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PubMed1993

Characterization of mesophilic Aeromonas from clinical specimens by computerized analysis of SDS-PAGE protein profiles and by enzymatic activity.

Mesophilic Aeromonas (Aeromonas hydrophila, Aeromonas sobria, Aeromonas caviae) have recently been considered important aetiological agents of human diseases, mainly gastrointestinal infections. Although several findings have pointed out the significance of this group of microorganisms as enteric pathogens and suggested the presence of virulence factors, epidemiological and clinical studies are limited by the difficulty of correctly identifying mesophilic Aeromonas at the species level. SDS-PAGE of radiolabelled total protein profiles and bacterial enzymatic activities were used to type 31 clinical isolates (6 A. hydrophila, 7 A. sobria and 18 A. caviae) from patients with gastroenteritis and from healthy controls. Analysis of SDS-PAGE protein patterns, reinforced by the UPGMA-grouping system (AMBIS software) provided a good characterization of A. caviae strains as a homogeneous group of microorganisms, possessing significant differences from the other two species of mesophilic Aeromonas, in good agreement with biochemical and enzymatic tests. Data obtained in analyzing A. sobria protein profiles clearly showed two groups, with a correlation coefficient (CC) = 0.70, which in our experience is a doubtful value for assigning two strains to the same species. Strains biochemically identified as A. hydrophila showed a CC = 0.64, which is equally not acceptable for species assignment. Inter-species comparison highlighted this heterogeneity, showing two mixed subgroups, both containing strains that were assigned to A. sobria and A. hydrophila species on the basis of biochemical features.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

The spectrum of Aeromonas-associated diarrhea in tropical Queensland, Australia.

During a twelve-month period (1 July 91-30 June 92), feces from 912 persons from the Townsville region in the dry tropics of Queensland, Australia were evaluated by culture and 45 (4.9%) immunocompetent patients were found to be carrying Aeromonas in their stools. All patients were index cases and no secondary cases from household or close contact of index cases were identified. Eight patients (9.3%) were from Palm Island, an Aboriginal community, and 37 (4.5%) were from the essentially Caucasian population of Townsville. This is a significant difference in incidence of cases between the two population groups. Infection occurred mainly in two age groups: the under five-year-old (27 cases) and the over 25-year-old age group (17 cases). Except for one patient, all cases of Palm Island Aborigines were children less than five years of age, and 13 of these infants (48%) were less than 1 year old, but none were neonates. Of the 37 Townsville patients, 20 cases (54%) were in the under five-year-old group. Signs and symptoms of Aeromonas-associated diarrhea in patients where Aeromonas was the sole pathogen isolated were diarrhea sometimes with vomiting, absence of fever and of fecal leukocytes and blood in the stools. No cases of Aeromonas-associated diarrhea with dysentery were encountered. After rotavirus (12.3%), Aeromonas was the second most common enteric pathogen detected, but was only marginally more common than Giardia and Salmonella. Of the aeromonad isolations, 50% were Aeromonas hydrophila, 22% were A. sobria, and 28% were A. caviae.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Abundance of Aeromonas spp. in river and lake waters in and around Dhaka, Bangladesh.

Aeromonas spp. are widely distributed in the aquatic environment. In Bangladesh, seasonal distribution of these organisms in aquatic environment was studied during July 1986-August 1987. Water, sediment, plant, and plankton samples were collected monthly from the Dhanmondi lake and the Buriganga river during the study period. Aeromonas spp. were isolated from all samples throughout the year. The seasonal peak of Aeromonas spp. was observed in warmer months (April-May) in the surface waters. In the sediment, the highest peak was observed in March and August. In most plants, the highest peak was observed during the winter months (December-February). In the plankton samples of the Dhanmondi lake and the Buriganga river, the highest counts were obtained in July and February respectively. In both the sampling sites, plants were observed to contain more Aeromonas than did the water and sediment samples. The prevalence of Aeromonas spp. throughout the year in aquatic environment suggests the autochthonous nature of these organisms and that there is an association of Aeromonas with the aquatic environment.

Aeromonas↗
PubMed1977

Aeromonas distribution and survival in a thermally altered lake.

Par Pond is a thermally enriched monomictic southeastern lake which receives heated effluent from a production nuclear reactor. Fish populations in the lake have lesions of epizooty from which Aeromonas spp. are readily isolated. Distribution and population densities of Aeromonas in the water column were measured along an oxygen and temperature gradient as well as seasonally. Greater population densities of Aeromonas occurred below the oxygen chemocline when the lake was stratified. Survival of Aeromonas hydrophila under in situ conditions in both epilimnetic and hypolimnetic waters was determined through the use of polycarbonate membrane diffusion chambers during two separate reactor operating conditions. Survival levels of pure cultures of A. hydrophila corresponded to the distribution patterns of the naturally occurring Aeromonas-like populations. The greater survival of A. hydrophila during full reactor operation suggests that the fish populations may be exposed to Aeromonas for a longer period of time than when the reactor is not operating.

Journal Article↗
PubMed1992

Virulence traits of Aeromonas strains in relation to species and source of isolation.

The virulence traits of 39 well-defined clinical (29 strains) and environmental (10 strains) isolates of Aeromonas (16 A. hydrophila, 12 A. sobria and 11 A. caviae) were examined by a variety of assays to delineate differences, if any, in the enteropathogenic potential in relation to species and the source of isolation. The distribution of enterotoxin (ent), cytotoxin (cyt) and haemolysin (hae) producing strains of Aeromonas did not correlate to species and source of isolation. The extracellular virulence phenotype Ent+ Cyt+ Hae+ was the most common one among all the three species although unique phenotypes associated prominently with either A. hydrophila or A. sobria were also discernible. None of the cytotoxin or haemolysin producing strains hybridized with the vt1/vt2 or the tdh/trh gene probes, respectively, indicating that these two factors of Aeromonas were distinct. Haemagglutination of human O group erythrocytes was not related to the source of isolation or production of enterotoxin, cytotoxin or haemolysin but appeared to be related to species. The strains which did not exhibit cell-associated haemagglutination belonged to either A. hydrophila or A. caviae. Haemagglutination unaffected by fucose, mannose and galactose was the dominant inhibition pattern exhibited mainly by the clinical haemagglutinating strains of the three species. Only one clinical strain of A. caviae showed a diffuse pattern of adherence to HeLa cells. Expression of the 5 bacterial enzymes by strains of Aeromonas did not fall into a readily discernible pattern in relation to species or source of isolation. From this study, it is clear that the mechanism of the pathogenesis of Aeromonas is a multifactorial one.

Aeromonas↗
PubMed1995

Distribution of Aeromonas phenospecies and genospecies among strains isolated from water, foods or from human clinical samples.

A total of 332 Aeromonas spp. originating from drinking water (n = 75), fresh water (n = 57), chicken and ground beef (107), human faecal samples in association with travelling (n = 49), human faecal samples not associated with travelling (n = 38), and six strains from human blood cultures were studied by phenotypic methods and by using analysis of ribopatterns as a molecular method for the identification of the 13 known hybridization groups (HGs). Also included were the reference strains of each HG. A. hydrophila HG 1, A. caviae HG 4 and A. veronii biotype sobria HG 8/10 were the most important genospecies identified in human faecal samples. A. hydrophila HG 2 and A. media HG 5B predominated in drinking water and A. hydrophila HG 2 and HG 3, A. media HG 5A and HG 5B predominated in fresh water. In drinking water only one isolate was A. hydrophila HG 1 and two isolates were A. caviae HG 4. Clinically important Aeromonas spp. HG 1 (A. hydrophila), HG 4 (A. caviae) and HG 8/10 (A. veronii biotype sobria) were common in chicken and ground beef. In contrast to the drinking water samples, HG 5A was common in chicken and ground beef samples. Atypical, unidentified isolates were most often found in fresh water samples (12/57 strains). Although water has been suspected of being an important source of human aeromonas infections, clinically important HGs were found to be in the minority among Aeromonas spp. identified in drinking water or fresh water. The distribution of Aeromonas spp. HGs among drinking water, chicken and ground beef samples was also different, suggesting that contamination of meat or chicken may not originate from water.

Adult↗
PubMed2002

Lateral flagella of Aeromonas species are essential for epithelial cell adherence and biofilm formation.

Mesophilic Aeromonas strains express a single polar flagellum in all culture conditions and produce lateral flagella on solid media. Such hyperflagellated cells demonstrate increased adherence. Nine lateral flagella genes, lafA-U for Aeromonas hydrophila, and four Aeromonas caviae genes, lafA1, lafA2, lafB and fliU, were isolated. Mutant characterization, nucleotide and N-terminal sequencing demonstrated that the A. hydrophila and A. caviae lateral flagellins were almost identical, but were distinct from their polar flagellum counterparts. The aeromonad lateral flagellins exhibited higher molecular masses on SDS-PAGE, and this aberrant migration was thought to result from post-translational modification through glycosylation. Mutation of the Aeromonas lafB, lafS or both A. caviae lateral flagellins caused the loss of lateral flagella and a reduction in adherence and biofilm formation. Mutations in lafA1, lafA2, fliU or lafT resulted in strains that expressed lateral flagella, but had reduced adherence levels. Mutation of the lateral flagella loci did not affect polar flagellum synthesis, but the polarity of the transposon insertions on the A. hydrophila lafTlU genes resulted in non-motility. However, mutations that abolished polar flagellum production also inhibited lateral flagella expression. We conclude that Aeromonas lateral flagella: (i) play a role in adherence and biofilm formation; (ii) are distinct from the polar flagellum; (iii) synthesis is dependent upon the presence of a polar flagellum filament; and (iv) that the motor proteins of the polar and lateral flagella systems appear to be shared.

Aeromonas↗
PubMed1997

Distribution and expression of beta-lactamase genes among Aeromonas spp.

Clinical and environmental isolates of Aeromonas spp. (20 Aeromonas caviae, 33 Aeromonas veronii and 21 Aeromonas hydrophila) were examined for their ability to yield mutants derepressed for beta-lactamase production and for the distribution of the three chromosomally encoded beta-lactamase genes, ampS and cepS from A. veronii bv. sobria and cphA from A. hydrophila. Of these isolates, 100% and 96% of the isolates from A. hydrophila and A. caviae, respectively, yielded beta-lactamase derepressed mutants but only 38% of A. veronii isolates yielded the resistant phenotype at 37 degrees C. However, when tested at 30 degrees C, all isolates gave rise to the derepressed mutants, indicating a temperature effect on the control mechanism. All mutants had significantly higher beta-lactamase activity against ampicillin, oxacillin, cephaloridine and imipenem. Hybridization studies with cloned aeromonas beta-lactamase genes indicated that the cephalosporinase gene, cepS, is almost ubiquitous for the three species tested. The cphA gene cross-hybridized with all isolates of A. veronii and A. hydrophila but not to A. caviae isolates. In contrast, hybridization studies using ampS revealed that only 25% of A. caviae, 45% of A. veronii and 38% of A. hydrophila tested carried the ampS gene or one closely homologous to it. Nonetheless, strains that failed to hybridize with ampS showed two serine beta-lactamases when analysed by isoelectric focusing.

Aeromonas↗
PubMed2000

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.

Aeromonas↗
PubMed1994

Diversity of siderophore genes encoding biosynthesis of 2,3-dihydroxybenzoic acid in Aeromonas spp.

Most species of the genus Aeromonas produce the siderophore amonabactin, although two species produce enterobactin, the siderophore of many enteric bacteria. Both siderophores contain 2,3-dihydroxybenzoic acid (2,3-DHB). Siderophore genes (designated aebC, -E, -B and -A, for aeromonad enterobactin biosynthesis) that complemented mutations in the enterobactin genes of the Escherichia coli 2,3-DHB operon, entCEBA(P15), were cloned from an enterobactin-producing isolate of the Aeromonas spp. Mapping of the aeromonad genes suggested a gene order of aebCEBA, identical to that of the E. coli 2,3-DHB operon. Gene probes for the aeromonad aebCE genes and for amoA (the entC-equivalent gene previously cloned from an amonabactin-producing Aeromonas spp.) did not cross-hybridize. Gene probes for the E. coli 2,3-DHB genes entCEBA did not hybridize with Aeromonas spp. DNA. Therefore, in the genus Aeromonas, 2,3-DHB synthesis is encoded by two distinct gene groups; one (amo) is present in the amonabactin-producers, while the other (aeb) occurs in the enterobactin-producers. Each of these systems differs from (but is functionally related to) the E. coli 2,3-DHB operon. These genes may have diverged from an ancestral group of 2,3-DHB genes.

Aeromonas↗
PubMed1989

Antimicrobial susceptibility of sixty human fecal isolates of Aeromonas species.

The MICs of 21 antimicrobial agents were determined for 60 strains of Aeromonas spp. isolated from human feces. All isolates tested were susceptible to aztreonam, tetracycline, imipenem, moxalactam, pipemidic acid, gentamicin, trimethoprim-sulfamethoxazole, pefloxacin and ciprofloxacin. Resistance to erythromycin and streptomycin was observed in all 60 strains. Aeromonas caviae was less susceptible to cefamandole, cefotaxime, norfloxacin, chloramphenicol, tetracycline, sulfamethoxazole and trimethoprim than was either Aeromonas hydrophila or Aeromonas sobria. It was concluded that cotrimoxazole or one of the newer quinolones can be considered for treatment of aeromonas-associated diarrhea.

Adult↗
PubMedDate not supplied

Clinical features of Aeromonas enteritis in Hawaii.

The incidence and clinical features of enteritis associated with Aeromonas in Honolulu were studied. The stool isolation rate was 2.9% for Aeromonas, the third most common bacterial pathogen in this population. Clinical features of Aeromonas-associated enteritis were compared with clinical features of enteritis without an associated bacterial pathogen. Although there was a trend toward more abdominal pain, tenderness, nausea and prolonged illness in patients with Aeromonas, these differences were not statistically significant. In most cases, Aeromonas enteritis is a self-limited illness, indistinguishable from other causes of diarrhoea seen in our clinic.

Aeromonas↗
PubMed1982

Cytotonic enterotoxin from Aeromonas hydrophila.

Aeromonas hydrophila produces two hemolysins and an enterotoxin during growth. Enterotoxin, separated from the hemolysins, gave positive reactions in the rabbit intestinal loop test, the rabbit skin test and the adrenal Y1 cell test. Neutralization experiments in the rabbit loop, rabbit skin and Y1 cell tests failed to demonstrate any immunological relationship between Aeromonas enterotoxin and cholera toxin or Escherichia coli heat-labile enterotoxin. Prior incubation of Aeromonas enterotoxin with gangliosides did not inhibit the positive test results in these systems. A co-agglutination test with antiserum to purified cholera toxin was negative for Aeromonas enterotoxin, which therefore seems to be immunologically distinct from cholera toxin. The Aeromonas enterotoxin induced steroid secretion in adrenal Y1 cells and increased the intracellular cyclic adenosine monophosphate (cAMP) content of Y1 cells as well as of rabbit intestinal epithelial cells. It thus seems to act via the adenylate cyclase-cAMP pathway and should be classified as a cytotonic enterotoxin according to the classification of Keusch and Donta (1975).

Adenylyl Cyclases↗
PubMed1991

Aeromonas and Plesiomonas as food- and waterborne pathogens.

Aeromonas and Plesiomonas have become increasingly recognized as human enteropathogens. Plesiomonas shigelloides has mainly been recovered from various sea foods, whereas Aeromonas sp. have also been cultured from pigs, broilers, eggs, milk and vegetables. Aeromonas sp. also multiply rapidly at +4 degrees C which is a significant risk in food storage. Aeromonas sp. have furthermore been recovered from fresh water sources, and some isolates are resistant to chlorination which makes it a further risk factor. No large food- or waterborne outbreaks have been reported so far with Aeromonas sp. Various virulence factors involved in intestinal infections are described such as enterotoxins, cytotoxins, and adhesins.

Aeromonas↗
PubMed1993

Heat and acid sensitivity of motile Aeromonas: a comparison with other food-poisoning bacteria.

The present study was undertaken to compare the heat and acid sensitivity of aeromonads with those of other food-poisoning bacteria. It became obvious that aeromonads were more sensitive to heat than Escherichia coli O157:H7, Staphylococcus aureus, and Salmonella typhimurium. Aeromonads were killed in peptone water within 2 min at 55 degrees C, while the other bacteria survived heating at 55 degrees C for more than 15 min. Aeromonas cells were also less resistant to heat in hamburger steaks. These findings suggest that Aeromonas infection can easily be prevented by heat treatment, although correct handling of food is required to avoid recontamination since aeromonads are very common in various kinds of food. E. coli, S. aureus and S. typhimurium cells survived in buffer at pH 3.2 and in foods seasoned with vinegar. By contrast, Aeromonas cells were found to be highly sensitive to acid. However, the resistance of Aeromonas to acid may be sufficient to allow it to infect the gastrointestinal tract since Vibrio parahaemolyticus, which causes numerous outbreaks of food-poisoning every year in Japan, was susceptible to acid to the same extent as Aeromonas.

Acetates↗
PubMed1995

Emerging pathogens: Aeromonas spp.

Aeromonas spp. are Gram-negative rods of the family Vibrionaceae. They are normal water inhabitants and are part of the regular flora of poiquilotherm and homeotherm animals. They can be isolated from many foodstuffs (green vegetables, raw milk, ice cream, meat and seafood). Mesophilic Aeromonas spp. have been classified following the AeroKey II system (Altwegg et al., 1990; Carnahan et al., 1991). The major human diseases caused by Aeromonas spp. can be classified in two major groups: septicemia (mainly by strains of A. veronii subsp. sobria and A. hydrophila), and gastroenteritis (any mesophilic Aeromonas spp. but principally A. hydrophila and A. veronii). Most epidemiological studies have shown Aeromonas spp. in stools to be more often associated with diarrhea than with the carrier state; an association with the consumption of untreated water was also conspicuous. Acute self-limited diarrhea is more frequent in young children, in older patients chronic enterocolitis may also be observed. Fever, vomiting, and fecal leukocytes or erythrocytes (colitis) may be present (Janda, 1991). The main putative virulence factors are: exotoxins, endotoxin (LPS), presence of S-layers, fimbriae or adhesins and the capacity to form capsules.

Aeromonas↗
PubMed1988

Biochemical and toxigenic characteristics of Aeromonas spp. isolated from diseased mammals, moribund and healthy fish.

In this study we describe biochemical, toxigenic and surface characteristics of 33 motile Aeromonas isolated from diseased mammals, 3 from moribund marine mammals, 24 from healthy fish and 4 from moribund fish. Aeromonas hydrophila, A. caviae and A. sobria were isolated from both mammals and fish but at a different incidence. Aeromonas hydrophila was the predominant species isolated from clinical specimens; it was isolated from pneumonia, wound infections, septicemia and abortion in horses, cattle and pigs. Aeromonas sobria was isolated from one mammal and 11 healthy fish. Aeromonas caviae was isolated in 2 cases from healthy fish and in 9 cases from diseased mammals. Variations in some biochemical tests including sorbitol, amylase and citrate, were observed between isolates from different sources. However, these differences did not allow the differentiation of isolates from diseased mammals and healthy fish. The majority of A. hydrophila isolates produced different extracellular products; A. sobria isolates produced less exotoxin. With A. caviae isolates no hemolysin, protease, enterotoxin or elastase were detected. There was no quantitative difference in hemolysin, protease, enterotoxin or elastase production between isolates from mammals and fish. It is suggested that A. hydrophila could be a potential pathogen for domestic animals, and fish may represent a potential reservoir of infection.

Aeromonas↗
PubMed1985

Biochemical and exoenzymatic properties of Aeromonas species.

One hundred twenty-seven isolates of Aeromonas comprising the three currently recognizable species (A. hydrophila, A. sobria, and A. caviae) were evaluated for biochemical and exoenzymatic properties. Aeromonas species were generally (greater than 90%) characterized as gram-negative fermentative rods that were oxidase-, catalase-, and beta-galactosidase-positive, produced arginine dihydrolase, and failed to decarboxylate ornithine. More than 95% of all isolates tested failed to grow on 6.5% salt or thiosulfate-citrate bile salts agar and were resistant to the vibriostatic agent 0/129. Most Aeromonas species produced acid from hexoses while failing to ferment alcoholic sugars or trisaccharides. In exoenzymatic studies, Aeromonas species were uniformly found to produce several exoenzymes, including amylase, DNase, RNase, esterase, lipase, gelatinase, protease, fibrinolysin, and chitinase. Within the genus, a number of biochemical and enzymatic properties were found to be associated with one or more of the taxonomically recognizable species. These properties included glycoside utilization, Heiberg grouping based upon fermentation of arabinose, sucrose, and mannose, and the elaboration of several extracellular enzymes (elastase, hemolysin, lecithinase, phosphatase). In addition, phenotypic markers previously associated with enterotoxigenic Aeromonas isolates were almost exclusively found among A. hydrophila and A. sobria species, suggesting that these species are the major enteric pathogens.

Aeromonas↗