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M Mehl

Publications and source records attributed to M Mehl.

At least 19 recordsLinked to original sources
PubMed2004

Antibacterial resistance of community-acquired respiratory tract pathogens recovered from patients in Germany and activity of the Ketolide Telithromycin: results from the PROTEKT surveillance study (1999-2000).

BACKGROUND: The Prospective Resistant Organism Tracking and Epidemiology for the Ketolide Telithromycin (PROTEKT) longitudinal global surveillance study examines the antibacterial susceptibility of community-acquired respiratory pathogens. METHODS AND RESULTS: Data from isolates collected in Germany in 1999-2000 in the PROTEKT study show that 8.3% of pneumococcal isolates (n = 325) had reduced susceptibility to penicillin and 2.2% were fully resistant. Erythromycin resistance was 15.7% overall and particularly high in Leipzig (31.6%). All penicillin- and erythromycin-resistant strains were inhibited by telithromycin (MIC < or =0.5 mg/l) and linezolid (MIC < or =2 mg/l). Beta-lactamase was produced by 3.2% of Haemophilus influenzae (9/284) and 89.5% of Moraxella catarrhalis strains (111/124). All Streptococcus pyogenes isolates (n = 87) were susceptible to penicillin, although 9.2% were resistant to macrolides. CONCLUSIONS: Penicillin resistance in Germany remains low; however, the prevalence of antimicrobial resistance among common respiratory pathogens is rising, particularly against macrolides. Continued surveillance is necessary to guide optimal empirical therapy, and new antimicrobials, like telithromycin, need to be developed with improved potency against target pathogens and low propensity for the development of resistance.

Anti-Bacterial Agents↗
PubMed2004

A peripheral primitive neuroectodermal tumor with generalized bone metastases in a puppy.

A peripheral primitive neuroectodermal tumor (pPNET), most consistent with a human Ewing's sarcoma, is described in a 5-month-old male Australian Shepherd puppy. The first tumor site detected was in the left frontal bone of the skull with apparent subsequent rapid metastases to multiple sites in the axial and appendicular skeleton and bone marrow, kidneys, and perihyphophyseal meninges. Radiographically, all bone lesions were lytic and there was also a humeral bone fracture. Histologically, the tumor was diagnosed as a small round blue cell tumor. At this stage, the differential diagnosis included a lymphoma, rhabdomyosarcoma, and a PNET of the peripheral nervous system. However, the cells had positive expression of triple neurofilament antigens as detected immunocytochemically. The cells were negative for a broad panel of canine-specific leucocyte cell marker antigens for desmin, smooth muscle actin, synaptophysin, and CD99. Ultrastructurally, the cells contained occasional dense core neurosecretory granules and intermediate filaments with intercellular desmosomal-like junctions and abundant glycogen clusters. Based on the age of the dog, the clinical history, the distribution of gross lesions, histologic characteristics of a small round blue cell tumor, and immunocytochemical and ultrastructural evidence of neuroectodermal differentiation, a diagnosis of a pPNET similar to a human Ewing's sarcoma was made.

Animals↗
PubMed2001

Pathological apoptosis by xanthurenic acid, a tryptophan metabolite: activation of cell caspases but not cytoskeleton breakdown.

BACKGROUND: A family of aspartate-specific cysteinyl proteases, named caspases, mediates programmed cell death, apoptosis. In this function, caspases are important for physiological processes such as development and maintenance of organ homeostasis. Caspases are, however, also engaged in aging and disease development. The factors inducing age-related caspase activation are not known. Xanthurenic acid, a product of tryptophan degradation, is present in blood and urine, and accumulates in organs with aging. RESULTS: Here, we report triggering of apoptotic key events by xanthurenic acid in vascular smooth muscle and retinal pigment epithelium cells. Upon exposure of these cells to xanthurenic acid a degradation of ICAD/DFF45, poly(ADP-ribose) polymerase, and gelsolin was observed, giving a pattern of protein cleavage characteristic for caspase-3 activity. Active caspase-3, -8 and caspase-9 were detected by Western blot analysis and immunofluorescence. In the presence of xanthurenic acid the amino-terminal fragment of gelsolin bound to the cytoskeleton, but did not lead to the usually observed cytoskeleton breakdown. Xanthurenic acid also caused mitochondrial migration, cytochrome C release, and destruction of mitochondria and nuclei. CONCLUSIONS: These results indicate that xanthurenic acid is a previously not recognized endogenous cell death factor. Its accumulation in cells may lead to accelerated caspase activation related to aging and disease development.

Apoptosis↗
PubMed2001

Time-resolved study of biofilm architecture and transport processes using experimental and simulation techniques: the role of EPS.

Cellular material and extracellular polymeric substances are the basic structural elements in biofilm systems. The structure and role of EPS for biofilm development and metabolic processes have not been precisely determined and, therefore, have not yet been included as a necessary element in modelling and simulation studies. This is due to the difficulty of experimentally detecting the extracellular polymeric substances in situ and differentiating them from cellular material on the one hand, and to the subsequent uncertainty about appropriate models--e.g. rigid hindrances, porous microstructure or visco-elastic structure--on the other hand. In this work, we report on the use of confocal laser scanning microscopy to monitor the development of a monoculture biofilm of Sphingomonas sp. grown in a flow cell. The bacterial strain was genetically labelled resulting in strong constitutive expression of the green fluorescent protein. The development of extracellular polymeric substances was followed by binding of the lectin concavalin A to cell exopolysaccharides. The growth of the resulting strain was digitally recorded by automated confocal laser scanning microscopy. In addition, local velocity profiles of fluorescent carboxylate-modified microspheres were observed on pathlines throughout the biofilm. The CLSM image stacks were used as direct input for the explicit modelling and three-dimensional numerical simulation of flow fields and solute transport processes based on the conservation laws of continuum mechanics. At present, a strongly simplifying EPS-model is applied for numerical simulations. The EPSs are preliminarily assumed to behave like a rigid and dense hindrance with diffusive-reactive solute transport.

Biofilms↗
PubMed1999

Prostacyclin synthase is localized in rat, bovine and human neuronal brain cells.

Using a new polyclonal antibody against prostacyclin (PGI2)-synthase this enzyme was shown to be present in neuronal cells of bovine, rat and human brain, most abundantly in Purkinje cells of the cerebellum and cortical neurons, but not in glial cells. Western blots confirmed the specificity of the antibody and applied to enriched neuronal and astrocyte cultures supported these immunohistochemical data. It was further shown that staining with an anti-nitrotyrosine antibody was positive for PGI2-synthase containing cells. Possible physiological and/or pathophysiological functions of the enzyme in brain are discussed.

Aged↗
PubMed1999

Peroxynitrite reaction with heme proteins.

We have reported that low levels of peroxynitrite (PN) can cause inactivation of the heme-thiolate protein prostacyclin (PGI2)-synthase by nitration of a tyrosine residue. To prove that iron catalysis is involved we studied the interaction of PN with microperoxidase and P450nor, a heme-thiolate protein of known structure. Spectral and kinetic analyses allow to conclude on a ferryl nitrogen dioxide complex as an intermediate which decomposes in the presence of an excess of PN under formation of dioxygen, nitrite, and nitrate. This occurs in a catalytic cycle which was more efficient with P450nor than with microperoxidase. If phenol was added to the reaction mixtures of PN and the ferric complexes the ratio of hydroxylated to nitrated phenols decreased compared to the metal-free system. Phenol competed with the formation of dioxygen indicating that the ferryl intermediate was involved in both pathways. One therefore can postulate that the ferryl complex reacts with phenol to give the phenoxyradical which is nitrated in the presence of nitrogen dioxide but does not give hydroxylated products as with metal-free PN. Alternately, the ferryl nitrogen dioxide complex can oxidize a second PN molecule to the radical, *OONO, which can decompose to dioxygen and NO. The latter forms N2O3, with the remaining *NO2 radical. A third pathway consists in the isomerization to nitrate which also is catalyzed by the heme proteins since the ratio of nitrite/nitrate does not change significantly during the catalytic reaction with excess of PN. Our data explain the mechanism of nitration of PGI2-synthase, suggest a role of P450nor as a PN scavenger, and favor heme-thiolate complexes for trapping PN.

Catalysis↗
PubMed1999

Effects of suramin on PMN interactions with different surfaces.

Human polymorphonuclear leukocytes (PMN) were found to tightly adhere on endothelial (lines EAhy926 and ECV304) and collagen surfaces under the influence of the chemotherapeutic drug suramin. This was observed by scanning electron microscopy and quantitated by myeloperoxidase assays. Suramin also inhibited Ca2+ ionophore A23187-stimulated leukotriene (LT) synthesis in PMN interaction with endothelial cells or with collagen surface. Suramin decreased the release of radiolabeled arachidonic acid (AA) and 5-lipoxygenase (5-LO) metabolites by prelabeled PMN stimulated with A23187. Using agents releasing the suramin-stimulated adhesion namely jasplakonolide and dextran sulfate, we observed a reversal of the suramin effect on leukotriene synthesis. Jasplakonolide released the adhesion of PMN on endothelial and collagen-coated surfaces and restored 5-LO activity. Dextran-sulfate released adhesion on collagen-coated surfaces and abolished suramin inhibition. Arachidonate could also overcome adhesion and inhibition of 5-LO. We conclude that suramin-induced tight attachment of PMN on to solid surfaces lead to decreased leukotriene synthesis during subsequent A23187 stimulation in the absence of exogenous substrates.

Arachidonate 5-Lipoxygenase↗
PubMed1998

New aspects in the reaction mechanism of phenol with peroxynitrite: the role of phenoxy radicals.

The decomposition of peroxynitrite (PON) in aqueous solutions was investigated by monitoring the release of dioxygen as a function of pH together with the various reaction products generated from phenol. This substrate was used as a mechanistic model for tyrosine nitration in prostacyclin synthase for which we have reported a highly efficient nitration and inhibition by PON (Zou, M., Martin, C., and Ullrich, V. (1997) Biol Chem. 378, 707-713). Nitrite as a contaminant and product of PON generated 4-nitrosophenol and some nitrophenols in the acidic pH range. In the alkaline range high amounts of 4-nitrosophenol originated from the disproportionation of PON yielding dioxygen and NOx species. The hydroxylation of phenol occurred between pH 3 and 8 with a maximum at 4.5. The nitration by PON also required a pH between 4 and 8 but had a second maximum between 10 and 12, suggesting that in this pH range phenolate was the reacting species. All isomeric biphenols were found as dimerization products as well as 4-phenoxyphenol (4-hydroxydiphenyl ether), indicating phenoxy radicals as intermediates. Since anisol when incubated under the same conditions yielded only hydroxylation but virtually no nitration products, it was concluded that nitration of phenolic compounds requires a one-electron oxidation as a primary step, followed by addition of the nitrogen dioxide radical.

Anisoles↗
PubMed1996

[Characterization of chick embryo fibroblast culture--overview of its effectiveness as a hybridoma cell].

The use of culture supernatant (added in a final concentration of 25% v/v) from chicken embryonal fibroblasts (CEF) for stimulation of established hybridoma cell lines has been shown. The proliferative effect on hybridoma cells from different origins was heatproof and was possible with a reduced serum part (FCS) in the culture medium. After a chromatografic separation the supernatant sections were tested and the positive effect was much lower in comparison to the total conditioned media.

Animals↗
PubMed1991

A solid-phase enzyme immunoassay for the detection of tetanus toxin using human and murine monoclonal antibodies.

Three human and three murine monoclonal antibodies were tested for their reactivity to tetanus toxin and toxoid and used to establish an enzyme immunoassay specific for tetanus toxin. The dissociation constants of the monoclonal antibodies were between 3.91 x 10(-9) and 8.48 x 10(-12). Two human monoclonal antibodies recognized conformation determinants on the toxin, whereas the others reacted to the heavy chain. Only a combination of antibodies of the two species allowed the development of an enzyme immunoassay for the detection of tetanus toxin with a lower detection limit of 1.2 micrograms/l.

Animals↗
PubMed1990

[Use of fermenter-dialysis culture for the cultivation of medically relevant microbes. III. Candida albicans].

For mass cultivation of Candida albicans (serotype A), a fermenter dialysis culture technique is described and compared with shaking culture and fermenter batch culture techniques. Important growth parameters such as yeast dry weight and viable cell counts demonstrate the advantage of the fermenter dialysis culture. Mannan, the major antigen from Candida albicans prepared by phenol-water extraction followed by gel chromatography was tested with the monoclonal IgM antibody H5.

Candida albicans↗
PubMed1990

[Trends in medical microbiology--gene probes in medical microbiology].

At first the principle of nucleic acid hybridisation, some important technics used heretofore, and methods to label nucleic acids are described. The advantages and disadvantages regarding to the application to microbiological diagnostics are discussed. The advantage, before all, is the high specificity of the test which allows to detect the presence and the properties of genes which are not expressed. The methods known up to now can only be applied if the probe is labelled radioactively, since under these conditions the sensitivity is high enough to identify bacteria contained in clinical isolates without prior cultivation. The comparable complex methods are restricted, presently, to special mostly epidemiological problems. To improve these technics regarding increased sensitivity, to the use of non-radioactively labelled probes, to higher speed, and to the automation of the test internationally much work is carried out with great intensity. The solution of these problems will create conditions for a wide application of DNA probes in the general microbiological laboratory.

Bacteria↗
PubMed1989

[The modification of phagocytosis by different K1 capsule preparations of Escherichia coli].

The influence of two different types of Escherichia coli K1 capsule preparation on the phagosytosis of an E. coli laboratory strain (LN 28) by polymorphnuclear leucocytes (PMNL) is described. Capsule material of E. coli 0.18 and 0.83 was prepared a) from the culture supernatant and b) from a bacterial pellet fraction. When capsule material from the pellet was added to opsonin, before mixing the laboratory strain with the PMNL, it decreased the rate of phagocytosis, compared with untreated opsonin. The preparation from the supernatant of capsule showed no alteration of phagocytosic rate or capacity. These results are explained by the different chemical compositions of the preparations.

Antigens, Bacterial↗
PubMed1989

[A fermenter dialysis cultivation technic for encapsulated pathogenic bacteria. II. Group B streptococci].

For mass cultivation of group B streptococci (B-III and B-variant streptococci), a fermenter dialysis culture technique is described and compared to conventional shaking culture and fermenter batch culture techniques. The influence of two kinds of cultivation media on the bacterial yield is demonstrated. The growth rate of the bacteria and the yield of the microbes is higher in modified POPE medium than that observed with Nährbouillon I. The type-specific polysaccharide of B-III-streptococci prepared by phenol-water extraction followed by gel-chromatography can be used as a screening antigen for the production of monoclonal antibodies against B-III-streptococci.

Antigens, Bacterial↗
PubMed1989

[Chemical characterization of Escherichia coli K 1 capsular polysaccharide].

The exact chemical characterization of the prepared Escherichia coli K 1 capsule polysaccharide is necessary and a prerequisite for using this antigen as a screening antigen in the production of monoclonal anti-K 1-antibodies. The K 1-antigen, prepared by phenol-water-extraction, was analyzed by protein, RNA, and neuraminic acid determination. An addition, the antigen was subjected to elementary analysis, infrared- and 13C-NMR-spectroscopy, and gelchromatography. After testing the serological specificity, the K 1-antigen was identified as a high molecular polyneuraminic acid.

Antigens, Bacterial↗
PubMed1989

[Loading of polystyrene solid phases with microbial agents and their polysaccharide antigens for the screening of monoclonal antibodies].

Before screening monoclonal antibodies using enzyme immuno assays, it is necessary to prove that the coating of the solid phases occurs efficiently. The adhesion of whole cells of group B streptococci, Escherichia coli K1, Haemophilus influenzae type b and Candida albicans as well as B-Streptococcus group antigen, H. influenzae type b capsular antigen, and C. albicans cell wall antigen to polystyrene solid phases was studied and detected by the following methods: Peroxidase competition procedure, scintillation measurement of 32phosphate-labelled germs, and reactions with monoclonal antibodies.

Antibodies, Monoclonal↗
PubMed1989

Occurrence of hybridomas producing multispecific IgM in human x (human-mouse) fusions with lymphocytes from different human immune compartments.

Human lymphocytes derived from peripheral blood, the spleen and lymph nodes were fused to the HAT-sensitive heteromyeloma cell line CB-F7. The Ig-producing initial cell lines were selected, and the supernatants were further analyzed for specific antigen binding (ELISA). IgM-antibodies were found which reacted with self- and non-self antigens of different molecular origin (nucleotides, proteins, carbohydrate structures). These antibodies were called multireactive (multispecific). The multispecific IgM-producing human hybridomas occurred with higher frequencies in the spleen (6.9% of IgM-producers) cell fusions than in experiments where peripheral blood-derived lymphocytes were fused (2.7%). There were no hybridomas producing multireactive antibodies detected in fusion material from lymph nodes. The greatest number of multireactive IgM was seen when PBL from SLE or anti-HIV-positive patients were hybridized to CB-F7 cells. Representative cell lines were cloned and recloned. The multireactivity of the IgM produced by really monoclonal cells, however, was preserved.

Animals↗