PubMed Health⌕ Search

Biomedical subjects

R Conrad

Publications and source records attributed to R Conrad.

At least 55 records · Page 3Linked to original sources

Methanogenic archaea and CO2-dependent methanogenesis on washed rice roots.

Washed excised roots of rice (Oryza sativa) immediately started to produce CH4 when they were incubated in phosphate buffer under anoxic conditions (N2 atmosphere), with initial rates varying between 2 and 70nmolh(-1)g(-1) dry weight of root material (mean +/- SE: 20.3 +/- 5.9 nmol h(-1) g(-1) dry weight; n = 18). Production of CH4 continued for at least 500 h, with rates usually decreasing slowly. CH4 production was not significantly affected by methyl fluoride, an inhibitor of acetoclastic methanogenesis. Less than 0.5% of added [2-14C]-acetate was converted to 14CH4, and conversion of 14CO2 to 14CH4 indicated that CH4 was almost exclusively produced from CO2. Occasionally, however, especially when the roots were incubated without additional buffer, CH4 production started to accelerate after about 200h reaching rates of > 100 nmol h(-1) g(-1) dry weight. Methyl fluoride inhibited methanogenesis by more than 20% only in these cases, and the conversion of 14CO2 to 14CH4 decreased. These results indicate that CO2-dependent rather than acetoclastic methanogenesis was primarily responsible for CH4 production in anoxically incubated rice roots. Determination of most probable numbers of methanogens on washed roots showed highest numbers (10(6)g(-1) dry roots) on H2 and ethanol, i.e. substrates that support CH4 production from CO2. Numbers on acetate (10(5) g(-1) dry roots) and methanol (10(4)g(-1) dry roots) were lower. Methanogenic consortia enriched on H2 and ethanol were characterized phylogenetically by comparative sequence analysis of archaeal small-subunit (SSU) ribosomal RNA-encoding genes (rDNA). These sequences showed a high similarity to SSU rDNA clones that had been obtained previously by direct extraction of total DNA from washed rice roots. The SSU rDNA sequences recovered from the H2/CO2-using consortium either belonged to a novel lineage of methanogens that grouped within the phylogenetic radiation of the Methanosarcinales and Methanomicrobiales or were affiliated with Methanobacterium bryantii. SSU rDNA sequences retrieved from the ethanol-using consortium either grouped within the genus Methanosarcina or belonged to another novel lineage within the phylogenetic radiation of the Methanosarcinales and Methanomicrobiales. Cultured organisms belonging to either of the two novel lineages have not been reported yet.

Acetates↗

[Spiral CT of the head-neck area: the advantages of the early arterial phase in the detection of squamous-cell carcinomas].

PURPOSE: To determine if scanning in the arterial phase improves detection of squamous cell carcinomas in the pharynx and larynx. METHODS: In a prospective clinical study 20 patients with a pharyngeal or laryngeal carcinoma were examined with by spiral CT. 80 ml lopromid were intravenously injected as a bolus with a rate of 3 ml/sec. Two consecutive spiral CT scans were performed with start-delay times of 20 and 70 seconds respectively. Delineation and contrast enhancement of tumours, cervical lymph nodes and vessels were evaluated. The radiodensities (HU) of tumors, lymph nodes vessels, pharyngeal wall and muscle were measured. RESULTS: Comparing early and late start delay time scans tumor assessment in the early phase was better in 58%, less in 16% and equal in both scans in 26%. 82% of the pathologic lymph nodes had more peripheral enhancement than surrounding muscle tissue. During the arterial phase the measured radiodensities of the common carotid artery and jugular vein were significantly higher than in the second phase. CONCLUSION: Contrast-enhanced special CT permits accurate morphologic assessment (size, infiltration) of pharyngeal and supraglottic laryngeal squamous cell carcinoma, while pathologic lymph nodes already have a sufficient contrast enhancement for the detection.

Adult↗

[The MRT of focal liver lesions: the value of gadolinium-enhanced dynamic studies of the whole organ with a fast 3D-turbo-gradient echo sequence].

PURPOSE: To determine the value of a dynamic Gd-enhanced ultrafast T1-weighted 3D-turbo-gradient-echo sequence (3D-TFE) in the detection and characterization of focal liver lesions. MATERIALS AND METHODS: 51 patients with 124 focal liver lesions (35 hemangiomas, 30 HCC, 24 metastases, 22 cysts, 5 FNH/adenoma, 8 other lesions) were examined using a 1.5 T system. The dynamic 3D-TFE sequence, achieving 40 slices with a thickness of 4.5 mm in a 17-s breath-hold, was compared with a fat-suppressed T2-weighted fast-spin-echo sequence (TSE SPIR), unenhanced and Gd-enhanced T1-weighted spin-echo sequences (SE), and a T1-weighted gradient-echo sequence (FFE). RESULTS: On 3D-TFE images more lesions (107/124) were identified than on T1-weighted SE (101/124) and T1-weighted FFE images (106/124), but less compared to T2-weighted TSE SPIR images (115/124). The 3D-TFE-sequence provided additional information in 65/107 (61%) detected lesions by delineating the dynamic enhancement pattern, most valuable in patients with HCCs in 90%. CONCLUSIONS: On dynamic 3D-TFE images more lesions could be depicted than on conventional T1-weighted SE and T1-weighted FFE images. Visualization of the dynamic enhancement pattern provided additional information for tumor characterization in 61% of the detected lesions on the 3D-TFE images.

Artifacts↗

High-affinity methane oxidation by a soil enrichment culture containing a type II methanotroph.

Methanotrophic bacteria in an organic soil were enriched on gaseous mixing ratios of <275 parts per million of volume (ppmv) of methane (CH4). After 4 years of growth and periodic dilution (>10(20) times the initial soil inoculum), a mixed culture was obtained which displayed an apparent half-saturation constant [Km(app)] for CH4 of 56 to 186 nM (40 to 132 ppmv). This value was the same as that measured in the soil itself and about 1 order of magnitude lower than reported values for pure cultures of methane oxidizers. However, the Km(app) increased when the culture was transferred to higher mixing ratios of CH4 (1,000 ppmv, or 1%). Denaturing gradient gel electrophoresis of the enrichment grown on <275 ppmv of CH4 revealed a single gene product of pmoA, which codes for a subunit of particulate methane monooxygenase. This suggested that only one methanotroph species was present. This organism was isolated from a sample of the enrichment culture grown on 1% CH4 and phylogenetically positioned based on its 16S rRNA, pmoA, and mxaF gene sequences as a type II strain of the Methylocystis/Methylosinus group. A coculture of this strain with a Variovorax sp., when grown on <275 ppmv of CH4, had a Km(app) (129 to 188 nM) similar to that of the initial enrichment culture. The data suggest that the affinity of methanotrophic bacteria for CH4 varies with growth conditions and that the oxidation of atmospheric CH4 observed in this soil is carried out by type II methanotrophic bacteria which are similar to characterized species.

Culture Media↗

Molecular analyses of the methane-oxidizing microbial community in rice field soil by targeting the genes of the 16S rRNA, particulate methane monooxygenase, and methanol dehydrogenase

Rice field soil with a nonsaturated water content induced CH4 consumption activity when it was supplemented with 5% CH4. After a lag phase of 3 days, CH4 was consumed rapidly until the concentration was less than 1.8 parts per million by volume (ppmv). However, the soil was not able to maintain the oxidation activity at near-atmospheric CH4 mixing ratios (i.e., 5 ppmv). The soil microbial community was monitored by performing denaturing gradient gel electrophoresis (DGGE) during the oxidation process with different PCR primer sets based on the 16S rRNA gene and on functional genes. A universal small-subunit (SSU) ribosomal DNA (rDNA) primer set and 16S rDNA primer sets specifically targeting type I methylotrophs (members of the gamma subdivision of the class Proteobacteria [gamma-Proteobacteria]) and type II methylotrophs (members of the alpha-Proteobacteria) were used. Functional PCR primers targeted the genes for particulate methane monooxygenase (pmoA) and methanol dehydrogenase (mxaF), which code for key enzymes in the catabolism of all methanotrophs. The yield of PCR products amplified from DNA in soil that oxidized CH4 was the same as the yield of PCR products amplified from control soil when the universal SSU rDNA primer set was used but was significantly greater when primer sets specific for methanotrophs were used. The DGGE patterns and the sequences of major DGGE bands obtained with the universal SSU rDNA primer set showed that the community structure was dominated by nonmethanotrophic populations related to the genera Flavobacterium and Bacillus and was not influenced by CH4. The structure of the methylotroph community as determined with the specific primer sets was less complex; this community consisted of both type I and type II methanotrophs related to the genera Methylobacter, Methylococcus, and Methylocystis. DGGE profiles of PCR products amplified with functional gene primer sets that targeted the mxaF and pmoA genes revealed that there were pronounced community shifts when CH4 oxidation began. High CH4 concentrations stimulated both type I and II methanotrophs in rice field soil with a nonsaturated water content, as determined with both ribosomal and functional gene markers.

Journal Article↗

Effect of temperature on structure and function of the methanogenic archaeal community in an anoxic rice field soil.

Soil temperatures in Italian rice fields typically range between about 15 and 30 degrees C. A change in the incubation temperature of anoxic methanogenic soil slurry from 30 degrees C to 15 degrees C typically resulted in a decrease in the CH4 production rate, a decrease in the steady-state H2 partial pressure, and a transient accumulation of acetate. Previous experiments have shown that these changes were due to an alteration of the carbon and electron flow in the methanogenic degradation pathway of organic matter caused by the temperature shift (K. J. Chin and R. Conrad, FEMS Microbiol. Ecol. 18:85-102, 1995). To investigate how temperature affects the structure of the methanogenic archaeal community, total DNA was extracted from soil slurries incubated at 30 and 15 degrees C. The archaeal small-subunit (SSU) rRNA-encoding genes (rDNA) of these environmental DNA samples were amplified by PCR with an archaeal-specific primer system and used for the generation of clone libraries. Representative rDNA clones (n = 90) were characterized by terminal restriction fragment length polymorphism (T-RFLP) and sequence analysis. T-RFLP analysis produced for the clones terminally labeled fragments with a characteristic length of mostly 185, 284, or 392 bp. Sequence analysis allowed determination of the phylogenetic affiliation of the individual clones with their characteristic T-RFLP fragment lengths and showed that the archaeal community of the anoxic rice soil slurry was dominated by members of the families Methanosarcinaceae (185 bp) and Methanosaetaceae (284 bp), the kingdom Crenarchaeota (185 or 284 bp), and a novel, deeply branching lineage of the (probably methanogenic) kingdom Euryarchaeota (392 bp) that has recently been detected on rice roots (R. Grosskopf, S. Stubner, and W. Liesack, Appl. Environ. Microbiol. 64:4983-4989, 1998). The structure of the archaeal community changed when the temperature was shifted from 30 degrees C to 15 degrees C. Before the temperature shift, the clones (n = 30) retrieved from the community were dominated by Crenarchaeota (70%), "novel Euryarchaeota" (23%), and Methanosarcinacaeae (7%). Further incubation at 30 degrees C (n = 30 clones) resulted in a relative increase in members of the Methanosarcinaceae (77%), whereas further incubation at 15 degrees C (n = 30 clones) resulted in a much more diverse community consisting of 33% Methanosarcinaceae, 23% Crenarchaeota, 20% Methanosaetaceae, and 17% novel Euryarchaeota. The appearance of Methanosaetaceae at 15 degrees C was conspicuous. These results demonstrate that the structure of the archaeal community in anoxic rice field soil changed with time and incubation temperature.

Archaea↗

Measurement of monosaccharides and conversion of glucose to acetate in anoxic rice field soil

Degradation of glucose has been implicated in acetate production in rice field soil, but the abundance of glucose, the temporal change of glucose turnover, and the relationship between glucose and acetate catabolism are not well understood. We therefore measured the pool sizes of glucose and acetate in rice field soil and investigated the turnover of [U-14C]glucose and [2-14C]acetate. Acetate accumulated up to about 2 mM during days 5 to 10 after flooding of the soil. Subsequently, methanogenesis started and the acetate concentration decreased to about 100 to 200 &mgr;M. Glucose always made up >50% of the total monosaccharides detected. Glucose concentrations decreased during the first 10 days from 90 &mgr;M initially to about 3 &mgr;M after 40 days of incubation. With the exception at day 0 when glucose consumption was slow, the glucose turnover time was in the range of minutes, while the acetate turnover time was in the range of hours. Anaerobic degradation of [U-14C]glucose released [14C]acetate and 14CO2 as the main products, with [14C]acetate being released faster than 14CO2. The products of [2-14C]acetate metabolism, on the other hand, were 14CO2 during the reduction phase of soil incubation (days 0 to 15) and 14CH4 during the methanogenic phase (after day 15). Except during the accumulation period of acetate (days 5 to 10), approximately 50 to 80% of the acetate consumed was produced from glucose catabolism. However, during the accumulation period of acetate, the rate of acetate production from glucose greatly exceeded that of acetate consumption. Under steady-state conditions, up to 67% of the CH4 was produced from acetate, of which up to 56% was produced from glucose degradation.

Journal Article↗

[The pathological/MR tomographic correlation and differential diagnosis of malignant kidney tumors].

PURPOSE: Evaluation of malignancy criteria in MRT of kidney tumors in correlation with the histopathological findings. MATERIALS AND METHODS: 41 patients with suspected malignant kidney tumors were examined using a T1 SE sequence (TR/TE 300/10 ms) before and after i.v. administration of 0.1 mmol/kg Gd-DTPA and a T2 SE sequence (TR/TE 5500/150 ms). The results were correlated with the pathological findings. RESULTS: 38 malignant tumors were found: 29 renal cell carcinomas (RCC), 13 with solid growth, 11 with tubulopapillary growth, and three with mixed growth forms, one cystic RCC, and one chromophobic RCC, in addition, 6 urothelial carcinomas and three other malignomas. Typical MRT criteria for RCC were an inhomogeneity of the tumor with regions of slightly increased signal intensity on the T1-weighted image (59%) and regions with reduced signal intensity on the T2-weighted image (96%) as compared with renal parenchyma; these were due to histomorphological hemorrhage and hemosiderin deposits, respectively. A further criterion for RCC was a hypointense pseudocapsule in the T2 TSE sequence in 79% of the cases. CONCLUSIONS: The low-signal nature of RCC in the T2-weighted image correlates with hemorrhage and hemosiderin deposits. The detection of a pseudocapsule is useful in the differential diagnosis of solid tumors in the kidney.

Carcinoma, Renal Cell↗

[Portal contrast medium-enhanced spiral computed tomography of the liver--the correlation of radiological and intraoperative findings and the evaluation of resectability].

PURPOSE: To evaluate the accuracy of spiral computed tomography during arterial portography (SCTAP) in the detection, localization, and resectability of liver tumors in a correlative study between radiology and intraoperative findings. METHOD AND MATERIALS: Retrospectively, SCTAP images of 168 consecutive patients before liver tumor resection were analyzed. The SCTAP studies (100 ml lopromid 300 by automated injector with a flow of 3 ml/s; slice thickness, table feed and reconstruction index 5 mm each; scan-delay 30 s; 120 kV; 250 mAs) were evaluated for the detection, localization, and resectability of focal liver lesions by three experienced radiologists in consensus and were correlated with histopathological and intraoperative findings where available (59/168). RESULTS: The sensitivity of SCTAP for the detection of liver tumors was 91% for all lesions and 84% for lesions < 1 cm. The specificity was only 19% due to a high rate of false-positive lesions (30%) and preselection effects. Typical pitfalls in false positive lesions were inhomogeneous liver perfusion near the portal vein, the falciform ligament, and the gallbladder (19/42). In 30% of the patients SCTAP correctly diagnosed inoperability, in 23% the intraoperative tumor expansion was larger than expected from SCTAP images, which would have changed operability. CONCLUSION: The SCTAP has a high sensitivity in the detection and localization of liver tumors and is a valuable method in the preoperative diagnostic procedure. The method is limited by many false-positive lesions often due to inhomogeneous liver perfusion and the insufficient evaluation of local tumor spread. Therefore, SCTAP should be replaced by MRI in the near future.

Adult↗

Sulfur oxidation in rice field soil: activity, enumeration, isolation and characterization of thiosulfate-oxidizing bacteria.

In rice paddy fields the bulk soil is anoxic, but oxygenated zones occur in the surrounding of the rice roots to where oxygen is transported via the aerenchyma system of the rice plants. In the anaerobic soil compartments sulfate is consumed by sulfate-reducing bacteria. In the rhizosphere the reduced sulfur compounds can be reoxidized by sulfur-oxidizing bacteria. Measurements of the potential activity of thiosulfate-oxidizing bacteria in soil slurries derived from planted rice soil microcosms showed turnover rates of 2-6 mumol d-1 g-dw-1. Thiosulfate was oxidized to sulfate with tetrathionate as intermediate. Most probable number (MPN) enumeration with three aerobic media and one anaerobic nitrate-amended medium showed that thiosulfate-oxidizing bacteria were abundant in paddy soil and in rhizosphere soil at numbers of 10(5) to 10(6) per gram dry weight soil. Nine isolates of S-oxidizing bacteria were obtained from enrichment cultures or from the highest dilutions of the MPN series and were affiliated to four different phylogenetic groups. These isolates were characterized by physiological properties and by comparative 16S rDNA sequence analysis. Three isolates (TA1-AE1, TA1-A1 and TA12-21) were shown to be facultatively chemolithoautotrophic strains of Ancylobacter aquaticus. Three further isolates (Tv6-2b, Z2A-6A and Z4A-2A) were also facultatively chemolithoautotrophic and were affiliated with the Xanthobacter sp. group, probably representing new strains of X. flavus or X. tagetidis. Strain SZ-2111 was phylogenetically related to Bosea thiooxidans. However, the genus Bosea is described as obligately heterotrophic, whereas strain 5Z-2111 was able to grow autotrophically. The isolates 5Z-C1 and TBW3 were obligate chemolithoautotrophs and were closely affiliated with Thiobacillus thioparus. Our results showed that S-oxidizing bacteria were abundant and active in rice paddy soil and consisted of physiologically and phylogenetically diverse populations.

Anaerobiosis↗

[Evaluation of the effects of bioadhesive substances as addition to oral contrast media: an experimental study].

PURPOSE: To evaluate the additional effect of bioadhesives in combination with iotrolan and barium as oral contrast media in an animal model. METHOD: The bioadhesives Noveon, CMC, Tylose and Carbopol 934 were added to iotrolan and barium. The solutions were administered to rabbits by a feeding tube. The animals were investigated by computed tomography (CT) and radiography after 0.5, 4, 12, 24 and in part after 48 hours. Mucosal coating and contrast filling of the bowel were evaluated. RESULTS: Addition of bioadhesives to oral contrast media effected long-term contrast in the small intestine and colon, but no improvement in continuous filling and coating of the gastrointestinal tract was detected. Mucosal coating was seen only in short regions of the caecum and small intestine. In CT the best results for coating were observed with tylose and CMC, in radiography additionally with carbopol and noveon. All contrast medium were well tolerated. CONCLUSION: The evaluated contrast medium solutions with bioadhesives have shown long-term contrast but no improvement in coating in comparison to conventional oral contrast media.

Acrylic Resins↗

Diagnostic value of p53 immunohistochemistry in Barrett's esophagus: an endoscopic study.

The aim of this study was to establish the diagnostic utility of p53 immunohistochemistry in Barrett's esophagus. Three pathologists reviewed endoscopic biopsy specimens and one surgical specimen derived from 102 subjects in a prospective follow-up series. Dysplasia was graded as negative, indefinite, low grade and high grade. p53 staining was assessed as negative, weak or patchy and strong. Kappa coefficients for interobserver agreement for the three combinations of observer pairs were moderate to substantial (0.48, 0.55 and 0.68) for dysplasia and substantial to near perfect (0.77, 0.82 and 0.89) for p53 immunostaining. In the consensus grading achieved for dysplasia, strong p53 staining was recorded in 0/79 samples that were negative or indefinite for dysplasia, 5/15 (33%) examples of low grade dysplasia and 7/8 (87%) examples of high grade dysplasia. Non-dysplastic p53 positive glands were seen in specimens from two subjects harbouring dysplasia or cancer elsewhere. Two p53 positive specimens were, upon review and discussion, re-assigned from low- to high-grade dysplasia. It is concluded that p53 immunohistochemistry facilitates the interpretation of Barrett's epithelium but need only be employed to confirm a suspected diagnosis of dysplasia and assist with the distinction between low- and high-grade dysplasia.

Barrett Esophagus↗

[Radiologic changes following cement-free implantation of hip prostheses. 5-year follow-up and clinical experience with the cement-free hip prosthesis Autophor-900-S].

PURPOSE: To evaluate early reliable radiographic signs of loosening in cementless total hip arthroplasty compared to clinical follow-up. METHODS: Within a time interval of 5 years 89 patients with 101 hips underwent total hip arthroplasty using the Autophor 900 S-prosthesis. Clinical and radiographic follow-up were first performed retrospectively followed by a prospective investigation. RESULTS: Radiographic evaluation showed prosthesis fixation in 93%. Loosening of the prosthesis was identified in 4 cases of the acetabular component and in 4 cases of the femoral stem. Pain was associated with radiographically detectable loosening of the cementless arthroplastic components in only two cases. CONCLUSION: Within a follow-up period of up to five years, loosening of cementless total hip arthroplasty occurs in about 7%. The most reliable radiographic signs of loosening are complete radiolucent zones wider than 2 mm at the bone-component interface, progressive subsidence, migration, or tilt of the component. Pain and movement disorders are not specific symptoms and do not necessarily indicate a loosening of the prosthesis.

Adult↗

[Oral contrast media in CT: improvement by addition of guar?].

PURPOSE: To evaluate the additional effect of guar with iotrolan as an oral contrast medium. METHOD: In a clinical double-blind randomised study a viscous iotrolan (11.2 mg iodine/ml)/guar (4 g/l)-suspension was compared with aqueous solutions of pure iotrolan (11.2 mg iodine/ml) and meglumine ioxithalamate (12 mg iodine/ml). The contrast media were evaluated according to filling, distribution, transit time, artifacts, radiodensity, patient acceptance and side effects. RESULTS: The addition of guar delayed the transit time of the contrast media. Consequently a more homogeneous filling of the bowel with fewer artifacts was observed in comparison to the aqueous contrast media. The results of the pure iotrolan solution were comparable to meglumine ioxithalamate, except for a higher radiodensity in the distal small intestine. The colon showed a better filling with non-viscous contrast media in the given time frame. Pure iotrolan had the best patient acceptance. Two patients considered the iotrolan/guar-solution impossible to drink, the other 18 patients found taste and consistency just about acceptable. CONCLUSION: In spite of the discussed advantages, due to a less subjective acceptance the guar/iotrolan solution is not suitable in routine-diagnosis, unless taste and consistency are greatly improved. Individual use is recommended in selected cases and long-term examinations.

Administration, Oral↗

Detecting immobilized protein kinase C isozymes with RNA aptamers.

Nucleic acids that can bind tightly and specifically to protein targets can be selected from random sequence pools. Just as antibodies have been used to detect proteins in a variety of formats, it is possible the nucleic acid binding species (aptamers) could be used to specifically detect proteins. Using a simple filter binding assay, aptamers have been used to detect protein kinase C (PKC) introduced into a cell extract. Aptamers that were relatively nonspecific could be used to simultaneously detect different PKC isozymes, while aptamers with higher specificities could discriminate between related isozymes. These results demonstrate the feasibility of using aptamers as diagnostic tools to detect proteins.

Animals↗

Oxidation of nitric oxide by a new heterotrophic Pseudomonas sp.

A new bacterial strain isolated from soil consumed nitric oxide (NO) under oxic conditions by oxidation to nitrate. Phenotypic and phylogenetic characterization of the new strain PS88 showed that it represents a previously unknown species of the genus Pseudomonas, closely related to Pseudomonas fluorescens and Pseudomonas putida. The heterotrophic, obligately aerobic strain PS88 was not able to denitrify or nitrify; however, strain PS88 oxidized NO to nitrate. NO was not reduced to nitrous oxide (N2O). Nitrogen dioxide (NO2) and nitrite (NO2-) as possible intermediates of NO oxidation to nitrate (NO3-) could not be detected. NO oxidation was inhibited under anoxic conditions and by high osmolarity, but not by nitrite. NO oxidation activity was inhibited by addition of formaldehyde, HgCl2, and antimycin, and by autoclaving or disintegrating the cells, indicating that the process was enzyme-mediated. However, the mechanism remains unclear. A stepwise oxidation at a metalloenzyme and a radical mechanism are discussed. NO oxidation in strain PS88 seems to be a detoxification or a co-oxidation mechanism, rather than an energy-yielding process.

Nitric Oxide↗