and 1 week cotreated with LPS) significantly reduced activated gliosis and various inflammatory markers and prevented neuroinflammation in the cortex and hippocampus of adult mice. Furthermore, quercetin rescued the mitochondrial apoptotic pathway and neuronal degeneration by regulating Bax/Bcl2, and decreasing activated cytochrome c, caspase-3 activity and cleaving PARP-1 in the cortical and hippocampal regions of the mouse brain. The quercetin treatment significantly reversed the LPS-induced synaptic loss in the cortex and hippocampus of the adult mouse brain and improved the memory performance of the LPS-treated mice. In summary, our results demonstrate that natural flavonoids such as quercetin can be beneficial against LPS-induced neurotoxicity in adult mice.

Dimerization and auto-processing induce caspase-11 protease activation within the non-canonical inflammasome.

Caspase-11 is a cytosolic sensor and protease that drives innate immune responses to the bacterial cell wall component, LPS. Caspase-11 provides defence against cytosolic Gram-negative bacteria; however, excessive caspase-11 responses contribute to murine endotoxic shock. Upon sensing LPS, caspase-11 assembles a higher order structure called the non-canonical inflammasome that enables the activation of caspase-11 protease function, leading to gasdermin D cleavage and cell death. The mechanism by which caspase-11 acquires protease function is, however, poorly defined. Here, we show that caspase-11 dimerization is necessary and sufficient for eliciting basal caspase-11 protease function, such as the ability to auto-cleave. We further show that during non-canonical inflammasome signalling, caspase-11 self-cleaves at site (D285) within the linker connecting the large and small enzymatic subunits. Self-cleavage at the D285 site is required to generate the fully active caspase-11 protease (proposed here to be p32/p10) that mediates gasdermin D cleavage, macrophage death, and NLRP3-dependent IL-1β production. This study provides a detailed molecular mechanism by which LPS induces caspase-11-driven inflammation and cell death to provide host defence against cytosolic bacterial infection.

Anti-PF4/Heparin Antibody Levels in Bacteremia, Fungemia and Sepsis

Heparin-induced thrombocytopenia (HIT) is caused by antibodies targeting platelet factor 4 (PF4)/heparin complexes. The immune response leading to HIT remains perplexing with many paradoxes. Unlike other drug induced reactions, anti-PF4/heparin antibody generation does not follow the classic immunologic response. As Greinacher and colleagues have shown, the primary immune response lacks IgM precedence and class switching, and heparin-induced antibodies can induce HIT by day 5 in heparin-naïve patients.Continued exposure to heparin also is puzzling with a weak or declining secondary immune response. Research by Krauel and colleagues suggests that that there is close interplay among infection, PF4 and the immune system. In 2010 they demonstrated that human and murine PF4 bind to Gram positive (S.aureus, S.pneumoniae, L.monocytogenes) and Gram negative (E.coli, N.meningitidis) bacteria in vitro, with bacterial surfaces acting as polyanions. High dose heparin inhibited this binding and anti-PF4/heparin antibodies from patients with HIT reacted with these PF4/bacterial complexes (S. aureus and E. coli). Using a murine model, they went on to show that polymicrobial sepsis in the absence of heparin led to antibody generation. In a separate study, Krauel and colleagues also showed that PF4 binds specifically to the lipid A component of Gram negative bacteria.In this analysis, we report on anti-PF4/heparin antibody levels in groups of patients hospitalized for sepsis, as compared to a control group without sepsis. We examined 200 patients with sepsis, retrospectively identified, from a hospital database of anti-PF4/heparin testing done in medical inpatients with thrombocytopenia but low pretest probability of HIT. This included patients with bacteremia (57), fungemia (7) and sepsis without septicemia (136). For comparison, data from 50 patients without sepsis during the same time period was used. Inclusion criteria for all groups were age 18 years and older and antibody testing within 4 days of admission. Exclusion criteria were diagnosis of HIT or heparin allergy, prior hospitalization or heparin exposure within 90 days of admission, cardiopulmonary bypass or orthopedic surgery within 6 months, hemodialysis, active or past malignancy, antiphospholipid syndrome, autoimmune disease or immunosuppressive therapy.All patients studied were on subcutaneous heparin at prophylactic doses only (i.e. no intravenous use, no therapeutic anticoagulation). UFH use predominated with prevalence of >85% in all groups. Testing was done using a commercially available standardized solid phase enzyme-linked immunoassay (EIA) to detect antibodies (IgG/IgA/IgM) directed against PF4 complexed with polyvinylsulfonate (Genetic Testing Institute, Wisconsin). All assays were performed in the central hospital laboratory according to manufacturer's specifications and measured in optical density (OD) units. The data sets demonstrated continuous unimodal distribution with high OD outliers, indicative of varying immune responses along a continuum. Statistical significance was calculated using independent t-testing with p-value set at 0.05 for significance.Results showed that patients hospitalized with sepsis have higher anti-PF4/heparin antibody levels. Both patients with bacteremia, and sepsis without bacteremia, had significantly higher OD than patients without sepsis (p<0.05). There was no significant difference between Gram negative and Gram positive bacteremia and antibody levels. This suggests that bacterial cell wall components of both classes have similar antigenicity. Interestingly, patients with fungemia had much lower antibody levels compared to bacteremia and sepsis. Despite the small sample size for fungemia, this difference trended strongly towards statistical significance (p=0.05). The threshold for a positive EIA is currently established at OD>0.400, a value based on sensitivity and set by the manufacturer. When the prevalence of a positive EIA was assessed, 16% patients with sepsis and bacteremia tested positive compared to 4% in the control group. In summary, there is an increased prevalence of anti-PF4/heparin antibodies in patients hospitalized with bacterial but not fungal sepsis. These results support the theory that bacterial infection has a role to play in preimmunization leading to anti-PF4/heparin antibody generation. DisclosuresNo relevant conflicts of interest to declare.

Quantification of Lipoteichoic Acid in Hemodialysis Patients With Central Venous Catheters.

Hemodialysis patients with central venous catheters (CVCs) have chronic systemic inflammation, the source of which may be related to intraluminal bacterial biofilm. There is currently no non-invasive method to adequately evaluate intraluminal biofilm. Lipoteichoic acid (LTA) is a Gram-positive bacterial cell wall component that is spontaneously shed. The purpose of this study was to determine whether LTA could be quantified in biological samples and to evaluate potential relationships to markers of inflammation. Heparin-locked catheter aspirate was drawn from both the arterial and venous ports of each CVC prior to dialysis initiation. Venous blood from the dialysis circuit was collected 30 min after dialysis initiation. LTA was quantified in aspirate and plasma. Key markers of inflammation (interleukin-6, and hepcidin) and endothelial dysfunction (soluble vascular endothelial cadherin) were also determined in plasma samples. Catheter aspirate and systemic blood samples were obtained from 40 hemodialysis patients. The median (range) duration of catheter use was 130 (20–1635) days. Unexpectedly, median (range) plasma LTA concentrations (ng/mL) were significantly higher than catheter aspirate LTA concentrations [3.93 (0.25–15) vs. 2.38 (0.1–8.1), respectively, p = 0.01] in the majority (70%) of patients. Area under the receiver operator characteristic (ROC) curve showed good potential prognostic value of catheter aspirate LTA predicting systemic LTA concentrations with an area under the curve of 0.815 (95% CI, 0.68–0.95). A significant correlation was found between LTA and serum ferritin (r = 0.32, p = 0.04), however, there were no significant correlations between LTA and the other inflammation biomarkers assessed. LTA is quantifiable in aspirate and plasma of hemodialysis patients with CVCs and warrants further investigation to determine potential clinical application to intraluminal biofilm evaluation.

Synthesis and Stereocontrolled Equatorially Selective Glycosylation Reactions of a Pseudaminic Acid Donor: Importance of the Side-Chain Conformation and Regioselective Reduction of Azide Protecting Groups.

Pseudaminic acid is an amino deoxy sialic acid whose glycosides are essential components of many pathogenic Gram-negative bacterial cell walls including those from Pseudomonas aeruginosa, Vibrio cholerae, Campylobacter jejuni, Campylobacter coli, Vibrio vulnificus, and Pseudoalteromonas distincta. The study of pseudaminic acid glycosides is however hampered by poor availability from nature and the paucity of good synthetic methods and limited to no understanding of the factors controlling stereoselectivity. Conformational analysis of the side chains of various stereoisomeric sialic acids suggested that the side chain of pseudaminic acid would take up the most electron-withdrawing trans, gauche-conformation, as opposed to the gauche, gauche conformation of N-acetyl neuraminic acid and the gauche, trans-conformtion of 7- epi N-acetyl neuraminic acid, leading to the prediction of high equatorial selectivity. This prediction is borne out by the synthesis of a suitably protected pseudaminic acid donor from N-acetyl neuraminic acid in 20 steps and 5% overall yield and by the exquisite equatorial selectivity it displays in coupling reactions with typical glycosyl acceptors. The selectivity of the glycosylation reactions is further buttressed by the development and implementation of conditions for the regioselective release of the two amines from the corresponding azides, such as required for the preparation of the lipopolysaccharides. These findings open the way to the synthesis and study of pseudaminic acid-based bacterial lipopolysaccharides and, importantly in the broader context of glycosylation reactions in general, underline the significant role played by side-chain conformation in the control of reactivity and selectivity.

Mechanistic Pathways for Peptidoglycan O-Acetylation and De-O-Acetylation.

The post-synthetic O-acetylation of the essential component of bacterial cell walls, peptidoglycan (PG), is performed by many pathogenic bacteria to help them evade the lytic action of innate immunity responses. Occurring at the C-6 hydroxyl of N-acetylmuramoyl residues, this modification to the glycan backbone of PG sterically blocks the activity of lysozymes. As such, the enzyme responsible for this modification in Gram-positive bacteria is recognized as a virulence factor. With Gram-negative bacteria, the O-acetylation of PG provides a means of control of their autolysins at the substrate level. In this review, we discuss the pathways for PG O-acetylation and de-O-acetylation and the structure and function relationship of the O-acetyltransferases and O-acetylesterases that catalyze these reactions. The current understanding of their mechanisms of action is presented and the prospects of targeting these systems for the development of novel therapeutics are explored.

In silico Analysis and Expression Patterns of TmLysozyme-like Gene in Tenebrio molitor

Lysozyme, the antibacterial protein, is well known to hydrolyse the bacterial cell wall component (peptidoglycan) in insects. In this study, we identified one lysozyme-like (TmLyso-like) gene from Tenebrio molitor EST database, and investigated gene structure and temporal/spatial expression patterns of TmLyso-like transcripts in T. molitor. TmLyso-like gene contains 417 bp of ORF sequence encoding 138 amino acid residues. Domain analysis showed a signal peptide region, and a C-type lysozyme/α-lactalbumin family domain. It also contains conserved eight cysteine residues which are involved in construction of 3D structure. Developmental expression analysis indicates that TmLyso-like mRNA is highly expressed in the young larvae (10th-12th instar larvae), 1 and 3-days old pupae and adults. Interestingly, TmLyso-like mRNA was mainly expressed in fat body and Malpighian tubules in late instar larvae, and integument, hemocytes and Malpighian tubules in 5-days old adults. Induction pattern analysis of TmLyso-like mRNA against microbial challenges showed that TmLyso-like mRNA was strongly induced by Escherichia coli at 3 and 12 h-post injection in fat body. In addition, the highest level of TmLyso-like mRNA was detected in early time point after injection of three different pathogens (E. coli, Staphylococcus aureus, and Candida albicans) in the hemocytes. However, it was not strongly induced by injection of these pathogens in the gut. In conclusion, TmLyso-like gene might play a role in innate immunity in T. molitor although precise function remains to be elucidated using recombinant TmLyso-like protein.

Bifidobacterium animalis ssp. lactis Bb12 induces IL-10 through cell membrane-associated components via TLR2 in swine.

AimTo investigate the role of Toll‐like receptor 2 (TLR2) in interleukin‐10 (IL‐10) production induced by Bifidobacterium animalis ssp. lactis Bb12 (Bb12) in swine immune cells.Methods and ResultsBlood‐monocytes and cells from mesenteric lymph nodes were obtained from pigs and cultured with live Bb12 for 4 and 12 h. Transcript levels of IL‐10 and TLR2 were analysed. Furthermore, TLR2 was blocked to determine its participation in IL‐10 production. TLR2 blockade was achieved with neutralizing antibodies, followed by stimulation with Bb12. Bifidobacteria induced IL‐10 production in both swine monocytes and mesenteric cells. Monocytes with TLR2 blockade had a decrease in IL‐10 transcripts, while mesenteric cells did not. Bacterial cell wall components were responsible for Bb12‐induced IL‐10 production since no IL‐10 was detected in the culture supernatant.ConclusionsWe demonstrated that IL‐10 production is largely mediated through the recognition of Bb12 structures by TLR2, as bacterial metabolites in the culture supernatant failed to induce IL‐10 expression.Significance and Impact of the StudyThe present study provides evidence for the potential use of Bb12 in the swine industry; these bacteria can also be used as additional method to treat intestinal inflammation and enhance intestinal health in pigs.