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Biomedical subjects

W Loeffler

Publications and source records attributed to W Loeffler.

At least 19 recordsLinked to original sources
PubMed1990

Rhizocticin A, an antifungal phosphono-oligopeptide of Bacillus subtilis ATCC 6633: biological properties.

Rhizocticin A, the main component of the antifungal, hydrophilic phosphono-oligopeptides of Bacillus subtilis ATCC 6633, was used for sensitivity testing and experiments into the molecular mechanism of the antibiotic action. Budding and filamentous fungi as well as the cultivated nematode Caenorhabditis elegans were found to be sensitive, whereas bacteria and the protozoon Paramecium caudatum were insensitive. Rhizoctonia solani was inhibited in agar dilution tests but not in diffusion tests. The antifungal effect of rhizocticin A was neutralized by a variety of amino acids and oligopeptides. Oligopeptide influence was mainly understood as transport antagonism, and it was concluded that the antibiotic enters the recipient cell via the peptide transport system. L- and D-cystine were also identified as potent, general antagonists of the oligopeptide transport. The rhizocticin-antagonism of four other amino acids was taken as a clue to the site of action. Provided that rhizocticin A is split by peptidases of the target cell into inactive L-arginine and toxic L-2-amino-5-phosphono-3-cis-pentenoic acid (L-APPA), the latter may interfere with the threonine or threonine-related metabolism.

Amino Acids↗
PubMed1990

The human brain: localized H-1 MR spectroscopy at 1.0 T.

Localized H-1 magnetic resonance (MR) spectroscopy of the human brain in vivo was performed at a field strength of 1.0 T. Investigations with the stimulated echo acquisition mode included studies in the right frontoparietal area, occipital lobe, cerebellum, and pons of healthy volunteers, as well as studies in two patients with astrocytomas. Prior to the acquisition of the H-1 MR spectra, all examinations included fast low angle shot MR imaging in three orientations to select the volumes of interest. The tumor spectra confirmed previous findings at higher field strengths by producing characteristic alterations from the spectra of normal brain tissue: markedly reduced resonances of N-acetyl-aspartate and creatine, increased signal intensities of cholines, and a strong resonance from lactate. The authors conclude that the results of this study clearly demonstrate the feasibility of H-1 MR spectroscopy at 1.0 T without significant losses in relative spectral resolution and signal-to-noise ratio of major metabolites with singlet resonances, compared with previous studies at 1.5 and 2.0 T.

Brain↗
PubMed1990

Magnetic resonance angiography.

Magnetic resonance imaging allows the visualization of vascular structures without the use of contrast agents. With three-dimensional imaging techniques, based on gradient echo sequences, up to 128 slices can be acquired within a maximum acquisition time of 21 minutes at a spatial resolution of approximately 1 mm. This allows the carotid arteries and major intracerebral vascular structures to be displayed. From the primary three-dimensional data set, projective images at arbitrary projection angles can be calculated. This technique is extremely helpful for assigning spatially complex vascular structures and identifying vascular disease. As a result of rapid technologic advances in magnetic resonance angiography, it is now necessary to assess its clinical utility for identifying atherosclerotic stenoses, aneurysms, and arteriovenous malformations. Limited experience to date has shown that magnetic resonance angiography, because of its high sensitivity to these vascular diseases, may play a clinically important role as a screening method.

Contrast Media↗
PubMed1986

Fengycin--a novel antifungal lipopeptide antibiotic produced by Bacillus subtilis F-29-3.

Fengycin is an antifungal lipopeptide complex produced by Bacillus subtilis strain F-29-3. It inhibits filamentous fungi but is ineffective against yeast and bacteria. The inhibition is antagonized by sterols, phospholipids and oleic acid, whereas two other unsaturated fatty acids increase the antifungal effect. Fengycin consists of two main components differing by one amino acid exchange. Fengycin A is composed of 1 D-Ala, 1 L-Ile, 1 L-Pro, 1 D-allo-Thr, 3 L-Glx, 1 D-Tyr, 1 L-Tyr, 1 D-Orn, whereas in fengycin B the D-Ala is replaced by D-Val. The lipid moiety of both analogs is more variable, as fatty acids have been identified as anteiso-pentadecanoic acid (ai-C15), iso-hexadecanoic acid (i-C16), n-hexadecanoic acid (n-C16), and there is evidence for further saturated and unsaturated residues up to C18.

Antifungal Agents↗
PubMed1986

Proton chemical shift imaging.

Proton resonance spectra contain two broad classes of hydrogen-containing compounds: those that are fat-like and those that are water-like. Proton chemical shift imaging is a means to produce water or fat proton images. Three methods of proton chemical shift imaging are discussed.

Lipids↗
PubMed1981

[Nuclear magnetic resonance tomography].

Imaging methods based on nuclear magnetic resonance allow the production of sectional images of the human body without ionizing radiation. It is possible to measure the density and relaxation times of the water protons in body fluids or tissue. This allows not only to obtain morphological information but also to get some insight into the spatial distribution of physiological data. Starting with a review of the principles of nuclear magnetic resonance it is explained how the measured signal can be associated with an image point; it is also explained what type of apparatus is necessary and what the physical limitations are. Possible risks the patient may be exposed to in an examination using nuclear magnetic resonance are discussed. The present state of the technical development enables the production of whole-body sectional images of a living person within about one minute. By means of some typical examples the nature and properties of these images are explained. Although extensive clinical studies will be necessary before a more general assessment can be made of this method, an outlook is provided on expected further developments and possible future fields of application.

Humans↗
PubMed1981

Physical principles of NMR tomography.

Using nuclear magnetic resonance tomography it is possible to produce sectional images of the density and relaxation times of the protons within the human body. After a review of the general principles of nuclear magnetic resonance it is explained how this physical effect can be used for generating tomographic images in medical diagnosis. The major components of an imaging system and the physical and technical potentials and limitations of this new method are described. The different appearance of tissue and body fluids in spin-density, T1 and T2 images, as well as resulting problems of interpretation are discussed with typical examples.

Animals↗
PubMed1979

[Genetic aspects of opportunistic fungi].

The etiologic agents of human mycoses are discussed in taxonomic order. Some fungal genera are used as examples to describe the general genetical behavior of the various groups. Special features of probable genetical and etiological relevance are mentioned.

Ascomycota↗
PubMed1977

Ophiocordin, an antifungal antibiotic of Cordyceps ophioglossoides.

An unknown antibiotic, ophiocordin, C21H22N2O8, MW: 430, was isolated from submerged cultures of Cordyceps ophioglossoides, strain TU 276, grown in a glycerol soybean meal medium at 27 degrees C. The antibiotic was extracted from acidified culture fluids with n-butanol and purified by subsequent column chromatography on DEAE-Sephadex and cellulose. Studies including nuclear magnetic resonance and mass spectrometry resulted in proposals of partial structures of the molecule. Inhibition by ophiocordin could be demonstrated for a small number of fungi belonging to different taxonomic groups. Bacteria were not inhibited. The antifungal effect was antagonized by ammonia and nitrate ions and by certain amino acids.

Antifungal Agents↗
PubMed1977

Antifungal agents.

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Antifungal Agents↗