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  • 1
    Electronic Resource
    Electronic Resource
    Strategies for the Development of Vaccines for Typhoid Fever, Shigellosis, and Cholera (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 569 (1989), S. 0 
    Details
    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
    URL: http://dx.doi.org/10.1111/j.1749-6632.1989.tb27365.x
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  • 2
    Electronic Resource
    Electronic Resource
    PmrA–PmrB-regulated genes necessary for 4-aminoarabinose lipid A modification and polymyxin resistance (1998)
    Oxford BSL : Blackwell Science Ltd, UK
    Molecular microbiology 27 (1998), S. 0 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00757.x
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  • 3
    Electronic Resource
    Electronic Resource
    Regulation of Salmonella typhimurium virulence gene expression by cationic antimicrobial peptides (2003)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 50 (2003), S. 0 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03675.x
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  • 4
    Electronic Resource
    Electronic Resource
    The Salmonella type III secretion translocon protein SspC is inserted into the epithelial cell plasma membrane upon infection (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 37 (2000), S. 0 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.02066.x
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  • 5
    Electronic Resource
    Electronic Resource
    Variation in lipid A structure in the pathogenic yersiniae (2004)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 52 (2004), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Important pathogens in the genus Yersinia include the plague bacillus Yersinia pestis and two enteropathogenic species, Yersinia pseudotuberculosis and Yersinia enterocolitica. A shift in growth temperature induced changes in the number and type of acyl groups on the lipid A of all three species. After growth at 37°C, Y. pestis lipopolysaccharide (LPS) contained the tetra-acylated lipid IVA and smaller amounts of lipid IVA modified with C10 or C12 acyl groups, Y. pseudotuberculosis contained the same forms as part of a more heterogeneous population in which lipid IVA modified with C16:0 predominated, and Y. enterocolitica produced a unique tetra-acylated lipid A. When grown at 21°C, however, the three yersiniae synthesized LPS containing predominantly hexa-acylated lipid A. This more complex lipid A stimulated human monocytes to secrete tumour necrosis factor-α, whereas the lipid A synthesized by the three species at 37°C did not. The Y. pestis phoP gene was required for aminoarabinose modification of lipid A, but not for the temperature-dependent acylation changes. The results suggest that the production of a less immunostimulatory form of LPS upon entry into the mammalian host is a conserved pathogenesis mechanism in the genus Yersinia, and that species-specific lipid A forms may be important for life cycle and pathogenicity differences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2004.04059.x
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  • 6
    Electronic Resource
    Electronic Resource
    Salmonella effectors translocated across the vacuolar membrane interact with the actin cytoskeleton (2003)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 48 (2003), S. 0 
    Details
    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
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.t01-1-03456.x
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  • 7
    Electronic Resource
    Electronic Resource
    Transcriptional activation of Salmonella typhimurium invasion genes by a member of the phosphorylated response-regulator superfamily (1996)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 22 (1996), S. 0 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1996.d01-1719.x
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  • 8
    Electronic Resource
    Electronic Resource
    Salmonella typhimurium secreted invasion determinants are homologous to Shigella lpa proteins (1995)
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Science Ltd
    Molecular microbiology 18 (1995), S. 0 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.mmi_18030479.x
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  • 9
    Electronic Resource
    Electronic Resource
    PhoP/PhoQ transcriptional repression of Salmonella typhimurium invasion genes: evidence for a role in protein secretion (1995)
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Scientific Publications
    Molecular microbiology 17 (1995), S. 0 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.mmi_17010169.x
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  • 10
    Electronic Resource
    Electronic Resource
    Salmonella typhimurium leucine-rich repeat proteins are targeted to the SPI1 and SPI2 type III secretion systems (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 34 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Salmonellae encode two virulence-associated type III secretion systems (TTSS) within Salmonella pathogenicity islands 1 and 2 (SPI1 and SPI2). Two Salmonella typhimurium genes, sspH1 and sspH2, that encode proteins similar to the Shigella flexneri and Yersinia species TTSS substrates, IpaH and YopM, were identified. SspH1 and SspH2 are proteins containing leucine-rich repeats that are differentially targeted to the SPI1 and SPI2 TTSS. sspH2 transcription was induced within RAW264.7 macrophages, and was dependent upon the SPI2-encoded regulator ssrA/ssrB. In contrast, sspH1 transcription is independent of SPI2, and is not induced after bacterial phagocytosis by eukaryotic cells. Infection of eukaryotic cells with strains expressing a SspH2–CyaA fusion protein resulted in SPI2 TTSS-dependent cAMP increases. In contrast, SspH1–CyaA-mediated cAMP increases were both SPI1 and SPI2 TTSS dependent. sspH2-like sequences were found in most Salmonella serotypes examined, whereas sspH1 was detected in only one S. typhimurium isolate, indicating that the copy number of sspH genes can be variable within Salmonella serotypes. S. typhimurium deleted for both sspH1 and sspH2 was not able to cause a lethal infection in calves, indicating that these genes participate in S. typhimurium virulence for animals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01651.x
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