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Matthias Frosch

Publications and source records attributed to Matthias Frosch.

At least 37 records · Page 2Linked to original sources
PubMed2005

Carbohydrate composition of meningococcal lipopolysaccharide modulates the interaction of Neisseria meningitidis with human dendritic cells.

Meningococcal lipopolysaccharide (LPS) is of crucial importance for the pathogenesis of invasive infection. We show that sialylation and elongation of the alpha-chain effectively shields viable unencapsulated Neisseria meningitidis from recognition by human dendritic cells (DC). In contrast, beta- and gamma- chain of the LPS carbohydrate moiety play only a minor role in the interaction with DC. The protective function of the LPS for the bacteria can be counteracted in vivo by phase variation of the lgtA gene encoding LPS glycosyltransferase A. Capsule expression protects N. meningitidis efficiently from recognition and phagocytosis by DC independent of the LPS structure. Despite the significant impact of LPS composition on the adhesion and phagocytosis of N. meningitidis no differences were found in terms of cytokine levels secreted by DC for IL1-beta, IL-6, IL-8, TNF-alpha, IFN-gamma and GM-CSF. However, significantly lower levels of the regulatory mediator IL-10 were induced by encapsulated strains in comparison to isogenic unencapsulated derivatives. IL-10 secretion was shown to depend on phagocytosis because poly alpha-2,8 sialic acid did not influence IL-10 secretion. The use of truncated LPS isoforms in vaccine preparations can therefore not only result in attenuation but also in more efficient targeting of DC.

Bacterial Capsules↗
PubMed2005

Interlaboratory comparison of PCR-based identification and genogrouping of Neisseria meningitidis.

Twenty clinical samples (18 cerebrospinal fluid samples and 2 articular fluid samples) were sent to 11 meningococcus reference centers located in 11 different countries. Ten of these laboratories are participating in the EU-MenNet program (a European Union-funded program) and are members of the European Monitoring Group on Meningococci. The remaining laboratory was located in Burkina Faso. Neisseria meningitidis was sought by detecting several meningococcus-specific genes (crgA, ctrA, 16S rRNA, and porA). The PCR-based nonculture method for the detection of N. meningitidis gave similar results between participants with a mean sensitivity and specificity of 89.7 and 92.7%, respectively. Most of the laboratories also performed genogrouping assays (siaD and mynB/sacC). The performance of genogrouping was more variable between laboratories, with a mean sensitivity of 72.7%. Genogroup B gave the best correlation between participants, as all laboratories routinely perform this PCR. The results for genogroups A and W135 were less similar between the eight participating laboratories that performed these PCRs.

Adolescent↗
PubMed2004

Genetic lineages and their traits in Neisseria meningitidis.

Neisseria meningitidis is a model organism for the study of bacterial population biology, for genome sequencing and pathogenicity research. In the recent years, our group has identified a variety of markers for hypervirulent lineages of meningococci, which in part could be validated for typing purposes. Furthermore, carrier strain collections of meningococci and N. lactamica were studied by multilocus sequence typing, and elucidated the impressive genetic variability of those species. Characterisation of meningococcal carrier strains allowed to define the capsule null locus (cnl) of meningococci, which frequently occurs among carrier isolates and renders strains constitutively unencapsulated. This finding poses the question about the yet unclear role of the meningococcal polysaccharide capsule in transmission and carriage. O-acetylation of the meningococcal polysaccharides is another variably expressed trait in meningococci. We identified the genes responsible for O-acetylation of the serogroup C, W-135 and Y capsules, and provided the genetic basis for understanding the variability of O-acetylation patterns in meningococci. The oatC and oatWY genes proved to be the first genes identified to be responsible for O-acetylation of polysialic acid.

Acetylation↗
PubMed2004

Genome-based vaccines.

Vaccination is an effective possibility to prevent many bacterial or viral infections, but for several important pathogens still no vaccines are available. The sequences of complete genomes are now decoded for an increasing number of bacterial pathogens and offer the possibility for comprehensive screenings to identify targets for vaccine development. In this article current genomic approaches to identify antigenic proteins of Neisseria meningitidis, Streptococcus pneumoniae, Staphylococcus aureus, and Chlamydia pneumoniae are summarized.

Antigens, Bacterial↗
PubMed2004

Genetics of capsule O-acetylation in serogroup C, W-135 and Y meningococci.

Capsular polysaccharides of serogroup C, W-135 and Y meningococci were previously reported to be O-acetylated at the sialic acid residues. There is evidence that O-acetylation affects the immunogenicity of polysaccharide vaccines. We identified genes indispensable for O-acetylation of serogroup C, W-135 and Y meningococci downstream of the capsule synthesis genes siaA-D. The genes were co-transcribed with the sia operon as shown by reverse transcription polymerase chain reaction analysis. The putative capsular polysaccharide O-acetyltransferases were designated OatC and OatWY. The protein OatWY of serogroups W-135 and Y showed sequence homologies to members of the NodL-LacA-CysE family of bacterial acetyltransferases, whereas no sequence homology with any known protein in the different databases was found for the serogroup C protein OatC. In serogroup W-135 and Y meningococci, several clonal lineages either lacked OatWY or OatWY was inactivated by insertion of IS1301. For serogroup C meningococci, we observed in vitro phase variation of O-acetylation, which resulted from slipped-strand mispairing in homopolymeric tracts. This finding explains the observation of naturally occurring de-O-acetylated serogroup C meningococci. Our report is the first description of sequences of sialic acid O-acetyltransferase genes that have not been cloned from either other bacterial or mammalian organisms.

Acetylation↗
PubMed2004

Osteomyelitis and skin ulcers caused by Mycobacterium szulgai in an AIDS patient.

Mycobacterium szulgai is a ubiquitious non-tuberculous mycobacterium causing infection in immunocompetent and immunocompromized patients. Clinically mimicking pulmonary tuberculosis in most cases described, rarely other manifestations occur. Here we report the case of an AIDS patient with osteomyelitis of the hand and toe, accompanied by multiple cutaneous ulcers of the chest and forearm. The case highlights the unusual combination of osteomyelitis and skin ulcers without pulmonary infection and describes the likely cutaneous route of infection in a patient who keeps tropical fish.

Acquired Immunodeficiency Syndrome↗
PubMed2004

Interaction of Neisseria meningitidis with human brain microvascular endothelial cells: role of MAP- and tyrosine kinases in invasion and inflammatory cytokine release.

Neisseria meningitidis traversal across the blood-cerebrospinal fluid barrier is an essential step in the pathogenesis of bacterial meningitis. We have previously shown that invasion of human brain microvascular endothelial cells (HBMEC) by meningococci is mediated by bacterial outer membrane protein Opc that binds fibronectin, thereby anchoring the bacterium to the integrin alpha 5 beta 1-receptor on the endothelial cell surface. However, subsequent signal transduction mechanisms essential for or regulated by N. meningitidis adhesion and invasion, or HBMEC responses to N. meningitidis are unknown. In this report we investigated the role of c-Jun N-terminal kinases 1 and 2 (JNK1 and JNK2), p38 mitogen-activated (MAP) kinase and protein tyrosine kinases in endothelial-N. meningitidis interaction. Binding of meningococci to HBMEC phosphorylated and activated JNK1 and JNK2 and p38 MAPK as well as their direct substrates c-Jun and MAP kinase activated kinase-2 (MAPKAPK-2), respectively. Non-invasive meningococcal strains lacking opc gene (opc mutants and sequence type 11 complex meningococci) still activated p38 MAPK, however, failed to activate JNK. Inhibition of JNK1 and JNK2 significantly reduced internalization of N. meningitidis by HBMEC without affecting its adherence. Blocking the endothelial integrin alpha 5 beta 1 also decreased N. meningitidis-induced JNK activation in HBMEC. These findings indicate the crucial role of JNK signalling pathway in N. meningitidis invasion in HBMEC. In contrast, p38 MAPK pathway was important for the control of interleukin-6 (IL-6) and IL-8 release by HBMEC. Genistein, a protein tyrosine kinase inhibitor, decreased both invasion of N. meningitidis into HBMEC and IL-6 and IL-8 release, indicating that protein tyrosine kinases, which link signals from integrins to intracellular signalling pathways are essential for both bacterial internalization and cytokine secretion by HBMEC.

Adult↗
PubMed2004

Bacteremia in an immunocompromised patient caused by a commensal Neisseria meningitidis strain harboring the capsule null locus (cnl).

We recently described the capsule null locus (cnl) of constitutively unencapsulated Neisseria meningitidis clonal lineages. cnl meningococci were recovered from healthy carriers at high frequency. We here report on the first case of invasive disease caused by cnl meningococci in a severely immunosuppressed patient with chronic graft-versus-host disease after allogeneic peripheral blood stem cell transplantation. The sequence type 845 strain was extensively typed and, furthermore, shown to be sensitive to serum bactericidal activity.

Adult↗
PubMed2003

RIDOM: comprehensive and public sequence database for identification of Mycobacterium species.

BACKGROUND: Molecular identification of Mycobacterium species has two primary advantages when compared to phenotypic identification: rapid turn-around time and improved accuracy. The information content of the 5' end of the 16S ribosomal RNA gene (16S rDNA) is sufficient for identification of most bacterial species. However, reliable sequence-based identification is hampered by many faulty and some missing sequence entries in publicly accessible databases. METHODS: In order to establish an improved 16S rDNA sequence database for the identification of clinical and environmental isolates, we sequenced both strands of the 5' end of 16S rDNA (Escherichia coli positions 54 to 510) from 199 mycobacterial culture collection isolates. All validly described species (n = 89; up to March 21, 2000) and nearly all published sequevar variants were included. If the 16S rDNA sequences were not discriminatory, the internal transcribed spacer (ITS) region sequences (n = 84) were also determined. RESULTS: Using 5'-16S rDNA sequencing a total of 64 different mycobacterial species (71.9%) could be identified. With the additional input of the ITS sequence, a further 16 species or subspecies could be differentiated. Only Mycobacterium tuberculosis complex species, M. marinum/M. ulcerans and the M. avium subspecies could not be differentiated using 5'-16S rDNA or ITS sequencing. A total of 77 culture collection strain sequences, exhibiting an overlap of at least 80% and identical by strain number to the isolates used in this study, were found in the GenBank. Comparing these with our sequences revealed that an average of 4.31 nucleotide differences (SD +/- 0.57) were present. CONCLUSIONS: The data from this analysis show that it is possible to differentiate most mycobacterial species by sequence analysis of partial 16S rDNA. The high-quality sequences reported here, together with ancillary information (e.g., taxonomic, medical), are available in a public database, which is currently being expanded in the RIDOM project http://www.ridom-rdna.de), for similarity searches.

DNA, Ribosomal↗
PubMed2003

Analysis of differential gene expression in Echinococcus multilocularis larval stages by means of spliced leader differential display.

All parasitic helminths process a large subset of their mRNA molecules via spliced leader trans-splicing. Here we describe a rapid and efficient method, 'spliced leader differential display', to generate comprehensive expression fingerprints of trans-spliced factors on silver-stained acrylamide gels. The method allows systematic screening of the entire trans-spliced transcriptome of parasitic organisms using only minute amounts of starting material. Spliced leader differential display selectively displays 5' end-fragments of trans-spliced messages thus facilitating the identification of associated proteins and the full-length characterisation of corresponding mRNAs. We employed spliced leader differential display to analyse gene expression patterns of in vitro cultivated protoscoleces and metacestode vesicles from Echinococcus multilocularis. These analyses revealed that the majority of trans-spliced mRNAs are expressed at equal amounts in both larval stages whereas about 25% of the identified transcripts displayed stage-specific differential expression. Full-length transcripts for several of the obtained fragments were isolated and their constitutive or differential expression was verified by competitive PCR and Virtual Northern blotting. Spliced leader differential display was further used to identify genes which are induced in the E. multilocularis metacestode stage under growth promoting conditions in the presence of host hepatocytes. One mRNA, encoding a putative member of the epidermal growth factor family of mitogens, was shown to be 10-fold induced upon co-incubation of metacestode vesicles with host cells which indicates a possible involvement of parasite-determined, epidermal growth factor-like signal transduction systems in metacestode proliferation and development. The successful application of spliced leader differential display to gene expression analyses of echinococcal larvae, combined with easy handling and a low rate of false positives, recommends this method not only for studies on the host-parasite interplay during alveolar echinococcosis, but also for investigations on other parasitic organisms.

Adolescent↗
PubMed2003

The complete genome sequence of the carcinogenic bacterium Helicobacter hepaticus.

Helicobacter hepaticus causes chronic hepatitis and liver cancer in mice. It is the prototype enterohepatic Helicobacter species and a close relative of Helicobacter pylori, also a recognized carcinogen. Here we report the complete genome sequence of H. hepaticus ATCC51449. H. hepaticus has a circular chromosome of 1,799,146 base pairs, predicted to encode 1,875 proteins. A total of 938, 953, and 821 proteins have orthologs in H. pylori, Campylobacter jejuni, and both pathogens, respectively. H. hepaticus lacks orthologs of most known H. pylori virulence factors, including adhesins, the VacA cytotoxin, and almost all cag pathogenicity island proteins, but has orthologs of the C. jejuni adhesin PEB1 and the cytolethal distending toxin (CDT). The genome contains a 71-kb genomic island (HHGI1) and several genomic islets whose G+C content differs from the rest of the genome. HHGI1 encodes three basic components of a type IV secretion system and other virulence protein homologs, suggesting a role of HHGI1 in pathogenicity. The genomic variability of H. hepaticus was assessed by comparing the genomes of 12 H. hepaticus strains with the sequenced genome by microarray hybridization. Although five strains, including all those known to have caused liver disease, were indistinguishable from ATCC51449, other strains lacked between 85 and 229 genes, including large parts of HHGI1, demonstrating extensive variation of genome content within the species.

Cell Movement↗
PubMed2003

Transcriptome-based antigen identification for Neisseria meningitidis.

The identification of suitable antigens is crucial to successful vaccine development based on subunit approaches. While many methods exist for the identification of vaccine candidates which are surface-exposed or secreted, immunogenic and conserved, contain B and T cell epitopes, most of these have a major drawback: they do not yield any information on whether the antigen is indeed expressed by the pathogen during infection. However, DNA microarrays offer a novel tool for the investigation of the transcriptional activity of all genes of a pathogenic microorganism under in vivo conditions. Employing whole genome DNA microarrays, we have analyzed the transcriptome of Neisseria meningitidis serogroup B bacteria during different stages of infection, i.e. exposure to human serum and the interaction with human epithelial and endothelial cells. Combined with data derived from genome-based approaches (such as reverse vaccinology) and immunogenicity studies, this novel transcriptome-based antigen identification should reveal ideal vaccine candidates against serogroup B meningococcal infection.

Antigens, Bacterial↗
PubMed2003

The role of human dendritic cells in meningococcal and listerial meningitis.

Few bacteria are capable of causing infections of the central nervous system (CNS), one of the most subtly shielded anatomical structures within the human body. Neisseria meningitidis is an important cause of bacterial meningitis and commonly affects otherwise healthy infants and adolescents. In contrast, Listeria monocytogenes is a cause of septicaemia and meningitis in neonates and immunocompromised adults. Dendritic cells (DCs) provide the physical link between the innate and adaptive immune system and play a crucial role in host defence against invading bacterial pathogens. The mechanisms of interaction of L. monocytogenes and N. meningitidis with DCs are entirely distinct. Whereas L. monocytogenes is readily phagocytosed by DCs by a serum-dependent mechanism, N. meningitidis is largely protected against phagocytotic uptake by its polysaccharide capsule. In addition, the pattern of secreted cytokines induced by L. monocytogenes is dominated by interleukin (IL)-12 and IL-18, capable of initiating a Th-1 response, whereas N. meningitidis induces high levels of proinflammatory cytokines. Therefore, we propose distinct functions of DCs in both types of bacterial meningitis.

Cytokines↗
PubMed2003

Biochemical and functional analyses of the Mip protein: influence of the N-terminal half and of peptidylprolyl isomerase activity on the virulence of Legionella pneumophila.

The virulence factor Mip (macrophage infectivity potentiator) contributes to the intracellular survival of Legionella pneumophila, the causative agent of Legionnaires' disease. The protein consists of two domains that are connected via a very long alpha-helix (A. Riboldi-Tunnicliffe et al., Nat. Struct. Biol. 8:779-783, 2001). The fold of the C-terminal domain (residues 100 to 213) is closely related to human FK506-binding protein (FKBP12), and like FKBP12, Mip exhibits peptidylprolyl cis/trans isomerase (PPIase) activity. The alpha-helical N-terminal domain is responsible for the formation of very stable Mip homodimers. In order to determine the importance of the homodimeric state of Mip for its biochemical activities and for infectivity of Legionella, a truncated, monomeric Mip variant [Mip((77-213))] was overexpressed in Escherichia coli and characterized biochemically. In vitro isomerase activity assays revealed that the altered protein exhibits full isomerase activity towards peptide substrates. However, the deletion resulted in a dramatic loss in the efficiency of refolding of reduced and carboxy-methylated RNase T(1). By cis complementation of the Mip-negative mutant strain L. pneumophila JR32-2, we constructed the strain L. pneumophila JR32-2.4, which expresses an N-terminally truncated variant of Mip. Infection studies with these strains revealed that the N-terminal part and the dimerization of Mip but not its PPIase activity are necessary for full virulence in Acanthamoeba castellanii. Infection of guinea pigs showed that strains with dimerization-deficient Mip (JR32-2.4) or a very low PPIase activity (JR32-2.2) were significantly attenuated in the animal model. These results suggest a different role of the PPIase activity and the N-terminally mediated dimeric state of Mip in monocellular systems and during the infection of guinea pigs.

Acanthamoeba↗
PubMed2003

Transcriptome analysis of Neisseria meningitidis during infection.

Neisseria meningitidis is the cause of septicemia and meningococcal meningitis. During the course of infection, N. meningitidis encounters multiple environments within its host, which makes rapid adaptation to environmental changes a crucial factor for neisserial pathogenicity. Employing oligonucleotide-based DNA microarrays, we analyzed the transcriptome of N. meningitidis during two key steps of meningococcal infection, i.e., the interaction with epithelial cells (HeLa cells) and endothelial cells (human brain microvascular endothelial cells). Seventy-two genes were differentially regulated after contact with epithelial cells, and 48 genes were differentially regulated after contact with endothelial cells, including a considerable proportion of well-known virulence genes. While a considerable number of genes were in concordance between bacteria adherent to both cell types, we identified several open reading frames that were differentially regulated in only one system. The data obtained with this novel approach may provide insight into the pathogenicity mechanisms of N. meningitidis and could demonstrate the importance of gene regulation on the transcriptional level during different stages of meningococcal infection.

Bacterial Adhesion↗