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Biomedical subjects

S A Walker

Publications and source records attributed to S A Walker.

At least 55 records · Page 3Linked to original sources
PubMed1995

Cooperative organization of inorganic-surfactant and biomimetic assemblies.

A model that makes use of the cooperative organization of inorganic and organic molecular species into three dimensionally structured arrays is generalized for the synthesis of nanocomposite materials. In this model, the properties and structure of a system are determined by dynamic interplay among ion-pair inorganic and organic species, so that different phases can be readily obtained through small variations of controllable synthesis parameters, including mixture composition and temperature. Nucleation, growth, and phase transitions may be directed by the charge density, coordination, and steric requirements of the inorganic and organic species at the interface and not necessarily by a preformed structure. A specific example is presented in which organic molecules in the presence of multiply charged silicate oligomers self-assemble into silicatropic liquid crystals. The organization of these silicate-surfactant mesophases is investigated with and without interfacial silicate condensation to separate the effects of self-assembly from the kinetics of silicate polymerization.

Benzene Derivatives↗
PubMed1995

Cloning and sequencing of LlaDCHI [corrected] restriction/modification genes from Lactococcus lactis and relatedness of this system to the Streptococcus pneumoniae DpnII system.

The natural 7.8-kb plasmid pSRQ700 was isolated from Lactococcus lactis subsp. cremoris DCH-4. It encodes a restriction/modification system named LlaDCHI [corrected]. When introduced into a phage-sensitive L. lactis strain, pSRQ700 confers strong phage resistance against the three most common lactococcal phage species, namely, 936, c2, and P335. The LlaDCHI [corrected] endonuclease was purified and found to cleave the palindromic sequence 5'-GATC-3'. It is an isoschizomer of Streptococcus pneumoniae DpnII. The plasmid pSRQ700 was mapped, and the genetic organization of LlaDCHI [corrected] was localized. Cloning and sequencing of the entire LlaDCHI [corrected] system allowed the identification of three open reading frames. The three genes (llaIIA, llaIIB, and llaIIC) overlapped and are under one putative promoter. A putative terminator was found at the end of llaIIC. The genes llaIIA and llaIIB coded for m6A methyltransferases, and llaIIC coded for an endonuclease. The LlaDCHI [corrected] system shares strong genetic similarities with the DpnII system. The deduced amino acid sequence of M.LlaIIA was 75% identical with that of M.DpnII, whereas M.LlaIIB was 88% identical with M.DpnA. However, R.LlalII shared only 31% identity with R.DpnII.

Amino Acid Sequence↗
PubMed1995

Expression of a Lactococcus lactis Phage Resistance Mechanism by Streptococcus thermophilus.

The 7.8-kb lactococcal plasmid pSRQ700 encodes the LlaII restriction/modification system which recognizes and cleaves the sequence 3(prm1)-GATC-5(prm1). When the plasmid pSRQ700 is introduced into a phage-sensitive Lactococcus lactis strain, strong phage resistance is conferred by the LlaII system. In this report, we show that pSRQ700 cannot replicate in Streptococcus thermophilus. However, if cloned into the vector pNZ123, the native LlaII system is expressed and strong phage resistance is conferred to various industrial S. thermophilus strains. Resistance against phages isolated from yogurt and mozzarella wheys was observed. To our knowledge, this is the first report of increased phage resistance in S. thermophilus.

Journal Article↗
PubMed1994

Ultrastructural studies of diffuse axonal injury in humans.

Diffuse axonal injury (DAI) is observed commonly in traumatically brain injured humans. However, traditional histologic methods have proven of limited use in identifying reactive axonal change early (< 12 h) in the posttraumatic course. Recently, we have reported, in both humans and animals, that antibodies targeting neurofilament subunits are useful in the light microscopic recognition of early reactive change. In the present study, we extend our previous efforts in humans by analyzing the progression of traumatic brain injury (TBI)-induced axonal change at the ultrastructural level. This effort was initiated to follow the subcellular progression of reactive axonal change in humans and to determine whether this progression parallels that described in animals. Two commercially prepared antibodies were used to recognize reactive axonal change in patients surviving from 6 to 88 h. The NR4 antibody was used to target the light neurofilament subunit (NF-L), and the SMI32 antibody was used to target the heavy neurofilament subunit (NF-H). Plastic-embedded tissue sections were screened for evidence of reactive axonal change, and once identified, this reactive change was analyzed at the ultrastructural level. At 6 h survival, focally enlarged, immunoreactive axons with axolemmal infolding or disordered neurofilaments were seen within fields of axons exhibiting no apparent abnormality. By 12 h, some axons exhibited continued neurofilamentous misalignment, pronounced immunoreactivity, vacuolization, and, occasionally, disconnection. At later stages, specifically 30 and 60 h survival, further accumulation of neurofilaments and organelles had led to the further expansion of the axis cylinder, and clearly disconnected reactive swellings were recognized. These contained a dense core of disordered immunoreactive neurofilaments partially encompassed by a cap of less densely aggregated organelles. At 88 h, the reactive axons were larger and elongated, consistent with the continued delivery of organelles by axoplasmic transport. At the later time points, considerable heterogeneity was observed, with focally enlarged disconnected axons being observed in relation to axons showing less advanced reactive change. Our findings suggest that neurofilamentous disruption is a pivotal event in axonal injury.

Adult↗
PubMed1992

Cloning, expression, and nucleotide sequence of genes involved in production of pediocin PA-1, and bacteriocin from Pediococcus acidilactici PAC1.0.

The production of pediocin PA-1, a small heat-stable bacteriocin, is associated with the presence of the 9.4-kbp plasmid pSRQ11 in Pediococcus acidilactici PAC1.0. It was shown by subcloning of pSRQ11 in Escherichia coli cloning vectors that pediocin PA-1 is produced and, most probably, secreted by E. coli cells. Deletion analysis showed that a 5.6-kbp SalI-EcoRI fragment derived from pSRQ11 is required for pediocin PA-1 production. Nucleotide sequence analysis of this 5.6-kbp fragment indicated the presence of four clustered open reading frames (pedA, pedB, pedC, and pedD). The pedA gene encodes a 62-amino-acid precursor of pediocin PA-1, as the predicted amino acid residues 19 to 62 correspond entirely to the amino acid sequence of the purified pediocin PA-1. Introduction of a mutation in pedA resulted in a complete loss of pediocin production. The pedB and pedC genes, encoding proteins of 112 and 174 amino acid residues, respectively, are located directly downstream of the pediocin structural gene. Functions could not be assigned to their gene products; mutation analysis showed that the PedB protein is not involved in pediocin PA-1 production. The mutation analysis further revealed that the fourth gene, pedD, specifying a relatively large protein of 724 amino acids, is required for pediocin PA-1 production in E. coli. The predicted pedD protein shows strong similarities to several ATP-dependent transport proteins, including the E. coli hemolysin secretion protein HlyB and the ComA protein, which is required for competence induction for genetic transformation in Streptococcus pneumoniae.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Taurine uptake in chicken leukocytes and erythrocytes.

1. The intracellular taurine concentration and rate of taurine uptake of chicken erythrocytes and two leukocyte populations were determined from one to six weeks of age. 2. Plasma taurine concentrations increased significantly from the time of hatching to week 2 and remained constant thereafter. 3. Intracellular taurine concentrations in both leukocyte populations increased significantly with age without any significant change in the erythrocytes. 4. Taurine uptake rate for erythrocytes was significantly higher at weeks 1-3 while both leukocyte populations showed no significant change during the six week period studied.

Animals↗
PubMed1986

Total and allergen-specific IgE in relation to allergic response pattern following bone marrow transplantation.

Total and allergen-specific serum IgE were measured in relation to allergic response pattern before and after bone marrow transplant (BMT) in seven sibling donor/recipient pairs. Two non-atopic recipients developed persistently raised total serum IgE levels but no apparent allergic response after BMT from non-atopic donors; three non-atopic recipients showed raised total serum IgE after BMT, with allergen-specific IgE to the same allergens as their respective atopic donors. A penicillin-tolerant recipient showed clinical sensitivity and specific IgE to penicillin after BMT from a penicillin-sensitive donor, but with this case both donor and recipient showed raised serum IgE levels. One atopic recipient showed decreased total IgE after BMT from a mildly atopic donor. These allergic response patterns could occur as a result of repopulation in the recipient with IgE-specific T lymphocytes having similar regulatory influences as in the donor. The pattern of acquired responses would also be consistent with reconstitution by primed B lymphocytes of donor origin.

Adolescent↗
PubMed1985

The action spectrum for benzanthrone photosensitization of mouse macrophages.

An in vitro method for determination of the phototoxic action spectrum of benzanthrone was established using a cover slip-test tube culture system with mouse peritoneal macrophages. The action spectrum peaked between 380 and 400 nm with abrupt fall-off to either side. These findings correlate closely with both the absorption spectrum of benzanthrone and the clinical action spectrum of phototoxicity in humans.

Animals↗
PubMed1984

Increased serum IgE concentrations during infection and graft versus host disease after bone marrow transplantation.

Serum IgE concentrations estimated in 25 bone marrow transplant recipients during episodes of infection or graft versus host disease, or both, were raised not only in some patients with acute graft versus host disease but also in many patients with infection. Raised values were not seen in chronic graft versus host disease. The routine estimation of serum IgE in bone marrow transplant recipients had minimal value because of the lack of specificity of the IgE response.

Acute Disease↗
PubMed1984

Value of serum C-reactive protein measurement in the management of bone marrow transplant recipients. Part I: Early transplant period.

Serum C-reactive protein concentrations were measured serially during the early transplant period in 68 bone marrow recipients transplanted for leukaemia (34), chronic granulocytic leukaemia (2), severe aplastic anaemia (6), and various inborn errors of metabolism (26). There were 116 clearly documented episodes of infection or acute graft versus host disease or both. Serum C-reactive protein concentrations in patients with viral (11) or fungal infection (6) were normal or only slightly raised. In 32 patients with isolated acute graft versus host disease, only three (10%) showed serum C-reactive protein concentrations above 40 mg/l. Values greater than 40 mg/l were strongly suggestive of bacterial infections and values above 100 mg/l were seen only in patients (43) with bacterial infections with or without acute graft versus host disease. These findings suggest that serum C-reactive protein concentrations are valuable both for diagnosis and monitoring of such infections.

Acute Disease↗
PubMed1984

Value of serum C-reactive protein measurement in the management of bone marrow transplant recipients. Part II: Late post-transplant period.

Seventeen bone marrow recipients transplanted for acute leukaemia (8), chronic leukaemia (1), severe aplastic anaemia (3), and various inborn errors of metabolism (5) had 22 episodes of documented infection in the late (greater than 3 months) post-transplant period. Serum C-reactive protein concentrations were considerably increased in patients with bacterial infections, but not in those with viral or fungal infections. Serum C-reactive protein values were normal in 20 patients transplanted for acute leukaemia (12), chronic leukaemia (1), severe aplastic anaemia (2), and various inborn errors of metabolism (5) who had active chronic graft versus host disease but no evidence of infection. These findings indicate that serum C-reactive protein concentrations are useful in the diagnosis and monitoring of bacterial infections even in the presence of chronic graft versus host disease.

Bacterial Infections↗
PubMed1984

The communication status of older people: differentiation and rehabilitation.

The communication integrity of the older individual is subject to many influences. Understanding and management of the elderly communication-handicapped can prove difficult because of the problems of differential diagnosis. The role of the speech therapist is acknowledged in acute geriatric rehabilitation but is not immediately associated with psychogeriatric care. The laws of language deterioration appear to apply irrespective of aetiology. Standard linguistic rehabilitation techniques may be equally applicable in both geriatric and psychogeriatric care.

Aged↗
PubMed1982

Electron microscopic observations comparing the gastric mucosal damage induced in rats and pigs by benoxaprofen and aspirin, reflecting their differing actions as prostaglandin-synthesis-inhibitors.

The ultrastructural changes in the gastric mucosa induced by oral administration of aspirin (2 x 125 mg/kg/day) were compared with the effects of benoxaprofen (20 mg/kg/day) in pigs and normal and arthritic rats after 10 or 14 days' treatment respectively. The object was to compare the effects of drugs having different effects on prostaglandin-synthesizing systems on the development of gastric mucosal damage. Benoxaprofen caused less gastric damage than aspirin. There were fewer lesions in benoxaprofen-treated animals and those which were seen were much less extensive. There were qualitative similarities between the effects of the drug treatments. There were also differences in the mucosal changes produced by both drugs in pigs and rats. This included (1) extravasation of erythrocytes which was seen in rats but not pigs, and (2) interstitial changes also seen in rats but not pigs. These interspecies variations may be due to differences in the resistance of the capillaries to drug effects. There were no differences in the mucosal-cell damage seen in normal compared with arthritic rats.

Animals↗