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PubMed1996

Combined effect of gamma-irradiation and conventional cooking on Aeromonas hydrophila in meatball.

Irradiation combined with a conventional cooking procedure was applied to meatball and the effects on bacterial load and inoculated Aeromonas hydrophila were determined. Meatball samples were irradiated by using a 60Co source at the dose levels of 0, 0.30, 0.75, 1.50, 2.50 kGy and cold stored at 4 +/- 1 degrees C for 7 days. Bacterial load and the count of A. hydrophila decreased when the irradiation dose level increased. A minimum inhibition effect was found at the dose of 0.30 kGy. Irradiation in combination with a conventional cooking procedure was found to be more effective in reducing A. hydrophila and the bacterial load in meatball. This study indicated that a dose of 0.75 kGy was sufficient to destroy approximately 10(4) cfu/g of A. hydrophila in meatball.

Aeromonas hydrophila↗
PubMed1992

Effect of Aeromonas hydrophila enterotoxins on function of mouse phagocytes.

Two enterotoxins produced by Aeromonas hydrophila isolate SSU have been characterized in this laboratory. One is a cholera toxin cross-reactive cytolytic enterotoxin (CTC toxin) and the other is a non-cholera toxin cross-reactive cytotonic enterotoxin (non-CTC toxin). The two enterotoxins are capable of causing fluid accumulation in animal models; however, only the CTC toxin is lethal to mice and expresses hemolytic as well as cytotoxic activities. In this study, we have investigated the effects of these two toxins on mouse phagocytes. Four hours after intraperitoneal injection of a sublethal dose (460 micrograms/kg of body weight) of CTC toxin, the chemiluminescence (CL) response of phagocytes in mouse blood was depressed significantly when compared with that observed for controls (intraperitoneal injection of only Hanks' balance salt solution, non-CTC toxin or before treatment with CTC toxin). When fresh whole blood was incubated with various concentrations (2.3, 11.5, 23, 230, 2300 ng/ml) of CTC toxin for 1.5 hr at 37 degrees C, the CL response of blood phagocytes was reduced strikingly in a dose-dependent fashion; however, non-CTC toxin did not inhibit the CL response. The inhibitory effect induced by CTC toxin of the phagocytic function not only was abolished completely, but phagocytosis was enhanced in the presence of interferon-gamma (IFN-gamma). In addition, IFN-gamma alone induced the largest enhancement of the CL response in mouse phagocytes. These results demonstrated that CTC toxin inhibits the phagocytic ability of phagocytes either in vivo or in vitro and that IFN-gamma pretreatment can overcome this toxic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Aeromonas hydrophila↗
PubMed1989

Stimulation of specific Aeromonas antibody secretion in rat intestine by gamma-aminobutyric acid.

This study was undertaken to assess a possible role for gamma-aminobutyric acid (GABA) in the regulation of intestinal secretion of IgA and IgG antibodies. Rats were immunized with culture supernatant of Aeromonas hydrophila isolate SSU. This culture supernatant contains a number of toxins that may be considered virulence factors. After 24 days of immunization, rats were anesthetized and a 10-cm intestinal segment was intubated and ligated at both ends in situ. The intestinal loop was perfused with phosphate-buffered saline (PBS). The effluents were collected for measurement of IgA and IgG by the ELISA. When compared with the effect of intravenous administration of normal saline in the control group, intravenous injection of GABA (30 mg/kg) resulted in a significant increase of IgA and IgG secretion in the experimental group. These stimulatory effects of GABA on secretion of IgA and IgG were abolished by bicuculline, a GABA-receptor antagonist, and by atropine, indicating that the GABA-stimulated secretion of IgA and IgG was mediated via the GABA receptors and cholinergic muscarinic receptors. These results suggest that GABA may participate in the nervous regulation of intestinal secretion of IgA and IgG antibodies in the rat.

Aeromonas↗
PubMedDate not supplied

The effect of N-formimidoyl thienamycin, ceftazidime, cefotiam, ceftriaxone and cefotaxime on non-fermentative Gram-negative rods, Aeromonas, Plesiomonas and Enterobacter agglomerans.

Thirty-one species (185 strains) of non-fermentative gram-negative rods (excluding Pseudomonas aeruginosa) as well as 45 strains of Aeromonas spp., 15 strains of Plesiomonas shigelloides and 68 strains of Enterobacter agglomerans were tested in microdilution procedures against N-formimidoyl thienamycin, ceftazidime, cefotiam, ceftriaxone and cefotaxime. N-formimidoyl thienamycin was the most effective drug as far as the spectrum of these bacterial groups and potency is concerned; ceftazidime was the second most effective agent. Ceftriaxone and cefotaxime were similar in their activity (against a smaller spectrum), while cefotiam showed little effect. There were occasional differences between MBC and MIC values which were most notable with ceftazidime, cefotiam, ceftriaxone and cefotaxime against E. agglomerans.

Aeromonas↗
PubMed1992

Aeromonas hydrophila: myofascial necrosis and sepsis.

An alcoholic patient with ascites was admitted to the intensive care unit for gastrointestinal bleeding. He subsequently developed spontaneous myonecrosis of the extremities culminating in sepsis syndrome. This was a unique, non-traumatic presentation of Aeromonas hydrophila soft tissue injury.

Adult↗
PubMed1994

Three beta-lactamases isolated from Aeromonas salmonicida, including a carbapenemase not detectable by conventional methods.

The beta-lactamases of seven strains of Aeromonas salmonicida subsp. achromogenes resistant to amoxicillin (MIC > 1024 mg/l) and responsible for furunculosis in farmed Atlantic salmon in Scotland were examined to establish the mechanisms of beta-lactam resistance. Separation of a cell-free extract on an isoelectric focusing gel stained with the chromogenic cephalosporin nitrocefin showed the presence of two beta-lactamases, one with a pI of 7.9 and the other with a pI of 6.0. Hydrolysis assays of cell-free extracts of these strains demonstrated carbapenemase, penicillinase and cephalosporinase activity. However, when the beta-lactamases were separated by anion exchange chromatography, the carbapenemase activity could not be retrieved in either of the peak fractions containing the separated enzymes that had been visualised by nitrocefin. Consequently, a novel carbapenemase was discovered which cannot be detected with nitrocefin.

Aeromonas↗
PubMed1975

Characterization of three Aeromonas and nine pseudomonas species by extracellular enzymes and haemolysins.

Strains from type culture collections and clinical isolates belonging to the Aeromonas and Pseudomonas genera were identified with conventional tests. Production of extra-cellular enzymes and haemolysins were detected by simple plate agar methods. The following enzymes were found to be of special value for a rapid and simple classification of certain species in both genera: potease (casein and gelatin agar), lecithinase (lecithin agar), and deoxyribonuclease (DNA agar). Elastase, staphylolytic enzyme, lipase, ribonuclease, amylase, and egg yolk reaction were other enzymes studied. However, these tests were not positive for more than 90% of any species. A. hydrophila, A. salmonicida, and P. aeruginosa were haemolytic on agar containing rabbit erythrocytes.

Aeromonas↗
PubMed2001

Virulence factors of clinical isolates of Aeromonas caviae.

The mechanism of pathogenicity of 13 Aeromonas caviae strains isolated from fecal specimens of children with diarrhea was examined. Isolates possessed several virulence agents. Six of 13 isolates produced cholera-like toxin, all strains exhibited adhesive ability and secreted catecholate siderophores. Six isolates were able to grow in heat-inactivated serum. Production of hemolysins was not detected. The isolates had relatively high values of LD50 in a mouse model, which suggests that there is no linkage between pathogenicity to mice and the diarrheagenic ability of the isolates.

Aeromonas↗
PubMed1997

Virulence factors-pathogenicity relationships for Aeromonas species from clinical and food isolates.

The presence of virulence factors in 96 Aeromonas strains isolated from food and clinical samples was studied. Neither cytotoxic activity and hydrophobicity, not the presence of pili or an extra surface layer made it possible to establish differences between food and clinical strains. Statistical studies showed that cytotoxin production was associated with a positive Voges-Proskauer reaction, inability to ferment arabinose and a positive lysine decarboxylation. Therefore, when comparing cytotoxic clinical and food strains with lysine decarboxylation phenotype, there was a significant difference (p < 0.05) between the two groups. The association of a cytotoxin production and lysine decarboxylation character should thus be considered as a possible virulence marker.

Aeromonas↗
PubMed2000

Amonabactin-mediated iron acquisition from transferrin and lactoferrin by Aeromonas hydrophila: direct measurement of individual microscopic rate constants.

The effectiveness and mechanism of iron acquisition from transferrin or lactoferrin by Aeromonas hydrophila has been analyzed with regard to the pathogenesis of this microbe. The ability of A. hydrophila's siderophore, amonabactin, to remove iron from transferrin was evaluated with in vitro competition experiments. The kinetics of iron removal from the three molecular forms of ferric transferrin (diferric, N- and C-terminal monoferric) were investigated by separating each form by urea gel electrophoresis. The first direct determination of individual microscopic rates of iron removal from diferric transferrin is a result. A. hydrophila 495A2 was cultured in an iron-starved defined medium and the growth monitored. Addition of transferrin or lactoferrin promoted bacterial growth. Growth promotion was independent of the level of transferrin or lactoferrin iron saturation (between 30 and 100%), even when the protein was sequestered inside dialysis tubing. Siderophore production was also increased when transferrin or lactoferrin was enclosed in a dialysis tube. Cell yield and growth rate were identical in experiments where transferrin was present inside or outside the dialysis tube, indicating that binding of transferrin was not essential and that the siderophore plays a major role in iron uptake from transferrin. The rate of iron removal from diferric transferrin shows a hyperbolic dependence on amonabactin concentration. Surprisingly, amonabactin cannot remove iron from the more weakly binding N-terminal site of monoferric transferrin, while it is able to remove iron from the more strongly binding C-terminal site of monoferric transferrin. Iron from both sites is removed from diferric transferrin and it is the N-terminal site (which does not release iron in the monoferric protein) that releases iron more rapidly! It is apparent that there is a significant interaction of the two lobes of the protein with regard to the chelator access. Taken together, these results support an amonabactin-dependent mechanism for iron removal by A. hydrophila from transferrin and lactoferrin. The implications of these findings for an amonabactin-dependent mechanism for iron removal by A. hydrophila from transferrin and lactoferrin are discussed.

Aeromonas hydrophila↗
PubMed2003

Role of Cys221 and Asn116 in the zinc-binding sites of the Aeromonas hydrophila metallo-beta-lactamase.

The CphA metallo-beta-lactamase produced by Aeromonas hydrophila exhibits two zinc-binding sites. Maximum activity is obtained upon binding of one zinc ion, whereas binding of the second zinc ion results in a drastic decrease in the hydrolytic activity. In this study, we analyzed the role of Asn116 and Cys221, two residues of the active site. These residues were replaced by site-directed mutagenesis and the different mutants were characterized. The C221S and C221A mutants were seriously impaired in their ability to bind the first, catalytic zinc ion and were nearly completely inactive, indicating a major role for Cys221 in the binding of the catalytic metal ion. By contrast, the binding of the second zinc ion was only slightly affected, at least for the C221S mutant. Mutation of Asn116 did not lead to a drastic decrease in the hydrolytic activity, indicating that this residue does not play a key role in the catalytic mechanism. However, the substitution of Asn116 by a Cys or His residue resulted in an approximately fivefold increase in the affinity for the second, inhibitory zinc ion. Together, these data suggested that the first zinc ion is located in the binding site involving the Cys221 and that the second zinc ion binds in the binding site involving Asn116 and, presumably, His118 and His196.

Aeromonas hydrophila↗
PubMed2000

A comparison of solid and liquid media for resuscitation of starvation- and low-temperature-induced nonculturable cells of Aeromonas hydrophila.

Like many other gram-negative bacteria, starved cells of Aeromonas hydrophila can be induced into a viable but nonculturable (VBNC) state by incubation at low temperature, as shown here by using various bacterial enumeration methods. Starved A. hydrophila strain HR7 cells at 4 degrees C reached the nonculturable stage in about 45 days. The cells were resuscitated by either a solid medium resuscitation method, using solid agar amended with H2O2-degrading agents, catalase or sodium pyruvate, or a liquid medium resuscitation method, by incubating nonculturable cells in liquid media containing these compounds before spreading onto plates. The liquid medium resuscitation method using catalase resulted in nearly complete recovery of nonculturable cells.

Aeromonas hydrophila↗
PubMed2001

G561 site-directed deletion mutant chitinase from Aeromonas caviae is active without its 304 C-terminal amino acid residues.

A G561 mutant of the Aeromonas caviae chitinase ChiA was made by PCR site-directed deletion mutagenesis in order to study the role of the 304 C-terminal amino acid residues of ChiA in the enzymatic hydrolysis of chitin. The recombinant ChiAG561 encoded on a 1.6-kb DNA fragment of A. caviae chiA was expressed in a heterologous Escherichia coli host using the pET20b(+) expression system. The His-Tag-affinity-purified recombinant ChiAG561 had a calculated molecular mass of 63,595 Da, which was consistent with the 67,000 Da estimated by SDS-PAGE. The G561 deletion mutant enzyme had the same optimum pH (6.5) as the full-length ChiA and a lower optimum temperature (37 degrees C instead of 42.5 degrees C). Biochemical properties of the recombinant ChiAG561 suggested that deletion of the 304 C-terminal amino acid residues of ChiA did not significantly affect ChiA enzyme activity. However, compared to the full-length ChiA, the mutant chitinase had a ten-fold higher relative activity with 4-methylumbelliferyl-N-N'-N"-triacetylchitotriose [4-MU-(GlcNAc)3] as a substrate, and higher rates of hydrolysis with both chitin and colloidal chitin substrates. Results obtained from this study suggest that the active region of A. caviae ChiA is located in the region before G561 of the protein molecule.

Aeromonas↗
PubMed2002

Starvation survival and viable but nonculturable states in Aeromonas hydrophila.

The behavior of Aeromonas hydrophila stored at 4 degrees C and 25 degrees C in nutrient-poor filtered sterilized distilled water was investigated. At 4 degrees C, the A. hydrophila population declined below the detection level (0.1 cell mL(-1)) after 7 weeks, whereas the number of cells with intact membrane as determined by the LIVE/DEAD method decreased only by 1 log unit. Although, this response is reminiscent of the so-called VBNC state, the cells could not be resuscitated by an upshift to 25 degrees C. A mixture of rods with normal size and elongated cells was observed in this state. At 25 degrees C, viable cells and cells with intact membrane declined only by 0.8 log unit over the 10-week storage period, and thus A. hydrophila entered the classical starvation survival state. During this state, a mixture of rods and cocci was observed. Prestarvation at 25 degrees C for 24 h and especially 49 days delayed significantly the rate of entry into the VBNC state. However, stationary phase cells were not significantly more tolerant than exponential phase cells. No significant improvements in recovery yield were obtained on LB agar plates amended with catalase or sodium pyruvate. During cold incubation, high variability in responses was observed. Intermittent cryptic regrowth might be responsible for this variability in responses.

Aeromonas hydrophila↗
PubMed2002

In vivo evolution of the Aeromonas punctata polyhydroxyalkanoate (PHA) synthase: isolation and characterization of modified PHA synthases with enhanced activity.

In vivo random mutagenesis of the polyhydroxyalkanoate (PHA) synthase gene from Aeromonas punctata was performed employing the mutator strain Escherichia coli XL1-Red. About 200,000 mutants were screened on Nile red-containing medium and five mutants with enhanced fluorescence were selected. Four of these mutants exhibited enhanced in vivo and in vitro PHA synthase activity. Mutant M1, which carried the single mutation F518I, showed a five-fold increase in specific PHA synthase activity, whereas the corresponding mediated PHA accumulation increased by 20%, as compared with the wild-type PHA synthase. Mutant M2, which carried the single mutation V214G, showed a two-fold increase in specific PHA synthase activity and PHA accumulation only increased by 7%. Overall, the in vitro activities of the overproducing mutants ranged from 1.1- to 5-fold more than the wild-type activity, whereas the amounts of accumulated PHA ranged over 107-126% of that of the wild type. Moreover, all mutants mediated synthesis of PHAs with an increased weight average molar mass, but the molar fractions of 3-hydroxybutyrate and 3-hydroxyhexanoate remained almost constant. In vivo random mutagenesis proved to be a versatile tool to isolate mutants exerting improved properties with respect to PHA biosynthesis.

Acyltransferases↗
PubMed2003

Production of poly(3-hydroxybutyrate- co-3-hydroxyhexanoate) with flexible 3-hydroxyhexanoate content in Aeromonas hydrophila CGMCC 0911.

Aeromonas hydrophila CGMCC 0911 isolated from lake water was found to be able to synthesize a polyhydroxyalkanoate (PHA) copolymer (PHBHHx) consisting of 3-hydroxybutyrate (HB) and 4-6 mol% 3-hydroxyhexanoate (HHx). The wild-type bacterium accumulated 49% PHBHHx containing 6 mol% HHx in terms of cell dry weight (CDW) when grown on lauric acid for 48 h. When A. hydrophila CGMCC 0911 expressed the Acyl-CoA dehydrogenase gene ( yafH) of Escherichia coli, the recombinant strain could accumulate 47% PHBHHx, while the HHx content reached 17.4 mol%. The presence of changing glucose concentration in the culture changed the HHx content both in wild type and recombinant A. hydrophila CGMCC 0911. When 5 g l(-1) glucose was added to a culture containing 5 g l(-1) lauric acid as co-substrate, 45% PHBHHx/CDW consisting of 8.8 mol% HHx was produced by wild-type A. hydrophila CGMCC 0911 compared with only 5% in the absence of glucose. When the recombinant A. hydrophila CGMCC 0911 was grown on a mixed substrate containing lauric acid and 8-10 g l(-1) glucose, the HHx content could be further increased to 35.6 mol%. When the glucose concentration exceeded 10 g l(-1), cell growth, PHA content and mole percentages of HHx in PHBHHx were significantly reduced.

3-Hydroxybutyric Acid↗
PubMed2005

Metabolic engineering of Aeromonas hydrophila for the enhanced production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

Wild-type Aeromonas hydrophila 4AK4 produced 35-45 wt.% poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) consisting of 10-15 mol% 3-hydroxyhexanoate (3HHx). To enhance PHBHHx production, vgb gene encoding Vitreoscilla haemoglobin or fadD gene encoding Escherichia coli acyl-CoA synthase was co-expressed with polyhydroxyalkanoates (PHA) synthesis-related genes including phbAB from Wautersia eutropha and phaPCJ from A. hydrophila. Expression of vgb increased PHBHHx content from 46 to 53 wt.% without affecting the polymer monomers composition, whereas fadD increased both PHBHHx content from 46 to 64 wt.% and its 3HHx fraction from 15 to 24 mol%. Co-expression of vgb or fadD gene with PHA-synthesis-related genes generally increased PHBHHx content over 60 wt.%. Co-expression of phbAB with vgb increased PHBHHx content and concentration up to about 70 wt.% and 4.0 g l-1, respectively. Fermentor study also showed that in the recombinants harboring vgb, CDW, PHBHHx concentration and productivity were significantly elevated up to 54 g l-1, 28.5 g l-1 and 0.791 g l-1 h-1, respectively, suggesting that vgb could promote PHA synthesis. In this strain, lac promoter could be used to constitutively express foreign genes such as phbA and phbB encoding beta-ketothiolase and NADPH-dependent acetoacetyl-CoA reductase of W. eutropha, respectively, without use of IPTG. The results showed that combined expression of different genes was a successful strategy to enhance PHA production, which could be useful for strain development to construct other recombinant PHA-producing strains.

3-Hydroxybutyric Acid↗
PubMed2005

Study on peptide hydrolysis by aminopeptidases from Streptomyces griseus, Streptomyces septatus and Aeromonas proteolytica.

We developed a spectrophotometric assay for peptide hydrolysis by aminopeptidases (APs). The assay enables the measurement of free amino acids liberated by AP-catalyzed peptide hydrolysis using 4-aminoantipyrine, phenol, peroxidase, and L-amino acid oxidase. We investigated the specificity of bacterial APs [enzymes from Streptomyces griseus (SGAP), Streptomyces septatus (SSAP), and Aeromonas proteolytica (AAP)] toward peptide substrates using this assay method. Although these enzymes most efficiently cleave leucyl derivatives among 20 aminoacyl derivatives, in peptide hydrolysis, the catalytic efficiencies of Phe-Phe hydrolysis by SGAP and SSAP exceed that of Leu-Phe hydrolysis. Furthermore, all enzymes showed the maximum catalytic efficiencies for Phe-Phe-Phe hydrolysis. These results indicate that the hydrolytic activities of bacterial APs are affected by the nature of the penultimate residue or flanking moiety and the length of the peptide substrate.

Aeromonas↗