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PubMed1990

Aeromonas in adult diarrhea: an enteropathogen or an innocent bystander?

This is a study from a district hospital in Israel serving a population of 250,000. During 1986-1987, 1,005 stool specimens were cultured from 932 adult inpatients with acute diarrhea. Seventeen yielded Aeromonas species. Of the 12 strains phenotyped, 10 qualified as enteropathogenic. Five hundred stool specimens from asymptomatic control subjects, inhabitants of the same region, were negative for Aeromonas. The finding of Aeromonas as the apparently sole pathogen in acute adult diarrhea in a geographical area with a negligible asymptomatic carriage rate lends support to the possibility that Aeromonas is an enteropathogen in adults.

Adolescent↗
PubMed1978

Snake-to-human transmission of Aeromonas (Pl) shigelloides resulting in gastroenteritis.

A healthy young man developed acute gastroenteritis after handling an infected bao constrictor. The animal died after contracting "mouth-rot disease", a progressive ulcerative stomatitis of snakes charactistically caused a Aeromonas species. Stool cultures from the patient yielded a heavy growth of Aeromonas (Plesiomonas) shigelloides but no other enteric pathogens. Treatment wit sulfamethoxazole-trimethoprim resulted in rapid relief of clinical symptoms. Aeromonas species are not considered part of the normal human fecal flora and gastroenteritis due to this organism is rare. Furthermore, this case appears to represent a new zoonosis: human Aeromonas (Plasiomonas) gastroenteritis derived from contact with an infected animal host.

Acute Disease↗
PubMed1992

Phylogenetic interrelationships of members of the genera Aeromonas and Plesiomonas as determined by 16S ribosomal DNA sequencing: lack of congruence with results of DNA-DNA hybridizations.

The phylogenetic interrelationships of members of the genera Aeromonas and Plesiomonas were investigated by using small-subunit ribosomal DNA (rDNA) sequencing. Members of the genus Aeromonas formed a distinct line within the gamma subclass of the Proteobacteria. Plesiomonas shigelloides also clustered within the confines of the gamma subclass of the Proteobacteria but exhibited a closer association with members of the family Enterobacteriaceae than with members of the family Aeromonadaceae. Species of the genus Aeromonas exhibited very high levels of overall sequence similarity (ca. 98 to 100%) with each other. Several of the relationships derived from an analysis of the rDNA sequence data were in marked disagreement with the results of chromosomal DNA-DNA pairing experiments. Diagnostic rDNA signatures that have possible value for differentiating most Aeromonas species were discerned.

Aeromonas↗
PubMed1995

Aeromonas encheleia sp. nov., isolated from European eels.

Four strains isolated from European eels in Valencia, Spain, were found to constitute a DNA relatedness group which is 0 to 50% related to the 13 species and DNA group 11 of the genus Aeromonas. Phenotypically, these strains have all of the properties that define the genus Aeromonas. However, they differ from the previously described Aeromonas species by three or more properties. The strains are positive for motility, growth at 37 degrees C, indole production, and arginine dihydrolase activity. They exhibit negative reactions in tests for growth at 42 degrees C and in thiosulfate-citrate-bile salts-sucrose medium (Oxoid), Simmons citrate tests, and tests for lysine and ornithine decarboxylase activities. They produce acid from salicin but not from L-arabinose, D-cellobiose, or lactose. All four strains hydrolyze esculin and arbutin but not elastin. They use L-serine as a sole carbon and energy source but cannot utilize L-arabinose, L-arginine, D-gluconate, or L-glutamine. The strains are resistant to ampicillin. The guanine-plus-cytosine content of the DNA is 59.4 to 60.8 mol%. The name Aeromonas encheleia sp. nov. is proposed for these strains; strain S181 (= CECT 4342) is the type strain. This new species is generally not pathogenic for eels or mice.

Aeromonas↗
PubMed2000

Production of an enterotoxin by a gastro-enteritis-associated Aeromonas strain.

The potential of motile Aeromonas species to cause human gastrointestinal infections has been recognised recently. Considerable worldwide epidemiological, microbiological and clinical investigations have shown that some strains of the different motile aeromonads are of increasing enteropathogenic significance, especially in children, the elderly and in immunocompromised individuals. Some of the diarrhoeal symptoms of Aeromonas-associated gastro-enteritis have been attributed to enterotoxins. In this study, 15 Aeromonas isolates from clinical and non-clinical sources, representing the three motile aeromonads commonly associated with gastro-enteritis (A. caviae, A. hydrophila and A. veronii biovar sobria), were tested for their ability to cause fluid accumulation in infant mice by the suckling mouse technique. Eight isolates were found to produce enterotoxin. Of these, an A. veronii biovar sobria strain (AS15), isolated from lamb kidney, was found to produce the highest enterotoxin score. An enterotoxin of c. 40 kDa produced by A. veronii biovar sobria AS15 was purified by Sephacryl S-100 gel filtration and high-performance liquid chromatography. This enterotoxin caused marked fluid accumulation in infant mice by the suckling mouse technique. The purified enterotoxin cross-reacted with cholera toxin antibodies and was readily inactivated by heating at 56 degrees C for 10 min. The production of a 'cholera-like' enterotoxin by Aeromonas isolates from samples of animal origin suggests that these organisms could be of public health significance in food products.

Aeromonas↗
PubMed1986

Comparison of direct plating with the use of enrichment culture for isolation of Aeromonas spp. from faeces.

Direct plating of faecal specimens on blood agar was compared with the use of enrichment culture for isolation of Aeromonas spp. from faeces during a large epidemiological study. Of enterotoxigenic strains isolated by direct plating, 89% were associated with acute diarrhoea and 7% with an episode of diarrhoea during the month before collection, but 79% of enterotoxigenic strains isolated only after enrichment were not associated with acute diarrhoea. With Aeromonas spp., as with intestinal pathogens, it appears that enrichment allows isolation of the bacteria when in low faecal concentrations likely to be found in convalescent patients, carriers and those with subclinical infection. The routine use of enrichment for isolation of faecal aeromonads, by detecting Aeromonas spp. in low numbers in patients without diarrhoea, is likely to confuse interpretation of epidemiological studies seeking to clarify the relationship between Aeromonas spp. and acute diarrhoea.

Aeromonas↗
PubMed1992

A 15-year study of the role of Aeromonas spp. in gastroenteritis in hospitalised children.

During a 15-year period, 146 strains of Aeromonas spp. were isolated from 32810 faecal specimens from 13,820 hospitalised patients up to 13 years of age. These isolates constituted 4% of all the pathogenic bacterial strains cultured. For the years 1978-1988, the files of children with gastro-enteritis revealed 81 whose faeces yielded Aeromonas spp. Most of them (94%) were < 3 years of age, 78% < 1 year old. The peak incidence was at 2-6 months, involving severe morbidity including dehydration and vomiting with acidaemia and azotaemia; the mean duration of illness and length of hospitalisation at this age were longer than at other ages. Bloody diarrhoea was found in 7% of the children. Almost all the strains of Aeromonas were resistant to ampicillin. We conclude that Aeromonas spp. are of aetiological significance in gastro-enteritis in small children; culture for this pathogen should be routine in the bacteriological examination of faeces.

Aeromonas↗
PubMed1994

Adhesion to and invasion of human colon carcinoma Caco-2 cells by Aeromonas strains.

The enteropathogenicity of Aeromonas strains that showed mannose-resistant adhesion to INT407 cells was evaluated by infecting Caco-2 cells and observing them by light and electronmicroscopy. Five of six strains adhered in large numbers to Caco-2 cells in the presence of mannose and caused cytopathic effects. Two strains of Aeromonas spp. seemed to invade Caco-2 cells, as membrane-bound bacteria were seen within the cytoplasm of these cells; however, staining by acridine orange-crystal violet appeared to show intracellular fluorescent bacteria in three strains. Fimbriae did not appear to play an important role in adhesion because fimbrial structures were not seen by transmission electronmicroscopy. Adhesion of four strains was inhibited by the addition of L-fucose. The strains were negative in the fluorescence actin staining test, which in enteropathogenic Escherichia coli strains correlates with the ability to attach and efface intestinal microvilli. The DNA of the Aeromonas strains did not hybridise with the E. coli eae and ipaB probes, associated with attaching and effacing ability and invasion, respectively. These results give support to the enteropathogenicity of adhesive strains of Aeromonas spp., although the mechanisms of adhesion, and possibly invasion, remain to be elucidated.

Acridine Orange↗
PubMed2003

Phylogenetic analysis of members of the genus Aeromonas based on gyrB gene sequences.

The phylogenetic relationships of all known species of the genus Aeromonas were investigated by using the sequence of gyrB, a gene that encodes the B-subunit of DNA gyrase. Nucleotide sequences of gyrB were determined from 53 Aeromonas strains, including some new isolates, which were also characterized by analysis of the 16S rDNA variable regions. The results support the recognition of the family Aeromonadaceae, as distinct from Plesiomonas shigelloides and other enteric bacteria. This phylogenetic marker revealed strain groupings that are consistent with the taxonomic organization of all Aeromonas species described to date. In particular, gyrB results agreed with 16S rDNA analysis; moreover, the former showed a higher capacity to differentiate between species. The present analysis was useful for the elucidation of reported discrepancies between different DNA-DNA hybridization sets. Additionally, due to the sequence diversity found at the intraspecies level, gyrB is proposed as a useful target for simultaneous identification of species and strains. In conclusion, the gyrB gene has proved to be an excellent molecular chronometer for phylogenetic studies of the genus Aeromonas.

Aeromonas↗
PubMed2003

Taxonomic study of sucrose-positive Aeromonas jandaei-like isolates from faeces, water and eels: emendation of A. jandaei Carnahan et al. 1992.

Fourteen sucrose-positive Aeromonas jandaei-like isolates from fresh water and reared European eels were subjected to a polyphasic study to determine their taxonomic position. Numerical taxonomy was used to analyse phenotypic data obtained for these isolates and 43 type and reference strains representative of recognized Aeromonas species. The A. jandaei cluster (phenon 1) was defined at 81.6 % similarity (S(J)); this included the A. jandaei-like isolates, the sucrose-positive strain Aeromonas veronii biogroup sobria CECT 4910 and nearly all A. jandaei reference strains used in the study. Four other reference strains of A. veronii biogroup sobria and the type strain of Aeromonas ichthiosmia were peripheral to the A. jandaei cluster. The supra-group 'A. jandaei-A.veronii biogroup sobria-A. ichthiosmia' was linked at 80.7 % similarity (S(J)) and was clearly segregated from the phenotypic core of the A. veronii biogroup sobria species, which was related to the reference strain Popoff 224 (CECT 4835). DNA relatedness between strains grouped in the A. jandaei cluster (phenon 1) and A. jandaei CECT 4228(T) ranged from 70 to 100 %, but was below 50 % when DNAs from A. veronii biogroup sobria CECT 4835, A. veronii biogroup veronii CECT 4257(T) and A. ichthiosmia CECT 4486(T) were used. In addition, DNA relatedness between peripheral A. veronii biogroup sobria strains and the species A. jandaei (CECT 4228(T)), A. veronii (CECT 4257(T), CECT 4835) and A. ichthiosmia (CECT 4486(T)) was always below 54 %, as it was between the species A. ichthiosmia (CECT 4486(T)) and A. veronii (CECT 4257(T), CECT 4835). Emendation of A. jandaei is proposed; this taxon now includes sucrose-positive clinical and environmental strains as well as environmental isolates that are pathogenic for fish and humans. Other new traits for this species are the ability to grow at 4-42 degrees C, acid production from glycerol but not from lactose, D-melibiose or D-raffinose, the use of D-gluconate, L-glutamate or L-proline but not L-lactate, L-alanine, L-arabinose or L-arginine, hydrolytic activity against casein, elastin, starch and lecithin and the inability to lyse arbutin. The DNA G+C content of A. jandaei is also reported for the first time; it ranges from 58.1 to 61.1 mol%. On the other hand, the DNA relatedness data support the classification of peripheral reference strains of A. veronii biogroup sobria outside this taxon, indicating that biogroup sobria requires further revision.

Aeromonas↗
PubMed2006

Genetic relationships of Aeromonas strains inferred from 16S rRNA, gyrB and rpoB gene sequences.

Genetic relationships among bacterial strains belonging to the genus Aeromonas were inferred from 16S rRNA, gyrB and rpoB gene sequences. Twenty-eight type or collection strains of the recognized species or subspecies and 33 Aeromonas strains isolated from human and animal specimens as well as from environmental samples were included in the study. As reported previously, the 16S rRNA gene sequence is highly conserved within the genus Aeromonas, having only limited resolution for this very tight group of species. Analysis of a 1.1 kb gyrB sequence confirmed that this gene has high resolving power, with maximal interspecies divergence of 15.2 %. Similar results were obtained by sequencing only 517 bp of the rpoB gene, which showed maximal interspecies divergence of 13 %. The topologies of the gyrB- and rpoB-derived trees were similar. The results confirm the close relationship of species within the genus Aeromonas and show that a phylogenetic approach including several genes is suitable for improving the complicated taxonomy of the genus.

Aeromonas↗
PubMed2004

Distribution of six virulence factors in Aeromonas species isolated from US drinking water utilities: a PCR identification.

AIMS: To examine whether Aeromonas bacteria isolated from municipally treated water had virulence factor genes. METHODS AND RESULTS: A polymerase chain reaction-based genetic characterization determined the presence of six virulence factors genes, elastase (ahyB), lipase (pla/lip/lipH3/alp-1) flagella A and B (flaA and flaB), the enterotoxins, act, alt and ast, in these isolates. New primer sets were designed for all the target genes, except for act. The genes were present in 88% (ahyB), 88% (lip), 59% (fla), 43% (alt), 70% (act) and 30% (ast) of the strains, respectively. Of the 205 isolates tested only one isolate had all the virulence genes. There was a variety of combinations of virulence factors within different strains of the same species. However, a dominant strain having the same set of virulence factors, was usually isolated from any given tap in different rounds of sampling from a single tap. CONCLUSIONS: These results show that Aeromonas bacteria found in drinking water possess a wide variety of virulence-related genes and suggest the importance of examining as many isolates as possible in order to better understand the health risk these bacteria may present. SIGNIFICANCE AND IMPACT OF THE STUDY: This study presents a rapid method for characterizing the virulence factors of Aeromonas bacteria and suggests that municipally treated drinking water is a source of potentially pathogenic Aeromonas bacteria.

Aeromonas↗
PubMed1997

Aeromonas sobria endophthalmitis.

BACKGROUND: Aeromonas sobria causes a rare Gram-negative bacterial water-borne infection. It has been found in waters of North Queensland and South-east Asia. Of all Aeromonas species, A. sobria is the most virulent and invasive and has been reported to cause soft tissue infection and corneal ulcer. METHODS: A 14-year-old Caucasian male from North Queensland presented following a penetrating eye injury in which a water bird (cormorant species) had pecked his eye while he was fishing. A fulminant endophthalmitis developed despite treatment with intravenous, intravitreal and topical antibiotics and initial wound repair. Enucleation was performed. RESULTS: Aeromonas sobria was isolated from the vitreous aspirate. CONCLUSION: Aeromonas sobria infection should be suspected in water-contaminated penetrating eye injuries. The prognosis in this case was poor.

Adolescent↗
PubMed1997

Plasmids and Aeromonas virulence.

Most putative virulence determinants of Aeromonas species are chromosomally encoded. However, several recent reports have indicated that some may be carried on or regulated by plasmids. Therefore, we examined the plasmid carriage rate of a total of 140 clinical and environmental Aeromonas isolates. Plasmid carriage was compared with the ability of an isolate to produce toxins and adhere to HEp-2 cells. Overall, plasmid incidence in Aeromonas species was low (23/140, 16%) and independent of the source of the isolate. Plasmids were, however, more common in environmental isolates of A. veronii biovar sobria than in clinical isolates of this species (P < 0.05). We could find no evidence to support the recent literature findings that plasmids may have a role in Aeromonas virulence.

Aeromonas↗
PubMed1996

Study of the intergenic exeF-exeG region and its application as a simple preliminary test for Aeromonas spp.

The exeF-exeG intergenic regions from different hybridization groups (HG) of Aeromonas were studied by PCR amplification using a single pair of primers. Six main classes of PCR products were identified according to size: 360 bp, 320 bp, 280 bp, 230-240 bp, 220 bp and 160 bp. Direct sequencing of the PCR products indicated that the shorter intergenic regions had probably originated from deletion of DNA segments between direct repeats. Correlation of certain PCR products with Aeromonas caviae (HG4), A. caviae (HG5), A. veronii (HG8) and A. salmonicida (HG3) was revealed. The PCR reaction was also shown to be generally specific for Aeromonas spp. Thus, the usefulness of this rapid, single colony-based PCR test for both identification and preliminary differentiation of Aeromonas spp. is demonstrated.

Aeromonas↗
PubMed1997

The synthesis, secretion and role in virulence of the paracrystalline surface protein layers of Aeromonas salmonicida and A. hydrophila.

The S-layers of the Aeromonas spp. studied to date are composed of identical protein subunits which are translocated across the cytoplasmic membrane, periplasm and outer membrane to the cell surface, where they are assembled and tethered to the cell via an interaction with the O-polysaccharide side chains of the lipopolysaccharide. Aeromonas S-layers have the ability to bind a number of host factors such as fibronectin, laminin and vitronectin as well as providing resistance to serum killing and protease digestion. Aeromonas mutants unable to produce an S-layer are altered in their ability to cause disease. In the case of Aeromonas salmonicida, the loss of ability to produce an S-layer effectively abolishes virulence. However, in the case of A. hydrophila, the reduction in virulence caused by the loss of the S-layer is less significant.

Aeromonas hydrophila↗
PubMed1985

Comparative in vitro activities of selected antimicrobial agents against Aeromonas species and Plesiomonas shigelloides.

The in vitro antimicrobial susceptibilities of fecal isolates of Aeromonas caviae, Aeromonas hydrophila, Aeromonas sobria, and Plesiomonas shigelloides were tested by agar dilution. This in vitro study suggested that ciprofloxacin, enoxacin, norfloxacin, tetracycline, and trimethoprim-sulfamethoxazole might be effective oral agents for treatment of diarrhea involving Aeromonas spp. or P. shigelloides.

Aeromonas↗
PubMed1988

Beta-lactam resistance in Aeromonas spp. caused by inducible beta-lactamases active against penicillins, cephalosporins, and carbapenems.

Use of cefoperazone in a patient with Aeromonas caviae in the respiratory tract selected a mutant that constitutively produced beta-lactamase. This mutant, in contrast to its parental strain with an inducible beta-lactamase, showed enhanced resistance to newer cephalosporins and aztreonam. This observation suggested that species of Aeromonas, like those of other genera with inducible beta-lactamases, may pose therapeutic problems associated with the rapid development of multiple beta-lactam resistance. Thus, a study was designed to identify the beta-lactamases in 12 strains representing four species of Aeromonas and assess their role in drug resistance. Eleven strains possessed inducible beta-lactamases. One strain showed no detectable activity. An analysis of substrate and inhibitor profiles, isoelectric points, and beta-lactam susceptibility patterns revealed the presence of at least four distinguishable inducible beta-lactamases. These enzymes were involved in the resistance of strains within the genus to penicillins, cephalosporins, aztreonam, and imipenem but not cefoxitin. Unlike most other organisms with inducible beta-lactamases, all four strains of A. caviae, one of four strains of A. sobria, and one of three strains of A. hydrophila possessed two distinct inducible beta-lactamases. Furthermore, substrate and inhibitor profiles revealed that many of these Aeromonas beta-lactamases were distinct from inducible enzymes that have been characterized in other genera of gram-negative bacteria.

Aeromonas↗