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Isolation and characterization of potentially human pathogenic, cytotoxin-producing aeromonas strains from retailed seafood in Berlin, Germany.

The presence of potentially human pathogenic strains of Aeromonas was investigated in 84 samples of seafood which were purchased from retail traders in Berlin, Germany in spring 2000. A total of 134 Aeromonas strains were isolated on selective [GSP agar and Aeromonas (Ryan) agar] and unselective (standard count agar and enterohaemolysin agar) media from 27 (32.1%) of the samples and were classified as Aeromonas hydrophila (67.9%), A. caviae (26.1%) and A. sobria (6.0%) by biotyping. Thirteen (48.1%) of the 27 positive samples contained more than one species of Aeromonas. Production of haemolysins on enterohaemolysin agar was found with 132 (98.5%) of the strains at 28 degrees C and with 130 strains (97.0%) at 37 degrees C growth temperature. Vero cytotoxins were produced by 99 (73.9%) of the strains when grown at 28 degrees C but only by 24 of the strains (17.9%) at 37 degrees C. The latter strains were identified as A. hydrophila (n = 22) and A. sobria (n = 2) which came from 17 (20.2%) samples of raw seafood and from ready-to-eat salted herring 'Matjes' products. Cytotoxin-encoding genes for aerolysin (aer) and haemolysin A (hlyA) were investigated by PCR. Aer and hlyA genes were detected in both, strains which produced toxins only at 28 degrees C and strains which produced toxins at 37 degrees C. Our data indicate that raw seafood and ready-to-eat fish products can harbour potential human pathogenic, cytotoxin producing Aeromonas strains.

Aeromonas↗

Rattus norvegicus: not a model for Aeromonas-associated gastroenteritis in man.

The lack of a suitable animal model of Aeromonas-associated diarrhoea has hampered investigations into Aeromonas pathogenic mechanisms. Hence, a published report that clindamycin-pretreated rats developed signs and symptoms of enteritis following intragastric inoculation of an Aeromonas strain required further investigation. Although we could demonstrate long-term colonisation (>12 days) and histological damage in this animal model with Pseudomonas aeruginosa isolated from patients with chronic diarrhoea, this was not seen with Aeromonas spp. Six Aeromonas strains, selected for their potential virulence and colonising abilities and including the strain from the original report, were either not recovered from stools or were recovered for no longer than 2 days post inoculation. Intestinal histology remained normal. Destruction of bacteria in vivo appeared to be due to immune mechanisms as inoculum strains were not 'suicidal' or unduly sensitive to low pH or clindamycin. This study was, therefore, unable to validate the clindamycin-treated rat model as a useful one for investigating the enteropathogenicity of Aeromonas species. Possible reasons for the discrepancy between our study and the original report are discussed.

Aeromonas↗

Persistence, transmission, and virulence characteristics of Aeromonas strains in a duckweed aquaculture-based hospital sewage water recycling plant in Bangladesh.

The persistence and transmission of Aeromonas in a duckweed aquaculture-based hospital sewage water treatment plant in Bangladesh was studied. A total of 670 samples from different sites of the hospital sewage water treatment plant, from feces of hospitalized children suffering from diarrhea, from environmental control ponds, and from feces of healthy humans were collected over a period of three years. In total, 1,315 presumptive Aeromonas isolates were biochemically typed by the PhenePlate rapid screening system (PhP-AE). A selection of 90 representative isolates was further analyzed with PhenePlate (PhP) extended typing (PhP-48), fatty acid methyl ester analysis, and amplified fragment length polymorphism (AFLP) fingerprinting. In addition, the prevalence of the putative virulence factors hemolysin and cytotoxin and the presence of the cytolytic enterotoxin gene (AHCYTOEN) were analyzed. Aeromonas was found at all sites of the treatment plant, in 40% of the samples from environmental control ponds, in 8.5% of the samples from hospitalized children suffering from diarrhea, and in 3.5% of samples from healthy humans. A significantly high number of Aeromonas bacteria was found in duckweed, which indicates that duckweed may serve as a reservoir for these bacteria. PhP-AE typing allowed identification of more than 192 distinct PhP types, of which 18 major PhP types (MTs) were found in multiple sites and during several occasions. AFLP fingerprinting revealed the prevalence of genotypically indistinguishable Aeromonas isolates among certain PhP MTs recovered from different sampling occasions and/or at multiple sites. Hemolytic and cytotoxic activities were observed in 43% of the tested strains, whereas 29% possessed the cytolytic enterotoxin gene AHCYTOEN. Collectively, two specific MTs associated with diarrhea were shown to exhibit high cytotoxicity. Furthermore, all tested isolates of these major types were positive for the cytolytic enterotoxin gene. In conclusion, our data indicate that certain phenotypically and genotypically stable clonal lineages of Aeromonas have persisted in the treatment system for a prolonged period and might spread from the hospitalized children suffering from diarrhea to fish produced for human consumption through the sewage water treatment system.

Aeromonas↗

Isolation, enumeration, and characterization of Aeromonas from polluted waters encountered in diving operations.

Counts of total viable, aerobic, heterotrophic bacteria, indicator organisms, and Aeromonas spp. were made at a diver training site on the Anacostia River in Washington, D.C. The numbers of Aeromonas cells in Anacostia River sediment and water increased during periods of elevated water temperature, to maxima of 4 x 10(5) cells per g of sediment and 300 cells per ml of water. Correspondingly, Aeromonas counts dropped 2 to 4 logs as the water temperature decreased to 0 to 0.5 degrees C. Cultures taken by sterile swabs from the ears and face masks of divers after a 30-min swim in the Anacostia River yielded bacterial types and numbers similar to those found in the river. The nasal passages of the divers apparently did not become contaminated by swimming, possibly because of the protective effect of the face masks used by the divers. Properties associated with virulence in Aeromonas hydrophila and Aeromonas sobria strains isolated from the river, sediment, and divers were investigated. Nearly 40% of the strains of both species collected during the study produced cytotoxic activity for mouse Y-1 adrenal cells, as well as elastase. Enterotoxin activity, as detected by the Y-1 assay, was observed in 3% (1 of 35) of the strains of A. sobria and in 6% (19 of 330) of the A. hydrophila strains. Fluid accumulation in rabbit ileal loops induced by both species of Aeromonas varied greatly among the 17 strains examined. Fluid accumulation of at least 0.4 ml/cm was correlated with positive cytotoxin- or enterotoxin-like response in the Y-1 tissue culture assay.

Aeromonas↗

Lateral flagella and swarming motility in Aeromonas species.

Swarming motility, a flagellum-dependent behavior that allows bacteria to move over solid surfaces, has been implicated in biofilm formation and bacterial virulence. In this study, light and electron microscopic analyses and genetic and functional investigations have shown that at least 50% of Aeromonas isolates from the species most commonly associated with diarrheal illness produce lateral flagella which mediate swarming motility. Aeromonas lateral flagella were optimally produced when bacteria were grown on solid medium for approximately 8 h. Transmission and thin-section electron microscopy confirmed that these flagella do not possess a sheath structure. Southern analysis of Aeromonas reference strains and strains of mesophilic species (n = 84, varied sources and geographic regions) with a probe designed to detect lateral flagellin genes (lafA1 and lafA2) showed there was no marked species association of laf distribution. Approximately 50% of these strains hybridized strongly with the probe, in good agreement with the expression studies. We established a reproducible swarming assay (0.5% Eiken agar in Difco broth, 30 degrees C) for Aeromonas spp. The laf-positive strains exhibited vigorous swarming motility, whereas laf-negative strains grew but showed no movement from the inoculation site. Light and scanning electron microscopic investigations revealed that lateral flagella formed bacterium-bacterium linkages on the agar surface. Strains of an Aeromonas caviae isolate in which lateral flagellum expression was abrogated by specific mutations in flagellar genes did not swarm, proving conclusively that lateral flagella are required for the surface movement. Whether lateral flagella and swarming motility contribute to Aeromonas intestinal colonization and virulence remains to be determined.

Aeromonas↗

Aeromonas schubertii, a new mannitol-negative species found in human clinical specimens.

In 1983 the vernacular name Enteric Group 501 was coined for a group of strains that had been referred to our laboratory as "possible Vibrio damsela that does not require NaCl for growth." By DNA-DNA hybridization (hydroxyapatite method, 32P, 60 and 75 degrees C), six strains of Enteric Group 501 were closely related to the labeled strain 2446-81 (70 to 95% at 60 degrees C and 71 to 93% at 75 degrees C; 0 to 1% divergence). Type strains of all Aeromonas species and reference strains of six other Aeromonas DNA hybridization groups were 26 to 42% related (60 degrees C) to strain 2446-81, but type strains of 27 Vibrio and Photobacterium species, including V. damsela, were 0 to 1% (75 degrees C) related. We propose the name Aeromonas schubertii for the highly related group of seven strains formerly known as Enteric Group 501. The type strain is designated as ATCC 43700 (CDC 2446-81). Strains of A. schubertii grew well at 36 degrees C and had positive reactions at this temperature for methyl red, Voges-Proskauer (1% NaCl, Coblentz method), lysine decarboxylase, arginine dihydrolase, motility, lipase, DNase, nitrate reduction to nitrite, oxidase, and growth in nutrient broth with 0 and 1% NaCl. There was no growth in 6% NaCl or on thiosulfate-citrate-bile salts-sucrose agar. The following sugars were fermented: D-glucose, D-galactose, maltose, D-mannose, and trehalose. The following sugars were not fermented: adonitol, L-arabinose, D-arabitol, cellobiose, dulcitol, erythritol, myo-inositol, lactose, D-mannitol, melibiose, alpha-CH3-D-glucoside, raffinose, L-rhamnose, salicin, D-sorbitol, sucrose, and D-xylose. Esculin was not hydrolyzed, and the string test was negative. The mannitol-negative reaction differtiates A. schubertii from other Aeromonas species. The antibiogram of this organism is typical of other Aeromonas strains (resistance to ampicillin and carbenicillin and susceptibility to most other agents). A. schubertii strains have been isolated from abscesses (two strains), wound (one), skin (one), pleural fluid (one), and blood (two). The two blood isolates suggest clinical significance typical of other Aeromonas species , but further information is needed on this group.

Aeromonas↗

Clinical and epidemiologic aspects of members of Aeromonas DNA hybridization groups isolated from human feces.

Between June 1982 and May 1987 Aeromonas species were isolated from 208 of 34,311 (0.61%) fecal samples submitted to a Regional Public Health Laboratory in The Netherlands. Aeromonas isolates were found most frequently in summer and rarely in winter. Of 169 Aermonas isolates that were available for further study, 19% were isolated from patients with a mixed infection, 5% from patients with underlying diseases, and 15% from patients who used medication that could predispose the intestinal tract to colonization with Aeromonas species. Aeromonas species that produced cytotoxins to Vero cells (cytotoxigenic) were found in hybridization groups 1 (11% of all isolates), 2 (1%), 3 (2%), and 8 (25%) and were identified phenotypically as A. hydrophila or A. sobria. Aeromonas species that did not produce cytotoxins to Vero cells (noncytotoxigenic) were found in hybridization groups 4 (57%) and 5A (4%) and were identified phenotypically as A. caviae. Distribution of Aeromonas species by age showed a predominance of noncytotoxigenic strains in children under the age of 5 years (46% of all noncytotoxigenic strains), while cytotoxigenic strains were mainly cultured from patients aged 50 years or older (54% of all cytotoxigenic strains). Significant correlations were found between cytotoxigenic strains and hospitalization, foreign travel, and contact with surface water. Cytotoxigenic strains were isolated significantly more often than noncytotoxigenic strains from patients with diarrhea, but in a multivariate analysis including age, previous medication, underlying disease, and foreign travel, this association was not significant.

Aeromonas↗

High frequency of coinfecting enteropathogens in Aeromonas-associated diarrhea of hospitalized Peruvian infants.

Rectal swabs from 391 infants less than 18 months of age who were hospitalized with acute diarrhea and from 138 similarly aged healthy infants were examined for the etiologic agents of diarrhea. Aeromonas spp. were recovered from 205 of 391 (52.4%) diarrheic patients, whereas they were recovered from 12 of 138 (8.7%) controls (P less than 10(-11). Among the 205 Aeromonas-positive diarrheic patients, 118 (57.6%) were found to be coinfected with other common enteropathogens. Of the 164 Aeromonas-positive initial diarrheic specimens, 82 (50.0%) had one or more other enteropathogens present; 30 patients were coinfected with rotavirus, 20 with enterotoxigenic Escherichia coli, 16 with Campylobacter spp., 14 with Shigella spp., 13 with enteropathogenic E. coli, 4 with Vibrio spp., 1 with Salmonella spp., and 1 with Plesiomonas spp. of Aeromonas strains from cases compared with that from controls supports an etiologic role for this organism. However, frequent concomitant infections with other well-recognized enteropathogens and a lack of disease correlation with common Aeromonas phenotypes suggest that only a subset of Aeromonas strains may be diarrhea causing and that such strains may be common to several of the existing species.

Aeromonas↗

Phenotypic identification of Aeromonas genomospecies from clinical and environmental sources.

A collection of 983 Aeromonas isolates from environmental and clinical sources have been identified to the genomospecies level. A phenotypic method identified 93% of the strains. The use of citrate and the production of acid from sorbitol enabled the members of the Aeromonas hydrophila complex to be separated. The most common genomospecies from intestinal sources were Aeromonas veronii biotype sobria and Aeromonas caviae. The former, together with A. hydrophila, was the most frequently isolated species of extraintestinal origin. Most pathogenic species were very prevalent in environmental samples, with A. veronii biotype sobria being the most common in lakes and reservoirs (41.5%) and in treated drinking water (25.0%), and A. caviae was the most common in sea water (26.0%) and milk products (35.5%). Aeromonas hydrophila (18.1%) was the second most prevalent species isolated in untreated drinking water. Since Aeromonas infections are generally regarded as a water- and food-borne diseases, the high environmental prevalence of these pathogenic genomospecies should be regarded as an important threat to public health.

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Serogroups, K1 antigen, and antimicrobial resistance patterns of Aeromonas spp. strains isolated from different sources in Mexico.

A total of 221 strains of Aeromonas species isolated in Mexico from clinical (161), environmental (40), and food (20) samples were identified using the automated system bioMérieux-Vitek. Antisera for serogroups O1 to 044 were tested using the Shimada and Sakazaki scheme. The K1 antigen was examined using as antiserum the O7:K1C of Escherichia coli. Besides, we studied the antimicrobial patterns according to Vitek AutoMicrobic system. Among the 161 clinical strains 60% were identified as A. hydrophila, 20.4% as A. caviae, and 19.25% as A. veronii biovar sobria. Only A. hydrophila and A. veronii biovar sobria were found in food (55 and 90% respectively) and environmental sources (45 and 10% respectively). Using "O" antisera, only 42.5% (94/221) of the strains were serologically identified, 55% (121/221) were non-typable, and 2.5% (6/221) were rough strains. Twenty-two different serogroups were found, O14, O16, O19, O22, and O34 represented 60% of the serotyped strains. More than 50% of Aeromonas strain examined (112/221) expressed K1 encapsulating antigen; this characteristic was predominant among Aeromonas strains of clinical origin. Resistance to ampicillin/sulbactam and cephazolin was detected in 100 and 67% of Aeromonas strain tested for their susceptibility to antibiotics. In conclusion, antibiotic-resistant Aeromonas species that possess the K1 encapsulating antigen and represent serogroups associated with clinical syndrome in man are not uncommon among Aeromonas strains isolated from clinical, food and environmental sources in Mexico.

Aeromonas↗

Prevalence and molecular characterization of Aeromonas spp. in ready-to-eat foods in Italy.

A survey was carried out in Italy to ascertain the prevalence of Aeromonas spp. in ready-to-eat foods (vegetables, cheeses, meat products, and ice creams) and the level of molecular heterogeneity of the isolates found by macrorestriction analysis of genomic DNA with pulsed-field gel electrophoresis (PFGE). In total, 46 (14.4%) of the 320 food samples examined were found positive for Aeromonas spp. The highest percentages of isolation were discovered in vegetables, particularly lettuce (45.0%), endive (40.0%), and rucola (20.0%). Ricotta was the only cheese type analyzed that showed a high frequency of isolation (45.0%). Among meat products, salami and raw ham (25.0% of samples positive) and, to a lesser extent, baloney (5.0%) were found positive for Aeromonas spp. Aeromonas hydrophila was the most common isolate from foods of animal origin, whereas Aeromonas caviae was the dominant species in vegetables. No motile aeromonads were found in ice cream samples. Aeromonas isolates showed a high level of genetic heterogeneity, because 24 PFGE patterns were identified among 27 A. hydrophila strains and 20 PFGE patterns were found in 23 A. caviae isolates. In conclusion, consumers of ready-to-eat foods in Italy are regularly exposed to many genetically distinct strains of A. hydrophila and A. caviae without evident signs of malaise, and therefore, few of these strains, if any, are likely to be pathogenic.

Aeromonas↗

Aeromonas intestinal infections in the United States.

To evaluate the clinical and epidemiologic aspects of aeromonas enteritis, we studied the cases of 34 persons nationwide from whom Aeromonas hydrophila had been isolated in large numbers from stool in 1984. Compared with 68 control subjects, these patients were more likely to have drunk untreated water, usually from private wells (odds ratio = 20.9; p less than 0.01). Eighteen of the isolates belonged to a single DNA-relatedness group of the eight described for Aeromonas species, but no clear correlation between illnesses in patients and any tested genotypic or phenotypic characteristic of recovered organisms was found. Gastrointestinal complaints tended to be chronic in infected adults and acute and severe in children. Nine patients had become ill after taking antimicrobial agents to which recovered Aeromonas species were resistant; 5 persons took antimicrobials to which their Aeromonas strains were susceptible and had alleviation or resolution of their gastrointestinal symptoms. These findings indicate that at least some Aeromonas strains are enteropathogenic for the normal host and that these organisms are acquired by drinking untreated water.

Adult↗

Isolation and identification of motile Aeromonas species from chicken.

In this study a total of 140 broiler carcasses and carcass parts purchased at different supermarkets in Ankara including 50 whole carcass, 30 wing, 30 leg and 30 breast samples were analysed for the presence of motile Aeromonas species. According to analysis findings, motile Aeromonas spp. were isolated from 116 (82.9%) of total 140 samples. The distribution of the isolates were 94%, 86.6%, 80%, 63.3% in broiler carcass, wing, leg and breast samples, respectively. Aeromonas hydrophila was isolated the most prevalent species with 56% the range followed by Aeromonas sobria with 29.3% and Aeromonas caviae with 14.7% from all of the carcass and carcass part samples, respectively. Consequently, it was supposed that, examined broiler carcass and carcass parts have been contaminated to important level with motile Aeromonas species and it has been risk for public health.

Aeromonas↗

Aeromonas-associated diarrhoea in north India.

The incidence of Aeromonas-associated diarrhoea in patients attending the hospital attached to the Dayanand Medical College, Ludhiana, India was investigated during May 1984-May 1987. Microbiological examination of single faecal samples from 2,661 patients showed the presence of various enteropathogens of which details of only Aeromonas isolations are given and discussed in the present article. A small control sample of 105 age-matched healthy volunteers were also examined. Only 55 patients (2.1% of all patients) showed Aeromonas spp. in their stool samples on culture. Aeromonas as a single pathogen was isolated from 37 patients and, from 18 patients it was mixed with other enteropathogens. Stools of healthy controls did not contain any pathogen. Seven of 25 isolates of A. caviae, all 18 isolates of A. sobria and all 7 isolates of A. hydrophilla were shown to be enterotoxigenic by rabbit ileal loop test. There was no immunological cross-reaction between Aeromonas enterotoxin and Escherichia coli labile toxin antiserum. The Aeromonas isolates were susceptible to most of the commonly used antimicrobial agents except ampicillin and cephalothin.

Adolescent↗

Ecology of mesophilic Aeromonas spp. in aquatic environments of a temperate region and relationship with some biotic and abiotic environmental parameters.

The Ecology of mesophilic Aeromonas species has been investigated since January 1988 to examine their occurrence and distribution in aquatic environments of Okayama Prefecture. Water and plankton samples were quantitatively as well as qualitatively analyzed throughout the seasons from five selected stations including fresh, brackish, and saline environments. Analysis of variance and correlation coefficients among the biotic and abiotic parameters were sought. The organisms were found in all the environs with high densities through all the seasons. Plankton samples yielded higher counts of Aeromonas than the water samples in all the environs. Water temperature seemed to play a significant role on their growth during the winter months, however, no significant seasonal variation nor any correlation with fecal pollution were observed in most of the environments. A reciprocal relationship was seen with salt concentration in the saline environment. Among the currently recognized mesophilic species; A. caviae, A. hydrophila, A. sobria, and A. media were isolated with the predominance of anaerobic biovar. The present study reveals that Aeromonas are widely distributed in fresh, brackish and saline environments of this region. The study also reveals that Aeromonas are autochthonous members in aquatic ecosystems and are indigenous to these environs. Aeromonas species isolated from our environments were found to exhibit drug resistance potential which differed from that of isolates from diverse geographical locales. The high incidence of clinically significant Aeromonas species in this aquatic region could be of public health significance for the inhabitants of this region, as well as a challenge to their dependence on aquatic resources.

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Aeromonas species bacteremia in nonimmunocompromised hosts. Two case reports and a review of the literature.

Aeromonas hydrophila septicemia usually occurs in immunocompromised hosts. We present two case reports of Aeromonas hydrophila septicemia in uncompromised patients from two medical centers. Three additional cases (two in immunocompromised hosts and one in a normal host) were found in these centers after retrospective screening of bacteriologic records over the last 3 years. A review of the English medical literature over four decades revealed only 24 additional cases of Aeromonas infection in the nonimmunocompromised host. The primary sources of Aeromonas bacteremia are abdominal and soft tissue infections. In the normal host the prognosis is good when antibiotic treatment is initiated early. Aeromonas are sensitive to aminoglycosides, second- and third-generation cephalosporins, chloramphenicol, cotrimoxazole and ureidopenicillin. There appears to be an increased recognition of this organism, as well as an increase in frequency of Aeromonas-related infection.

Aeromonas↗

Aeromonas-related diarrhea in adults.

We have reviewed the incidence of Aeromonas in patients with enteric disease at our hospital and found it to be the highest of any potential enteric pathogen. Eighty adult patients with diarrhea had Aeromonas isolated from feces, and in 73 Aeromonas was the only potential bacterial or parasitic pathogen detected. The spectrum of illness in patients with Aeromonas-related diarrhea ranged from acute, self-limited diarrhea to a chronic, indolent diarrheal illness. Sixteen percent (13/80) of the patients had evidence of colitis noted during sigmoidoscopy or colonoscopy. Our data (and those from other studies) indicate that Aeromonas is relatively common in the feces of adults with diarrhea; they also indicate the need for prospective, controlled clinical and bacteriological studies to determine whether or not Aeromonas is an important enteric pathogen in adults.

Adult↗

Isolation and characterization of Aeromonas from seafoods in Taipei.

A total of 124 fresh seafoods and 158 processed seafoods collected from the retail markets and supermarkets in Taipei were tested for the contamination with motile Aeromonas spp. Of the fresh seafoods analyzed, 88% displayed the presence of Aeromonas. The isolation rates of various samples were as follows: 100%, freshwater fish; 95%, seawater fish; 78%, fish fillets; 84%, shrimp and crab of the crustacea group; 83%, bivalve shellfish and 84%, non-bivalve shellfish of the mollusca group, and 100%, seaweed. Of the 158 processed seafoods, 11% were contaminated by Aeromonas. The isolation rates were as follows: 0%, canned, dried, or frozen fresh seafood; 18%, salted seafood; 30%, fish cake; 7% vacuum-packaged fish cakes; 14%, frozen seafood dumplings; 8%, cooked seafoods. One hundred and eighty-three Aeromonas strains isolated in this survey were characterized to species level and tested for their ability to produce beta-hemolysin. Ninety-eight percent (98%) of the A. hydrophila produced beta-hemolysin on 5% blood agar, 94% of the A. sobria and 33% of the A. caviae produced beta-hemolysin. Thus it is likely that fresh seafoods are potentially significant sources of the virulent Aeromonas species and may play an important role in the epidemiology of Aeromonas-associated gastroenteritis.

Aeromonas↗