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PubMed2007

Characterization of extracellular proteins produced by Aeromonas hydrophila AH-1.

Aeromonas hydrophila is a ubiquitous Gram-negative bacterium which can cause motile aeromonad septicemia in both fish and humans. A. hydrophila secretes many extracellular proteins associated with pathogenicity and environmental adaptability. In this study, an extracellular proteome map of A. hydrophila AH-1 was constructed. The major extracellular virulence factors were characterized by comparing the proteomes of various deletion mutants with that of the wild type. The results suggested that serine protease was involved in the processing of a toxin and secreted enzymes such as hemolysin, glycerophospholipid-cholesterol acyltransferase and metalloprotease. We also showed that expressions of polar and lateral flagellins were under the control of temperature, FlhA, LafK, and RpoN. In addition, three novel proteins (potential effector proteins including one ExoT-like protein) were revealed to be secreted via the type III secretion system (TTSS) of A. hydrophila AH-1. Another novel finding was the demonstration of a crosstalk between the lateral flagellar system and the TTSS in A. hydrophila. These results showed that proteomics is a powerful tool for characterizing virulence factors. The construction of proteome maps will provide a valuable means of finding potential candidates for developing suitable diagnostics and therapeutics for this emerging pathogen.

Aeromonas hydrophila↗
PubMed2003

The C-terminal module of Chi1 from Aeromonas caviae CB101 has a function in substrate binding and hydrolysis.

The chitinase gene chi1 of Aeromonas caviae CB101 encodes an 865-amino-acid protein (with signal peptide) composed of four domains named from the N-terminal as an all-beta-sheet domain ChiN, a triosephosphate isomerase (TIM) catalytic domain, a function-unknown A region, and a putative chitin-binding domain (ChBD) composed of two repeated sequences. The N-terminal 563-amino-acid segment of Chi1 (Chi1DeltaADeltaChBD) shares 74% identity with ChiA of Serratia marcescens. By the homology modeling method, the three-dimensional (3D) structure of Chi1DeltaADeltaChBD was constructed. It fit the structure of ChiA very well. To understand fully the function of the C-terminal module of Chi1 (from 564 to 865 amino acids), two different C-terminal truncates, Chi1DeltaChBD and Chi1DeltaADeltaChBD, were constructed, based on polymerase chain reaction (PCR). Comparison studies of the substrate binding, hydrolysis capacity, and specificity among Chi1 and its two truncates showed that the C-terminal putative ChBD contributed to the insoluble substrate-protein binding and hydrolysis; the A region did not have any function in the insoluble substrate-protein binding, but it did have a role in the chitin hydrolysis: Deletion of the A region caused the enzyme to lose 30-40% of its activity toward amorphous colloidal chitin and soluble chitin, and around 50% toward p-nitrophenyl (pNP)-chitobiose pNP-chitotriose, and its activity toward low-molecular-weight chitooligomers (GlcNAc)3-6 also dropped, as shown by analysis of its digestion processes. This is the first clear demonstration that a domain or segment without a function in insoluble substrate-chitinase binding has a role in the digestion of a broad range of chitin substrates, including low-molecular-weight chitin oligomers. The reaction mode of Chi1 is also described and discussed.

Aeromonas↗
PubMed2005

Elucidation of the molecular structure of lipid A isolated from both a rough mutant and a wild strain of Aeromonas salmonicida lipopolysaccharides using electrospray ionization quadrupole time-of-flight tandem mass spectrometry.

The chemical structure of lipid A, isolated by mild acid hydrolysis from a rough mutant and a wild strain of Aeromonas salmonicida lipopolysaccharide, was investigated using electrospray ionization quadrupole time-of-flight (QqToF) hybrid tandem mass spectrometry and showed a great degree of microheterogeneity. The chemical structure of the main constituent of this heterogeneous mixture was identified as a beta-D-(1 --> 6) linked D-glucosamine disaccharide substituted by two phosphate groups, one being bound to the non-reducing end at position O-4' and the other to the position O-1 of the reducing end of the D-glucosamine disaccharide. The location of the fatty acids linked to the disaccharide backbone was established by identifying diagnostic ions in the conventional QqToF-MS scan. Low-energy collision tandem mass spectrometry analysis of the selected precursor diagnostic ions confirmed, unambiguously, their proposed molecular structures. We have established that myristyloxylauric (C14:0(3-O(12:0))) acid residues were both N-2' and O-3' linked to the non-reducing end of the D-GlcN residue, and that two 3-hydroxymyristic (C14:0(3-OH)) acid chains acylated the remaining positions of the reducing end. The MS and MS/MS data obtained allowed us to determine the complex molecular structure of lipid A. The QqToF-MS/MS instrument has shown excellent superiority over a conventional quadrupole-hexapole-quadrupole tandem instrument which failed to fragment the selected precursor ion.

Aeromonas salmonicida↗
PubMed2000

Suppression of the humoral immune response of Atlantic salmon, Salmo salar L. by the 64 kDa serine protease of Aeromonas salmonicida.

Bacteria-free supernatants of broth cultures of Aeromonas salmonicida inhibited the humoral immune response, but not the cell-mediated immune response, of Atlantic salmon to bacteriophage MS2. The immunosuppressive factor was the 64 kDa serine protease secreted by A. salmonicida. The suppressive activity was not due to degradation of epitopes of MS2, and although serine protease degraded the heavy chain of salmon IgM in vitro there was no evidence for significant degradation in vivo. The principal lethal toxin of A. salmonicida, the glycerophospholipid: cholesterol acyltransferase did not inhibit the immune response of salmon.

Aeromonas↗
PubMed2001

Immunological parameters of Javanese carp Puntius gonionotus (Bleeker) exposed to copper and challenged with Aeromonas hydrophila.

This study was to determine the median lethal concentration (LC50) of copper to Javenese carp, Puntius gonionotus (Bleeker), and the immune response after the fish were exposed to sublethal levels of copper and challenged with formalin killed Aeromonas hydrophila. The LC50 of copper on P. gonionotus at 24, 48, 72, 96 and 120 h were estimated as 2.17, 0.91, 0.57, 0.53 and 0.42 mg l(-1), respectively. To determine the effect of copper on the immune system, fish were exposed for 66 days to 0.05, 0.10 and 0.15 mg Cu l(-1). After 56 days of initial exposure to copper, fish were challenged with 0.1 ml of 4.5 x 10(5) cfu ml(-1) formalin killed A. hydrophila and maintained in the same concentration of copper. After the challenge, the immune response was monitored for 2 weeks using haematological and serological assays. During the initial phase of exposure to copper, significant changes were noted in the white blood cell, lysozyme, potential killing activity, total plasma protein, total immunoglobulin and haematocrit levels between the control and treated fish. One week after challenge with A. hydrophila, there was a significant increase in the values of white blood cells, total protein and total immunoglobulin compared to the values before the challenge. However, these values were not significantly different (P>0.05) between the control and the treated fish. In contrast, NBT and lysozyme assays exhibited a significant difference (P<0.05) in fish exposed to 0.10 mg Cu l(-1) (0.525 +/- 0.17; 24.42 +/- 3.35 x 10(2) micromg ml(-1)) and 0.15 mg Cu 1(-1) (0.536 +/- 0.19; 21.78 +/- 1.29 x 10(2) micromg ml(-1)) compared to the control (0.746 +/- 0.31; 30.73 +/- 5.42 x 10(2) micromg ml(-1)) after the bacterial challenge (day 61). There was however no significant difference (P>0.05) in NBT and lysozyme levels in fish exposed to lower level of copper (0.05 mg Cu l(-1)), suggesting the absence of immunosuppressive effects at lower level of exposure.

Aeromonas↗
PubMed2001

Effect of ascorbic acid on the immune response of the catfish, Mystus gulio (Hamilton), to different bacterins of Aeromonas hydrophila.

Ascorbic acid is one of the essential vitamins for normal physiological activities of any organism. The present study demonstrates an immunostimulatory effect of vitamin C on the humoral and cell mediated immunity of the bagrid catfish, Mystus gulio, determined using different bacterins of Aeromonas hydrophila. Humoral as well as cell mediated immune responses were elucidated in the vitamin supplemented, vaccinated and unvaccinated groups. The vitamin supplemented lipopolysaccharide (LPS) vaccinated group exhibited greater immune (both humoral and cell mediated) responses than its formalin killed (FK) and heat killed (HK) bacterin vaccinated counterparts. Nevertheless, in the challenge study, the relative percent survival (RPS) was found to be the same for both FK and LPS immunised vitamin treated groups while lower for the HK immunised vitamin treated group.

Aeromonas↗
PubMed2002

Temperature dependent activation of leucocyte populations of rainbow trout, Oncorhynchus mykiss, after intraperitoneal immunisation with Aeromonas salmonicida.

The temperature dependence of in vivo activation of rainbow trout Oncorhynchus mykiss, leucocyte populations after intraperitoneal injection (i.p.) of fish with a T-cell independent antigen Aeromonas salmonicida (strain MT423) was investigated using a proliferation assay and flow cytometric analysis with mab specific for trout leucocyte surface markers. In trout kept at 15-17 degrees C a prominent activation of blood and spleen leucocytes was found. Also, drastic changes of the percentage of the leucocyte populations in blood and spleen occurred: the amount of monocytes in the blood increased between day 2 and day 7 post injection (p.i.), whereas in spleen the amount of monocytes stayed at a high level (approximately 35%) after a depression between day 4 and day 7 p.i. The percentage of B-lymphocytes was increased first in spleen and then in blood. The percentage of granulocytes in blood was elevated during the whole experiment compared to control fish. In trout kept at 10-12 degrees C only blood leucocytes showed a weak activation after i.p. injection of A. salmonicida, whereas spleen leucocytes showed nearly no reaction. Only the percentage of granulocytes in the blood (day 2-14 p.i.) and of monocytes in the spleen (day 2 and day 8 p.i.) was changed compared to phosphate buffered saline (PBS)-injected fish. However, the development of A. salmonicida specific antibodies was contrary to the cellular reaction. Whereas antibodies could first be detected after 16-18 days p.i. in both groups the amount of antibodies was significantly higher in sera of trout kept at 10-12 degrees C at day 22 and day 28 p.i. than in sera of trout kept at 15-17 degrees C. These results indicate stronger A. salmonicida induced activation of monocytes, granulocytes and B-lymphocytes at higher temperature. However, the development of a specific antibody response against A. salmonicida seemed to be more effective at lower temperatures.

Aeromonas↗
PubMed2002

Production of superoxide anion by head-kidney leucocytes of Indian major carps immunised with bacterins of Aeromonas hydrophila.

On contact with micro-organisms or any other antigenic particles which are recognised as phagocytosable, the leucocytes of vertebrates raise their oxygen consumption suddenly (respiratory burst). The consumed oxygen is then converted into reactive oxygen species (ROS). An effort has been made in the present study to estimate the production of superoxide anion, one of the ROS, by the resident as well as activated head-kidney leucocytes of Indian major carps. Activation was accomplished by immunisation with formalin killed (FK) and heat killed (HK) whole cell bacterins of Aeromonas hydrophila. In the ex vivo experiment conducted, activated leucocytes yielded a significant increase in O.D. values for nitroblue tetrazolium (NBT) reduction reaction, reflecting an increase in superoxide anion production, from day 1 post immunisation. Of the three species of Indian major carps immunised, Catla catla showed the greatest production of superoxide anion, followed by Labeo rohita and then by Cirrhinus mrigala. The enhancement of superoxide anion production of leucocytes by immunisation justifies the role of immunisation in the microbicidal defence mechanism of fish.

Aeromonas hydrophila↗
PubMed2002

Immunisation of Indian major carps against Aeromonas hydrophila by intraperitoneal injection.

The Indian major carps Catla catla, Labeo rohita and Cirrhinus mrigala were immunised against the potent bacterial fish pathogen, Aeromonas hydrophila by the intraperitoneal route, in field conditions. Two different polyvalent antigen preparations namely, whole cell and extracellular products (ECP) were used. Immunisation schedule consisting of a single booster dose given 28 days after priming resulted in a good agglutinating antibody response in the carps. Kinetics of the response were similar in the three carp species with both whole cell and ECP. Upon challenge with virulent strains, relative percent survival as high as 80-90% was recorded. Indian major carps are the most important freshwater species cultured in India and it is essential that they are protected against infections of A. hydrophila, a scourge of freshwater fish worldwide.

Aeromonas hydrophila↗
PubMed2000

Responses of giant freshwater prawn (Macrobrachium rosenbergii) to challenge by two strains of Aeromonas spp.

The virulence of two Aeromonas strains (A. veronii and A. caviae) isolated from the hepatopancreas of apparently healthy giant freshwater prawns (Macrobrachium rosenbergii) was compared using a challenge by injections. For the A. veronii strain, challenge with 3.7 x 10(5) cells/g of body weight led to 100% mortality; for the A. caviae strain, 3.8 x 10(6) cells/g produced 100% mortality. The 50% lethal doses (LD50) were 2.0 x 10(3) cells/g for A. veronii and 51.2 x 10(3) cells/g for A. caviae. Use of different culture media (trypticase soy broth vs prawn muscle extract) did not significantly affect the virulence of A. veronii. Injection of a sublethal dose (1 x 10(3) cells/g) of A. veronii led to a significant decrease in the total hemocyte count (THC) between 4 and 24 h after injection. Saline injections also caused a similar though less decrease in THC. In the first 24 h after injection of A. veronii (1 x 10(3) cells/g), the change in the percentages of granulocytes (both granular cells and semigranular cells) in the hemolymph was significantly different. After a significant initial increase, the percentage of hyaline cells fell by a factor of 4, from 9 to 2%. Phenoloxidase activity increased fourfold immediately after injection and returned to preinjection levels at 24 h.

Aeromonas↗
PubMed1993

Distribution of surface-exposed and non-accessible amino acid sequences among the two major structural domains of the S-layer protein of Aeromonas salmonicida.

The tetragonally arranged crystalline surface protein array (A-layer) of the fish pathogenic bacterium Aeromonas salmonicida is a virulence factor. Circular dichroism studies in the presence or absence of 0.1% sodium dodecyl sulfate showed that the secondary structure of A-protein, and its 39,439 molecular weight amino-terminal trypsin-resistant peptide, were altered. In both cases alpha-helix was increased significantly at the expense of beta-structure when SDS was added. Western and dot immunoblotting, immuno-microscopy and enzyme-linked immunosorbent assay with monospecific polyclonal antiserum and eight monoclonal antibodies specific for epitopes exposed on the surface of native A-layer showed that the 481 residue A-protein subunit and the surface of A-layer were conserved antigenically. Mimeotope analysis of nonapeptides representing the sequence of A-protein allowed identification of 146 residues in presumed linear epitopes accessible on the surface of A-layer. Inaccessible or non-epitopic residues accounted for 70% of the protein. The majority of inaccessible residues were in the N-terminal 301 residues of A-protein. Dispersed among these were 65 surface-accessible residues in five linear epitope clusters illustrating the complex folding of this major structural domain of A-protein. The C-terminal 180 residues carried fewer linear epitopes but contained the major region of A-layers surface-accessible sequence, including four linear epitopes in predominantly hydrophobic sequence. Four A-layer surface-binding monoclonal antibodies also bound to this minor structural domain, although the epitopes of only two were identified by mimeotope analysis. The epitopes of six A-layer surface-binding monoclonals could not be identified, suggesting that A-layer may also contain conformation dependent surface epitopes.

Aeromonas↗
PubMed1993

Effects of the acetylcholinesterase toxin of Aeromonas hydrophila on the central nervous system of fish.

The purified acetylcholinesterase (AcChE) toxin, crude extracellular products (ECP) or viable virulent Aeromonas hydrophila were injected intraperitoneally into rainbow trout in different sublethal and lethal doses. When fish showed signs of morbidity, brain tissue was excised and assayed for acetylcholinesterase activity. In all cases there was a large increase in AcChE activity (about 40-fold for purified AcChE-toxin). This was shown to be due to an accumulation of the fish's own AcChE and not the bacterial toxin. Nevertheless, the latter was detected in brain homogenates from fish in all treatment groups using a rabbit antiserum to the purified toxin to probe Western blots of brain homogenates, demonstrating that the toxin does gain access to brain tissue and is produced during in vivo infection. The results strongly suggest that this toxin plays a central role in the pathogenesis of A. hydrophila infection.

Acetylcholinesterase↗
PubMed1993

The role of a 40-megadalton plasmid in the adherence and hemolytic properties of Aeromonas hydrophila.

A cured strain of Aeromonas hydrophila, MS-2PC, was examined for phenotypic changes in antibiotic resistance, adherence, and hemolysis. Parental strain MS-2 was resistant to ampicillin, novobiocin, and carbenicillin; MS-2PC, which lacked a 40-MDa plasmid, was also resistant to ampicillin but was sensitive to novobiocin and carbenicillin. The adherence of these isolates to CaCo-2 and HeLa cells was examined. MS-2PC demonstrated greater attachment to both cell lines than did strain MS-2 (p < 0.05). MS-2PC also demonstrated greater hemolysis activity than did MS-2 (p < 0.01). The 40-Mda plasmid was isolated and reintroduced into MS-2PC. The resulting transformant, 20T, regained resistance to carbenicillin and novobiocin. The attachment ability of 20T was equal to that of MS-2, and both strains demonstrated significantly lower attachment ability than that of MS-2PC (p < 0.01). Strains MS-2 and 20T exhibited the same hemolysis pattern, which was markedly less than that of strain MS-2PC. These results indicate that the 40-Mda plasmid which codes for antibiotic resistance also controls other functions of A. hydrophila MS-2.

Aeromonas hydrophila↗
PubMed1995

Purification and characterization of a CHO cell-elongating toxin produced by Aeromonas hydrophila.

A Chinese hamster ovary (CHO) cell-elongating toxin produced by Aeromonas hydrophila was purified from cell-free supernatant fluids by ammonium sulfate precipitation and fast protein liquid chromatography. The purified toxin had an isolelectric point (pl) of 3.7 and a molecular weight of 70,000 in a single band on isoelectric focusing (IEF) gels and SDS-PAGE gels, respectively. The N-terminal sequence, amino acids 1-20, and the amino acid content were determined from Western blots of the 70 kDa band. No homology with any known microbial toxin was found. CHO cell activity was not neutralized by antiserum to cholera toxin (anti-CT), and the toxin did not react with anti-CT on Western blots. The toxin did not increase cyclic AMP, cyclic GMP, or prostaglandin E2 levels in CHO cells. No cytotoxic activity was observed. Intragastric administration of purified toxin (5 x 10(4) and 5 x 10(8) CHO cell units) induced intestinal fluid accumulation in infant mice. These results suggest that this toxin may be a novel cytotonic toxin distinct from previously described toxins produced by A. hydrophila or A. sobria.

Aeromonas hydrophila↗
PubMed1996

Using a new inbred fish model and cultured fish tissue cells to study Aeromonas hydrophila and Yersinia ruckeri pathogenesis.

An inbred strain of the southern platyfish, Xiphophorus maculatus, was used as a host for Aeromonas hydrophila and Yersinia ruckeri infections. The infections were initiated by holding the platyfish in inoculation baths containing dilutions of virulent A. hydrophila or Y. ruckeri strains. Inoculating the platyfish in this manner resulted in a dose-dependent mortality over a range of bacterial input from 10(5) to 10(8) A. hydrophila and 10(6) to 10(8) Y. ruckeri/ml. Clinical manifestations of A. hydrophila infections were noted in infected platyfish that eventually died, but not in platyfish that survived. In this model, the Y. ruckeri infected fish died before obvious signs of infection were detected. The A. hydrophila strain used to establish the infections was recovered from the kidney and intestine of infected fish that died, but not from survivors receiving the same inoculation dose. Both infective bacteria were tested for the ability to invade a number of different fish and human cultured cells. A hydrophila strain TF7 did not invade of the cells tested, whereas the Y. ruckeri strain invaded fish derived cultured cells, but not human derived Hep-2 cells.

Aeromonas hydrophila↗
PubMed1996

The role of the O-antigen lipopolysaccharide on the colonization in vivo of the germfree chicken gut by Aeromonas hydrophila serogroup O:34.

We compared the ability of different Aeromonas hydrophila strains from serogroup O:34 grown at different temperatures to colonize in vivo the germfree chicken gut. We found a good colonization when the strains were grown at 20 degrees C but not when they were grown at 37 degrees C. We previously described that these strains were able to form the O-antigen lipopolysaccharide (LPS) when they grow at low temperature but not at high temperature. We also obtained by transposon mutagenesis mutants only devoid of the O-antigen LPS (rfb mutants), and showed that they were unable to colonize the germfree chicken gut. All these results prompted us to conclude that the O-antigen LPS, in these strains, is a main factor for colonization in this animal model system.

Aeromonas hydrophila↗
PubMed1996

The cell surface of Aeromonas salmonicida determines in vitro survival in cultured brook trout (Salvelinus fontinalis) peritoneal macrophages.

Aeromonas salmonicida strains phenotypically differing in their A-layer, lipopolysaccharide, and macrophage cytotoxicity were tested in vitro for survivability in brook trout (Salvelinus fontinalis) serum with or without antibodies, and in vivo following intraperitoneal injection. The ability of brook trout peritoneal macrophages to phagocytize and kill the different phenotypes was investigated in an in vitro assay. The virulent strain, A. salmonicida 80204, which has the full complement of known virulence factors, as well as the recently described macrophage cytotoxin, was resistant in vitro to both the bactericidal activity of normal and immune serum, and to brook trout peritoneal macrophages. A. salmonicida SS-70.1, which possesses the A-layer but lacks the cytotoxin, was resistant to the bactericidal activity of normal and immune serum but was avirulent and killed by macrophages. Phenotypes lacking the A-layer, regardless of whether or not they possessed the macrophage cytotoxin were avirulent, susceptible to normal and immune serum and the bactericidal activity of peritoneal macrophages. A. salmonicida virulence expression requires both the A-layer and the macrophage cytotoxin.

Aeromonas↗
PubMed1997

Complement resistance of capsulated strains of Aeromonas salmonicida.

The complement resistance of Aeromonas salmonicida strains grown under conditions promoting capsule formation was investigated using well characterized strains and their isogenic mutants. Complement resistance was previously studied using the same strains growing under non-capsulating conditions. The serum resistant strains were found to activate complement, but rapidly degrade C3b preventing productive formation of the lytic complex C5b-9. Isogenic lipopolysaccharide rough mutants grown under non-capsulating conditions were serum sensitive, binding a large amount of C3b and leading to productive formation of C5b-9. When grown under conditions promoting capsule formation, these mutants were partially resistant to complement because less C3b is bound to them and also partially degraded, with a concomitant reduction in lytic C5b-9.

Aeromonas↗