Search PubMed⌕ Search

Biomedical subjects

S A Martin

Publications and source records attributed to S A Martin.

At least 55 records · Page 3Linked to original sources
PubMed1998

Effects of chlorhexidine diacetate on ruminal microorganisms.

The objectives of this study were to examine the effects of chlorhexidine diacetate on growth and L-lactate production by Streptococcus bovis JB1 as well as the effects of this antimicrobial compound on the mixed ruminal microorganism fermentation. Addition of 1.8 microM chlorhexidine diacetate to glucose medium resulted in a lag in growth by S. bovis JB1, and growth was completely inhibited in the presence of 3.6, 9.0, and 18 microM chlorhexidine. When 6.2 microM chlorhexidine diacetate was added to glucose medium after 2 h of incubation, glucose utilization and L-lactate production by S. bovis JB1 were reduced. Phosphoenolpyruvate-dependent phosphorylation of 14C-glucose by toluene-treated cells of S. bovis JB1 was inhibited by increasing concentrations (1.8 to 18 microM) of chlorhexidine, whereas only the 18 microM concentration reduced the membrane potential (delta psi). Chlorhexidine diacetate was a potent inhibitor of L-lactate and methane production from glucose fermentation by mixed ruminal microorganisms. However, because chlorhexidine also decreased acetate and propionate concentrations and increased ammonia concentrations in mixed-culture incubations, this antimicrobial compound may have limited application as a ruminant feed additive.

Animals↗
PubMed1998

Integrated YAC contig map of the Prader-Willi/Angelman region on chromosome 15q11-q13 with average STS spacing of 35 kb.

Prader-Willi syndrome and Angelman syndrome are associated with parent-of-origin-specific abnormalities of chromosome 15q11-q13, most frequently a deletion of an approximately 4-Mb region. Because of genomic imprinting, paternal deficiency of this region leads to PWS and maternal deficiency to AS. Additionally, this region is frequently involved in other chromosomal rearrangements including duplications, triplications, or supernumerary marker formation. A detailed physical map of this region is important for elucidating the genes and mechanisms involved in genomic imprinting, as well as for understanding the mechanism of recurrent chromosomal rearrangments. An initial YAC contig extended from D15S18 to D15S12 and was comprised of 23 YACs and 21 STSs providing an average resolution of about one STS per 200 kb. To close two gaps in this contig, YAC screening was performed using two STSs that flank the gap between D15S18 and 254B5R and three STSs located distal to the GABRA5-149A9L gap. Additionally, we developed 11 new STSs, including seven polymorphic markers. Although several groups have developed whole-genome genetic and radiation hybrid maps, the depth of coverage for 15q11-q13 has been somewhat limited and discrepancies in marker order exist between the maps. To resolve the inconsistencies and to provide a more detailed map order of STSs in this region, we have constructed an integrated YAC STS-based physical map of chromosome 15q11-q13 containing 118 YACs and 118 STSs, including 38 STRs and 49 genes/ESTs. Using an estimate of 4 Mb for the size of this region, the map provides an average STS spacing of 35 kb. This map provides a valuable resource for identification of disease genes localized to this region as well as a framework for complete DNA sequencing.

Angelman Syndrome↗
PubMed1998

Effects of laidlomycin propionate and monensin on glucose utilization and nutrient transport by Streptococcus bovis and Selenomonas ruminantium.

The objective of this study was to compare the effects of laidlomycin propionate and monensin on cell growth, glucose fermentation, and glucose uptake in Streptococcus bovis strain JB1 and Selenomonas ruminantium strain HD4. Experiments were also conducted to compare the effects of both ionophores on sodium-dependent serine transport and cell yield in S. bovis. Batch cultures (500 mL) of each bacterium were grown on 3.6 g/L D-glucose in semidefined medium and treated with either 5 ppm monensin or 2 ppm laidlomycin propionate (n=2). Cell growth was monitored by measuring optical density at 600 nm (OD600). Glucose and L-lactate concentrations were measured using coupled enzyme assays. In S. bovis, both monensin and laidlomycin propionate decreased OD600, glucose utilization, and L-lactate production. Neither ionophore had any effect on glucose utilization by S. ruminantium. [14C]Glucose uptake between 5 and 30 min by both bacteria was not altered by either ionophore. Sodium-dependent [14C]serine uptake by S. bovis was inhibited by monensin but not laidlomycin propionate. When S. bovis was grown in glucose-limited continuous culture (dilution rate=.10 h(-1)) at extracellular pH 6.7, increasing concentrations of both ionophores decreased bacterial yield, and both ionophores were more potent at an extracellular pH of 5.7. However, monensin was a more potent inhibitor than laidlomycin propionate at pH 6.7 and 5.7. Collectively, these results suggest that the ionophore laidlomycin propionate inhibits the Gram-positive bacterium S. bovis in a manner similar to that of monensin, but, at the concentrations used in this study, laidlomycin propionate seems to be less potent than monensin in inhibiting serine uptake and cell yield.

Animals↗
PubMed1998

Manipulation of ruminal fermentation with organic acids: a review.

The dicarboxylic acids aspartate, fumarate, and malate stimulate lactate utilization by the predominant ruminal bacterium, Selenomonas ruminantium. Malate stimulates lactate uptake by S. ruminantium more than does aspartate or fumarate, and it seems that malate and sodium are involved in stimulating lactate utilization by this bacterium. Based on the ability of S. ruminantium to grow on malate in the presence of extracellular hydrogen and produce succinate, malate may be acting as an electron sink for hydrogen in the succinate-propionate pathway used by S. ruminantium. Incorporation of DL-malate into soluble starch and cracked corn fermentations with mixed ruminal microorganisms changed final pH, CH4, and VFA in a manner analogous to ionophore effects. When compared with either dicarboxylic acids or monensin alone, dicarboxylic acid plus monensin addition to cracked corn incubations stimulated the mixed ruminal microorganism fermentation to produce more propionate, less lactate, and increased final pH. Reduced lactate concentrations in dicarboxylic acid- and monensin-treated incubations most likely represents an additive effect of decreased lactate production by monensin-sensitive bacteria (i.e., Streptococcus bovis) and increased lactate utilization by the monensin-resistant S. ruminantium. The inclusion of malate as a feed additive into the diets of ruminants is currently not economically feasible; however, forages rich in organic acids might serve as vehicles for providing malate to ruminants. When five alfalfa varieties and three bermudagrass hay varieties were surveyed for malate content, the concentration of malate in both plant species declined as maturity increased. However, after 42 d of maturity, the concentration of malate in both forages ranged between 1.9 and 4.5% of the DM. These results suggest that the incorporation of forage varieties that are high in malate may include malate economically into the diet and reduce losses associated with ruminal acidosis.

Animals↗
PubMed1998

Urinary and biliary excretion of ergot alkaloids from steers that grazed endophyte-infected tall fescue.

Ergot alkaloids cause fescue toxicosis when livestock graze endophyte-infected (E+) tall fescue. Little is known about the bioavailability of the ergot alkaloid classes (lysergic acid, lysergic acid amides, or ergopeptine alkaloids) in livestock, and this hampers development of pharmacological strategies to ameliorate the toxicosis. One method used to determine bioavailability of ergot alkaloids is to examine urinary and biliary excretion patterns. Thus, our objectives were to compare ergot alkaloid excretion via urinary or biliary systems and to determine the rate of appearance or clearance of these alkaloids in cattle that were grazing E+ or endophyte-free (E-) tall fescue. In autumn 1996, bile and urine samples were collected from eight steers (203 kg), each grazing E+ and E- tall fescue, and total alkaloid excretion was quantified using competitive ELISA. Approximately 96% of the ergot alkaloids were excreted in urine. The same steers were used to examine the rate of appearance in, or clearance from, urine when switched from E+ to E-, or from E- to E+, pastures in comparison with steers that were continuously grazing E+ or E- tall fescue at 0, 2, 5, and 7 d. Steers were returned to their original pastures after 7 d, and urine was collected at 2, 5, and 7 d. Urinary alkaloid concentrations in steers switched from E- to E+ pastures were similar (P = .55) to those in steers that continuously grazed E+ tall fescue after 2 d. Steers switched from E+ to E- pastures had urinary alkaloid concentrations similar (P = .91) to those in steers that continuously grazed E- pastures after 2 d. In 1997, two trials were conducted in which steers (191 kg) were switched or remained on E+ or E- pastures, and urine was collected at 0, 12, 24, 48, and 96 h to estimate rate of alkaloid appearance or clearance. Steers switched from E- to E+ 1) had about 33% as much urinary alkaloids as steers grazing E+ pasture after 12 h, 2) were not different after 24 h (P = .76), 3) had twice those of the E+ steers at 48 h (P < .05), and 4) were not different after 96 h. Steers switched from E+ to E- tall fescue had approximately 33% less (P < .05) urinary alkaloids than those grazing E+ at 12 h, 67% less (P < .05) at 24 and 48 h, and were not different (P = .86) from steers continuously grazing E- pastures after 96 h. Urinary alkaloid excretion patterns were similar to ergot alkaloid solubility patterns from in vitro digestion of E+ tall fescue. We suggest that alkaloids, liberated from the forage by ruminal microorganisms, were rapidly absorbed as lysergic acid amides and biotransformed ergopeptine alkaloids.

Animal Feed↗
PubMed1997

Matrix-assisted laser desorption/ionization for sequencing single-stranded and double-stranded DNA.

The DNA sequence of a single-stranded and double-stranded template was determined. The templates were sequenced using the chain termination method and cycle sequencing method and detected by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The sequencing products were analyzed successfully without the laborious and expensive methods for removal of the template. Direct sequencing of the double-stranded template was achieved with minimal post-reaction purifications, which could be extremely important for mutation analysis and clinical diagnosis. A systematic study of the mechanisms and kinetics of sequencing reactions was also performed. The details of this analysis and directions for future improvements of the quality of sequencing are presented.

Base Sequence↗
PubMed1997

Multidimensional chromatography coupled with mass spectrometry for target-based screening.

The synthesis of structural analogs and the process of drug discovery have evolved dramatically through recent advances in solid-phase synthesis reagents and automated screening systems. As molecular diversity strategies emerge, the need for automated target-based selection of lead candidates becomes equally important. Multidimensional automated chromatographic techniques coupled to electrospray ionization mass spectrometry facilitate the selection process and provide maximum characterization information in a single screening run. The capture of tightly bound affinity leads by target biomolecules, followed by subsequent release and high-resolution separation with sensitive detection, significantly reduces the time required to identify and characterize lead compounds. This automated multidimensional chromatographic approach coupled with mass spectrometry, Selectronics, was used with several organic and natural libraries to demonstrate an automated target-based screening technique to select for high-affinity binders as potential lead compounds.

Amino Acid Isomerases↗
PubMed1997

Iron deficiency enhances cholesterol gallstone formation.

BACKGROUND: Cholesterol gallstones occur most commonly in multiparous women, but the causes for this phenomenon remain unclear. This same patient population is prone to chronic iron deficiency anemia. In addition, iron is known to play an important role in hepatic enzyme metabolism. Therefore, we tested the hypotheses that iron deficiency would alter hepatic cholesterol metabolism and enhance gallstone formation. METHODS: Forty adult prairie dogs were fed either a control iron-supplemented (200 ppm), an iron-deficient (8 ppm), a 0.4% cholesterol iron-supplemented (200 ppm), or a 0.4% cholesterol iron-deficient (8 ppm) diet. After 8 weeks gallbladder bile, serum, and liver were harvested. Gallbladder bile was examined for cholesterol crystals and gallstones. Bile lipids and hepatic enzymes were measured, and a cholesterol saturation index (CSI) was calculated. RESULTS: Animals receiving the iron-deficient diet were more likely to have cholesterol crystals in their bile than were animals on the control diet (80% vs. 20%; p < 0.05). Animals on the 0.4% cholesterol iron-deficient diet had more cholesterol crystals per high-powered field (79 +/- 10 vs. 49 +/- 9; p = 0.07), a higher molar % cholesterol (6.0 +/- 0.3 vs 4.4 +/- 0.5; p < 0.05), and a higher CSI (1.27 +/- 0.10 vs. 0.91 +/- 0.07; p < 0.05) compared to animals receiving the 0.4% cholesterol iron supplemented diet. The 7 alpha-hydroxylase levels were lower in the animals on the iron-deficient diet compared to those receiving the control diet (0.42 +/- 0.08 vs 1.17 +/- 0.40 pmol/mg per minute; p = 0.07). CONCLUSIONS: These data suggest that an iron-deficient diet (1) alters hepatic enzyme metabolism, which, in turn, (2) increases gallbladder bile cholesterol and promotes cholesterol crystal formation. We conclude that iron deficiency plays a previously unrecognized role in the pathogenesis of cholesterol gallstone formation in women.

Animals↗
PubMed1997

A cytidine deaminase expressed in the post-infective L3 stage of the filarial nematode, Brugia pahangi, has a novel RNA-binding activity.

A number of genes have been identified that are highly expressed in the post-infective L3 stage of the filarial parasite, Brugia pahangi. Amongst these was a cDNA with homology to the cytidine deaminase (CDD) gene family. Phylogenetic analysis of the various cytosine nucleoside deaminases suggest that Brugia pahangi CDD evolved with significant divergence from the RNA editing family. In order to characterize its function, we have expressed Brugia pahangi CDD in bacteria as a chimera with maltose-binding protein (MBP). Biochemical analysis demonstrates the MBP-CDD fusion protein functions as an authentic cytidine deaminase with an obligate requirement for zinc. In addition to cytidine deaminase activity, however, the fusion protein demonstrates RNA binding activity with specificity for AU-rich sequences and was found to bind an RNA template spanning the edited site of mammalian apolipoprotein B (apoB) mRNA. This RNA binding activity was not found in two different recombinant bacterial CDD proteins. In vitro RNA editing assays revealed that MBP-CDD failed to mediate cytidine deamination of a mammalian apoB RNA template. Furthermore, binding of MBP-CDD to the apoB RNA did not inhibit in vitro editing of this template by apobec-1. The data suggest that the cytosine nucleoside deaminases and RNA editing deaminases have acquired different mechanisms of binding to an AU-rich RNA template, presumably with different functional implications.

Amino Acid Sequence↗
PubMed1997

Accurate mass measurements using MALDI-TOF with delayed extraction.

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry is now an essential tool in biopolymer analysis. Sensitivity and mass range are unsurpassed, but mass measurement accuracy and resolution have been limited. With delayed extraction and a reflecting analyzer, mass measurements using MALDI-TOF can be made with an accuracy of a few parts per million (ppm). It is possible to distinguish Lys from Gln in peptides, and to determine the elemental composition of smaller molecules (mass 100-500). In database searching strategies, a smaller mass window, resulting from an increase in mass accuracy, greatly decreases the number of possible candidates. Mass measurement accuracy with errors less than 5 ppm is demonstrated on a mixture of 12 peptides ranging in mass from ca. 900 to 3700 Da. Mass measurements on 13 peaks in an unseparated tryptic digest of myoglobin gave results with an overall average error less than 3.5 ppm, with a maximum error of 7 ppm.

Adrenocorticotropic Hormone↗
PubMed1997

Major bile duct injuries during laparoscopic cholecystectomy. Follow-up after combined surgical and radiologic management.

OBJECTIVE: The authors provide the results of follow-up evaluation after combined surgical and radiologic management of 89 patients with major bile duct injuries during laparoscopic cholecystectomy. SUMMARY BACKGROUND DATA: The incidence and mechanism of injury of major bile duct injuries during laparoscopic cholecystectomy has been clearly defined. Furthermore, a number of series have described the management of these injuries by surgical, endoscopic, and radiologic techniques with excellent short-term results. Long-term follow-up data, however, are lacking in the management of these injuries. METHODS: Data were collected prospectively on 89 patients treated at a single institution with major bile duct injuries after laparoscopic cholecystectomy managed between July 1, 1990, and July 1, 1996. Patients referred with injuries underwent early percutaneous transhepatic cholangiography and biliary drainage. Based on the cholangiographic appearance and clinical situation, patients were managed by either percutaneous balloon dilatation or surgical reconstruction with a Roux-en-Y hepaticojejunostomy with transanastomotic stenting. Follow-up was obtained by personal interview during October 1996. RESULTS: Two patients died without an attempt at definitive therapy. Both deaths were caused by sepsis and multisystem organ failure present at the time of transfer to the authors' institution. The remaining 87 patients were managed initially by either balloon dilatation (N = 28) or surgical reconstruction (N = 59). Ten patients have not completed treatment and still have biliary stents in place. Evaluation of 25 patients completing treatment after balloon dilatation (mean follow-up, 27.8 months) showed a success rate of 64%. Evaluation of 52 patients completing treatment after surgical reconstruction (mean follow-up, 33.4 months) showed a success rate of 92%. All failures were managed successfully by either surgical reconstruction or balloon dilatation. CONCLUSIONS: Major bile duct injuries can be managed successfully by combined surgical and radiologic techniques. This series provides, for the first time, significant follow-up on a large number of patients with overall success rates of 64% after balloon dilatation and 92% after surgical reconstruction. The combination of surgery and balloon dilatation resulted in a successful outcome in 100% of patients treated.

Adult↗
PubMed1997

Factors affecting lactate and malate utilization by Selenomonas ruminantium.

Lactate utilization by Selenomonas ruminantium is stimulated in the presence of malate. Because little information is available describing lactate-plus-malate utilization by this organism, the objective of this study was to evaluate factors affecting utilization of these two organic acids by two strains of S. ruminantium. When S. ruminantium HD4 and H18 were grown in batch culture on DL-lactate and DL-malate, both strains coutilized both organic acids for the initial 20 to 24 h of incubation and acetate, propionate, and succinate accumulated. However, when malate and succinate concentrations reached 7 mM, malate utilization ceased, and with strain H18, there was a complete cessation of DL-lactate utilization. Malate utilization by both strains was also inhibited in the presence of glucose. S. ruminantium HD4 was unable to grow on 6 mM DL-lactate at extracellular pH 5.5 in continuous culture (dilution rate, 0.05 h-1) and washed out of the culture vessel. Addition of 8 mM DL-malate to the medium prevented washout on 6 mM DL-lactate at pH 5.5 and resulted in succinate accumulation. Addition of malate also increased bacterial protein, acetate, and propionate concentrations in continuous culture. These results suggest that 8 mM DL-malate enhances the ability of strain HD4 to grow on 6 mM DL-lactate at extracellular pH 5.5.

Animals↗
PubMed1997

Effects of cellobiose and monensin on in vitro fermentation of organic acids by mixed ruminal bacteria.

The objective of this study was to determine the effects of cellobiose and monensin on the in vitro fermentation of organic acids (L-aspartate, fumarate, and DL-malate) by mixed ruminal bacteria. Ruminal fluid was collected from a steer fed 36.7 kg of forage and 4.5 kg of concentrate supplement once per day. Ruminal fluid was centrifuged to sediment feed particles and protozoa, and the resulting supernatant, which contained bacteria, was added (33%, vol/vol) to anaerobic media (500 ml). Incubations (n = 2) were performed in batch culture at 39 degrees C and sampled at 0, 2, 4, 6, 8, 12, and 24 h. Organic acids were added to achieve a final concentration of 7.5 mM. Cellobiose was added to obtain a final concentration of 5 mM, and monensin dissolved in ethanol was included at concentrations of 0 or 5 ppm. Addition of cellobiose to organic acid fermentations increased the rate of organic acid utilization by the mixed bacterial population. Total concentrations of volatile fatty acids were increased by the addition of cellobiose to all fermentations. A lag period (< or = 8 h) occurred in fermentations that were treated with monensin before organic acids were utilized. Total concentrations of volatile fatty acids were increased, and the acetate to propionate ratio was decreased, by monensin treatment. When cellobiose and monensin were added together, propionate production and organic acid utilization were increased. Both cellobiose and monensin affected the in vitro fermentation of organic acids by mixed ruminal bacteria by providing a carbon and energy source and by influencing electron disposal.

Acetates↗
PubMed1997

Malate content of forage varieties commonly fed to cattle.

The objective of this study was to determine the concentration of malate in forage varieties at different stages of maturity. Five alfalfa varieties (Alfagraze, Apollo Supreme Cimarron, Crockett, and Magnum III) and three bermudagrass varieties (Coastal, Tifton-78, and Tifton-85) were collected at different stages of maturity. Samples were collected from replicate plots (n = 3) of each alfalfa variety at 9, 18, 28, 35, and 42 d of maturity; bermudagrass hay samples were composited from six bales of each variety from two cuttings staged to be harvested at 27 and 41 d of maturity. Malate was extracted from the samples and quantitated by high performance liquid chromatography using an organic acid column. As maturity increased, the concentration of malate declined in both plant species. Concentrations of malate were numerically higher in two alfalfa varieties (Crockett and Magnum III) at 35 and 42 d of maturity than in all other alfalfa varieties. Concentrations of malate in bermudagrass at 41 d of maturity were lower than concentrations of malate in all alfalfa varieties at 42 d of maturity. Malate declined as maturity increased in the Coastal and Tifton-78 varieties. Because malate stimulates the utilization of lactate by the predominant ruminal bacterium Selenomonas ruminantium, some of the benefits associated with alfalfa in the diets of dairy cattle may be due to the malate in this forage.

Acidosis↗
PubMed1997

Effects of a Saccharomyces cerevisiae culture on ruminal bacteria that utilize lactate and digest cellulose.

The objective of this study was to determine the effects of a yeast (Saccharomyces cerevisiae) culture on lactate utilization and cellulose digestion by ruminal bacteria. Growth of Selenomonas ruminantium HD4 in medium that contained 5 g/L of DL-lactate, Trypticase, and yeast extract was stimulated 7 and 15% by 1 and 5% (vol/vol) yeast culture filtrate respectively. The 1 and 5% yeast culture filtrate stimulated growth of Selenomonas ruminantium H18 and Megasphaera elsdenii B159 and T81 on 5 g/L of DL-lactate in medium without Trypticase or yeast extract. Growth of Fibrobacter succinogenes S85 and Ruminococcus albus B199 on 6 g/L of cellobiose was stimulated by the addition of yeast culture filtrate to medium without Trypticase or yeast extract. The yeast culture filtrate increased the concentrations of acetate and total volatile fatty acids that were produced by Sel. ruminantium HD4 and increased the concentrations of propionate and total volatile fatty acids that were produced by Sel. ruminantium H18 but did not alter end-product formation of M. elsdenii or cellulolytic bacteria. Treatment with yeast culture increased the initial rate but not the extent of cellulose digestion by F. succinogenes S85 and Ruminococcus flavefaciens FD1. Collectively, these results suggest that yeast culture provides soluble growth factors (i.e., organic acids, B vitamins, and amino acids) that stimulate growth of ruminal bacteria that utilize lactate and digest cellulose.

Acetates↗
PubMed1996

Sequencing oligonucleotides by exonuclease digestion and delayed extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

A protocol was developed for sequencing oligonucleotides by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. Oligonucleotides were partially hydrolyzed in separate time-course digestions with 3' --> 5' and 5' --> 3' acting phosphodiesterases in a MALDI-compatible buffer or in the MALDI matrix itself. The partial digests were analyzed by MALDI-TOF mass spectrometry employing an instrument equipped with delayed ion extraction and the sequence was inferred from the mass differences between adjacent peaks. Resolution, mass accuracy, and sensitivity were considerably enhanced with delayed extraction, in comparison with the standard MALDI technique. Much longer lengths of DNA can be unambiguously sequenced with delayed extraction MALDI compared with standard MALDI-MS.

Base Sequence↗