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Biomedical subjects

A E Ellis

Publications and source records attributed to A E Ellis.

At least 73 records · Page 4Linked to original sources
PubMed1991

An extracellular acetylcholinesterase produced by Aeromonas hydrophila is a major lethal toxin for fish.

A hitherto unrecognised lethal toxin from the extracellular products (ECP) of Aeromonas hydrophila is described. The pure toxin was 300 times more toxic than the crude ECP and is the most toxic substance so far described from this bacterium, with a minimum lethal dose of 0.05 micrograms g-1 fish. The toxin had high acetylcholinesterase activity and occurred in native ECP as a monomeric 15.5 kDa polypeptide. The purified toxin had five isoelectric focusing forms ranging from pl 4.45 to 4.70. The ECP of each of six strains of A. hydrophila isolated from fish possessed acetylcholinesterase activity suggesting that the toxin is common in this species. The toxin was not a cytolysin and produced no gross pathology in injected fish. Its enzymic nature, low lethal dose, lack of tissue pathology and its apparent narcotic effect suggest that this toxin may act upon the central nervous system of the fish.

Acetylcholinesterase↗
PubMed1991

Siderophore production by Aeromonas salmonicida.

Growth under conditions of iron-restriction and the production of siderophores was examined in 21 typical and 14 atypical strains of Aeromonas salmonicida. With the exception of one atypical strain, all strains grew and multiplied in the presence of the high-affinity iron chelators ethylenediamine di(o-hydroxyphenylacetic acid), alpha, alpha'-dipyridyl or transferrin. Chrome azurol S agar was used to screen bacterial strains growing under these conditions for the production of siderophores. Siderophore production was detected only in the typical strains. Siderophores were also detected in the iron-restricted culture supernatants of typical strains. Siderophores were also detected in the iron-restricted culture supernatants of typical strains, where they were associated with an iron-binding activity. The siderophore was extracted from iron-restricted culture supernatant of one strain by adsorption onto an XAD-7 resin; it behaved as a 2,3-diphenol-catechol in several colorimetric assays. The results indicate that although both typical and atypical strains of A. salmonicida grow and multiply under conditions of iron-restriction, they use different iron-uptake mechanisms, siderophore-mediated and siderophore-independent, respectively. In cross-feeding assays, growth of typical strains was stimulated only by homologous iron-restricted supernatant, suggesting strain differences in the siderophore produced. However, one strain produced a culture supernatant with growth-stimulating activity for other typical and also atypical strains.

Aeromonas↗
PubMed1990

Glycerophospholipid:cholesterol acyltransferase complexed with lipopolysaccharide (LPS) is a major lethal exotoxin and cytolysin of Aeromonas salmonicida: LPS stabilizes and enhances toxicity of the enzyme.

An extracellular lethal toxin produced by Aeromonas salmonicida was purified by fast-protein liquid ion-exchange chromatography. The toxin is composed of glycerophospholipid:cholesterol acyltransferase (GCAT) (molecular mass, 25 kilodaltons) aggregated with lipopolysaccharide (LPS), the GCAT/LPS complex having a molecular mass of about 2,000 kilodaltons, estimated by gel filtration chromatography. The toxin is lethal for Atlantic salmon (Salmo salar L.) at a concentration of 0.045 micrograms of protein per g of body weight. The toxin is a hemolysin (T-lysin, active on fish erythrocytes), leukocytolysin, and cytotoxin. Antiserum to the purified toxin neutralized the lethal toxicity of the crude extracellular toxins, indicating this toxin to be the major lethal factor produced by A. salmonicida. In the crude extracellular products, small amounts of free GCAT were also present. This has been purified, and its activities and properties have been compared with those of the GCAT/LPS complex. The presence of LPS did not influence the GCAT activity of the enzyme with egg yolk or phosphatidylcholine (lecithin) as a substrate, but the specific hemolytic activity and lethal toxicity was about eightfold higher in the complexed form. Furthermore, the free GCAT was more susceptible to proteolytic and heat inactivation than was the GCAT/LPS complex. Recombination of LPS (phenol extracted from extracellular products of A. salmonicida) with free GCAT enhanced the hemolytic activity, lethal toxicity, and heat stability of the latter but did not influence its lecithinase activity. In native polyacrylamide gel electrophoresis, the GCAT/LPS complex and the recombined GCAT-LPS both showed a high-molecular-mass band which did not enter the gel, while the free GCAT produced a single band with low molecular mass. In isoelectric focusing gels, the GCAT/LPS and recombined GCAT-LPS produced a nonfocusing smear with pIs from pI 5.0 to 5.8, while the free GCAT produced a single band with pI 4.3. These data show that free GCAT can combine with LPS to produce a high-molecular-mass complex with enhanced toxicity and heat stability compared with those of free GCAT, similar to the preexisting GCAT/LPS complex, and indicate that the LPS moiety of the toxin plays an active role in toxicity.

Acyltransferases↗
PubMed1989

The quantitative relationship of lethality between extracellular protease and extracellular haemolysin of Aeromonas salmonicida in Atlantic salmon (Salmo salar L.).

An additive relationship of lethality between purified protease and haemolysin of the extracellular products (ECP) of Aeromonas salmonicida was demonstrated by i.p. injection in Atlantic salmon (Salmo salar L.). The lethal toxicity of the combinations of protease and haemolysin follow a linear regression line y = -54.54x + 2400. The LD50 of protease and haemolysin when injected separately was 2400 ng/g fish and 44 ng protein/g fish, respectively.

Aeromonas↗
PubMed1989

Ultrastructural study of the response of eosinophil granule cells to Aeromonas salmonicida extracellular products and histamine liberators in rainbow trout Salmo gairdneri Richardson.

Intraperitoneal injections of Aeromonas salmonicida extracellular products (ECP), Compound 48/80 and Concanavalin A were found to degranulate the eosinophil granule cells (EGC) in the lower intestine and rectum of the rainbow trout Salmo gairdneri Richardson. Ultrastructurally, the EGC response resembled the anaphylactic granule extrusion of mammalian mast cells. Varying degrees of granule vacuolation and loss of electron density occurred. Labyrinthine channels were observed at the peak of degranulation. EGC response however, differed from mammalian mast cells in two respects. Firstly, degranulation involved the release of intact electron lucent granules and the subsequent disintegration of the granule matrix extracellularly. Mammalian mast cells on the other hand, release their granules by direct exocytosis. Secondly, the 48/80 and Con A-stimulated EGC degranulation was inhibited by antihistamines, promethazine and cimetidine. In mast cells, antihistamines do not prevent granule release but block histamine receptors in target cells. The degranulation of the ECGs was a non-cytotoxic event and the cells were capable of regeneration. As soon as the cells lost most of their granules, increased cytoplasmic activity was observed. This involved the expansion of the Golgi-endoplasmic reticulum complex.

Aeromonas↗
PubMed1988

The humoral immune response of rainbow trout (Salmo gairdneri) immunised by various regimes and preparations of Aeromonas salmonicida antigens.

Antibody production in rainbow trout to extracellular antigens was investigated. The following antigen preparations and immunisation regimes were used: native extracellular products (ECP) in Freund's complete adjuvant (FCA), intraperitoneally (i.p.) with and without booster; formalinized ECP in FCA, i.p. with and without booster; washed, formalinized A. salmonicida cells in FCA, i.p., with booster; native ECP in saline, i.m., four weekly injections at two different doses, 45 micrograms and 6 micrograms each injection (after the protocol of Shieh, 1985). Using crossed normal rainbow trout serum, i.p., single injection (after the protocol of Sakai, 1985). Using crossed immunoelectrophoresis all antisera contained precipitating antibodies to three to five ECP components except that from fish immunised i.m. with 6 micrograms protein where antibodies were undetectable. In no case were specific antibodies to ECP protease or haemolysin detected. In a rabbit immunised with formalinized ECP in FCA under a similar regime to the rainbow trout, antibodies to at least 15 ECP components, including protease and haemolysin, were detected. The assumption of a specific immune response to the protease, at least in respect of antibody production, in recent reports of protection afforded by vaccines composed of either crude ECP or partially purified protease (Shieh, 1985) or partially purified protease inactivated by normal serum (Sakai, 1985) is not supported by the present findings.

Aeromonas↗
PubMed1988

Differential susceptibility of salmonid fishes to furunculosis correlates with differential serum enhancement of Aeromonas salmonicida extracellular protease activity.

Rainbow trout, Atlantic salmon and brown trout, respectively, exhibit an increasing order of susceptibility to furunculosis. We investigated if this may be due to a differential sensitivity to exotoxins or ability to inhibit the exoprotease which is required by the bacterium to digest protein for growth. Differences were slight in susceptibility to exotoxins and serum inhibition of exoprotease at high exotoxin:serum ratios. However, at low ratios brown trout serum markedly enhanced protease activity, salmon serum had little effect and rainbow trout serum maintained 50% inhibition. This implies that during the early stages of infection the potential for growth of the bacterium would be highest in brown trout and lowest in rainbow trout. Determinations of growth rates in fresh serum support this hypothesis. The enhancement of exoprotease activity by serum of susceptible species may represent an important virulence mechanism.

Aeromonas↗
PubMed1987

Inhibition of the Aeromonas salmonicida extracellular protease by alpha 2-macroglobulin in the serum of rainbow trout.

One of the major pathogenic factors of Aeromonas salmonicida, the bacterium causing furunculosis in fish, is considered to be a protease secreted in the extracellular products. This protease can be inhibited by normal trout and rabbit serum but the factor responsible has not hitherto been identified. The present results demonstrate that the A. salmonicida protease is inhibited by the alpha 2-macroglobulin of rainbow trout serum. This inhibitor accounts for about 9% of the total trypsin inhibiting capacity of trout serum, is alpha-migrating in electrophoresis, is moderately stable on storage at -20 degrees C, is destroyed by heating at 45 degrees C, has no requirement for cations and is inactivated by methylamine. The A. salmonicida protease is resistant to inhibition by 91.9% of the total trout serum trypsin inhibitors, without inactivating them, and to human alpha 1-antiproteinase. It is proposed that trout alpha 2M may have a defensive function against furunculosis but the resistance of the bacterial protease to inhibition by the majority of the serum protease inhibitors may represent pathogenic adaptation.

Aeromonas↗
PubMed1986

Characterization of extracellular metallo- and serine-proteases of Aeromonas hydrophila strain B51.

The extracellular proteases of Aeromonas hydrophila B51 were stable on heating (56 degrees C) and on storage at 4 degrees C or -20 degrees C. Inhibitor studies showed that 72% of the total activity was inhibited by EDTA (a metalloprotease inhibitor) and 26% was inhibited by phenylmethanesulphonyl fluoride (a serine protease inhibitor). Analytical isoelectric focussing revealed the presence of 33 proteins in the crude extracellular products. Using a casein overlay technique three separate zones of proteolytic activity were detected: a zone with pI 6.5-6.8, formed of two closely focussed bands (possibly isomers of the same protease) and completely inhibited by EDTA; a single band with pI 7.0, which was inhibited by EDTA; and a diffuse zone with pI 8.3-8.5, which was only partially inhibited by EDTA. It is concluded that the serine protease activity focussed in this latter zone. These results indicate the presence of at least four, and possibly five proteases. Our results differ substantially from those reported by other workers using different isolates and it is suggested that significant differences in the character of extracellular products and extracellular proteases exist between different isolates of A. hydrophila.

Aeromonas↗
PubMed1986

The function of teleost fish lymphocytes in relation to inflammation.

Teleost fish exhibit inflammatory reactions which closely resemble those of mammals, but little is known about the mechanisms of inflammation in fish. While the leucocytes associated with inflammatory responses of fish bear close morphological similarity to those of mammals, it is not yet clear how comparable they are in function. Recently much work has been done to investigate the presence of lymphocyte subpopulations in fish, and while much of the data suggest the presence of mammalian T- and B-like lymphocytes the situation is still not clear and important differences appear to exist. Less information is available on the function of other inflammatory cell types, the neutrophils and macrophages, but once again differences between these cells in fish and mammals are apparent. The largest group of fish (the teleosts) comprises over 16,000 species which are widely evolved and differences between species should be expected and are indeed evident. Generalization concerning physiological responses of fish should therefore be made with caution.

Animals↗
PubMed1985

Eosinophilic granular cells (EGC) and histamine responses to Aeromonas salmonicida toxins in rainbow trout.

The function of eosinophilic granular cells (EGCs) in salmonids is unknown. In a previous study of the pathogenesis of A. salmonicida, injection of crude exotoxins into rainbow trout were shown to reproduce the lesions associated with furunculosis and an accompanying lesion, the dispersion and degranulation of EGCs in the intestinal wall was reported. The present study investigated this phenomenon in relationship to the histamine content of the gut. In fish injected i/p with A. salmonicida exotoxins in a dose causing death in six hours, a coincidental decrease in the histamine content of the gut, appearance of histamine in the blood, and degranulation of the EGCs in the intestinal wall was observed 45 minutes post-injection. The fish developed behaviour patterns similar to that described by other workers for fish undergoing systemic anaphylaxis. Other features were pale gills, defaecation and widespread vasodilatation. The possible role of the EGC as a histaminogenic cell in rainbow trout is discussed.

Aeromonas↗
PubMed1982

The effect of primary and secondary immunization on the lymphoid tissues of the carp, Cyprinus carpio L.

Mirror carp immunized with human gamma globulin (HGG) in Freund's complete adjuvant (FCA) show a proliferative response involving cells whose cytoplasm stains deep red with methyl green-pyronin (pyroninophilic cells). This response occurs particularly in the haemopoietic parenchyma of the pronephros and mesonephros. It peaks at week 3, with the formation of clusters of pyroninophilic cells in the pronephros. Immunization with Aeromonas salmonicida elicited a less intense pyroninophilic response but caused a larger increase in pigment-containing cells. After a secondary immunization with HGG in FCA, a distinct response was observed in the spleen: Pyroninophilic cells collected within the ellipsoid sheaths in large numbers and formed nodules. The reticulum of such nodules acquired spherical proportions and resembled the white pulp reticulum of the tetrapod spleen. The roles of such pyroninophilic cells and the possibility that aggregations of them may be functionally analogous to homoiotherm germinal centres are discussed.

Aeromonas↗
PubMed1982

Localization of immune complexes and heat-aggregated immunoglobulin in the carp Cyprinus carpio L.

In carp Cyprinus carpio L. preimmunized with a protein antigen, human gamma globulin (HGG), rapid localization of antigen occurred in the splenic ellipsoids within 1 day of a secondary immunization given 8 weeks later. Furthermore, after injection of immune complexes or heat-aggregated HGG, antigen was trapped more quickly in the pronephros than when antigen was injected alone. These results support the conclusion that in fish, as in homoiotherms, this form of antigen trapping is antibody-dependent.

Animals↗
PubMed1975

Surface immunoglobulins on the lymphocytes of the skate Raja naevus.

Living lymphocytes of the Elasmobranch fish, Raja naevus, have been examined for surface immunoglobulin (Ig) by treatment with a fluorescent anti-Ig system. Large numbers of Ig-positive cells (60-80%) were found in peripheral blood, spleen and thymus. Following modulation of the surface Ig with anti-Ig, resynthesis occurred, showing that the surface Ig is a product of the individual lymphocytes rather than material passively absorbed from the serum. Formation of caps was independent of temperature, occurring as readily at 4 degrees C as at 20 degrees C, a finding which presumably reflects the environmental conditions normally experienced by the skate. The presence of Ig-bearing lymphocytes in the adult skate thymus suggests a similarity to the amphibian larval thymus, which may be a primary lymphoid organ for the production of both T and B lymphocyte analogues.

Amphibians↗