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PubMed1995

Cloning, sequence and regulation of expression of the lexA gene of Aeromonas hydrophila.

The lexA gene of Aeromonas hydrophila (Ah) has been isolated by using a specific one-step cloning system. The Ah LexA repressor is able to block Escherichia coli (Ec) SOS gene expression and is likely to be cleaved by the activated RecA protein of this bacterial species after DNA damage. Ah lexA would encode a protein of 207 amino acids (aa), which is 75% identical to the LexA repressor of Ec. Two Ec-like SOS boxes have been located upstream from Ah lexA, the distance between them being 4 bp, whereas this same distance in Ec lexA is 5 bp. The structure and sequence of the DNA-binding domain of the LexA repressor of Ec, as well as the region at which its hydrolysis occurs, are highly conserved in Ah LexA. Moreover, a residue of the region implicated in the specific cleavage reaction, and which is present in all known RecA-cleavable repressors, is changed in the Ah LexA. Expression of Ah lexA is DNA-damage inducible in both the Ah and Ec genetic backgrounds to the same extent. In contrast, Ec lexA is poorly induced in DNA-injured Ah cells.

Aeromonas hydrophila↗
PubMed1995

Amino-acid residues involved in biological functions of the cytolytic enterotoxin from Aeromonas hydrophila.

Some amino acid (aa) residues within the cytolytic enterotoxin (Act) of Aeromonas hydrophila essential for biological activity were identified. Act is a 52-kDa polypeptide, possessing hemolytic, cytotoxic and enterotoxic activities. By deletion analysis, generation of anti-peptide Ab, and site-directed mutagenesis we showed that two regions in Act (aa 245-274 and 361-405) were very important for biological functions. As shown by competitive inhibition assays, peptide 2 (aa 245-274) blocked cytotoxic activity of Act, and aa Tyr256, Trp270 and Gly274 were essential for cytotoxicity. Within peptide 3 (aa 361-405), Trp394 and Trp396 were important for biological activities. Mutations in other regions of the toxin (e.g., Gly169, Asp170, Gly171, Trp172, Asn177,178, Asp179 and His144,209,355) also decreased biological activity. The reactivity of these mutant toxins with Ab in immunoblots was not altered. Data reported in this study suggested the role of some aa residues in biological function(s) of Act.

Aeromonas hydrophila↗
PubMed1995

Cloning and study of the genetic organization of the exe gene cluster of Aeromonas salmonicida.

The Aeromonas salmonicida (As) exe gene cluster, an additional member of the pul-related operon family required for general signal-sequence-dependent secretion of proteins from Gram- bacteria, was cloned in the broad-host-range cosmid pLAFR3. Twelve genes, exeC-N, were identified by partial nucleotide (nt) sequence analyses (exeE-N) or determination of the complete sequence (exeC and exeD). The organisation of the exeC-N genes is similar to that of several other operons of this family. These genes are arranged contiguously and are apparently transcribed in the same direction. On alignment of As and A. hydrophila exe sequences a 73-bp 'silent' deletion was identified close to the end of the As exeF gene. No gene encoding prepilin peptidase (the PulO homolog) was detected in this region. The exeN gene is evidently the last gene of this operon; it is followed by an ORF encoding a putative transcription regulator.

Aeromonas↗
PubMed1996

An Aeromonas salmonicida gene required for the establishment of infection in rainbow trout (Oncorhynchus mykiss).

The asoB gene of Aeromonas salmonicida is located approximately 9 kb downstream of the structural gene (vapA) for the surface layer (A-layer). The nucleotide sequence of asoB was determined and found to encode a putative polytopic cytoplasmic membrane protein which exhibited homology to a number of bacterial transport proteins. Allele exchange mutagenesis of asoB resulted in a mutant (A449-D) which was avirulent when administered by bath immersion. However, when administered by intraperitoneal injection, A449-D is as lethal as wild type. Characterization of the phenotype of A449-D showed that there were pleiotropic effects on VapA secretion, haemolysis and outer membrane protein composition. Mobilization of cloned asoB on a broad-host-range plasmid into A449-D resulted in the complementation of VapA translocation, haemolytic activity and virulence.

Aeromonas↗
PubMed1996

Cloning, characterization and expression of the recA gene of Aeromonas salmonicida.

The Aeromonas salmonicida A449 recA gene has been cloned, sequenced and expressed in vitro. The predicted amino acid sequence of A. salmonicida RecA was determined and, when compared to other RecA, was found to possess a number of domains identical to those characterized in Escherichia coli RecA. The A. salmonicida recA was mobilized into an E. coli recA mutant strain and was shown to allow increased survival in the presence of the chemical mutagen MMS and after ultraviolet (UV) irradiation. The A. salmonicida recA also possesses a potential regulatory SOS box in the DNA 5' of the gene. The rate of A. salmonicida-mediated recombination in E. coli was increased by exposure to UV light, which suggests that SOS induction in A. salmonicida parallels that of E. coli.

Aeromonas↗
PubMed1996

Application of a modified disc diffusion technique to antimicrobial susceptibility testing of Vibrio anguillarum and Aeromonas salmonicida clinical isolates.

Two techniques for antimicrobial susceptibility testing of Vibrio anguillarum and Aeromonas salmonicida strains were compared. The first method was the reference test that determines Minimal Inhibitory Concentrations (MIC); the second was a modified diffusion test that measures the Inhibitory Concentrations in Diffusion (ICD) by carrying out the diffusion test with five discs of differing contents. ICD measurement was not applicable for the susceptibility testing of oxytetracycline and sulfadimethoxine. On the other hand, a good correlation between the MICs and the ICDs was observed for oxolinic acid, sarafloxacin, chloramphenicol and trimethoprim. Moreover, the ICD values were close to those obtained for the MIC values. A. salmonicida resistant strains were detected by ICD determination. Thus, ICD could be used instead of MIC for oxolinic acid, sarafloxacin, trimethoprim and chloramphenicol susceptibility testings. The ICD technique is easy to carry out and is not dependent on the growth characteristics of bacteria.

Aeromonas↗
PubMed1987

Does Aeromonas hydrophila preferentially colonize the bowels of patients with hematologic malignancies?

Weekly cultures of stools from neutropenic patients and bone marrow transplant recipients yielded Aeromonas hydrophila from 8% of 88 patients over a 2-yr period. During this time stools in the routine enteric laboratory yielded A. hydrophila in 0.24% of 1632 patients. Although the patient groups and culture methods were not directly comparable, this significant difference in isolation rate (p less than 0.001) may reflect a higher colonization rate in the immunocompromised patient.

Adult↗
PubMed1988

Enzymatic characterization of three aeromonas species using API Peptidase, API "Osidase," and API Esterase test kits.

An enzymatic characterization of 16 strains of Aeromonas species including A. hydrophila (7), A. sobria (5), and A. caviae (4) was carried out using API Peptidase (strips numbered 1, 2, 3, 4, 5, and 6); API Esterase and API "Osidase" test strips. A total of 89 substrates was used in the assay and included 59 arylamides (aminopeptides), 10 esters, and 20 carbohydrates. All three species were remarkably uniform in their reactivities. Nineteen (32%) of the arylamide substrates used were hydrolyzed by all three species. Very strong arylamidase activity was displayed by all three species for L-lysine, L-hydroxyproline, L-arginine, L-alanine, L-proline, and L-leucyl-L-alanine. Esterase activity was strongest against caproate (C6), caprylate (C8), nonanoate (C9), and caprate (C10) substrates. Only a limited number of carbohydrate substrates were hydrolyzed; strong N-acetyl-beta-D-glucosaminidase activity was given by all strains. Both A. hydrophila and A. caviae gave strong beta-D-glucosidase reactivities, while A. sobria appeared to be negative for this enzyme. The results of our preliminary study show that some of the enzymes examined may be useful in the identification and differentiation of these species. The API enzyme assays yielded rapid (4 hr) results. The assays were easy to perform, relatively inexpensive and reproducible. The importance of replicate testing and the inclusion of uninoculated (buffer only) controls as part of the assay is emphasized.

Aeromonas↗
PubMedDate not supplied

Lomefloxacin (SC 47111 or NY-198), a new difluorinated quinolone: comparison of the in vitro activity with other broad spectrum antimicrobials against Enterobacteriaceae, Acinetobacter spp, Aeromonas spp, and Pseudomonas aeruginosa.

Using a broth microdilution method, we compared the in vitro activity of lomefloxacin to other broad spectrum antimicrobials against clinical strains of Enterobacteriaceae, Acinetobacter spp, Aeromonas spp, and P. aeruginosa. Against the Enterobacteriaceae and A. hydrophila, lomefloxacin showed excellent activity with MIC50 values ranging from 0.12-0.5 micrograms/ml and MIC90 values ranging from 0.12-1.0 micrograms/ml. By comparison, lomefloxacin had superior activity to nalidixic acid and difloxacin, comparable activity to norfloxacin and fleroxacin, and slightly less activity than ciprofloxacin. Lomefloxacin was also more active than imipenem, ceftazidime, aztreonam, ticarcillin/clavulanic acid (T-CA), and gentamicin. Lomefloxacin was less active (MIC90, 4 micrograms/ml) against Acinetobacter strains than Enterobacteriaceae strains. Against these same Acinetobacter strains, lomefloxacin was 8- to 64-fold more active than ceftazidime, aztreonam, T-CA, and gentamicin but slightly less active than imipenem. Lomefloxacin was 2- to 8-fold more active than fleroxacin, difloxacin, and nalidixic acid against strains of P. aeruginosa. However, lomefloxacin was less active than ciprofloxacin and norfloxacin. Lomefloxacin had comparable activity to imipenem but was 2- to 16-fold more active than ceftazidime, aztreonam, T-CA, and gentamicin. Thus, lomefloxacin demonstrated comparable activity to other fluorinated quinolones in that it possesses high active against clinical strains of Enterobacteriaceae and had good-to-moderate activity against most strains of Acinetobacter and P. aeruginosa.

4-Quinolones↗
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↗
PubMed1991

Surface-disorganized, attenuated mutants of Aeromonas salmonicida as furunculosis live vaccines.

A slow-growing, aminoglycoside-resistant mutant and a rapidly-growing pseudo-revertant were isolated from Aeromonas salmonicida, the causative agent of salmonid furunculosis. These mutants continued to elicit a variety of classical virulence factors associated with A. salmonicida pathogenesis. They differed morphologically from the wild-type and from one another with respect to A-layer organization, membrane antagonist sensitivity and particularly to aerobic metabolism. Both mutants were drastically altered in the architecture of the 2D crystalline surface array (A-layer), although both were similar to wild-type with respect to cell surface composition. The slow-growing, antibiotic-resistant mutant differed significantly from the wild-type by the apparent loss of virtually all aerobic metabolism; the pseudo-revertant had partially recovered the ability to aerobically metabolize certain carbon sources. Both mutants were avirulent and incapable of tissue persistence. The rapidly-growing, antibiotic-sensitive pseudo-revertant, when administered either intraperitoneally or by immersion, effectively protected salmonid fish from challenge by a heterologous virulent stain suggesting its candidature as a live, attenuated furunculosis vaccine.

Aeromonas↗
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

Nucleotide sequence and expression of an extracellular hemolysin gene of Aeromonas hydrophila.

The extracellular hemolysin (AHH1) gene of Aeromonas hydrophila ATCC7966 was cloned into Charomid9-28 in Escherichia coli DH1, and its complete nucleotide sequence determined. Escherichia coli carrying this gene expressed an extracellular heat-labile hemolysin for rabbit red blood cells. The minimum size of the coding region of the 2.6 kilobase-pair BamHI-SphI fragment was subcloned into pUC118 and pUC119, selecting for hemolytic activity. The nucleotide sequence of this region contained a single open reading frame of 1734 base pairs, corresponding to a protein of 577 amino acid residues (63,658 daltons). A consensus promoter sequence was present upstream of the AHH1 open reading frame. Maxicell analysis of [35S]methionine-labelled proteins in E. coli CSR603 carrying the AHH1 plasmid suggested that AHH1 gene codes for an approximately 60,000 dalton polypeptide. By colony DNA-DNA hybridization analysis, the AHH1 gene was detected in 43 of 62 hemolysin-producing strains of A. hydrophila (isolated from various sources and areas) and in all 43 hemolysin-producing strains of A. salmonicida (isolated from fish). Three hemolysin-negative strains of A. hydrophila did not react with the AHH1 probe, whereas three non-hemolytic A. salmonicida strains hybridized with the probe.

Aeromonas hydrophila↗
PubMed1991

Characterization of classic and atypical serogroup O:11 Aeromonas: evidence that the surface array protein is not directly involved in mouse pathogenicity.

A number of different techniques were used to analyse classic and atypical serogroup O:11 Aeromonas isolates. Five of seven atypical O:11, S layer-negative strains lacking a homogeneous LPS side-chain pattern exhibited varying degrees of mouse pathogenecity. One virulent atypical strain (AH-77) synthesized a surface array protein (SAP) but was unable to anchor it to the cell surface in an intact form, presumably due to a defect in its LPS architecture. Proteinase K digestion to remove the SAP, or growth at elevated temperatures (42 degrees C) to reduce the proportion of SAP synthesized from classic O:11 S layer-positive strains, did not alter their LD50 values in outbred mice. In addition, a spontaneous mutant, AS-180-1, that was S layer-negative was as virulent as the parental S layer-positive strain in the mouse model. These results suggest neither the SAP nor the characteristic serogroup O:11 homogeneous LPS side-chain pattern are directly involved in mouse pathogenicity.

Aeromonas↗
PubMed1992

Purification and characterisation of an extracellular metalloprotease, serine protease and haemolysin of Aeromonas hydrophila strain B32: all are lethal for fish.

Three different lethal (for rainbow trout, Salmo gairdneri) extracellular toxins were purified by HPLC from the culture supernatants of Aeromonas hydrophila strain B32 which had been isolated from rainbow trout. A metalloprotease, MW 38 kDa, was stable at 56 degrees C for 10 min, had no cytotoxic activity and and LD50 of 150 ng/g fish. In narrow range isoelectric-focusing (IEF) the enzyme had 11 isomers with (pls) between 4.12 and 4.8. A serine protease (22 kDa) was stable at 56 degrees C for 10 min, possessed cytotoxic activity and had an LD50 of 150 ng/g fish. In IEF, multiple isomers possessed pls between 4.5-5.2. The haemolysin had alpha-haemolytic activity (68 kDa) multiple isomers in IEF with pl range 4.5-5.1 and an LD50 of 2 micrograms/g fish. It was stable after heating to 56 degrees C for 20 min, 60 degrees C for 10 min and possessed esterase activity on beta-naphthyl acetate. These latter properties suggest it may be a novel haemolysin distinct from alpha- and beta-haemolysin.

Acetylcholinesterase↗
PubMed1988

Three-dimensional structure of the crystalline surface layer from Aeromonas hydrophila.

The three-dimensional (3D) structure of the crystalline surface layer of Aeromonas hydrophila has been determined to a resolution of 1.3 nm by crystallographic electron microscopy. The S-layer has tetragonal symmetry, with a unit cell dimension of 12.0 nm and a thickness of 5.6 nm. The 3D reconstruction reveals a distinct domain structure, with one main protein mass at one of the fourfold symmetry axes and a minor part at the other.

Aeromonas↗
PubMed1990

Identification of the cell surface receptor for bacteriophage 18 from Aeromonas hydrophila.

Bacteriophage 18 was previously isolated by multiplication in Aeromonas hydrophila. The bacteriophage receptor was shown to be the lipopolysaccharide (LPS), specifically the low MW polysaccharide fraction (LPS core oligosaccharide) A. hydrophila mutants, resistant to this phage were isolated and found to be devoid of LPS O antigen by several criteria and had alterations in the lipopolysaccharide core.

Aeromonas↗
PubMedDate not supplied

Novel structural patterns in divalent cation-depleted surface layers of Aeromonas salmonicida.

The fish pathogen Aeromonas salmonicida possesses a regular surface layer (or A-layer) which is an important virulence determinant. The A-protein, a single bilobed protein organized in a p4 lattice of M4C4 arrangement with two morphological domains, comprises this layer. The role of divalent cations in the A-layer structure was studied to better understand A-protein subunit interactions affecting structural flexibility and function. Divalent cation bridges were found to be involved in the integrity of the A-layer. Two novel A-layer patterns were formed as the result of growth under calcium limitation or by chelation of divalent cations with EDTA or EGTA, thereby constituting the first reported case of formation of distinct regular arrays upon divalent cation depletion. Furthermore, under these conditions A-protein was sometimes released as tetrameric units, rather than in monomeric form. The formation of the two novel patterns is best explained by a sequence of structural rearrangements, following disruption of only one of the two A-layer morphological units, that is, those held together by divalent cation bridges. The free tetrameric units represent four A-protein subunits clustered around the unaffected four-fold axis.

Aeromonas↗