PubMed Health⌕ Search

Biomedical subjects

R M Stevenson

Publications and source records attributed to R M Stevenson.

At least 19 recordsLinked to original sources
PubMed2006

A semiconductor source of triggered entangled photon pairs.

Entangled photon pairs are an important resource in quantum optics, and are essential for quantum information applications such as quantum key distribution and controlled quantum logic operations. The radiative decay of biexcitons-that is, states consisting of two bound electron-hole pairs-in a quantum dot has been proposed as a source of triggered polarization-entangled photon pairs. To date, however, experiments have indicated that a splitting of the intermediate exciton energy yields only classically correlated emission. Here we demonstrate triggered photon pair emission from single quantum dots suggestive of polarization entanglement. We achieve this by tuning the splitting to zero, through either application of an in-plane magnetic field or careful control of growth conditions. Entangled photon pairs generated 'on demand' have significant fundamental advantages over other schemes, which can suffer from multiple pair emission, or require post-selection techniques or the use of photon-number discriminating detectors. Furthermore, control over the pair generation time is essential for scaling many quantum information schemes beyond a few gates. Our results suggest that a triggered entangled photon pair source could be implemented by a simple semiconductor light-emitting diode.

Journal Article↗
PubMed2005

Evidence for high-efficiency laser-heated hohlraum performance at 527 nm.

A series of experiments conducted on the HELEN laser system [M. J. Norman, Appl. Opt.4120023497], into thermal x-ray generation from hohlraum targets using 527 nm (2omega) wavelength laser light, has shown that it is possible to exceed radiation temperatures previously thought limited by high levels of superthermal or hot electron production or stimulated backscatter. This Letter questions whether the assumptions traditionally applied to hohlraum design with respect to hot plasma filling and the use of 2omega light are too conservative.

Journal Article↗
PubMed2001

Host factors associated with the detection of Aeromonas salmonicida and Yersinia ruckeri in Ontario, Canada government fish hatcheries.

This paper presents an epidemiological investigation of Ontario Ministry of Natural Resources Fish Health Laboratory data from 1981 to 1997, to determine whether fish species and age were associated with lot-level detection of Aeromonas salmonicida and Yersinia ruckeri in hatchery fish. In stepwise logistic regression, the species brook trout and back-cross (lake trout crossed with the hybrid "splake") were more likely to test A. salmonicida-positive compared to all other species reared in the hatcheries. Similarly, the species brook trout was significantly more likely to test Y. ruckeri-positive compared to all other species. For both pathogens, the 1-5-month age group was associated significantly with detection. These findings suggest that purposive sampling of higher-risk fish lots could increase the likelihood of detecting both study pathogens.

Aeromonas↗
PubMed2000

Effects of hen egg yolk immunoglobulin in passive protection of rainbow trout against Yersinia ruckeri.

Anti-Yersinia ruckeri egg yolk immunoglobulin (IgY) was transferred to egg yolk after immunization of White Leghorn hens with formalin-killed whole cells of serovar 1 (RS1154) and serovar 2 (RS1153)Y. ruckeri and its lipopolysaccharide (LPS). The IgY was specific for its homologous LPS in western immunoblot, whereas some protein bands were commonly recognized, even by IgY from eggs of unimmunized hens. Purified LPS from both Y. ruckeri serovar types 1 and 2 had a very poor immunogenicity. The IgY activity was stable when processed into pellet form by a microbial transglutaminase treatment and showed a considerable resistance against acid pepsin for at least 2 h. Feeding specific anti-serovar 1 Y. ruckeri IgY to fish either before or after immersion infection produced marginal reductions in mortalities and in intestine infection. The same IgY did passively protect rainbow trout against infection when administered by intraperitoneal injection 4 h before an immersion challenge.

Animals↗
PubMed1999

Production of the 57 kDa major surface antigen by a non-agglutinating strain of the fish pathogen Renibacterium salmoninarum.

The major surface antigen of Renibacterium salmoninarum, p57, is associated with cell autoagglutination and implicated as a virulence factor in fish infections. An autoagglutinating strain, JD24, caused 92% mortality when 2 x 10(7) cells were injected intraperitoneally into rainbow trout Oncorhynchus mykiss, while a non-agglutinating strain, MT 239, produced only 7% mortality after 100 d. The p57 antigen was present in the supernates of broth cultures of both strains when examined by western immunoblotting, and the gene for p57 was detected in both strains by PCR. Electron microscopy of cryopreserved thin sections showed an amorphous layer associated with the cell surface of JD24 which was not seen with MT 239. While p57 from JD24 could reassociate with cells of both strains, p57 from MT 239 failed to restore haemagglutination activity to either strain. Biotinylation of bacterial surfaces demonstrated the presence of a carbohydrate component of p57 from JD24 which was absent from the p57 produced by MT 239. The higher virulence of JD24 may depend not only on the production of p57, but also its direct association with the bacterial cell surface.

Animals↗
PubMed1998

The natural decomposition of adipocere.

Adipocere is a waxy substance which sometimes forms from the adipose tissue of dead bodies, especially when they are under water. A disinterment in southern Ontario lead to the recovery of extensive adipocere from an interment which occurred in AD 1869. Subsequent laboratory research was designed to explore the conditions under which adipocere will disappear, the goal being to identify strategies for estimating a range of time since death in cases where adipocere is present. Varieties of aerobic or facultatively anaerobic microorganisms from the surface of the adipocere were separated and identified. In culture, the gram positive bacteria were able to degrade the adipocere. We propose that the persistence of adipocere is related to the exclusion of gram positive bacteria from the burial environment. The role of bacteria in adipocere formation and degradation must be understood before we can use the presence of adipocere to extrapolate information about the post-death interval.

Adipose Tissue↗
PubMed1997

Immunization with bacterial antigens: yersiniosis.

Yersinia ruckeri causes salmonid fish diseases called yersiniosis or enteric redmouth disease (ERM). Isolates include several serological varieties and disease outbreaks are frequently associated with stress or poor environmental factors. As a result, it is difficult to define clearly the significant virulence factors and pathogenic mechanisms of the bacterium, which introduces uncertainties about the appropriate formulation of bacterins for immunization. An enteric redmouth bacterin was the first commercially-produced fish vaccine, and the formalin-killed whole-cell product continues to be highly effective whether administered by immersion, spray, injection, or oral routes. Serovar 1, "Hagerman" strains are the basis for most commercial bacterins, and serovar 2 is not included, despite epizootics in chinook salmon and brook trout. Vaccination studies report different degrees of cross-protection between serogroups of Y. ruckeri, but the basis for the cross-protection is not clear. Lipopolysaccharide (LPS) of serovar 1 Y. ruckeri elicits negligible or weak antibody responses in fish and low cell-proliferation memory responses compared with serovar 2 strains. These observations raise fundamental questions about the kinds of immune responses that are involved in the highly effective vaccine-protection provided by commercial vaccines.

Animals↗
PubMed1993

Nutrient Requirements of Renibacterium salmoninarum on Agar and in Broth Media.

In well-aerated broth cultures, good growth of Renibacterium salmoninarum was obtained in a serum-free medium consisting of 1% peptone, 1% yeast extract, and 0.1% l-cysteine (PYC broth). In contrast, serum or charcoal is required for growth on agar medium. Charcoal treatment of broth media, either before bacterial inoculation or during growth, increased the growth of R. salmoninarum, whereas the surfactants Tween 20 and Tween 80 inhibited growth. l-Cysteine was essential for optimal growth. Other organic sulfur compounds, such as d-cysteine, l-methionine, homocysteine, homocysteine thiolactone, and reduced glutathione, supported only lower levels of growth, while cystine and dithiothreitol did not allow growth.

Journal Article↗
PubMed1993

Antibody specificities of polyclonal rabbit and rainbow trout antisera against Vibrio ordalii and serotype 0:2 strains of Vibrio anguillarum.

Polyclonal rabbit antisera raised against Vibrio ordalii and serotype 02 strains of Vibrio anguillarum showed extensive cross-reactivity with lipopolysaccharide from these bacterial pathogens of fish when tested in western immunoblot analysis. Results with absorbed polyclonal antisera indicated that lipopolysaccharide molecules from these strains had both common and strain-specific antigenic determinants, which allowed the antisera to be used to differentiate between V. ordalii and serotype 02 strains of V. anguillarum. Unlike rabbits, the immune response in rainbow trout to serotype 02 common antigenic epitopes was dependent on the source of the immunizing lipopolysaccharide antigens. Serum from fish immunized with V. ordalii antigens reacted more extensively with serotype 02 common antigens. In contrast, fish anti-V. anguillarum 02 serum did not interact with O antigens from the V. ordalii strains. Lipopolysaccharide from V. anguillarum serotype 02 and 02a strains showed identical antibody binding properties when interacted with rabbit or fish antiserum to either V. anguillarum 02 or V. ordalii. Lipopolysaccharide from V. anguillarum 02b strains did not interact with the tested rabbit or fish polyclonal sera. The results from this study suggest that fish and rabbits recognise different antigenic determinants in lipopolysaccharide from V. ordalii and serotype 02 V. anguillarum strains; that V. ordalli and serotype 02 strains of V. anguillarum should be regarded as distinct serotype 02 subgroups based on the strain-specific antigenic determinants; and finally that the serological classification of V. anguillarum serotype 02b strains should be reexamined.

Animals↗
PubMed1990

Characterization of the Renibacterium salmoninarum haemagglutinin.

Water-extracted proteins from nine geographically diverse strains of Renibacterium salmoninarum, all of which agglutinated rabbit erythrocytes and rainbow trout spermatozoa, were compared by SDS-PAGE. Extracts from eight strains, including the type strain, ATCC 33209, were similar, containing a major protein of 57 kDa and a minor protein of 58 kDa. The SDS-PAGE protein profile of the Char strain did not contain the 58 kDa protein. A non-agglutinating strain, MT-239, which was also non-hydrophobic, did not produce any water-extractable protein. Immunoblot reactions with rabbit antiserum prepared against whole cells of the type strain demonstrated that the water-extracted haemagglutinins from the various strains were antigenically related. When purified by polyacrylamide gel zone electrophoresis, the haemagglutinin from R. salmoninarum ATCC 33209 formed a doublet band with molecular masses of 57 and 58 kDa, similar to the previously described F antigen. The water-extracted haemagglutinin agglutinated salmonid spermatozoa, was degraded by protease K and trypsin, and was shown to self-assemble onto the cell surface.

Animals↗
PubMed1990

Restriction endonuclease fingerprinting analysis of Canadian isolates of Aeromonas salmonicida.

Restriction endonuclease fingerprinting (REF) analysis was used to examine total cellular DNA prepared from 56 independent field isolates of the fish pathogen, Aeromonas salmonicida. DNA was digested singly with the restriction enzymes EcoRI and HindIII, and the resulting fragments separated by polyacrylamide gel electrophoresis and visualized by silver staining. The REF patterns of typical isolates of A. salmonicida subsp. salmonicida were distinct from those of A. hydrophila, A. salmonicida subsp. achromogenes, A. salmonicida subsp. masoucida, and atypical isolates of A. salmonicida subsp. salmonicida. Differences between strains of typical A. salmonicida subsp. salmonicida could also be distinguished. Canadian isolates examined could be assigned to 1 of 12 different groups (REF groups), with the majority of the isolates belonging to REF groups 1 and 5. REF group 1 strains were isolated from British Columbia and New Brunswick while REF group 5 isolates were found in Ontario. None of the European strains examined had REF patterns identical to those of Canadian isolates. Based on REF analysis, there was little genetic heterogeneity detected among 23 isolates from two short-term studies of naturally occurring infections. Several different REF groups were seen among A. salmonicida collected over a 10-year period from coho salmon from the Credit River. Consistent with earlier biochemical and hybridization studies, the REF data suggest that A. salmonicida is a clonal pathogen. REF analysis can, however, permit the identification of subgroups, which may be useful in epidemiological studies.

Aeromonas↗
PubMed1988

Tn5-induced protease-deficient strains of Aeromonas hydrophila with reduced virulence for fish.

Protease-deficient strains of Aeromonas hydrophila TF7 were induced by transposon Tn5 mutagenesis, with Escherichia coli 1830(pJB4JI) as the Tn5 donor. The parent strain has the cell surface characteristics associated with virulence for fish, and as it produces a single metalloprotease, mutants could be distinguished by direct plating on brain-heart infusion skim milk agar. Mutants Pd-7 and Pd-10 still produced metalloprotease, but at reduced levels and only after prolonged incubation. The activities of other exoenzymes and hemolysin were unaffected, and the mutants autoagglutinated in broth, indicating that the cell surface characteristics of A. hydrophila TF7 had been retained. Unlike the parent strain, the mutants did not produce lesions or mortalities in rainbow trout (Salmo gairneri) when 5 X 10(6) CFU were injected intramuscularly. The bacterial cells were completely cleared from the site of the injection and the organs within 7 days. For 60-g rainbow trout held at 10 degrees C, the 50% lethal dose of Pd-10 was greater than 10(7) CFU, compared with 8.1 X 10(5) CFU for the parent strain. The mutants were significantly more susceptible than the parent strain to the bactericidal effect of fresh normal trout serum in vitro. Mutants Pd-7 and Pd-10 grew as well as the parent on M9 salts-glucose medium but more slowly on heat-inactivated fish serum. Thus, protease appears to be able to contribute to the establishment of A. hydrophila infection in fish both by overcoming initial host defenses and by providing nutrients for cell proliferation.

Aeromonas↗
PubMed1986

Experimental induction of the carrier state in yearling brook trout: a model challenge protocol for IPNV immunization.

Brook trout fry (Salvelinus fontinalis) were not protected from infectious pancreatic necrosis virus (IPNV) challenge by immersion vaccination with inactivated, purified virus at concentrations of 10(7) to 10(9) pfu/ml. Mortalities in vaccinated groups were higher than for the unvaccinated control group and appeared to be dose-dependent. A challenge protocol for adult brook trout was developed for future vaccine trials. A single intraperitoneal injection of virulent, purified virus was sufficient to make long-lasting carriers of 16 month-old trout. Fish underwent a transient viremia, identified by virus isolation from plasma and leucocytes. Feces were the most reliable samples for identification of IPNV carriers by non-sacrificial testing. Many fish in the remaining infected group were still carriers 12 and 27 weeks post-infection.

Animals↗
PubMed1985

Antimicrobial susceptibility patterns and R plasmid-mediated resistance of the fish pathogen Yersinia ruckeri.

Fifty strains of Yersinia ruckeri, the causative agent of enteric redmouth disease of salmonid fish, were tested for susceptibility to 23 antimicrobial agents by using an agar dilution procedure. The MICs were generally uniform for all serological varieties. Two of the 50 strains carried a 36-megadalton plasmid which determined resistance to tetracyclines and sulfonamides and was transferable to both Escherichia coli and Y. ruckeri recipients. The serovars did differ in their response to polymyxin B. Strains of serovars II, III, and V were highly resistant (MICs of 128 to 512 micrograms/ml), whereas most serovar I strains were susceptible to less than or equal to 2.0 micrograms/ml. Of 33 serovar I strains, 6 were highly resistant to polymyxin B, which is a characteristic that may divide serovar I (Hagerman) strains into two distinct subgroups.

Animals↗
PubMed1985

Charcoal agar, a new growth medium for the fish disease bacterium Renibacterium salmoninarum.

Charcoal is an effective replacement for serum in media for the isolation and culture of Renibacterium salmoninarum, the causative agent of bacterial kidney disease in salmonid fish. The medium, KDM-C, contains 10 g of peptone, 0.5 g of yeast extract, 1 g of L-cysteine hydrochloride, 1 g of activated charcoal, and 15 g of agar per liter and is adjusted to pH 6.8 with NaOH before autoclaving. Eight strains of R. salmoninarum grew from dilute inocula as well on KDM-C as on a standard serum-containing medium (KDM-2). The medium was effective for both primary isolations from fish and repeated transfers and has potential value for antigen preparation and physiological studies.

Agar↗
PubMed1984

Isolation of Yersinia ruckeri Bacteriophages.

Eight bacteriophages effective against Yersinia ruckeri, the enteric redmouth disease bacterium, were isolated. Phage YerA41, a tailed icosahedral virus isolated from sewage enrichments, lysed 34 of 35 strains of Y. ruckeri serovar I, but was inactive against 15 strains belonging to three other serological groups. Six other phages lysed strains of serovars II, V, and I', a subgroup of serovar I. YerL62, a phage obtained by mitomycin C induction, was specific for one of three serovar V strains. These bacteriophages, particularly YerA41, have potential value for fish disease diagnostic work.

Journal Article↗