scholarly journals Phagocytosis and intracellular killing of MD-2 opsonized Gram-negative bacteria depend on TLR4 signaling

Blood ◽  
2008 ◽  
Vol 111 (9) ◽  
pp. 4637-4645 ◽  
Author(s):  
Vishal Jain ◽  
Annett Halle ◽  
Kristen A. Halmen ◽  
Egil Lien ◽  
Marie Charrel-Dennis ◽  
...  
Keyword(s):  
Mutant Form ◽  
Gram Negative Bacteria ◽  
Dependent Manner ◽  
Intracellular Killing ◽  
Toll Like Receptor 4 ◽  
Cellular Activation ◽  
Gram Negative ◽  
Signaling Axis ◽  
Deficient Mice

AbstractBoth Toll-like receptor 4 (TLR4)– and MD-2–deficient mice succumb to otherwise nonfatal Gram-negative bacteria inocula, demonstrating the pivotal role played by these proteins in antibacterial defense in mammals. MD-2 is a soluble endogenous ligand for TLR4 and a receptor for lipopolysaccharide (LPS). LPS-bound MD-2 transmits an activating signal onto TLR4. In this report, we show that both recombinant and endogenous soluble MD-2 bind tightly to the surface of live Gram-negative bacteria. As a consequence, MD-2 enhances cellular activation, bacterial internalization, and intracellular killing, all in a TLR4-dependent manner. The enhanced internalization of MD-2–coated bacteria was not observed in macrophages expressing Lpsd, a signaling-incompetent mutant form of TLR4, suggesting that the enhanced phagocytosis observed is dependent on signal transduction. The data confirm the notion that soluble MD-2 is a genuine opsonin that enhances proinflammatory opsonophagocytosis by bridging live Gram-negative bacteria to the LPS transducing complex. The presented results extend our understanding of the role of the TLR4/MD-2 signaling axis in bacterial recognition by phagocytes.

Escherichia coli tol and rcs genes participate in the complex network affecting curli synthesis

Microbiology ◽  
2005 ◽  
Vol 151 (7) ◽  
pp. 2487-2497 ◽  
Author(s):  
Anne Vianney ◽  
Grégory Jubelin ◽  
Sophie Renault ◽  
Corine Dorel ◽  
Philippe Lejeune ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Biofilm Formation ◽  
Membrane Integrity ◽  
Regulatory Proteins ◽  
Gram Negative Bacteria ◽  
Dependent Manner ◽  
Dominant Effect ◽  
Gram Negative ◽  
E Coli

Curli are necessary for the adherence of Escherichia coli to surfaces, and to each other, during biofilm formation, and the csgBA and csgDEFG operons are both required for their synthesis. A recent survey of gene expression in Pseudomonas aeruginosa biofilms has identified tolA as a gene activated in biofilms. The tol genes play a fundamental role in maintaining the outer-membrane integrity of Gram-negative bacteria. RcsC, the sensor of the RcsBCD phosphorelay, is involved, together with RcsA, in colanic acid capsule synthesis, and also modulates the expression of tolQRA and csgDEFG. In addition, the RcsBCD phosphorelay is activated in tol mutants or when Tol proteins are overexpressed. These results led the authors to investigate the role of the tol genes in biofilm formation in laboratory and clinical isolates of E. coli. It was shown that the adherence of cells was lowered in the tol mutants. This could be the result of a drastic decrease in the expression of the csgBA operon, even though the expression of csgDEFG was slightly increased under such conditions. It was also shown that the Rcs system negatively controls the expression of the two csg operons in an RcsA-dependent manner. In the tol mutants, activation of csgDEFG occurred via OmpR and was dominant upon repression by RcsB and RcsA, while these two regulatory proteins repressed csgBA through a dominant effect on the activator protein CsgD, thus affecting curli synthesis. The results demonstrate that the Rcs system, previously known to control the synthesis of the capsule and the flagella, is an additional component involved in the regulation of curli. Furthermore, it is shown that the defect in cell motility observed in the tol mutants depends on RcsB and RcsA.

scholarly journals Central Role of Toll-Like Receptor 4 Signaling and Host Defense in Experimental Pneumonia Caused by Gram-Negative Bacteria

2005 ◽  
Vol 73 (1) ◽  
pp. 532-545 ◽  
Author(s):  
Jill R. Schurr ◽  
Erana Young ◽  
Pat Byrne ◽  
Chad Steele ◽  
Judd E. Shellito ◽  
...  
Keyword(s):  
Gene Expression ◽  
Adaptor Protein ◽  
Mouse Strains ◽  
Gram Negative Bacteria ◽  
Toll Like Receptor ◽  
Toll Like Receptor 4 ◽  
Tlr4 Signaling ◽  
Gram Negative ◽  
Experimental Pneumonia

ABSTRACT Toll-like receptor 4 (TLR4) has been identified as a receptor for lipopolysaccharide. However, the precise role of TLR4 in regulating gene expression in response to an infection caused by gram-negative bacteria has not been fully elucidated. The role of TLR4 signaling in coordinating gene expression was assessed by gene expression profiling in lung tissue in a mouse model of experimental pneumonia with a low-dose infection of Klebsiella pneumoniae. We analyzed four mouse strains: C57BL/6 mice, which are resistant to bacterial dissemination; 129/SvJ mice, which are susceptible; C3H/HeJ mice, which are susceptible and have defective TLR4 signaling; and their respective control strain, C3H/HeN (intermediate resistance). At 4 h after infection, C57BL/6 and C3H/HeN mice demonstrated the greatest number of genes, with 67 shared induced genes which were TLR4 dependent and highly associated with the resistance phenotype. These genes included cytokine and chemokine genes required for neutrophil activation or recruitment, growth factor receptors, MyD88 (a critical adaptor protein for TLR signaling), and adhesion molecules. TLR4 signaling accounted for over 74% of the gene expression in the C3H background. These data suggest that early TLR4 signaling controls the vast majority of gene expression in the lung in response to an infection caused by gram-negative bacteria and that this subsequent gene expression determines survival of the host.

scholarly journals Toll-Like Receptor 4 Protects Against Clostridium perfringens Infection in Mice

2021 ◽  
Vol 11 ◽  
Author(s):  
Masaya Takehara ◽  
Keiko Kobayashi ◽  
Masahiro Nagahama
Keyword(s):  
Clostridium Perfringens ◽  
Gram Negative Bacteria ◽  
Toll Like Receptor ◽  
Toll Like Receptor 4 ◽  
Gram Positive ◽  
Gram Negative ◽  
Tlr4 Agonist ◽  
Innate Ability ◽  
Recognition Receptor

Toll-like receptor 4 (TLR4) has been reported to protect against Gram-negative bacteria by acting as a pathogen recognition receptor that senses mainly lipopolysaccharide (LPS) from Gram-negative bacteria. However, the role of TLR4 in Gram-positive bacterial infection is less well understood. Clostridium perfringens type A is a Gram-positive bacterium that causes gas gangrene characterized by severe myonecrosis. It was previously demonstrated that C. perfringens θ-toxin is a TLR4 agonist, but the role of TLR4 in C. perfringens infection is unclear. Here, TLR4-defective C3H/HeJ mice infected with C. perfringens showed a remarkable decrease in survival rate, an increase in viable bacterial counts, and accelerated destruction of myofibrils at the infection site compared with wild-type C3H/HeN mice. These results demonstrate that TLR4 plays an important role in the elimination of C. perfringens. Remarkable increases in levels of inflammatory cytokines, such as interleukin-1β (IL-1β), interleukin-6 (IL-6), and granulocyte colony-stimulating factor (G-CSF), were observed in C. perfringens-infected C3H/HeN mice, whereas the increases were limited in C3H/HeJ mice. Generally, increased G-CSF accelerates granulopoiesis in the bone marrow and the spleen to exacerbate neutrophil production, resulting in elimination of bacteria. The number of neutrophils in the spleen was increased in C. perfringens-infected C3H/HeN mice compared with non-infected mice, while the increase was lower in C. perfringens-infected C3H/HeJ mice. Furthermore, DNA microarray analysis revealed that the mutation in TLR4 partially affects host gene expression during C. perfringens infection. Together, our results illustrate that TLR4 is crucial for the innate ability to eliminate C. perfringens.

scholarly journals MexAB-OprM Efflux Pump Interaction with the Peptidoglycan of Escherichia coli and Pseudomonas aeruginosa

2021 ◽  
Vol 22 (10) ◽  
pp. 5328
Author(s):  
Miao Ma ◽  
Margaux Lustig ◽  
Michèle Salem ◽  
Dominique Mengin-Lecreulx ◽  
Gilles Phan ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Pseudomonas Aeruginosa ◽  
Cell Division ◽  
Membrane Proteins ◽  
Outer Membrane ◽  
Efflux Pump ◽  
Gram Negative Bacteria ◽  
Gram Negative ◽  
Active Efflux

One of the major families of membrane proteins found in prokaryote genome corresponds to the transporters. Among them, the resistance-nodulation-cell division (RND) transporters are highly studied, as being responsible for one of the most problematic mechanisms used by bacteria to resist to antibiotics, i.e., the active efflux of drugs. In Gram-negative bacteria, these proteins are inserted in the inner membrane and form a tripartite assembly with an outer membrane factor and a periplasmic linker in order to cross the two membranes to expulse molecules outside of the cell. A lot of information has been collected to understand the functional mechanism of these pumps, especially with AcrAB-TolC from Escherichia coli, but one missing piece from all the suggested models is the role of peptidoglycan in the assembly. Here, by pull-down experiments with purified peptidoglycans, we precise the MexAB-OprM interaction with the peptidoglycan from Escherichia coli and Pseudomonas aeruginosa, highlighting a role of the peptidoglycan in stabilizing the MexA-OprM complex and also differences between the two Gram-negative bacteria peptidoglycans.

The role of Gram-negative bacteria in skin and soft tissue infections

2021 ◽  
Vol Publish Ahead of Print ◽  
Author(s):  
Alessandro Russo ◽  
Enrico Maria Trecarichi ◽  
Carlo Torti
Keyword(s):  
Soft Tissue ◽  
Gram Negative Bacteria ◽  
Soft Tissue Infections ◽  
Gram Negative

scholarly journals Human genetic deficiencies reveal the roles of complement in the inflammatory network: Lessons from nature

2009 ◽  
Vol 106 (37) ◽  
pp. 15861-15866 ◽  
Author(s):  
Knut Tore Lappegård ◽  
Dorte Christiansen ◽  
Anne Pharo ◽  
Ebbe Billmann Thorgersen ◽  
Bernt Christian Hellerud ◽  
...  
Keyword(s):  
Inflammatory Responses ◽  
Gram Negative Bacteria ◽  
Enzyme Release ◽  
Experimental Conditions ◽  
Gram Negative ◽  
Cytokines And Chemokines ◽  
Ifn Γ ◽  
Inducible Protein ◽  
The Complement System

Complement component C5 is crucial for experimental animal inflammatory tissue damage; however, its involvement in human inflammation is incompletely understood. The responses to Gram-negative bacteria were here studied taking advantage of human genetic complement-deficiencies—nature's own knockouts—including a previously undescribed C5 defect. Such deficiencies provide a unique tool for investigating the biological role of proteins. The experimental conditions allowed cross-talk between the different inflammatory pathways using a whole blood model based on the anticoagulant lepirudin, which does not interfere with the complement system. Expression of tissue factor, cell adhesion molecules, and oxidative burst depended highly on C5, mediated through the activation product C5a, whereas granulocyte enzyme release relied mainly on C3 and was C5a-independent. Release of cytokines and chemokines was mediated to varying degrees by complement and CD14; for example, interleukin (IL)-1β and IL-8 were more dependent on complement than IFN-γ and IL-6, which were highly dependent on CD14. IL-1 receptor antagonist (IL-1ra) and IFN-γ inducible protein 10 (IP-10) were fully dependent on CD14 and inversely regulated by complement, that is, complement deficiency and complement inhibition enhanced their release. Granulocyte responses were mainly complement-dependent, whereas monocyte responses were more dependent on CD14. Notably, all responses were abolished by combined neutralization of complement and CD14. The present study provides important insight into the comprehensive role of complement in human inflammatory responses to Gram-negative bacteria.

scholarly journals Relationship Between Membrane Vesicles, Extracellular ATP and Biofilm Formation in Antarctic Gram-Negative Bacteria

2020 ◽  
Author(s):  
Nicolas Baeza ◽  
Elena Mercade
Keyword(s):  
Biofilm Formation ◽  
Membrane Vesicles ◽  
Metabolic Cost ◽  
Extracellular Atp ◽  
Gram Negative Bacteria ◽  
Bacterial Survival ◽  
Gram Negative ◽  
Two Factors ◽  
And Control

Abstract Biofilms offer a safe environment that favors bacterial survival; for this reason, most pathogenic and environmental bacteria live integrated in biofilm communities. The development of biofilms is complex and involves many factors, which need to be studied in order to understand bacterial behavior and control biofilm formation when necessary. We used a collection of cold-adapted Antarctic Gram-negative bacteria to study whether their ability to form biofilms is associated with a capacity to produce membrane vesicles and secrete extracellular ATP. In most of the studied strains, no correlation was found between biofilm formation and these two factors. Only Shewanella vesiculosa M7T secreted high levels of extracellular ATP, and its membrane vesicles caused a significant increase in the speed and amount of biofilm formation. In this strain, an important portion of the exogenous ATP was contained in membrane vesicles, where it was protected from apyrase treatment. These results confirm that ATP influences biofilm formation. Although the role of extracellular ATP in prokaryotes is still not well understood, the metabolic cost of its production suggests it has an important function, such as a role in biofilm formation. Thus, the liberation of extracellular ATP through membrane vesicles and its function deserve further study.

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