Experimental studies on the pathogenicity of Vibrio mimicus strains isolated in Bangladesh

Vibrio mimicus, a newly described species of the genus Vibrio has been isolated from stools of 14 patients with diarrhoea. Live cells of all the 14 strains tested caused accumulation of fluid in rabbit gut loops and diarrhoea in infant rabbits. Culture filtrates of all the strains caused increased capillary permeability in rabbit skin; however, five of the filtrates resembled cholera toxin in that they gave positive reactions in rabbit loops, chinese hamster ovarian and mouse adrenal cell monolayers and GM1 ELISA tests and were neutralized by cholera antitoxin. None of the strains produced heat-stable toxin or possessed invasive capability as determined by Sereny's test. Thus, V. mimicus strains were divided into a group which produced a toxin immunobiologically similar to cholera toxin and the rest producing a heat-labile toxin unrelated to that of V. cholerae

Resistance to hydride formation in zirconium: An emerging possibility

Fully recrystallized Zircaloy 2 was subjected to hydride formation through gaseous hydrogen charging. Primarily grain boundary hydrides were observed. To describe the relative preference, if any, a hydride preference index (HPI) was proposed: HPIQ = f(h,Q)/f(r-Q), where f(h,Q) and f(r,Q) are the respective fractions of Q-type boundary present among hydrided boundaries and present in the total sample. HPIQ values were estimated from 1200 distinctly hydrided boundaries and showed a clear preference for hydride formation and grain boundary nature. Coincident site lattice boundaries were, in general, resistant to hydride formation. Elastically harder grains or orientations also arrested the formation of hydrides. The study indicates a clear possibility: a previously unknown/uncharted possibility of suitably 'tailored' zirconium microstructures, microstructures with reduced potential for 'hydride embrittlement' and delayed hydrogen cracking. (c) 2006 Acta Materialia Inc

Campylobacter jejuni diarrhea model in infant chickens.

To study the pathogenic mechanisms of Campylobacter jejuni infection, 36- to 72-h-old chickens were fed 10(3) to 10(6) live cells, using strains isolated from 40 patients with watery diarrhea and 6 with bloody mucoid diarrhea from whom no other known enteropathogen was detected. Chickens of Starbro strain were more likely to develop C. jejuni-induced diarrhea than were White Leghorn chickens. Diarrhea was defined on the basis of amounts of gut fluid in 288 chicks fed with live C. jejuni versus 183 saline-fed control as an accumulation greater than or equal to 0.4 ml of fluid in the guts (excluding ceca) of chickens. Twenty-five percent of the chickens developed diarrhea on day 2, 49% on day 4, and 81% on day 5. The intestines, including ceca, were distended with watery fluid. The majority of the strains, irrespective of whether they were isolated from watery or bloody mucoid enteritis patients, caused watery diarrhea in chickens, and a few caused mucoid diarrhea. No correlation was observed between the source of a strain and the outcome in the experimental model. Bloody diarrhea was never observed in chickens. The peak incidence of diarrhea on day 5 coincided with the mean of maximum fluid accumulation. The organisms multiplied by 3 to 4 logs in all parts of the intestine, with a steady increase in number until day 5. Systemic invasion occurred frequently: C. jejuni could be recovered from the spleen in 47% of the chickens on day 5, in 25% from the liver on day 6, and in 11% from heart blood on day 4. Histopathological examination of gut tissue of the chickens having watery diarrhea did not reveal any abnormality except slight submucosal edema. However, in chickens with mucoid diarrhea, the organisms were found to adhere to brush borders and penetrate into the epithelial cells with formation of a breach in continuity of the brush border lining. The electrolyte composition of the intestinal fluid from chickens infected with C. jejuni and from saline-fed controls did not show significant differences, except for depletion of K+ in the test group. The results obtained in this highly reproducible chicken diarrhea model indicate that (i) most chickens develop nonexudative watery diarrhea 2 to 5 days after oral feeding of 10(3) to 10(6) live cells of C. jejuni; (ii) the organism multiples in all parts of a chicken intestine, (iii) systemic invasion is common, and (iv) local invasion is sometimes observed

Immunobiological relationships between Vibrio fluvialis and Vibrio cholerae enterotoxins

A total of 26 strains of Vibrio fluvialis was included in this study, which were isolated from patients with diarrhoea and other sources. The GM1 enzyme linked immunosorbent assays performed with the culture filtrates of V. fluvialis yielded negative results, indicating that their receptor site is different from that of the known labile toxin. The cholera antitoxin failed to neutralize the skin permeability factor activities of all the V. fluvialis culture filtrates and none of the concentrated culture filtrates gave any precipitin band, when tested against the cholera antitoxin in Ouchterlony's gel diffusion test. These observations suggest that the toxin of V. fluvialis differs from the known cholera toxin in receptor site, mode of action and antigenicity

Evolution of microstructure, microtexture and texture in dilute zirconium based structural components of pressurized heavy water reactors

Microstructure and texture of Zr alloys plays a significant role in deciding the material properties and its performance in nuclear reactor. In order to understand the development of microstructure, it is important to know the phase transformations mechanism in these alloys. Dilute Zr-Nb alloys exhibit a range of diffusional, diffusion less and hybrid phase transformations which includes martensitic omega and hydride transformation. With these points in view detail studies on the physical metallurgy aspects of the binary, ternary and quaternary Zirconium base alloys has been carried out in this study. Electron Diffraction and X-ray diffraction techniques have been used to determine the phases, defects and their crystallographic features. Hydriding is most important corrosion problem in the Zirconium cladding alloys. The mechanism of hydride phase transformation and their crystallographic and microstructural aspects has been presented in detail in some Zirconium alloys. Zirconium alloys being crystallographically asymmetric it shows deformation and annealing texture. Result of the studies on bulk and micro texture in some zirconium alloys and some micro-textural aspects on hydride formation is presented in this paper

Microstructural and textural developments during Zircaloy-4 fuel tube fabrication

Developments in crystallographic texture and in microstructure were characterized during the fabrication steps of Zircaloy-4 fuel tube. Textural developments were generalized in terms of (10 (1) over bar0) and (0001) fibers. These two fibers were observed to get enhanced by the processes of deformation and annealing respectively. Microstructural evolution, on the other hand, ranged from bimodal grain size and shape distribution of the hot extruded stage, to visible heterogeneous deformation associated with pilgering and to fully or partially recrystallized structures after annealing. Textural evolution, associated with individual processing steps during both deformation as well as annealing, had a stronger contribution from relatively larger grains. (C) 2008 Published by Elsevier B.V