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  • Articles  (16)
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  • 1
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A phospholipase C which cleaves phosphatidylinositol and glycosylphosphatidylinositol (GPI) anchors was identified in Listeria monocytogenes. This 36kDa protein is encoded by the gene plcA, and is homologous to the Bacillus cereus, Bacillus thuringiensis and eukaryotic phosphatidylinositol-specific phospholipases C (PI-PLC). Expression of the plcA gene in Escherichia coli correlates with the appearance of PI-PLC activity in the cells. In Listeria monocytogenes, the activity is secreted to the culture medium. PI-PLC activity was only found in the two pathogenic species of the genus Listeria, namely L. monocytogenes and L. ivanovii. PI-PLC activity was lost and virulence decreased when the plcA gene was disrupted in the chromosome. This suggests that the PI-PLC of L. monocytogenes might be involved in virulence.
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  • 2
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Listeriotysjn O (LLO), a major virulence factor of the intracellular bacterium Listens monocytogenes, shares with other known ‘thiol-activated toxins’ a conserved undecapeptide, ECTGLAWEWWR, located in the C-terminal region of the protein and containing the unique cysteine of the molecule. Single amino acid substitutions were created in this region to study the role of cysteine and tryptophan residues in the lytic activity of LLO as well as in the virulence of the bacterium. Transformation of a transposon-induced non-haemolytic mutant with plasmids carrying the mutated genes allowed allele exchange and transfer of mutations on to the chromosome by in vivo recombination. The mutant strains secreted a full-length 59 kilodalton LLO. A decrease of 25% in the haemolytic activity in culture supernatants was observed in the case of mutation Cys-484 to Ala and of 80% for mutation Cys-484 to Ser. Mutations Trp-491 and Trp-492 to Ala decreased activity by, respectively, 95% and 99.9%. LLOs produced by the mutants, as the wild type, were active at low pH, inhibited by cholesterol, and able to bind to cell membranes. A close relationship was found between virulence of mutants in the mouse model and haemolytic activity in their culture supematants. These results demonstrate that the thiol group of Cys-484 is not essential for either haemolytic activity in vitro or virulence in vivo. In contrast, Trp-492 appears to be required for both haemolytic activity and virulence. The finding that the nearly non-haemolytic mutant Trp-492-Ala persisted in the spleen for several days after inoculation indicates that mutagenesis of a virulence determinant can attenuate virulence and provides a novel approach to the development of live vaccine strains.
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  • 3
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cloning and sequence of the regulatory region of the threonine operon of E. coli K12 carried by a constitutive mutant are presented. In this mutant the transcription termination signal, located upstream from the first structural gene, is deleted. These results strongly support the model of attenuation for the regulation of the threonine operon as first proposed by Gardner (1979)
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 9 (1993), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
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  • 5
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Entry of Listeria monocytogenes into epithelial cells requires expression of inlA, the first gene of an operon comprising two genes: inlA, which encodes internalin, a 800-amino-acid protein, and inlB, which encodes a 630-amino-acid protein. We report here that the inl locus is transcribed on two transcripts in constant relative ratio: a 5 kb transcript spanning inlA and inlB, and a 2.9 kb transcript that covers only inlA. The promoter is located 397 bp from the GTG initiator of inlA and displays in its -35 region a palindrome similar to that found in promoters controlled by the pleiotropic activator prfA. Transcription of the inl locus is, as are several other L. monocytogenes virulence genes, activated by prfA and regulated by temperature—with higher expression at 37°C versus 25°C — and bacterial growth state. It is maximal during exponential growth and correlates with maximal invasivity of the bacteria in the human epithelial cell line Caco-2. It also correlates with maximum amounts of internalin present on the bacterial surface. Internalin is also detected in substantial amounts in culture supernatants. Taken together, these data suggest that surface-bound internalin plays an important role in bacterial entry but do not exclude a role for the released form.
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  • 6
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Listeria monocytogenes is a Gram-positive intracellular bacterium responsible for severe opportunistic infections in humans and animals. Signature-tagged mutagenesis (STM) was used to identify a gene named fbpA, required for efficient liver colonization of mice inoculated intravenously. FbpA was also shown to be required for intestinal and liver colonization after oral infection of transgenic mice expressing human E-cadherin. fbpA encodes a 570-amino-acid polypeptide that has strong homologies to atypical fibronectin-binding proteins. FbpA binds to immobilized human fibronectin in a dose-dependent and saturable manner and increases adherence of wild-type L. monocytogenes to HEp-2 cells in the presence of exogenous fibronectin. Despite the lack of conventional secretion/anchoring signals, FbpA is detected using an antibody generated against the recombinant FbpA protein on the bacterial surface by immunofluorescence, and in the membrane compartment by Western blot analysis of cell extracts. Strikingly, FbpA expression affects the protein levels of two virulence factors, listeriolysin O (LLO) and InlB, but not that of InlA or ActA. FbpA co-immunoprecipitates with LLO and InlB, but not with InlA or ActA. Thus, FbpA, in addition to being a fibronectin-binding protein, behaves as a chaperone or an escort protein for two important virulence factors and appears as a novel multifunctional virulence factor of L. monocytogenes.
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  • 7
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Evidence for ptelotropic activation of virulence genes in Listeria monocytogenes is presented. A complementation study of a spontaneous prfA-deletion mutant and analysis of cassette and transposon insertion mutants showed that the gene prfA activates the transcription of four independent genes which code for a phosphatidyl-inositol-specific phospholipase C (gene plcA), listeriolysin O (gene hlyA), a metallo-protease (gene prtA) and a lecithinase (gene prtC). Transcription of prfA is not constitutive. During the growth phase, two peaks of prfA transcript accumulation were observed: the first was during exponential growth, and the second was at the beginning of the stationary phase. In addition, two prf4-specific transcripts of 2.2 kb and 1 kb are detected. Early in exponential growth, prfA is co-transcribed with plcA which lies upstream prfA, giving rise to the 2.2 kb plcA-prfA transcript. In late-exponential growth and at the beginning of the stationary phase, prfA transcripts of 1 kb are predominantly detected. Our results demonstrate that since prfA controls plcA transcription, it also regulates its own synthesis.
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  • 8
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Listeria monocytogenes and Shigella flexneri are two unrelated facultative intracellular pathogens which spread from cell to cell by using a similar mode of intracellular movement based on continuous actin assembly at one pole of the bacterium. This process requires the asymmetrical expression of the ActA surface protein in L. monocytogenes and the lcsA (VirG) surface protein in S. flexneri. ActA and lcsA share no sequence homology. To assess the role of the two proteins in the generation of actin-based movement, we expressed them in the genetic context of two non-actin polymerizing, non-pathogenic bacterial species, Listeria innocua and Escherichia coli. In the absence of any additional bacterial pathogenicity determinants, both proteins induced actin assembly and propulsion of the bacteria in cytoplasmic extracts from Xenopus eggs, as visualized by the formation of characteristic actin comet tails. E. coli expressing lcsA moved about two times faster than Listeria and displayed longer actin tails. However, actin dynamics (actin filament distribution and filament half-lives) were similar in lcsA- and ActA-induced actin tails suggesting that by using unrelated surface molecules, L. monocytogenes and S. flexneri move intracellularly by interacting with the same host cytoskeleton components or by interfering with the same host cell signal transduction pathway.
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  • 9
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Through the analysis of a non-motile mutant of Listeria monocytogenes, we identified and characterized a locus containing the cheR, motA and motB genes. These three genes are homologous to the cheR, and motA/B genes of Bacillus subtilis which in this organism are 954 kb apart. The gene organization in Listeria is also not similar either to that of Escherichia coli in which cheR and motAB are 5.9 kb apart. CheR and motA/B, as previously reported for flaA, the flagellin gene, are thermoregulated with a higher expression at 25°C and low expression at 37°C. In a ΔprfA strain, motA expression was derepressed at 37°C, suggesting that PrfA, the transcriptional activator of virulence genes, downregulates motility genes in Listeria at 37°C.
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  • 10
    ISSN: 1439-0973
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Wir haben in Kulturüberständen einer Tn1545-induzierten, nicht-hämolysierenden Mutante vonListeria monocytogenes mittels Immunblotting mit Antiserum gegen gereinigtes Listeriolysin ein Eiweißmolekül von 52000D entdeckt (das sezernierte Listeriolysin O hat ein Molekulargewicht von 60000D). Die Insertionsstelle des Transposon wurde kloniert und einer Sequenzanalyse unterworfen. Das Transposon hatte an einem offenen Ableseraster (ORF) inseriert. Zwischen diesem ORF, Streptolysin O und Pneumolysin wurden Homologien festgestellt, die zeigen, daß das Transposon tatsächlich am Listeriolysin-Gen inseriert hatte. Da die nicht-hämolysierende Mutante avirulent war, konnten wir mit unserer Arbeit nachweisen, daß für die Virulenz die Anwesenheit des Listeriolysin-Gen oder seiner angrenzenden Region erforderlich ist.
    Notes: Summary In culture supernatants of a Tn 1545-induced non-hemolytic mutant ofListeria monocytogenes, by immunoblotting with an anti-serum raised against purified listeriolysin O, we have detected the presence of a truncated protein of 52,000D (the secreted listeriolysin O is 60,000D). The region of insertion of the transposon has been cloned and sequenced. The transposon had inserted in an open reading frame. The homologies detected between this ORF, streptolysin O and pneumolysin demonstrate the the transposon had indeed inserted in the listeriolysin O gene. As the non-hemolytic mutant was non-virulent, our work demonstrated that a genetic determinant essential for virulence is the listeriolysin O gene or its adjacent region.
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