Biomedical subjects

A Dmitriev

Publications and source records attributed to A Dmitriev.

15 recordsLinked to original sources

PubMed2003

Temperature dependence of the surface anisotropy of Fe ultrathin films on Cu(001).

We report an experimental approach to separate temperature dependent reversible and irreversible contributions to the perpendicular magnetic anisotropy of Fe films grown at low temperatures on Cu(001) substrates. The surface anisotropy K(S)(T) is found to decrease linearly with temperature, causing a thermally induced spin reorientation into the plane. The irreversible shift of the spin reorientation transition and the coercivity of the iron films are directly correlated to the increasing Fe island size during annealing. The increased coercivity is discussed in terms of domain wall energy inhomogeneities provided by the islands.

Journal Article↗

PubMed2003

The presence of insertion elements IS861 and IS1548 in group B streptococci.

The presence of insertion elements (IS) IS861 and IS1548 in the collection of 211 Streptococcus agalactiae strains isolated from pregnant women and dairy cows was assayed. IS861 was found in 67 human strains (59%) and 36 bovine strains (37%), IS1548 in 13 human strains (12%) and 16 bovine strains (16%). Two combinations, IS861+ IS1548- and IS861- IS1548-, were widely distributed in both human and bovine strains. The copy number and the restriction fragment length polymorphism (RFLP) of the two IS were determined in human group B streptococcus (GBS) strains. A minimum of 8 copies of IS1548 were detected in GBS strains while the copy number of IS861 varied from 1 to 9. The number of different hybridizing patterns with IS861 and IS1548 probes was 9 and 6, respectively. These hybridization patterns were divided into several clusters. All strains with IS were also clustered according to pulsed field-gel electrophoresis (PFGE) patterns. A correlation was found between the results of PFGE- and IS-based clustering.

Animals↗

PubMed2002

Chromosomal analysis of group B streptococcal clinical strains; bac gene-positive strains are genetically homogenous.

A collection of 45 epidemiologically unrelated Streptococcus agalactiae strains (group B Streptococcus, GBS), belonging to different serotypes, isolated from pregnant women in China and Russia was studied. Strains were characterized by pulsed-field gel electrophoresis (PFGE) employing hybridization with nine genes potentially involved in virulence. Molecular sizes of GBS genomes varied from 2030 to 2290 kb. Location of the genes under study bac, bca, glnA, scpB, cyl, hylB, lmb, scaA and cfb on the GBS genomes was found to be conserved irrelevant to the serotype. Potential virulence genes scpB, hylB, lmb were located on a 91-kb SmaI fragment that is equal to 4.5% of total genome. Ribotyping of the strains under study revealed three different HindIII, nine EcoRI and 12 PvuII ribotypes among 45 strains. A strong correlation between the PvuII ribotype and the presence of the bac gene was observed, with 21 of 22 bac-positive strains belonging to the same PvuII ribotype P1. PFGE patterns of bac-positive strains were also similar. The possibility of close genetic relatedness of all bac-positive strains is discussed.

Antigens, Bacterial↗

PubMed2002

Genetic heterogeneity of the pathogenic potentials of human and bovine group B streptococci.

One-hundred seventy-two B-streptococcal strains of human and bovine origin were analyzed for the presence of 9 genes potentially involved in virulence. Some of genes (glnA, cyl, hylB, scaA and cfb) were revealed in all the strains. However, the presence of others (bca, bac, scpB, lmb) varied from strain to strain. Taken together, 3 and 5 different types of pathogenic potential were found among human and bovine group B streptococci (GBS) strains, respectively, and only one type (bca+ bac scpB+ glnA+ cyl+ hylB+ lmb+ scaA+ cfb+) was common for both kinds of strains. We propose that different virulence genes can be involved in the development of infectious processes in humans and animals. A reliable PCR protocol with 3 pairs of primers (for the genes bca, bac and scpB) in the same reaction mixture was developed for the fast identification of the pathogenic potential of GBS. In comparison with the classical immunological methods this procedure displayed higher specificity and sensitivity as well as a shorter time of analysis. It can be recommended for use in the clinical and veterinary practice for studying the epidemiological relationship between the isolates and the ready identification of the clone causing the infection.

Animals↗

PubMed2000

Use of the molecular typing methods to evaluate the control of Listeria monocytogenes contamination in a raw milk and dairy products.

Nineteen serogroup 1/2a Listeria monocytogenes strains isolated from raw milk, dairy products and salt water in one dairy were analyzed. Pulsed field gel electrophoresis (PFGE) and ribotyping were used to determine whether these strains isolated over a 8-month period are epidemiologically related. The samples of raw milk were contaminated by different L. monocytogenes clones. The clones isolated from dairy products (with the exception of one sample) and salt water were identical. Comparative genetic analysis of the clones isolated from raw milk, salt water and dairy products revealed the source of contamination and identified the L. monocytogenes strain involved in this process.

Animals↗

PubMed1999

Comparative genetic study of group B streptococcal strains of human and bovine origin.

The presence and restriction fragment length polymorphism (RFLP) of DNA fragments hybridizing with virulence and "house keeping" gene probes were analyzed for 87 group B streptococcal (GBS) strains of human and bovine origin. Most characteristics obtained for bovine strains were similar when compared with those for human strains. The most significant degree of RFLP was discovered for the sizes of HindIII fragments containing bca gene. Human GBS strains with bac gene, encoding beta antigen with IgA binding capacity, were characterized by almost identical complex hybridization patterns with multiple gene probes. At the same time bac gene was not found among bovine GBS strains. Gene scpB that encodes C5a peptidase in all human GBS strains was detected only in 9 of 39 strains of bovine origin. These two characteristics effectively distinguished bovine GBS strains from GBS strains of human origin.

Animals↗

PubMed1999

Resistance of retinal extracellular space to Ca2+ level decrease: implications for the synaptic effects of divalent cations.

Ion-sensitive microelectrodes were used to measure the variations of [Ca2+]o induced by application of low Ca2+ media in the superfused eyecup preparation of the Pseudemys turtle. The aim of the experiments was to evaluate the possibility, suggested by previous studies, that in the deep, sclerad, layers of the retina [Ca2+]o may remain high enough to sustain chemical synaptic transmission even after prolonged application of low-Ca2+ saline. It was found that, at depths of 100-200 micron from the vitreal surface, [Ca2+ ]o did not fall below 1 mM even after application for periods of 30-60 min of nominally Ca2+-free media, and it was >0.3 mM after 30-min application of media containing EGTA and with a Ca2+ concentration of 1 nM. Previous studies in isolated salamander photoreceptors have shown that a reduction of [Ca2+ ]o to 0.3-1.0 mM may result in a paradoxical increase of Ca2+ influx into synaptic terminals due to the reduced screening of negative charge on the external face of the plasma membrane. On the basis of these results, the persistence or enhancement of synaptic transmission from photoreceptors to horizontal cells observed in various retinas treated with low-Ca2+ media may be accounted for within the classical Ca2+-dependent theory of synaptic transmission without invoking a Ca2+-independent mechanism.

Animals↗

PubMed1998

Physical and genetic chromosomal maps of Streptococcus agalactiae, serotypes II and III; rRNA operon organization.

A detailed analysis of two Streptococcus agalactiae (group B streptococcus, GBS) strains was performed by pulsed field gel electrophoresis (PFGE). Digestion of the chromosomal DNA with SmaI and SgrAI endonucleases, followed by separation and analysis of fragments by PFGE was carried out. Physical chromosomal maps of serotype II/(alpha + beta) and III/alpha strains of S. agalactiae were constructed. The GBS genome size was estimated to be 2200 kb. Sixteen GBS genes were used as probes and were located on the restriction maps of both strains by DNA-DNA hybridization. Six copies of ribosomal operons were found in the genome of the analyzed strains. Significant differences in the restriction patterns of chromosomal DNA and DNA-DNA hybridization between the two analyzed strains were detected so that DNA restriction patterns may be used to trace outbreaks of disease. The overall GBS chromosomal organization as determined is fairly conserved.

Base Sequence↗

PubMed1998

Energetic particle fluxes data base of "CORONAS-I" satellite observations.

The data base DB SCR uses data obtained by the SCR instrument package on the CORONAS-I satellite. DB SCR contains information about fluxes of relativistic electrons (0.5-124 MeV), protons (1-300 MeV), nuclei (1-19 MeV/nucl) and gamma-radiation (0.1-7 MeV) in the low altitude region (500 km). The time resolution of the data is 2.5 s. Magnetic field parameters (B, magnetic latitude and longitude), L-shell and local times (LT and MLT) are included in DB SCR. Since all parameters are equivalents it is possible to perform the multidimensional analysis for any set of DB SCR parameters. The additional DB SCR software packages may be used to develop different semi-empirical models.

Databases, Factual↗

PubMed1998

Distribution of energetic particles and secondary radiation according to orbital station "MIR" data obtained in 1991.

A set of instruments for measuring energetic particle fluxes, containing two neutron detectors under different plexiglas shielding thicknesses, a scintillation detector, measuring energy release >0.1 MeV and 0.5 MeV and a Geiger counter were launched onboard OS 'MIR'. The latitude dependencies of the cosmic ray measurements were obtained and studied. The distributions of primary particle fluxes (protons and elections) as well as secondary particle fluxes (bremsstrahlung gamma-rays and neutrons) produced in interactions of radiation belt particles with the station materials were obtained. The electron belt, generated during the storm of March 24 1991, is studied.

Cosmic Radiation↗

PubMed1997

Molecular analysis of clinical group B streptococcal strains by use of alpha and beta gene probes.

Group B streptococci (GBS) are a leading cause of neonatal sepsis and meningitis. Besides the type-specific capsule, which is considered to be a major virulence factor of the species, some proteins are believed also to be virulence determinants and have been found to elicit protective immunity. In the present work, the genes for two surface proteins, the alpha and beta antigens, were detected in hybridization tests with chromosomal DNA of clinical GBS isolates. Using as a probe a PCR-generated 1.5 kb part of the beta gene, hybridization was found for 4/19 type Ia, 8/11 type Ib, 5/6 type II but for 0/8 type III strains. Positive outcome of hybridization coincided with an ability of the strains to bind IgA. A 200 bp alpha gene probe hybridized with all tested strains of serotypes Ia, Ib or II but only with 4/17 type III strains. By Southern blot, it was found that the size of the EcoRI chromosomal gene fragments hybridizing with the alpha gene probe correlated with the genomic presence or absence of the beta gene, possibly reflecting evolutionary relationship between the two genes. This assumption was further supported by pulsed field gel hybridization analysis which, however, showed the chromosomal positions of these two genes not to be adjacent.

Antigens, Surface↗

PubMed1994

Modification by cyclic adenosine monophosphate of basolateral membrane chloride conductance in chick retinal pigment epithelium.

PURPOSE: We investigated the hypothesis that cyclic adenosine monophosphate (cAMP) modifies the basolateral membrane chloride conductance of chick retinal pigment epithelium (RPE). METHODS: Placing freshly dissected chick retina-RPE-choroid tissues in a perfusion chamber that allows separate perfusion of its retinal and choroidal sides, the authors examined the effect of choroidal perfusion of forskolin (50 mM), an adenylate cyclase activator, on extracellular and intracellular RPE potentials, resistances, light-evoked responses, and chloride diffusion potentials. RESULTS: Forskolin hyperpolarized the RPE basolateral membrane, decreased the apical/basal membrane resistance ratio, increased the amplitude of the RPE membrane c-wave hyperpolarizations, decreased the amplitude of the transepithelial c-wave, and suppressed the light peak. In addition, forskolin decreased the basolateral membrane chloride diffusion potential by 31%. The effects of forskolin were diminished by pretreatment of the basolateral membrane with DIDS, a chloride channel blocker, or by pretreatment of the apical membrane with bumetanide, a blocker of NaK2Cl cotransport. Transepithelial potential, resistance, and c-wave amplitude were not changed by 1,9-dideoxyforskolin, which does not elevate cAMP levels. CONCLUSIONS: Elevation of cAMP results in diminished basolateral membrane chloride conductance in chick RPE. This could be due to a direct effect on the chloride channel or due to a decrease in intracellular chloride concentration secondary to inhibition of apical membrane NaK2Cl cotransport.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1994

Light-dependent hydration of the space surrounding photoreceptors in chick retina.

PURPOSE: To characterize the light-evoked increase in the volume (or hydration) of the subretinal space (SRS) of chick retina and to investigate its retinal pigment epithelial (RPE) origin. METHODS: The authors perfused chick retina-RPE-choroid preparations with the extracellular space marker, tetramethylammonium (TMA+), and estimated its concentration ([TMA+]o) using double-barreled, ion-selective electrodes. They recorded dark-light changes in subretinal [TMA+]o and studied the effects of drugs that suppress RPE ion transport and conductances. RESULTS: The authors observed a slow, light-evoked decrease in subretinal [TMA+]o, about 7% in amplitude, that slowly returned to baseline and then increased at light OFF. It was 40% to 65% inhibited by bumetanide and furosemide, known to inhibit RPE apical membrane Na-K-Cl cotransport; 70% to 80% inhibited by DIDS, an inhibitor of RPE basal membrane chloride conductance, and 50% inhibited by 0.5 mM BaCl2, a blocker of the K+ conductance of the RPE apical membrane. Decreases in subretinal [TMA+]o also were produced when the authors lowered [Cl-]o or [K+]o in the SRS by reducing concentrations in the retinal perfusate. The effect on [TMA]o was larger for [Cl-]o than for [K+]o and was inhibited by bumetanide and DIDS. CONCLUSIONS: Changes in subretinal ion concentrations in light and darkness, most likely [K+]o, modify SRS hydration by modulating RPE apical membrane Na-K-Cl cotransport, as well as the conductive effluxes of K+ across the apical membrane and Cl- across the basal membrane. These changes depend principally on the movement of water into or out of the RPE. In turn, subretinal hydration modifies local ion concentrations and the composition of the interphotoreceptor matrix.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMedDate not supplied

[Factors and genetics of pathogenicity of group B Streptococci].

In this review data on the pathogenicity factors of streptococci and their genetic control are presented. Attention is paid mainly to protein antigens alpha and beta, C5a peptidase, CAMP factor, R, Rib and X proteins. The problems of making the genetic and physical charts of the genome of group B streptococci, the genetic regulation of the synthesis of pathogenicity factors and the specific features of the damaging action of the infective agent are discussed.

Animals↗

PubMedDate not supplied

Systemic acquired resistance in sunflower (Helianthus annuus L.).

Systemic acquired resistance (SAR) to infection by Botrytis cinerea in the leaves of sunflower (Helianthus annuus L.) plants was induced following cotyledon inoculation with B. cinerea or treatment with abiotic inducers. Salicylic acid (SA), benzo-(1,2,3)-thiadiazole-7-carbothioic S-methyl ester (BTH), 2,6-dichloroisonicotinic acid (INA) or EDTA protected sunflower plants against Botrytis infection, that was revealed by a reduction in the number and area of the necrotic lesions in upper leaves after challenge inoculation with the pathogen. SA and BTH were more potent inducers than INA, EDTA or pre-inoculation with the fungus. In addition to resistance to B. cinerea, the upper leaves have also developed resistance to maceration by a mixture of cell wall-degrading enzymes. Calcium nitrate inhibited both the protective effect and the resistance of leaf discs to cell-wall degrading enzymes. All the tested chemicals increased the synthesis and excretion of sunflower phytoalexins--coumarins scopoletin and ayapin and induced the PR-proteins chitinase and 1,3-beta-glucanase, being the inducer effect of each activator correlated with the level of protection against B. cinerea (BTH > SA > INA > EDTA). Thus, SAR induction is mediated by general increase of plant defence responses. This is the first report on SAR in sunflower.

Anti-Infective Agents↗