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Biomedical subjects

R W Barker

Publications and source records attributed to R W Barker.

14 recordsLinked to original sources
PubMed1992

Isolation of Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) from Ixodes scapularis and Dermacentor albipictus ticks (Acari: Ixodidae) in Oklahoma.

Borrelia burgdorferi was isolated from Ixodes scapularis Say and Dermacentor albipictus Packard that were removed as partially fed adults from white-tailed deer, Odocoileus virginianus Zimmermann, in Oklahoma. Isolation in media was accomplished only after homogenates of pooled field-collected ticks were inoculated into laboratory-reared Peromyscus leucopus and reisolated from the urinary bladder into BSK II media. Both isolates were confirmed by western blot analysis and reactivity with monoclonal antibody H5332. These are the first reported isolates of B. burgdorferi from Oklahoma from these two tick species and are the first isolates from ticks from the south-central United States that were infective for laboratory-reared P. leucopus.

Animals↗
PubMed1992

Attempted transmission of Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) (JDI strain) by Ixodes scapularis (Acari: Ixodidae), Dermacentor variabilis, and Amblyomma americanum.

Laboratory-reared Ixodes scapularis Say, Amblyomma americanum (L.), and Dermacentor variabilis (Say) were fed on New Zealand white rabbits experimentally infected with Borrelia burgdorferi (JDI strain). At repletion, spirochetes could be detected by dark-field microscopy only in I. scapularis. Acquisition rates were 18 and 21%. When previously exposed nymphs of each species were fed on susceptible rabbits, I. scapularis was the only tick of the three species that transmitted B. burgdorferi. When a single rabbit was experimentally infected with B. burgdorferi and infested at 7-d intervals with I. scapularis, A. americanum, D. variabilis, and a second time with I. scapularis, B. burgdorferi was detected again only in cultures from the two groups of I. scapularis. When molted nymphs from each tick species were allowed to feed on susceptible rabbits, spirochetes again were isolated only at necropsy from the rabbits on which the two groups of I. scapularis fed.

Animals↗
PubMed1992

Isolation of Borrelia burgdorferi from Peromyscus leucopus in Oklahoma.

Borrelia burgdorferi was isolated from a field-caught Peromyscus leucopus from central Oklahoma (USA). The strain was identified as B. burgdorferi by reaction with monoclonal antibody H5332 specific for the outer surface protein OspA of B. burgdorferi. This represents the first isolation of B. burgdorferi from a wild mouse outside of the normal range of the known vectors Ixodes dammini and I. pacificus.

Animals↗
PubMed1990

Attempted transmission of Ehrlichia risticii, causative agent of Potomac horse fever, by the ticks, Dermacentor variabilis, Rhipicephalus sanguineus, Ixodes scapularis and Amblyomma americanum.

Dermacentor variabilis, Rhipicephalus sanguineus, Amblyomma americanum, and Ixodes scapularis ticks were investigated for their ability to transmit Potomac horse fever. Larval and nymphal ticks were exposed to Ehrlichia risticii by feeding on mice inoculated with the organism. Molted exposed ticks were then allowed to feed on susceptible ponies or mice. No evidence of transmission, either clinically or by detection of antibodies to E. risticii in mice or ponies, was observed for any tick species examined.

Animals↗
PubMed1990

Fecundity of partially engorged female Dermacentor albipictus (Acari: Ixodidae) removed by cattle grooming.

Eight Hereford heifer calves were infested 28 times over a 64-d period with approximately 49,560 Dermacentor albipictus (Packard) larvae per calf. The fecundity of partially engorged and small, fully engorged female ticks, prematurely removed by grooming behavior of the calves, were compared. A total of 3,532 females of various engorged weights was collected from all calves, resulting in a mean female tick yield of 1.78% based on the number of larvae used for all infestations. The ratio of partially to fully engorged females was 1:16. Female oviposition success was 96%. The mean (+/- SE) values for female weight, number of larvae, and percentage larval eclosion of 50 partially engorged females that ranged in weight from 54 to 397 mg was 174 +/- 99, 1,272 +/- 931 and 85 +/- 14, respectively. The correlation between preoviposition weight and number of larvae from partially engorged females was highly significant (r = 0.95, P less than 0.0001). A prediction model (Y = -354.6 + 9.07X) showed that the preoviposition weight of partially engorged females and larval fecundity from a separate study was highly correlated (r = 0.92, P less than 0.0001). There was no significant difference between mean values of larval numbers and percentage eclosion for partially engorged and small, fully engorged females of similar weight.

Animals↗
PubMed1990

Failure to transmit Ehrlichia canis (Rickettsiales: Ehrlichieae) with Otobius megnini (Acari: Argasidae).

An ear tick, Otobius megnini (Dugès) recovered from a child who had serologic evidence of ehrlichiosis, was examined for Ehrlichia species microscopically and by inoculation into a susceptible dog; no evidence of infection was found in the tick. Experimental transmission of E. canis by laboratory-reared O. megnini was attempted; neither transstadial nor transovarial transmission occurred.

Animals↗
PubMed1990

Experimental transmission of a granulocytic form of the tribe Ehrlichieae by Dermacentor variabilis and Amblyomma americanum to dogs.

Transstadial transmission of granulocytic Ehrlichieae in dogs was attempted using ticks, Amblyomma americanum and Dermacentor variabilis. Ticks were exposed by feeding as nymphs on acutely infected pups; adult ticks then fed to repletion on susceptible adult dogs that were monitored daily for signs of infection. Evidence of transmission was not observed in control dogs or in those exposed to D variabilis. In contrast, dogs exposed to A americanum developed serologic or clinical evidence of infection, but organisms were not seen in blood smears until corticosteroids were administered, causing recrudescence and accompanying parasitemia. At 12 days after subinoculation of blood obtained from donor adult dogs, before corticosteroids were administered, a febrile response, thrombocytopenia, and appearance of morulae in neutrophilic granulocytes were observed in 2 susceptible recipient dogs.

Animals↗
PubMed1979

Pathogenic organisms.

Explore the source record for details and available documents.

Bacterial Physiological Phenomena↗
PubMed1976

Human placental diamine oxidase. Improved purification and characterization of a copper- and manganese-containing amine oxidase with novel substrate specificity.

1. Isoelectric focusing studies of human placental diamine oxidase showed the pI value of the active enzyme to be 6.5. This information was used in modifying the enzyme purification by incorporating column chromatography on DEAE-Sephadex with ionic strength and pH gradient elution and this, together with affinity chromatography on concanavalin A--Sepharose, gave a highly purified preparation, with a specific activity of 7.0 units/mg. 2. The enzyme gave the expected stoicheiometry with p-dimethylaminomethylbenzylamine as substrate (Keq. 2700) and also oxidized [8-arginine]vasopressin, [8-lysine]vasopressin, collagen and tropocollagen. Polyacrylamide gel slices showed identical migration of diamine-oxidizing and [8-lysine]vasopressin-oxidizing activity. 3. The molecular weight, determined by ultracentrifugation, sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, variable polyacrylamide-gel electrophoresis and Sephadex G-200 column chromatography, was estimated to be approx. 70000. 4. E.s.r. spectroscopy showed that copper and manganese were present in the purified enzyme. This result was confirmed by atomic absorption spectroscopy, which indicated a stoicheiometry for copper and manganese of approx. 1.0 and 1.2g-atom respectively/70000mol.wt. unit. 5. The e.s.r. spectral intensity did not decrease nor did the spectral line shape change when excess of p-dimethylaminomethylbenzylamine was added to the enzyme. 6. Addition of K13CN to the enzyme eliminated the copper e.s.r. signal without affecting the manganese signal. 7. The placental enzyme therefore appears to differ from other amine oxidases in terms of its metal cofactor requirement, molecular weight and substrate specificity, and possible roles in vivo for this enzyme are discussed.

Amine Oxidase (Copper-Containing)↗
PubMed1976

Insect growth regulators and in vitro volatile fatty acid production.

Three insect growth regulators were tested for their effects on in vitro volatile fatty acid production. Each material was tested at 100 and 200 ppm of feed in a triplicated trial. At the concentrations used, there was a trend toward lowered acetate:propionate ratios with inconsistent effects on total volatile fatty acid production for all materials. Of the individual acids, only the relative production of valeric was affected significantly.

Alkenes↗
PubMed1975

NMR studies on phospholipid bilayers. Some factors affecting lipid distribution.

1. 1H-NMR and 31P-NMR are used to measure the outside/inside distribution of phospholipids in mixed vesicles. 2. Ferricyanide is a suitable shift reagent for measuring the outside/inside ratio of lecithin using 1H-NMR even when the phospholipid mixture contains negative lipids. 3. 31P-NMR can be used to measure the distribution of all phospholipids present provided the resonances are separated. 4. At 36.4 MHz the inside and outside phosphorus in lecithin vesicles have different chemical shifts. The separation at room temperature is 4-5 Hz and the individual linewidths are about 4Hz. 5. In a mixture of lecithin with phosphatidylethanolamine the latter has preference for the inside layer of the bilayer. The same holds for mixtures of lecithin with phosphatidylserine, phosphatidylinositol and phosphatidic acid. 6. In mixtures of lecithin and phosphatidylserine the preference of the latter for the inside is increased at lower pH under which conditions the negative charge of the phosphatidylserine is decreased. 7. In mixtures of lecithin with sphingomyelin the lecithin has a higher concentration at the inside. 8. The effect of vesicle size on the 31P-NMR linewidth and the temperature dependence of this linewidth is in agreement with the conclusion of Berden et al. (FEBS Lett. (1974), 46, 55-58) that the chemical shift anisotropy, modulated by the isotropic tumbling of the vesicles, makes a contribution to the linewidth. The chemical shift difference between outside and inside phosphorus can be used as a parameter for the measurement of the packing density at the inside and of the size of the vesicles. 9. It is concluded that both charge and the packing properties of the head group are major factors in determining the distribution of phospholipids in mixed vesicles.

Binding Sites↗
PubMed1975

Nuclear magnetic resonance studies of anaesthetic interactions with haemoglobin.

The use of 270 MHz Fourier Transform nuclear magnetic resonance (NMR) spectrometer, combined with signal processing techniques to improve resolution, enabled proton resonances from the individual aromatic residues of haemoglobin to be distinguished. In the presence of clinical concentrations of the general anaesthetic drugs halothane and methoxyflurane, specific changes in the NMR spectrum can be distinguished which probably reflect local changes of conformation. When higher concentrations of anaesthetic are used, extensive changes in the NMR spectrum occur which are consistent with non-specific binding of the anaesthetic to the hydrophobic parts of the haemoglobin molecule.

Chemical Phenomena↗