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Herbert Hof

Publications and source records attributed to Herbert Hof.

15 recordsLinked to original sources
PubMed2006

Deletion of the gliP gene of Aspergillus fumigatus results in loss of gliotoxin production but has no effect on virulence of the fungus in a low-dose mouse infection model.

Gliotoxin is a secondary metabolite produced by several fungi including the opportunistic human pathogen Aspergillus fumigatus. As gliotoxin exerts immunosuppressive effects in vitro and in vivo, a role as a virulence determinant in invasive aspergillosis has been discussed for a long time but evidence has not been provided until now. Here, by the use of different selection marker genes A. fumigatus knock-out strains were generated that are deficient for the non-ribosomal peptide synthetase GliP, the putative key enzyme of the gliotoxin biosynthesis. Deletion of the gliP gene resulted in loss of gliotoxin production, as analysed by high performance liquid chromatography and tandem mass spectrometry. No differences in morphology or growth kinetics between wild-type and gliP-deletion strains were observed. In vitro, the culture supernatant of the gliP-deficient strains showed a reduced cytotoxic effect on both macrophage-like cells and T cell lines. In a low-dose murine infection model of invasive aspergillosis, gliotoxin was detected in the lung and absent when mice were infected with the gliP deletion strain. However, gliP deletion strains showed no difference in virulence compared with the corresponding wild-type strains. Taken together, the non-ribosomal peptide synthetase GliP is essential for gliotoxin production in A. fumigatus. Gliotoxin is not required for pathogenicity of the fungus in immunocompromised mice, despite the fact that a reduced cytotoxicity of the culture supernatant of gliP deletion strains was demonstrated.

Animals↗
PubMed2004

[Tinea capitis].

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Antifungal Agents↗
PubMed2004

[Oral candidiasis].

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Antifungal Agents↗
PubMed2004

An update on the medical management of listeriosis.

It is still not quite well understood why there is no optimal or even a satisfactory antibiotic therapy for listeriosis. Although almost all Listeria strains that induce sepsis, meningitis and encephalitis, as well as many other manifestations--in particular, in immunocompromised individuals--are susceptible to most of the common antibiotics, the cure rate is only approximately 70%. The most effective regimen still consists of a combination of an aminopenicillin (amoxicillin or ampicillin) plus an aminoglycoside. In vitro, this combination is bactericidal, whereas aminopenicillin alone only exerts a weak bactericidal activity against Listeriae. These antibiotics only poorly penetrate the cerebrospinal fluid and thus, only high doses given over a prolonged period of 2-3 weeks are curative. Furthermore, Listeria monocytogenes belongs to the group of facultative intracellular bacteria, which means that a certain population is inaccessible for antibiotics. Theoretically, a drug which is endowed with bactericidal activity superior to that of ampicillin would be preferable. Furthermore, the candidate drug should easily cross the blood-brain barrier into the CNS, be able to accumulate within host cells, reach the cytoplasm and be active under these unusual conditions. Because of all these arguments, the new quinolones are of particular interest; but broad clinical data are still lacking. It is unclear as to whether antibiotics alone will be sufficient to increase the prognosis. Adjunctive therapy with immunomodulators, which are able to reconstitute the defective defence capacities, would presumably create the conditions necessary to finally resolve listeriosis.

Anti-Bacterial Agents↗
PubMed2003

Water birth: microbiological colonisation of the newborn, neonatal and maternal infection rate in comparison to conventional bed deliveries.

INTRODUCTION: The risk of infectious complications after water birth which might be due to water contaminated by faecal bacteria or environmental microbes from the water supply system is still in discussion. MATERIALS AND METHODS: We performed a microbiological study comparing neonatal bacterial colonisation after water birth to conventional bed deliveries with or without relaxation bath. In all three groups (96 deliveries) we isolated most frequently from ear and palate of the newborns Staphylococcus epidermidis, E. coli and enterococci, which belong to the normal vaginal flora. RESULTS: Neonatal outcome, infantś and maternal infection rate did not differ between the three groups.

Baths↗
PubMed2003

Listeriosis: therapeutic options.

Since overt listeriosis occurs mainly in immunocompromised persons it is quite consistent to try to restore the hampered defence system by supportive measurements. For direct antimicrobial treatment a series of different antibiotics is available, since Listeria strains isolated from patients are in general susceptible to a wide range of antibiotics, except fosfomycin, quinolones and cephalosporins of the third generation, although a few exceptional strains exist. Unfortunately, most antibiotics are not bactericidal for Listeria. Drug combinations may exert a synergistic effect. Furthermore, the efficacy of therapy is limited by the fact of intracellular habitat of pathogenic Listeria. Few agents, such as macrolides and quinolones, are accumulated within host cells and may attack the intracellular Listeriae. The clinical experience shows that the combination of amoxicillin and gentamicin is the best option.

Animals↗
PubMed2002

Cross-presentation of Listeria monocytogenes-derived CD4 T cell epitopes.

Listeriolysin O (LLO) mediates the evasion of Listeria monocytogenes from the phagolysosome into the cytoplasm of the host cell. The recognition of infected cells by CD4 T cells is thought to be limited by the evasion of bacteria from the phagolysosome and also by the direct LLO-mediated inhibition of CD4 T cell activation. To analyze the influence of these immunoevasive mechanisms on the antilisterial CD4 T cell response, the expansion of L. monocytogenes-specific CD4 and CD8 T cells was monitored in infected mice. It was found that expansion of L. monocytogenes-specific CD4 T cells occurred synchronously with CD8 T cell expansion. The analysis of Ag presentation by macrophages and dendritic cells isolated from spleens of infected mice revealed efficient presentation of L. monocytogenes-derived CD4 T cell epitopes that was not dependent on the actA-mediated intercellular spread of bacteria. The further in vitro Ag presentation analysis revealed that although L. monocytogenes-infected macrophages and dendritic cells were poor presenters of CD4 T cell epitopes, more efficient presentation occurred after cocultivation of noninfected dendritic cells or macrophages with infected cells. These data indicate that the suppressive effect of LLO on the antilisterial CD4 T cell response is maintained only in infected APC and support the hypothesis that cross-priming plays a role in the induction of the strong CD4 T cell response in Listeria-infected mice.

Animals↗
PubMed2002

Individual acid aspartic proteinases (Saps) 1-6 of Candida albicans are not essential for invasion and colonization of the gastrointestinal tract in mice.

In order to investigate whether there is a role for individual secreted aspartic proteinases (Saps) of Candida albicans in gastrointestinal infection of mice we compared the differential expression of SAP1-6 genes and production of Sap1-6 proteins with invasion and persistence of SAP knockout strains in the gastrointestinal tract. Using an in vivo expression technology (IVET) we found a high percentage of expression of SAP4-6 genes which increased steadily in the course of infection. Expression of SAP1-3 genes was detected occasionally and in lower percentages than that of SAP4-6 genes. With reverse transcriptase-polymerase chain reaction (RT-PCR), mRNA for SAP 4 and SAP6 were detected in the stomach of all mice, whereas SAP2, SAP3 and SAP5 mRNA were detected not in all animals and SAP1 mRNA was not detectable. Also with immunoelectron microscopy we demonstrated production of Saps1-3 as well as Saps4-6 with antibodies cross-reacting with either Saps1-3 or Saps4-6. In contrast to the fact that gene expression and production of Saps were readily detectable, we were unable to demonstrate differences in the ability to invade the stomach, to disseminate to the brain as well as in the duration of faecal shedding and the number of fungi persisting in the faeces of mice infected with SAP knockout strains in comparison to control strains. We conclude that although Saps were produced, individual Saps were not indispensable factors for virulence during gastrointestinal infection of mice.

Animals↗
PubMed2002

Functional analysis of a vacuolar ABC transporter in wild-type Candida albicans reveals its involvement in virulence.

ATP-driven transport proteins belonging to the ATP-binding cassette (ABC) superfamily perform important functions in cell metabolism and detoxification. Compounds can be actively transported across membranes, including the plasma membrane or organellar membranes. The vacuole is an important organelle in fungal cells required for compartmentalization of metabolites as well as toxic substances. Sequestration into the vacuole is often energy-dependent. We present the first isolation and molecular analysis of a vacuolar ABC transporter gene in the opportunistic fungal pathogen Candida albicans. The protein encoded by the MLT1 gene is highly similar to Multiple Drug Resistance-associated Protein (MRP)-like transporters of yeast and higher organisms that form the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)/MRP subfamily of ABC transporters, a class of proteins so far not characterized in C. albicans. MLT1 expression is extensively growth phase-regulated, and gene transcripts are inducible by metabolic poisons. Gene replacement mutants generated in wild-type C. albicans with the dominant selection marker MPAR showed a profound reduction in virulence in a mouse peritonitis model that was reversed by complementation with an intact MLT1 gene. Hence, this report provides primary evidence for the involvement of vacuolar ABC transporters in fungal virulence.

ATP-Binding Cassette Transporters↗
PubMed2002

Host versus in vitro signals and intrastrain allelic differences in the expression of a Candida albicans virulence gene.

The yeast Candida albicans is a harmless colonizer of mucosal surfaces in healthy people but can become a serious pathogen in immunocompromised patients, causing superficial as well as systemic infections. The evolution of gene families encoding pathogenicity-related functions, like adhesins and secreted aspartic proteinases (Saps), which are differentially induced by host signals at various stages of colonization and infection, may have allowed C. albicans an optimal adaptation to many different host niches. We found that even the two alleles of a single gene can be differentially regulated in the diploid C. albicans. In the model strain SC5314, the in vitro expression of one of the two SAP2 alleles, SAP2-1, depended on the presence of a functional SAP2-2 allele. In contrast, inactivation of SAP2-1 did not in-fluence the expression of SAP2-2. The proteinase encoded by the SAP2-2 allele serves as a signal sensor and amplifier to enhance its own expression as well as to induce the SAP2-1 allele to achieve maximal proteolytic activity under appropriate conditions. Using in vivo expression technology, we could demonstrate that the SAP2-1 allele is significantly activated only in the late stages of systemic candidiasis in mice, whereas the SAP2-2 allele is induced much earlier. The differential regulation of the two SAP2 alleles was due to differences in their pro-moters, which contained a variable number of two pentameric nucleotide repeats. Mutations that reduced or increased the copy number of these repeats diminished the inducibility of the SAP2 promoter during infection but not in vitro, suggesting that the mutations affected interactions of regulatory factors that are necessary for SAP2 activation in vivo but dispensable for its induction in vitro. Therefore, the signals and signal transduction pathways that mediate SAP2 expression within certain host niches may differ from those that activate the gene in vitro. In addition to the generation of gene families whose members exhibit functional and regulatory diversification, C. albicans seems to use its diploid genome to create further variability and host adaptation by differential evolution of even the two alleles of a single gene.

Alleles↗
PubMed2002

Molecular characterization of the genes encoding DNA gyrase and topoisomerase IV of Listeria monocytogenes.

The genes encoding subunits A and B of DNA gyrase and subunits C and E of topoisomerase IV of Listeria monocytogenes, gyrA, gyrB, parC and parE, respectively, were cloned and sequenced. Compared with the sequences of quinolone-susceptible bacteria, such as Escherichia coli and Bacillus subtilis, the quinolone resistance-determining region (QRDR) of DNA gyrase subunit A was altered; the deduced amino acid sequences revealed the substitutions Ser-84-->Thr and Asp/Glu-88-->Phe, two amino acid variations at hot spots, commonly associated with resistance to quinolones. No relevant divergences from QRDR consensus sequences were observed in GyrB or both topoisomerase IV subunits. Thus, it could be argued that the amino acid substitutions in GyrA would explain the intrinsic resistance of L. monocytogenes to nalidixic acid. In order to analyse the actual role of the GyrA alterations, a plasmid-encoded gyrA allele was mutated and transformed into L. monocytogenes. However, these heterodiploid strains were not affected in their resistance to nalidixic acid. The effects of the mutant plasmids on ciprofloxacin and sparfloxacin susceptibility were only modest.

4-Quinolones↗
PubMed2002

Transcriptional regulators Cph1p and Efg1p mediate activation of the Candida albicans virulence gene SAP5 during infection.

The opportunistic fungal pathogen Candida albicans can cause superficial as well as systemic infections. Successful adaptation to the different host niches encountered during infection requires coordinated expression of various virulence traits, including the switch between yeast and hyphal growth forms and secretion of aspartic proteinases. Using an in vivo expression technology that is based on genetic recombination as a reporter of gene activation during experimental candidiasis in mice, we investigated whether two signal transduction pathways controlling hyphal growth, a mitogen-activated protein kinase cascade ending in the transcriptional activator Cph1p and a cyclic AMP-dependent regulatory pathway that involves the transcription factor Efg1p, also control expression of the SAP5 gene, which encodes one of the secreted aspartic proteinases and is induced by host signals soon after infection. Our results show that both transcriptional regulators are important for SAP5 activation in vivo. SAP5 expression was reduced in a cph1 mutant, although filamentous growth in infected tissue was not detectably impaired. SAP5 expression was also reduced, but not eliminated, in an efg1 null mutant, although this strain grew exclusively in the yeast form in infected tissue, demonstrating that in contrast to in vitro conditions, SAP5 activation during infection does not depend on growth of C. albicans in the hyphal form. In a cph1 efg1 double mutant, however, SAP5 expression in infected mice was almost completely eliminated, suggesting that the two signal transduction pathways are important for SAP5 expression in vivo. The avirulence of the cph1 efg1 mutant seemed to be caused not only by the inability to form hyphae but also by a loss of expression of additional virulence genes in the host.

Animals↗