(1/265) Quorum sensing-dependent regulation and blockade of exoprotease production in Aeromonas hydrophila.

In Aeromonas hydrophila, the ahyI gene encodes a protein responsible for the synthesis of the quorum sensing signal N-butanoyl-L-homoserine lactone (C4-HSL). Inactivation of the ahyI gene on the A. hydrophila chromosome abolishes C4-HSL production. The exoprotease activity of A. hydrophila consists of both serine protease and metalloprotease activities; in the ahyI-negative strain, both are substantially reduced but can be restored by the addition of exogenous C4-HSL. In contrast, mutation of the LuxR homolog AhyR results in the loss of both exoprotease activities, which cannot be restored by exogenous C4-HSL. Furthermore, a substantial reduction in the production of exoprotease by the ahyI+ parent strain is obtained by the addition of N-acylhomoserine lactone analogs that have acyl side chains of 10, 12, or 14 carbons. The inclusion of N-(3-oxododecanoyl)-L-homoserine lactone or N-(3-oxotetradecanoyl)-L-homoserine lactone at 10 microM in overnight cultures of A. hydrophila abolishes exoprotease production in azocasein assays and reduces the activity of all the exoprotease species seen in zymograms.  (+info)

(2/265) Kinetic and spectroscopic characterization of native and metal-substituted beta-lactamase from Aeromonas hydrophila AE036.

Two metal ion binding sites are conserved in metallo-beta-lactamase from Aeromonas hydrophila. The ligands of a first zinc ion bound with picomolar dissociation constant were identified by EXAFS spectroscopy as one Cys, two His and one additional N/O donor. Sulfur-to-metal charge transfer bands are observed for all mono- and di-metal species substituted with Cu(II) or Co(II) due to ligation of the single conserved cysteine residue. Binding of a second metal ion results in non-competitive inhibition which might be explained by an alternative kinetic mechanism. A possible partition of metal ions between the two binding sites is discussed.  (+info)

(3/265) Cloning, sequencing, and role in serum susceptibility of porin II from mesophilic Aeromonas hydrophila.

We cloned and sequenced the structural gene for Aeromonas hydrophila porin II from strain AH-3 (serogroup O:34). The genetic position of this gene, like that of ompF in Escherichia coli, is adjacent to aspC and transcribed in the same direction. However, upstream of the porin II gene no similarities with E. coli were found. We obtained defined insertion mutants in porin II gene either in A. hydrophila (O:34) or A. veronii sobria (serogroup O:11) serum-resistant or -sensitive strains. Furthermore, we complemented these mutants with a plasmid harboring only the porin II gene, which allowed us to define the role of porin II as an important surface molecule involved in serum susceptibility and C1q binding in these strains.  (+info)

(4/265) The cytotoxic enterotoxin of Aeromonas hydrophila induces proinflammatory cytokine production and activates arachidonic acid metabolism in macrophages.

An aerolysin-related cytotoxic enterotoxin (Act) of Aeromonas hydrophila possesses multiple biological activities, which include its ability to lyse red blood cells, destroy tissue culture cell lines, evoke a fluid secretory response in ligated intestinal loop models, and induce lethality in mice. The role of Act in the virulence of the organism has been demonstrated. In this study, we evaluated the potential of Act to induce production of proinflammatory cytokines associated with Act-induced tissue injury and Act's capacity to activate in macrophages arachidonic acid (AA) metabolism that leads to production of eicosanoids (e.g., prostaglandin E(2) [PGE(2)]). Our data indicated that Act stimulated the production of tumor necrosis factor alpha and upregulated the expression of genes encoding interleukin-1beta (IL-1beta) and IL-6 in the murine macrophage cell line RAW264.7. Act also activated transcription of the gene encoding inducible nitric oxide synthase. Act evoked the production of PGE(2) coupled to the cyclooxygenase-2 (COX-2) pathway. AA is a substrate for PGE(2), and Act produced AA from phospholipids by inducing group V secretory phospholipase A(2). We also demonstrated that Act increased cyclic AMP (cAMP) production in macrophages. cAMP, along with PGE(2), could potentiate fluid secretion in animal models because of infiltration and activation of macrophages resulting from Act-induced tissue injury. After Act treatment of RAW cells, we detected an increased translocation of NF-kappaB and cAMP-responsive element binding protein (CREB) to the nucleus using gel shift assays. Act also upregulated production of antiapoptotic protein Bcl-2 in macrophages, suggesting a protective role for Bcl-2 against cell death induced by proinflammatory cytokines. The increased expression of genes encoding the proinflammatory cytokines, COX-2, and Bcl-2 appeared correlated with the activation of NF-kappaB and CREB. This is the first report of the detailed mechanisms of action of Act from A. hydrophila.  (+info)

(5/265) Molecular analysis of genetic differences between virulent and avirulent strains of Aeromonas hydrophila isolated from diseased fish.

Aeromonas hydrophila, a normal inhabitant of aquatic environments, is an opportunistic pathogen of a variety of aquatic and terrestrial animals, including humans. A. hydrophila PPD134/91 is defined as virulent whereas PPD35/85 is defined as avirulent on the basis of their different LD50 values in fish. Suppression subtractive hybridization (SSH) was used to identify genetic differences between these two strains. Sixty-nine genomic regions of differences were absent in PPD35/85, and the DNA sequences of these regions were determined. Sixteen ORFs encoded by 23 fragments showed high homology to known proteins of other bacteria. ORFs encoded by the remaining 46 fragments were identified as new proteins of A. hydrophila, showing no significant homology to any known proteins. Among these PPD134/91-specific genes, 22 DNA fragments (21 ORFs) were present in most of the eight virulent strains studied but mostly absent in the seven avirulent strains, suggesting that they are universal virulence genes in A. hydrophila. The PPD134/91-specific genes included five known virulence factors of A. hydrophila: haemolysin (hlyA), protease (oligopeptidase A), outer-membrane protein (Omp), multidrug-resistance protein and histone-like protein (HU-2). Another 47 DNA fragments (44 ORFs) were mainly present in PPD134/91, indicating the heterogeneity among motile aeromonads. Some of these fragments encoded virulence determinants. These included genes for the synthesis of O-antigen and type II restriction/modification system. The results indicated that SSH is successful in identifying genetic differences and virulence genes among different strains of A. hydrophila.  (+info)

(6/265) A major secreted elastase is essential for pathogenicity of Aeromonas hydrophila.

Aeromonas hydrophila is an opportunistic pathogen and the leading cause of fatal hemorrhagic septicemia in rainbow trout. A gene encoding an elastolytic activity, ahyB, was cloned from Aeromonas hydrophila AG2 into pUC18 and expressed in Escherichia coli and in the nonproteolytic species Aeromonas salmonicida subsp. masoucida. Nucleotide sequence analysis of the ahyB gene revealed an open reading frame of 1,764 nucleotides with coding capacity for a 588-amino-acid protein with a molecular weight of 62,728. The first 13 N-terminal amino acids of the purified protease completely match those deduced from DNA sequence starting at AAG (Lys-184). This finding indicated that AhyB is synthesized as a preproprotein with a 19-amino-acid signal peptide, a 164-amino-acid N-terminal propeptide, and a 405-amino-acid intermediate which is further processed into a mature protease and a C-terminal propeptide. The protease hydrolyzed casein and elastin and showed a high sequence similarity to other metalloproteases, especially with the mature form of the Pseudomonas aeruginosa elastase (52% identity), Helicobacter pylori zinc metalloprotease (61% identity), or proteases from several species of Vibrio (52 to 53% identity). The gene ahyB was insertionally inactivated, and the construct was used to create an isogenic ahyB mutant of A. hydrophila. These first reports of a defined mutation in an extracellular protease of A. hydrophila demonstrate an important role in pathogenesis.  (+info)

(7/265) Microbial iron transport via a siderophore shuttle: a membrane ion transport paradigm.

A mechanism of ion transport across membranes is reported. Microbial transport of Fe(3+) generally delivers iron, a growth-limiting nutrient, to cells via highly specific siderophore-mediated transport systems. In contrast, iron transport in the fresh water bacterium Aeromonas hydrophila is found to occur by means of an indiscriminant siderophore transport system composed of a single multifunctional receptor. It is shown that (i) the siderophore and Fe(3+) enter the bacterium together, (ii) a ligand exchange step occurs in the course of the transport, and (iii) a redox process is not involved in iron exchange. To the best of our knowledge, there have been no other reports of a ligand exchange mechanism in bacterial iron transport. The ligand exchange step occurs at the cell surface and involves the exchange of iron from a ferric siderophore to an iron-free siderophore already bound to the receptor. This ligand exchange mechanism is also found in Escherichia coli and seems likely to be widely distributed among microorganisms.  (+info)

(8/265) Prevalence of enterotoxin genes in Aeromonas spp. isolated from children with diarrhea, healthy controls, and the environment.

Aeromonads are causative agents of a number of human infections. Even though aeromonads have been isolated from patients suffering from diarrhea, their etiological role in gastroenteritis is unclear. In spite of a number of virulence factors produced by Aeromonas species, their association with diarrhea has not been clearly linked. Recently, we have characterized a heat-labile cytotonic enterotoxin (Alt), a heat-stable cytotonic enterotoxin (Ast), and a cytotoxic enterotoxin (Act) from a diarrheal isolate of Aeromonas hydrophila. Alt and Ast are novel enterotoxins which are not related to cholera toxin; Act is aerolysin related and has hemolytic, cytotoxic, and enterotoxic activities. We studied the distribution of the alt, ast, and act enterotoxin genes in 115 of 125 aeromonads isolated from 1, 735 children with diarrhea, in all 27 aeromonads isolated from 830 control children (P = 7 x 10(-4) for comparison of rates of isolation of aeromonads from cases versus those from controls), and in 120 randomly selected aeromonads from different components of surface water in Bangladesh. Aeromonas isolates which were positive only for the presence of the alt gene had similar distributions in the three sources; the number of isolates positive only for the presence of the ast gene was significantly higher for the environmental samples than for samples from diarrheal children; and isolates positive only for the presence of the act gene were not found in any of the three sources. Importantly, the number of isolates positive for both the alt and ast genes was significantly higher for diarrheal children than for control children and the environment. Thus, this is the first study to indicate that the products of both the alt and ast genes may synergistically act to induce severe diarrhea. In 26 patients, Aeromonas spp. were isolated as the sole enteropathogen. Analysis of clinical data from 11 of these patients suggested that isolates positive for both the alt and ast genes were associated with watery diarrhea but that isolates positive only for the alt gene were associated with loose stools. Most of the isolates from the three sources could be classified into seven phenospecies and eight hybridization groups. For the first time, Aeromonas eucrenophila was isolated from two children, one with diarrhea and another without diarrhea.  (+info)

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10

• 1
• 2