| 1. |
- Beiter, Katharina, et al.
(author)
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An endonuclease allows Streptococcus pneumoniae to escape from neutrophil extracellular traps
- 2006
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In: Current Biology. - : Elsevier BV. - 1879-0445 .- 0960-9822. ; 16:4, s. 401-407
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Journal article (peer-reviewed)abstract
- Streptococcus pneumoniae (pneumococcus) is the most common cause of community-acquired pneumonia, with high morbidity and mortality worldwide. A major feature of pneumococcal pneumonia is an abundant neutrophil infiltration . It was recently shown that activated neutrophils release neutrophil extracellular traps (NETs), which contain antimicrobial proteins bound to a DNA scaffold. NETs provide a high local concentration of antimicrobial components and bind, disarm, and kill microbes extracellularly. Here, we show that pneumococci are trapped but, unlike many other pathogens, not killed by NETs. NET trapping in the lungs, however, may allow the host to confine the infection, reducing the likelihood for the pathogen to spread into the bloodstream. DNases are expressed by many Gram-positive bacterial pathogens, but their role in virulence is not clear. Expression of a surface endonuclease encoded by endA is a common feature of many pneumococcal strains. We show that EndA allows pneumococci to degrade the DNA scaffold of NETs and escape. Furthermore, we demonstrate that escaping NETs promotes spreading of pneumococci from the upper airways to the lungs and from the lungs into the bloodstream during pneumonia.
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| 2. |
- Bletsa, Eleni, et al.
(author)
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Highly durable photocatalytic titanium suboxide–polymer nanocomposite films with visible light-triggered antibiofilm activity
- 2023
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In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 454, part 1
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Journal article (peer-reviewed)abstract
- Bacterial biofilms on medical devices may result in infections with significant societal burden. One drug-free strategy against biofilms is photocatalysis, in which a semiconducting coating is applied on the medical device and irradiated with light to generate reactive oxygen species providing an on-demand disinfection approach. However, most photocatalytic materials are active in the harmful UV range rendering them unsuitable for biomedical applications. Furthermore, the main manufacturing bottleneck today for antibiofilm coatings is their poor durability. To address these challenges, here we produced silver/titanium-suboxide nanoparticles that are photocatalytically active in the visible-light range. Moreover, we directly deposited the nanoparticles as porous coatings on substrates in situ during their aerosol synthesis. To enhance their durability, we infused the fabricated porous coatings with a polymer solution barely covering the photocatalytic particle film, resulting in the formation of polymer nanocomposite coatings. The optimized polymer nanocomposite films exhibit several cycles of triggered, on-demand biofilm eradication activity under short visible light illumination of 15–90 min with no significant intrinsic cytotoxicity to mammalian cells. The developed films can be considered as a suitable coating material for medical devices, such as catheters, ventilators, wound meshes, and others, that may require repeated disinfection during use.
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| 3. |
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| 4. |
- Daniels, Robert, et al.
(author)
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Disulfide Bond Formation and Cysteine Exclusion in Gram-positive Bacteria
- 2010
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In: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 285:5, s. 3300-3309
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Journal article (peer-reviewed)abstract
- Most secretion pathways in bacteria and eukaryotic cells are challenged by the requirement for their substrate proteins to mature after they traverse a membrane barrier and enter a reactive oxidizing environment. For Gram-positive bacteria, the mechanisms that protect their exported proteins from misoxidation during their post-translocation maturation are poorly understood. To address this, we separated numerous bacterial species according to their tolerance for oxygen and divided their proteomes based on the predicted subcellular localization of their proteins. We then applied a previously established computational approach that utilizes cysteine incorporation patterns in proteins as an indicator of enzymatic systems that may exist in each species. The Sec-dependent exported proteins from aerobic Gram-positive Actinobacteria were found to encode cysteines in an even-biased pattern indicative of a functional disulfide bond formation system. In contrast, aerobic Gram-positive Firmicutes favor the exclusion of cysteines from both their cytoplasmic proteins and their substantially longer exported proteins. Supporting these findings, we show that Firmicutes, but not Actinobacteria, tolerate growth in reductant. We further demonstrate that the actinobacterium Corynebacterium glutamicum possesses disulfide-bonded proteins and two dimeric Dsb-like enzymes that can efficiently catalyze the formation of disulfide bonds. Our results suggest that cysteine exclusion is an important adaptive strategy against the challenges presented by oxidative environments.
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| 5. |
- Littmann, Marie, et al.
(author)
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Streptococcus pneumoniae evades human dendritic cell surveillance by pneumolysin expression
- 2009
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In: EMBO Molecular Medicine. - : EMBO. - 1757-4684 .- 1757-4676. ; 1:4, s. 211-222
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Journal article (peer-reviewed)abstract
- Dendritic cells (DCs) protect the respiratory epithelium via induction of innate immune responses and priming of naive T cells during the initiation of adaptive immunity. Streptococcus pneumoniae, a commonly carried asymptomatic member of the human nasopharyngeal microflora, can cause invasive and inflammatory diseases and the cholesterol-dependent cytotoxin pneumolysin is a major pneumococcal virulence factor implicated in compounding tissue damage and mediating inflammatory responses. While most studies examining the impact of pneumolysin have been based on murine models, we have focused this study on human DC responses. We show that expression of haemolytic pneumolysin inhibits human DC maturation, induction of proinflammatory cytokines and activation of the inflammasome. Furthermore, intracellular production of pneumolysin induces caspase-dependent apoptosis in infected DCs. Similarly, clinical isolates with non-haemolytic pneumolysin were more proinflammatory and caused less apoptosis compared to clonally related strains with active pneumolysin. This study describes a novel role of pneumolysin in the evasion of human DC surveillance that could have a profound clinical impact upon inflammatory disease progression and highlights the need to study human responses to human-specific pathogens.
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| 6. |
- Lopez-Valladares, Gloria, 1963-, et al.
(author)
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Human isolates of Listeria monocytogenes in Sweden during half a century (1958-2010)
- 2014
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In: Epidemiology and Infection. - 0950-2688 .- 1469-4409. ; 142, s. 2251-2260
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Journal article (peer-reviewed)abstract
- Isolates of Listeria monocytogenes (n=932) isolated in Sweden during 1958–2010 from human patients with invasive listeriosis were characterized by serotyping and pulsed-field gel electrophoresis (PFGE) (AscI). Of the 932 isolates, 183 different PFGE types were identified, of which 83 were each represented by only one isolate. In all, 483 serovar 1/2a isolates were distributed over 114 PFGE types; 90 serovar 1/2b isolates gave 32 PFGE types; 21 serovar 1/2c isolates gave nine PFGE types; three serovar 3b isolates gave one PFGE type; and, 335 serovar 4b isolates gave 31 PFGE types. During the 1980s in Sweden, several serovar 4b cases were associated with the consumption of European raw soft cheese. However, as cheese-production hygiene has improved, the number of 4b cases has decreased. Since 1996, serovar 1/2a has been the dominant L. monocytogenes serovar in human listeriosis in Sweden. Therefore, based on current serovars and PFGE types, an association between human cases of listeriosis and the consumption of vacuum-packed gravad and cold-smoked salmon is suggested.
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| 7. |
- Mellroth, Peter, et al.
(author)
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LytA, Major Autolysin of Streptococcus pneumoniae, Requires Access to Nascent Peptidoglycan
- 2012
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In: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 287:14, s. 11018-11029
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Journal article (peer-reviewed)abstract
- Background: The regulation of cell wall hydrolysis by the pneumococcal autolysin LytA is poorly understood. Results: The cell wall is susceptible to extracellular LytA only during the stationary phase or after cell wall synthesis inhibition. Conclusion: LytA is regulated on the substrate level, where peptidoglycan modifications likely prevent LytA hydrolysis. Significance: The control of amidases is essential for bacterial survival, cell-wall synthesis, and division.
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| 8. |
- Mellroth, Peter, et al.
(author)
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Structural and Functional Insights into Peptidoglycan Access for the Lytic Amidase LytA of Streptococcus pneumoniae
- 2014
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In: mBio. - 2161-2129 .- 2150-7511. ; 5:1, s. e01120-13-
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Journal article (peer-reviewed)abstract
- The cytosolic N-acetylmuramoyl-L-alanine amidase LytA protein of Streptococcus pneumoniae, which is released by bacterial lysis, associates with the cell wall via its choline-binding motif. During exponential growth, LytA accesses its peptidoglycan substrate to cause lysis only when nascent peptidoglycan synthesis is stalled by nutrient starvation or beta-lactam antibiotics. Here we present three-dimensional structures of LytA and establish the requirements for substrate binding and catalytic activity. The solution structure of the full-length LytA dimer reveals a peculiar fold, with the choline-binding domains forming a rigid V-shaped scaffold and the relatively more flexible amidase domains attached in a trans position. The 1.05-angstrom crystal structure of the amidase domain reveals a prominent Y-shaped binding crevice composed of three contiguous subregions, with a zinc-containing active site localized at the bottom of the branch point. Site-directed mutagenesis was employed to identify catalytic residues and to investigate the relative impact of potential substrate-interacting residues lining the binding crevice for the lytic activity of LytA. In vitro activity assays using defined muropeptide substrates reveal that LytA utilizes a large substrate recognition interface and requires large muropeptide substrates with several connected saccharides that interact with all subregions of the binding crevice for catalysis. We hypothesize that the substrate requirements restrict LytA to the sites on the cell wall where nascent peptidoglycan synthesis occurs. IMPORTANCE Streptococcus pneumoniae is a human respiratory tract pathogen responsible for millions of deaths annually. Its major pneumococcal autolysin, LytA, is required for autolysis and fratricidal lysis and functions as a virulence factor that facilitates the spread of toxins and factors involved in immune evasion. LytA is also activated by penicillin and vancomycin and is responsible for the lysis induced by these antibiotics. The factors that regulate the lytic activity of LytA are unclear, but it was recently demonstrated that control is at the level of substrate recognition and that LytA required access to the nascent peptidoglycan. The present study was undertaken to structurally and functionally investigate LytA and its substrate-interacting interface and to determine the requirements for substrate recognition and catalysis. Our results reveal that the amidase domain comprises a complex substrate-binding crevice and needs to interact with a large-motif epitope of peptidoglycan for catalysis.
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| 9. |
- Muschiol, Sandra, et al.
(author)
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A small-molecule inhibitor of type III secretion inhibits different stages of the infectious cycle of Chlamydia trachomatis
- 2006
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In: National Academy of Sciences, USA. - Washington : Proceedings of the National Academy of Sciences. ; , s. 14566-71
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Conference paper (other academic/artistic)abstract
- The intracellular pathogen Chlamydia trachomatis possesses a type III secretion (TTS) system believed to deliver a series of effector proteins into the inclusion membrane (Inc-proteins) as well as into the host cytosol with perceived consequences for the pathogenicity of this common venereal pathogen. Recently, small molecules were shown to block the TTS system of Yersinia pseudotuberculosis. Here, we show that one of these compounds, INP0400, inhibits intracellular replication and infectivity of C. trachomatis at micromolar concentrations resulting in small inclusion bodies frequently containing only one or a few reticulate bodies (RBs). INP0400, at high concentration, given at the time of infection, partially blocked entry of elementary bodies into host cells. Early treatment inhibited the localization of the mammalian protein 14-3-3beta to the inclusions, indicative of absence of the early induced TTS effector IncG from the inclusion membrane. Treatment with INP0400 during chlamydial mid-cycle prevented secretion of the TTS effector IncA and homotypic vesicular fusions mediated by this protein. INP0400 given during the late phase resulted in the detachment of RBs from the inclusion membrane concomitant with an inhibition of RB to elementary body conversion causing a marked decrease in infectivity.
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| 10. |
- Parihar, Vishal Singh, et al.
(author)
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Characterization of human invasive isolates of Listeria monocytogenes in Sweden 1986-2007
- 2008
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In: Foodborne pathogens and disease. - : Mary Ann Liebert. - 1535-3141 .- 1556-7125. ; 5:6, s. 755-761
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Journal article (peer-reviewed)abstract
- Since 1986, 68% of the Listeria monocytogenes isolates from human cases of invasive listeriosis in Sweden are available for retrospective studies. The aim of the present study was to characterize 601 human invasive isolates of L. monocytogenes in Sweden from 1986 to 2007 by using serotyping and pulsed-field gel electrophoresis. Since 1996, serovar 4b was permanently reduced to the second or third most common serovar in human cases in Sweden. During the latter period, 2000-2007, only 13% belonged to serovar 4b and 71% to 1/2a. The dendrogram, based on pulsovars, reveals two clusters with different serovars. Cluster 1 exhibits serovars 4b and 1/2b, whereas cluster 2 consists of serovar 1/2a. Serovar 1/2a seems to be more heterogeneous than serovar 4b.
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