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  • 1
    Electronic Resource
    Electronic Resource
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Scientific Publications
    Molecular microbiology 17 (1995), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Previously, the PhoP-repressed locus prgH was identified as important for signalling epithelial cells to endocytose Salmonella typhimurium. Characterization of prgH revealed that it is an operon of four genes encoding polypeptides of 392 (prgH), 80 (prgl), 101 (prgJ) and 252 amino acid residues (prgK). Synthesis of the 2.6 kb prgHIJK transcript was repressed in bacteria that activate PhoP/PhoQ, indicating that PhoP/PhoQ regulates prgHIJK by transcriptional repression. The prgl, prgJ and prgK predicted gene products were similar to Shigella flexneri and Yersinia enterocolitica proteins required for secretion of lpa and Yop virulence factors. Analysis of the culture supernatants from wild-type S. typhimurium demonstrated that at least 25 polypeptides larger than 14 kDa could be detected. In contrast, prgH1::TnphoA, phoP-constitutive and hil-deletion mutants had significant defects in their supernatant protein profiles. The invasion and supernatant protein profile defects of the prgH1::TnphoA mutant were both complemented by a 5.1 kb plasmid that included prgHIJK. These results suggest that PhoP/PhoQ regulates extracellular transport of proteins by transcriptional repression of secretion determinants and that secreted proteins may be involved in signalling epithelial cells to endocytose bacteria.
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 436 (2005), S. 1171-1175 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Biofilms are adherent aggregates of bacterial cells that form on biotic and abiotic surfaces, including human tissues. Biofilms resist antibiotic treatment and contribute to bacterial persistence in chronic infections. Hence, the elucidation of the mechanisms by which biofilms are formed may ...
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 435 (2005), S. 702-707 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Type III secretion systems (TTSSs) are multi-protein macromolecular ‘machines’ that have a central function in the virulence of many Gram-negative pathogens by directly mediating the secretion and translocation of bacterial proteins (termed effectors) into the cytoplasm of ...
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Notes: Enteric fevers and diarrheal diseases are major causes of morbidity and mortality throughout the developing world.1 Traditional approaches to the development of vaccines for bacterial diseases include the parenteral injection of purified components or killed organisms.2 These methods require technologically advanced preparation and are relatively expensive despite their proven benefits. Live oral vaccine strains have several advantages over parenteral vaccines: low cost, ease of administration, and simple preparation.The development of live vaccines has been limited by lack of understanding of the pathogenesis of disease on a molecular level. Candidate live vaccine strains require nonrevertable genetic alterations that affect the virulence of the organism, but not its induction of an immune response. Work defining the mechanisms of toxigenesis of Vibrio cholerae has made it possible to create live vaccine strains based on deletion of the toxin genes.3,4 We will discuss below recent studies that have begun to define the molecular basis of Salmonella typhimurium macrophage survival and virulence. This may lead to the development of a live oral Salmonella typhi vaccine that can be used as a carrier for heterologous antigens. This approach has the advantage that immunity to multiple diseases could be generated with a single vaccine strain. Attenuated Salmonella typhi would deliver heterologous antigens directly to the immune effector cell, the macrophage, and generate cell-mediated as well as humoral immune response.5
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 48 (2003), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A family of nine Salmonella typhimurium type III secretion effectors with a conserved amino-terminus have been defined. Three family members (SifA, SifB and SseJ) have previously been demonstrated to localize to the Salmonella-containing vacuole and to Salmonella-induced filaments. In contrast, we demonstrate that two other family members, SspH2 and SseI, co-localized with the polymerizing actin cytoskeleton. These proteins also interacted with the mammalian actin cross-linking protein filamin in the yeast two-hybrid assay through their highly conserved amino-terminal domains. This amino-terminus was sufficient to direct localization to the polymerizing actin cytoskeleton, suggesting that the interaction with filamin is important for this subcellular localization. In addition, SspH2 co-localized with vacuole-associated actin polymerizations (VAP) induced by intracellular bacteria through the Salmonella pathogenicity island (SPI)-2 type III secretion system (TTSS). SspH2 interacted with the actin-binding protein profilin in the yeast two-hybrid assay and by affinity chromatography. This interaction was highly specific to SspH2 and was mediated by its carboxy-terminus. Furthermore, SspH2 inhibited the rate of actin polymerization in vitro, suggesting that it functions to reduce or remodel VAP. Strains with mutations in sspH2 and sseI retained the ability to form VAP. However, a third intracellular virulence factor, spvB, which ADP-ribosylates actin, strongly inhibited VAP formation in HeLa cells, suggesting a more subtle effect for SspH2 and SseI on the actin cytoskeleton.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Science Ltd
    Molecular microbiology 18 (1995), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Salmonella typhimurium secreted proteins (Ssp) were previously implicated in epithelial cell invasion. Here we describe four genes (sspB, sspC, sspD, and sspA), located between spaT and prgH, which encode proteins of 63, 42, 36, and 87 kDa, respectively. These Ssp are homologous to Shigella flexneri secreted proteins lpaB, lpaC, lpaD and lpaA. A non-invasive mutant with a transposon insertion in sspC lacks Ssp of 87,42 and 36 kDa. Complementation analyses show that sspC and sspD encode the 42 and the 36 kDa Ssp, while the 87 kDa Ssp is encoded by sspA. sspC and sspD, but not sspA are required for invasion. Amino-terminal sequencing shows that SspC and SspA are secreted without amino-terminal processing. We further demonstrate that Ssp secretion requires proteins encoded by prgHIJK, homologous to the Shigella lpa secretion system, since SspA is abundantly secreted by wild-type bacteria but is completely retained within the cellular fraction of a prgHIJK mutant. A precipitate containing abundant SspC and three other major Ssp of 63,59 and 22 kDa was isolated from culture supernatants of wild-type bacteria. These data indicate that major secreted invasion determinants of S. typhimurium are structurally and functionally homolgous to S. flexneri lpa proteins.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 50 (2003), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Cationic antimicrobial peptides (CAMP) represent a conserved and highly effective component of innate immunity. During infection, the Gram-negative pathogen Salmonella typhimurium induces different mechanisms of CAMP resistance that promote pathogenesis in animals. This study shows that exposure of S. typhimurium to sublethal concentrations of CAMP activates the PhoP/PhoQ and RpoS virulence regulons, while repressing the transcription of genes required for flagella synthesis and the invasion-associated type III secretion system. We further demonstrate that growth of S. typhimurium in low doses of the α-helical peptide C18G induces resistance to CAMP of different structural classes. Inducible resistance depends on the presence of PhoP, indicating that the PhoP/PhoQ system can sense sublethal concentrations of cationic antimicrobial peptides. Growth of S. typhimurium in the presence of CAMP also leads to RpoS-dependent protection against hydrogen peroxide. Because bacterial resistance to oxidative stress and CAMP are induced during infection of animals, CAMP may be an important signal recognized by bacteria on colonization of animal tissues.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 37 (2000), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Salmonella species translocate effector proteins into the host cell cytoplasm using a type III secretion system (TTSS). The translocation machinery probably contacts the eukaryotic cell plasma membrane to effect protein transfer. Data presented here demonstrate that both SspB and SspC, components of the translocation apparatus, are inserted into the epithelial cell plasma membrane 15 min after Salmonella typhimurium infection. In addition, a yeast two-hybrid interaction between SspC and an eukaryotic intermediate filament protein was identified. Three individual carboxyl-terminal point mutations within SspC that disrupt the yeast two-hybrid interaction were isolated. Strains expressing the mutant SspC alleles were defective for invasion, translocation of effector molecules and membrane localization of SspC. These data indicate that insertion of SspC into the plasma membrane of target cells is required for invasion and effector molecule translocation and that the carboxyl terminus of SspC is essential for these functions.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd, UK
    Molecular microbiology 27 (1998), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Antimicrobial peptides are distributed throughout the animal kingdom and are a key component of innate immunity. Salmonella typhimurium regulates mechanisms of resistance to cationic antimicrobial peptides through the two-component systems PhoP–PhoQ and PmrA–PmrB. Polymyxin resistance is encoded by the PmrA–PmrB regulon, whose products modify the lipopolysaccharide (LPS) core and lipid A regions with ethanolamine and add aminoarabinose to the 4′ phosphate of lipid A. Two PmrA–PmrB-regulated S. typhimurium loci (pmrE and pmrF ) have been identified that are necessary for resistance to polymyxin and for the addition of aminoarabinose to lipid A. One locus, pmrE, contains a single gene previously identified as pagA (or ugd ) that is predicted to encode a UDP-glucose dehydrogenase. The second locus, pmrF, is the second gene of a putative operon predicted to encode seven proteins, some with similarity to glycosyltransferases and other complex carbohydrate biosynthetic enzymes. Genes immediately flanking this putative operon are also regulated by PmrA–PmrB and/or have been associated with S. typhimurium polymyxin resistance. This work represents the first identification of non-regulatory genes necessary for modification of lipid A and subsequent antimicrobial peptide resistance, and provides support for the hypothesis that lipid A aminoarabinose modification promotes resistance to cationic antimicrobial peptides.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 22 (1996), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Salmonella typhimurium PhoP-repressed locus prgHIJK encodes components of a sec-independent type III secretion apparatus. This apparatus is composed of at least 17 proteins encoded on a 40kb pathogenicity island located at centisome 63 on the S. typhimurium chromosome. The secretion apparatus and some of its targets, SspB, SspC and SspD, are necessary for epithelial cell invasion. The transcription of many invasion genes, including prgHIJK, is co-ordinately activated by HilA, a transcription factor encoded within the pathogenicity island. In this report we identify sirA, a gene located outside the pathogenicity island that is essential for induction of prgHIJK and hilA transcription. sirA encodes a 234-amino-acid protein that is essential for S. typhimurium Ssp (Salmonella secreted protein) secretion and invasion and is similar to response regulators of two-component regulatory systems. sirA-mutant phenotypes could be suppressed by two DNA clones from unlinked loci, designated sirB and sirC. These data suggest that SirA may be phosphorylated in response to S. typhimurium sensing a mammalian microenvironment. Furthermore, SirA phosphorylation is predicted to initiate a cascade of transcription-factor synthesis which results in invasion-gene transcription, Ssp secretion, and bacterial invasion of epithelia.
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