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PubMed1982

Cell surface of the fish pathogenic bacterium Aeromonas salmonicida. II. Purification and characterization of a major cell envelope protein related to autoagglutination, adhesion and virulence.

The purification of the major protein of the membrane fraction of an autoagglutinating strain of Aeromonas salmonicida is described. This protein, designated as additional cell envelope protein, is water-insoluble, has a molecular weight of about 54 000 and its amino terminal sequence is H2N-Asp-Val-Leu-Leu. Neither sulphur-containing amino acids nor sugar residues were detected. Its amino acid composition, which shows that the additional cell envelope protein is hydrophobic in nature, is remarkably similar to those of various proteins known to be present in additional surface layers of other bacteria, to the adhesive K88 fimbriae of enteropathogenic Escherichia coli and to a pore protein of the outer membrane of E. coli K12.

Aeromonas↗
PubMed1985

Biochemical and immunological characterization of the cell surface of the fish pathogenic bacterium Aeromonas salmonicida.

The identification of lipopolysaccharide as periodic acid-Schiff positive material, present in the membrane fraction of the fish pathogenic Gram-negative bacterium Aeromonas salmonicida, analyzed by SDS-polyacrylamide gel electrophoresis, is shown. Such analysis has revealed several periodic acid-Schiff positive bands and many membrane proteins among which a pathogenicity-related Mr 54000 protein as a constituent of an additional surface layer outside the outer membrane (Evenberg et al., (1982) Biochim. Biophys. Acta 684, 241-248). The latter protein, designated as additional cell envelope protein or ACE protein, has been purified and characterized in our laboratory (Evenberg and Lugtenberg, (1982) Biochim. Biophys. Acta 684, 249-254). Most strains produce both high and low molecular weight lipopolysaccharide species, presumably corresponding with the presence and (virtual) absence, respectively, of an O-antigenic chain. The property to produce high molecular weight lipopolysaccharide can be lost upon subculturing in laboratory growth media and such is greatly enhanced by the prior loss of the ability to produce ACE protein. Lipopolysaccharide and ACE protein were identified as the major antigens. A new polysaccharide-like antigen, designated as PS-antigen, was detected. Moreover, immunological indications for the presence of a lipoprotein in A. salmonicida are described. The surface localization of the antigens was determined by testing whether preadsorption of antisera by intact cells decreased the binding of IgG to these antigens, or decreased the ability of the sera to agglutinate cells. According to these criteria lipopolysaccharide, ACE protein and PS-antigen are the major surface-located antigens. Material cross-reactive with lipopolysaccharide, ACE protein and PS-antigen has been found in a large number of strains. Several lines of evidence indicate the presence of interactions between ACE protein and lipopolysaccharide. Based on these results a molecular model of the cell envelope of virulent A. salmonicida is presented.

Aeromonas↗
PubMed1983

One hundred fold increased activity of Aeromonas aminopeptidase by sequential substitutions with Ni(II) or Cu(II) followed by zinc.

Full substitution of Cu(II) or Ni(II) for the two g-atom zinc in Aeromonas aminopeptidase hyperactivates the enzyme 6.5 and 25 fold respectively. Even greater enhancements of activity can be achieved with mixed metal substitutions. Thus, apoenzyme reactivated by first adding one g-atom zinc followed by one g-atom of either Cu(II) or Ni(II) is 15 and 22 times more active than the native enzyme. Reversing the order, i.e. by first adding either one g-atom Cu(II) or Ni(II) followed by one g-atom zinc, activates the enzyme nearly 100 fold. The order of metal addition is critical and suggests the existence of two non-identical metal sites, each with a different function.

Aeromonas↗
PubMed1993

Physical and chemical characterization of the oligomerization state of the Aeromonas hydrophila lipase/acyltransferase.

Aeromonas glycerophospholipid:cholesterol acyl transferase undergoes a conformational transition upon activation by treatment with trypsin. Chemical cross-linking and sedimentation velocity analysis showed that the lipase dimerizes due to removal of a region near its C-terminus. The lipase monomer has a sedimentation coefficient s20.w = 2.83 S, whereas the dimer has s20.w = 3.65 +/- 0.22 S. Hydrodynamic analysis using these sedimentation values and the masses determined by mass spectrometry indicated that the monomers are aligned side-by-side in the dimer. An important change occurs in the apparent partial specific volume of the molecule upon activation.

Acyltransferases↗
PubMed1996

Characterisation of the heptameric pore-forming complex of the Aeromonas toxin aerolysin using MALDI-TOF mass spectrometry.

Aerolysin, a virulence factor secreted by Aeromonas hydrophila, is representative of a group of beta-sheet toxins that must form stable homooligomers in order to be able to insert into biological membranes and generate channels. Electron microscopy and image analysis of two-dimensional membrane crystals had previously revealed a structure with 7-fold symmetry suggesting that aerolysin forms heptameric oligomers [Wilmsen et al. (1992) EMBO J. 11, 2457-2463]. However, this unusual molecularity of the channel remained to be confirmed by an independent method since low-resolution electron crystallography had led to artefactual data for other pore-forming toxins. In this study, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used to measure the mass of the aerolysin oligomer preparation. A mass of 333 850 Da was measured, fitting very well with a heptameric complex (expected mass: 332 300 Da). These results confirm the earlier evidence that the aerolysin oligomer is a heptamer and also show that MALDI-TOF mass spectrometry could be a valuable tool to study non-covalent association of proteins.

Aeromonas hydrophila↗
PubMed1990

Crystallization of a proform of aerolysin, a hole-forming toxin from Aeromonas hydrophila.

Crystals of proaerolysin, the precursor of the hole-forming toxin from Aeromonas hydrophila, have been obtained. The mature form of this protein binds to a receptor on mammalian cells, aggregates and forms 30 A holes in the membrane. The crystals are tetragonal, space group P4(3)2(1)2, a = b = 104.00 A, c = 222.0 A. They contain a dimer in the asymmetric unit and diffract to a resolution of 2.6 A.

Aeromonas↗
PubMed1992

Roles of structural domains in the morphology and surface anchoring of the tetragonal paracrystalline array of Aeromonas hydrophila. Biochemical characterization of the major structural domain.

The tetragonally arranged S-layer of Aeromonas hydrophila contains two morphological domains. The mature S-layer protein of A. hydrophila has a subunit molecular weight of 52,000, and has been reported to contain two structural domains. Here a mutant has been isolated which produces an S-layer of subunit molecular weight 38,650 as determined by sedimentation analysis. This truncated S-protein was exported via the periplasm to the cell surface, but could not self-assemble into a tetragonal array or be anchored to the cell surface. Instead the truncated protein formed cup-like structures which were purified and characterized biochemically. Automated Edman degradation showed that the truncated protein comprised the amino-terminal structural domain of the S-protein. This domain had an increased hydrophobic amino acid content relative to the wild-type protein, and contained approximately 42% beta-sheet, 10% alpha-helix, and 19% beta-turn. Differences in alpha-helix and beta-turn contents between the wild-type and truncated proteins were observed when the effects of pH and SDS were examined, indicating that the carboxy terminus influences the effects of environmental change on the conformation of the S-protein. This lesser carboxy-terminal array also appears to be required for both correct array morphology, and array anchoring, while the greater amino-terminal domain appears to comprise the major morphological core of the surface array.

Aeromonas hydrophila↗
PubMed1982

Two membrane damaging toxins from Aeromonas hydrophila.

The effects of two hemolysins (alpha and beta) from Aeromonas hydrophila on human lung fibroblasts were investigated. The toxins differed with respect to relative size of lesions induced in the plasma membrane, morphological effects, reversibility of effects and adsorption to fibroblasts. The effect of alpha-hemolysin appears to be restricted to the plasma membrane level, whereas the beta-hemolysin is strongly cytotoxic and probably acts on some intracellular target in addition to the primary target, the plasma membrane.

Aeromonas↗
PubMed1989

Purification and characterization of Aeromonas hydrophila beta-hemolysin.

Aeromonas hydrophila hemolysin was excreted in our culture conditions during the stationary growth phase. The toxin was purified to homogeneity by a three-step method: ultrafiltration, acid precipitation in the presence of RNA and anion exchange chromatography with FPLC apparatus. Beta-hemolysin is a protein not associated with lipids, carbohydrates or nucleic acids whose subunit mol. wt is 51,000. The mol. wt determined by polyacrylamide gel electrophoresis suggests that the molecule is in a trimeric form. The toxin is thermolabile and inactivated by proteolytic enzymes such as trypsin, chymotrypsin, pronase, subtilisin and proteinase K. Antibodies raised against the beta-hemolysin neutralize both hemolytic and cytotoxic activities. When injected at high dose, this purified hemolytic protein causes a positive rabbit ileal loop test, thus indicating that beta-hemolysin could be the main virulence factor involved in intestinal symptoms.

Aeromonas↗
PubMed1985

Immunity to Aeromonas salmonicida in coho salmon (Oncorhynchus kisutch) induced by modified Freund's complete adjuvant: its non-specific nature and the probable role of macrophages in the phenomenon.

Juvenile coho salmon (Oncorhynchus kisutch), vaccinated with one intraperitoneal injection of formalin-killed virulent Aeromonas salmonicida cells suspended in saline, showed increased protection against approximately one LD60 of homologous challenge administered at 30 days post-vaccination. Under similar conditions, coho vaccinated with a modified complete Freund's adjuvant (MFCA) alone were also equally protected. When measured against a more severe A. salmonicida challenge of approximately one LD95, the strength of the MFCA-induced protection was found to exceed that produced by the homologous bacterin administered in saline or incomplete adjuvant, and the protection was still evident at 90 days post-treatment. Other more precise measurements indicated the LD50 for MFCA-treated coho to be up to 450 times that for saline-treated coho. Two other tested adjuvants, levamisole and MDP (N-acetyl-muramyl-L-alanyl-D-isoglutamine), administered in a modified Freund's incomplete adjuvant, also enhanced anti-A. salmonicida immunity but to a lesser degree. The active factor in MFCA was a killed Mycobacterium butyricum preparation, and the anti-A. salmonicida immunity it induced was non-specific because the immunity extended to two other serologically distinct fish pathogens tested: A. hydrophila (LD50 increase of 5.3-fold) and Vibrio ordalii (LD50 increase of 560-fold). Macrophages are believed to account for the M. butyricum-induced anti-A. salmonicida immunity because the immunity was a) non-specific, b) very rapid in onset (it was measurable by 4 days), and c) influenced by particulate preparations, known to affect macrophage function and immunity in mammals. The possible benefits of adjuvant-induced non-specific immunity in cultured fish are discussed.

Aeromonas↗
PubMed1985

Humoral response and memory formation in carp after injection of Aeromonas hydrophila bacterin.

The humoral immune response of carp (Cyprinus carpio) upon a bacterial fish pathogen Aeromonas hydrophila was studied in relation to memory formation. After a single intramuscular (i.m.) injection of formalin killed A. hydrophila cells (F-Ah), maximum serum Ab (Ab) titers were observed at day 20. Distinct titers were still seen at day 360 in the groups injected with a medium or high antigen (Ag) dose (10(7) respectively 10(9) F-Ah). The effect of a second immunization with a high Ag dose was studied in fish primed 1, 3, 8 or 12 months earlier with 10(5), 10(7) or 10(9) F-Ah. The height of the secondary Ab response was positively correlated with the height of the priming Ag dose. Challenge with a low Ag dose (10(6) F-Ah) gave the best results with 10(7) F-Ah primed animals. The highest secondary responses were obtained with combinations of corresponding priming and challenge dosages. It is concluded that fish are able to form immunological memory to this bacterial Ag. However, optimal memory levels are reached after a relative long period (3-8 months).

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↗
PubMedDate not supplied

Toxicity of Aeromonas salmonicida cells to Atlantic salmon Salmo salar peritoneal macrophages.

Several strains of Aeromonas salmonicida were toxic to cultured peritoneal macrophages of Atlantic salmon, Salmo salar, in minimum doses of 5 x 10(6) CFU, whereas other strains were not. There was no correlation between cytotoxicity and in vivo virulence of the bacteria, the presence or absence of the two major surface components of A. salmonicida (namely, the A-layer and the O-polysaccharide chain of the LPS) nor, finally, with the ability of the strains to produce the following enzymes in vitro: protease, hemolysin, elastase and lecithinase. Toxicity was only observed with metabolically active bacteria and not with formalin- or heat-killed bacteria. The exact nature of the toxic factor remains unknown but is most likely associated with the surface of the bacteria. It is not extracellular since 24 and 48 h culture supernatants of the cytotoxic strains had no apparent effect on macrophages. The cytotoxic effect was found to be severe and rapid, it is likely a major virulence factor of A. salmonicida, but the exact role of such a potent toxin in the pathology of furunculosis has yet to be clarified.

Aeromonas↗
PubMed1986

The characterization of a conjugative R-plasmid isolated from Aeromonas salmonicida.

We have analyzed two related R-plasmids isolated from Aeromonas salmonicida: pAr32 and pJA8102-1, which encode resistance to chloramphenicol, streptomycin, and sulfonamides (Su). The genetic map of pJA8102-1 indicated that this plasmid consists of at least three functionally different regions. One is the region conferring ability to transfer (tra), one is the region coding for drug resistance genes (r-det), and one is the region encoding the replication functions (rep). Both plasmids contain repeated sequences (RS); pJA8102-1 has four copies of this RS, while pAr-32 has three copies. The RS sequence of pJA8102-1 are located adjacent to each of the drug-resistance genes. These sequences might have been responsible for the duplication of the Su-resistance gene on this plasmid.

Aeromonas↗
PubMed1993

Fatal septicaemia caused by Aeromonas hydrophila in a patient with cirrhosis.

In this case report from Italy we describe a fatal infection caused by A. hydrophila in a 39 yr old cirrhotic patient. This pathogen was isolated as a pure single culture from the patient's blood sample. The patient died on the second day of hospitalization from overwhelming sepsis. The A. hydrophila isolate was tested for different potential virulence properties, such as invasiveness, adherence, exotoxins production, presence of fimbriae and for the patterns of resistance to a variety of antimicrobial agents. Although, the Aeromonas species are infrequently reported as a cause of human infections, the present case study confirms the capability of these pathogens to induce serious human infections.

Adult↗