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PubMed1982

Aeromonas hydrophila toxins - intestinal fluid accumulation and mucosal injury in animal models.

Strains of Aeromonas hydrophila were earlier shown to produce a heat-labile enterotoxin and two cytolytic toxins, alpha- and beta-haemolysin. These investigations have been extended. When separated from the cytolysins, the enterotoxin elicited fluid accumulation in rabbit intestinal loops. The electrolyte and albumin content of the fluid was similar to that of cholera toxin. The enterotoxin was non-injurious to the mucosa. Purified hemolysins did not give a positive loop test. They produced hemorrhagic enteritis with leakage of small amounts of hemorrhagic fluid. In electrolyte and albumin content this fluid differed from the fluid elicited by the enterotoxin. Prostaglandin inhibitors did not reduce the diarrheal response to Aeromonas enterotoxin. The cAMP inhibitor chlorpromazine reduced the fluid accumulation in rat and mice intestinal loops by 60%. Cholera toxin and Aeromonas enterotoxin may have a common pathway in the elicitation of intestinal fluid accumulation. By passage in intestinal loops, strains of A. hydrophila could regain lost enterotoxicity. Experimental diarrhea could not be induced in rabbits and rats with various enterotoxigenic strains of Aeromonas.

Aeromonas↗
PubMed1989

Aeromonas spp. in foods: a significant cause of food poisoning?

From a total of 563 samples of various foodstuffs purchased from retail outlets in the Reading area 287 were found to contain mesophilic Aeromonas spp. The types of sample which were most frequently contaminated were poultry (79.3%) and offal (84.3%). Of three media compared for their efficiency in recovering Aeromonas spp. after enrichment in alkaline peptone water, Difco Aeromonas was the most efficient. Cytotoxin was produced by approximately 50% of the A. hydrophila and A. sobria strains but by none of A. caviae strains. It is concluded that both raw and cooked foods are potential sources for infecting human beings with Aeromonas spp.

Aeromonas↗
PubMed1991

Behavior of Aeromonas species at refrigeration temperatures.

The ability of many strains of Aeromonas hydrophila and A. sobria to produce several types of virulence factors has been documented. The presence of Aeromonas in drinking water, as well as in river and saline waters and on various finfish and shellfish taken from them, has caused some concern relative to the role this bacterium plays as a causative agent of human gastroenteritis. The fairly common occurrence of Aeromonas on red meats, poultry and fresh produce and its ability to grow at 4 degrees C gives rise to further concern over public health risks which may be associated with consumption of these foods. A brief overview of the behavior of Aeromonas species at refrigeration temperatures is presented.

Aeromonas↗
PubMed1993

Distribution of mesophilic Aeromonas species in raw and ready-to-eat fish and meat products in Switzerland.

A total of 829 poultry, meat, shellfish and fish products commonly consumed in Switzerland were qualitatively and quantitatively examined for the presence of mesophilic Aeromonas spp. Overall, aeromonads occurred in 24.1% of the samples. Raw food products were frequently contaminated (e.g. 94.1% in minced meat), with colony counts up to 6.0 x 10(6)/g. Some ready-to-eat products had a relatively high percentage of positive samples as well, such as cooked ham in slices (38.2%), mortadella (12.9%), smoked cooked sausage (15.6%), hot and cold smoked fish (10.9-14.3%) and gravad salmon (10.5%). Colony counts, however, were somewhat lower (up to 1.7 x 10(3)/g). The high contamination rate of cooked or hot smoked foods suggests recontamination after cooking or smoking, e.g., at the slicing and packaging stage. 61.2% of the identified strains were Aeromonas hydrophila, followed by 22.5% Aeromonas caviae and 16.3% Aeromonas sobria.

Aeromonas↗
PubMed1993

The public health significance of Aeromonas spp. in foods.

There is now evidence that some strains of Aeromonas species are enteropathogens. Such strains possess virulence properties, such as the ability to produce enterotoxins, cytotoxins, haemolysins and/or the ability to invade epithelial cells. Strains with these properties are common contaminants of drinking water and a wide range of foods. Contact or consumption of contaminated water, especially in summer, is a major risk factor in Aeromonas-associated gastroenteritis. Aeromonas-contaminated foods may also be vehicles of infection. Given the properties of strains that have been described in foods it has been suggested that food-borne illness could result not only from colonization and in vivo expression of virulence factors, but possibly also by intoxication following ingestion of foods that have been stored for a period of time, even under refrigeration. This paper reviews what is known about Aeromonas spp. in foods, their expression of virulence determinants, particularly at refrigeration temperatures, and the questions remaining to be answered to evaluate the risk they pose, so that an appropriate public health response can be determined.

Aeromonas↗
PubMed1996

Aeromonas bacteraemia in burn patients.

Human aeromonas infection is uncommon and is usually associated with immunosuppression, chronic disease or trauma in an aquatic setting. Burn injury may induce a state of immunosuppression, making the thermally injured patient a suitable host for aeromonas infection. We reviewed the experience of one burn centre with this pathogen. Retrospective examination of blood culture results from 8151 patients admitted between 1959 and 1994 disclosed eight patients with clinically relevant Aeromonas hydrophilia bacteraemia. Five were burned outside the USA. Aquatic exposure was known or suspected in only three cases. Five of the eight patients died. Aeromonas infection in burn patients is rare but may occur in the absence of aquatic exposure.

Adult↗
PubMed1983

Aeromonas species in clinical microbiology: significance, epidemiology, and speciation.

Over a one-year period, 32 strains (31 clinical, 1 environmental) of Aeromonas sp. were recovered. Chief sources of isolation were the gastrointestinal tract (48%), wounds (19%), and blood (13%). Gastrointestinal isolates were most often recovered from young (less than 5 yrs) children with diarrhea; wound or blood isolates were recovered more often from an older (avg. 56 yrs) population with one of several underlying disorders. Regardless of body site of isolation, most strains of Aeromonas appeared to be community acquired and not nosocomially transmitted. Over 70% of all isolates recovered during this year period were isolated during summer or fall months, suggesting a seasonal distribution of this microorganism. Speciation of Aeromonas isolates revealed A. hydrophila to be the predominant species isolated from clinical specimens, although significant percentages of other Aeromonas sp. were also recovered from clinical material.

Adult↗
PubMed1992

Rapid identification of motile Aeromonas.

The clinical relevance and taxonomy of motile Aeromonas species are areas of current controversy. Strains of motile Aeromonas isolates (n = 60) from various sources were identified to species level using the following tests (all incubated at 30 degrees and 37 degrees C): esculin hydrolysis; formation of gas from glucose; production of acetoin; production of acid from mannitol and arabinose; decarboxylation of lysine and ornithine, dihydrolation of arginine; and pyrazinamide hydrolysis in a semisolid medium. The tests' results were similar at incubation temperatures of 30 degrees and 37 degrees C. Of the strains, 59 (98%) of 60 were identified to species level by the full battery of tests: 25 as A. hydrophila, 18 as A. caviae, 14 as A. sobria, one as A. veronii, and one as A. schubertii. (The only A. veronii and A. schubertii isolates identified were ATCC strains). All (25 of 25) strains of A. hydrophila and 17 (94%) of 18 of A. caviae hydrolyzed pyrazinamide in less than 24 hr, whereas all strains of A. sobria showed no pyrazinamidase activity. Absence of pyrazinamidase was, thus, a convenient phenotypic marker for A. sobria. Four additional tests (esculin hydrolysis, acetoin production, lysine decarboxylation, and gas production from glucose) identified within 24 hr all examples of the three common species of Aeromonas. Recently proposed species did not contribute to our ability to discriminate among stool, other clinical, and environmental isolates of Aeromonas spp.

Aeromonas↗
PubMed2005

In vitro susceptibility of antibiotics against Vibrio spp. and Aeromonas spp. isolated from Penaeus monodon hatcheries and ponds.

Susceptibility patterns to 16 different antibiotics were investigated against pathogenic Vibrio spp. and Aeromonas spp. isolated from shrimp culture hatcheries and ponds in India. Thirteen species of Vibrio (N = 90) and two species of Aeromonas (N = 7) isolates were tested by agar disk diffusion. The results show that 100% of the isolates were resistant to ampicillin, and that 43.2% and 47.4% were sensitive to chlortetracycline and erythromycin, respectively. Susceptibility patterns of another 160 isolates belonging to the genera Vibrio and Aeromonas obtained from the water samples of shrimp hatcheries and ponds were tested against six commonly used antibiotics. Results indicate that isolates from the hatcheries were more resistant to antimicrobials than isolates from the ponds. The minimum inhibitory concentrations of five antibiotics against the different Vibrio spp. and Aeromonas spp. were determined. Ciprofloxacin was found to be the most effective in controlling the isolates from hatcheries and ponds compared with the other antibiotics used in the study. Our results reveal that antibiotic-resistant bacteria are widespread in the shrimp culture hatcheries and ponds in India. Potential risk to human health was not addressed in this study and remains to be elucidated.

Aeromonas↗
PubMed2006

Detection of the frequency, antimicrobial susceptibility, and genotypic discrimination of Aeromonas strains isolated from municipally treated tap water samples by cultivation and AP-PCR.

The frequency, antibiotic susceptibility, and genotypic discrimination of Aeromonas strains isolated from municipally treated drinking tap water distribution systems were investigated in this study. We have analyzed 148 tap water samples collected from 8 different locations by bacterial cultivation and arbitrarily primed polymerase chain reaction (AP-PCR). Gram negative, hemolytic, oxidase (+) and catalase (+) bacterial colonies were applied to the study. Identification of bacterial colonies was done by conventional biochemical method and API ID 20E panel (BioMerieux-France). Molecular epidemiological discrimination of the isolates was done by AP-PCR. Aeromonas spp. was detected in 6 of 148 (4%) tap water samples from 8 different locations. Five isolates were identified as Aeromonas hydrophila and one isolate was identified as Vibrio fluvialis by conventional biochemical method. These data were also confirmed by API 20E panel. One of 6 isolates was resistant to gentamicin, 2 of 6 isolates were resistant to trimethoprim/sulfamethoxazole, 4 of 6 isolates were resistant to ampicillin and ampicillin-sulbactam and all of 6 isolates were resistant to cephalothin. All isolates were found to be susceptible to amikacin, aztreonam, ceftazidime, ceftriaxone, ciprofloxacin. All 6 strains of Aeromonas were discriminated by AP-PCR and were determined that all isolates were from different genotypic sources. Although the frequency of the isolates was under the standard limits, the results indicate that hemolytic A. hydrophila are present in municipally treated tap water samples in Mersin City. While all strains were genotypically distinct, all of them were resistant to first generation beta lactam antibiotics tested in this study.

Aeromonas↗
PubMed2006

Influence of food system conditions on N-acyl-L-homoserine lactones production by Aeromonas spp.

Eleven of 13 Aeromonas strains were shown to produce AHLs. Results of TLC showed that N-butanoyl-L-homoserine lactone (C4-HSL) was the main AHL produced in LB medium at 30 degrees C. The influence of different carbon sources, temperature, pH values and salt concentrations on AHL production was determined in eight A. hydrophila and one A. caviae strain. Additionally a quantitative study of C4-HSL production by A. hydrophila strain 519 under different conditions was performed. Positive results were found in the AHL induction assay for some Aeromonas strains in cultures in LB agar incubated at 12 degrees C after 72-96 h. The induction of the sensor strains by Aeromonas spp. occurred in LB medium supplemented with all carbon sources in a concentration of 0.5%. The production of C4-HSL by A. hydrophila 519 was found until 3.5% (w/v) of NaCl. For pHs close to the neutrality the C4-HSL production by A. hydrophila was evident after 24-48 h of incubation. A. hydrophila 519 produced C4-HSL under anaerobic conditions. Also, the AHL production by Aeromonas strains was studied in simulate agar of shrimp, fish and some vegetables. The production of AHLs was evident by almost all the test strains in shrimp simulated agar. In fish agar only for one of three fish species tested, positive results were found. Induction assay in vegetables simulated agar showed principally negative results, probably because of the presence of inhibitory compounds in these vegetables.

4-Butyrolactone↗
PubMed2006

Characterization of integrons and tetracycline resistance determinants in Aeromonas spp. isolated from South African aquaculture systems.

An increasing incidence of multidrug resistance amongst Aeromonas spp. isolates, which are both fish pathogens and emerging opportunistic human pathogens, has been observed worldwide. This can be attributed to the horizontal transfer of mobile genetic elements, viz.: plasmids and class 1 integrons. The antimicrobial susceptibilities of 37 Aeromonas spp. isolates, from tilapia, trout and koi aquaculture systems, were determined by disc-diffusion testing. The plasmid content of each isolate was examined using the alkaline lysis protocol. Tet determinant type was determined by amplification using two degenerate primer sets and subsequent HaeIII restriction. The presence of integrons was determined by PCR amplification of three integrase genes, as well as gene cassettes, and the qacEDelta1-sulI region. Thirty-seven Aeromonas spp. isolates were differentiated into six species by aroA PCR-RFLP, i.e., A. veronii biovar sobria, A. hydrophila, A. encheleia, A. ichtiosoma, A. salmonicida, and A. media. High levels of resistance to tetracycline (78.3%), amoxicillin (89.2%), and augmentin (86.5%) were observed. Decreased susceptibility to erythromycin was observed for 67.6% of isolates. Although 45.9% of isolates displayed nalidixic acid resistance, majority of isolates were susceptible to the fluoroquinolones. The MAR index ranged from 0.12 to 0.59, with majority of isolates indicating high-risk contamination originating from humans or animals where antibiotics are often used. Plasmids were detected in 21 isolates, with 14 of the isolates displaying multiple plasmid profiles. Single and multiple class A family Tet determinants were observed in 27% and 48.7% of isolates, respectively, with Tet A being the most prevalent Tet determinant type. Class 1 integron and related structures were amplified and carried different combinations of the antibiotic resistance gene cassettes ant(3'')Ia, aac(6')Ia, dhfr1, oxa2a and/or pse1. Class 2 integrons were also amplified, but the associated resistance cassettes could not be identified. Integrons and Tet determinants were carried by 68.4% of isolates bearing plasmids, although it was not a strict association. These plasmids could potentially mobilize the integrons and Tet determinants, thus transferring antimicrobial resistance to other water-borne bacteria or possible human pathogens. The identification of a diversity of resistance genes in the absence of antibiotic selective pressure in Aeromonas spp. from aquaculture systems highlights the risk of these bacteria serving as a reservoir of resistance genes, which may be transferred to other bacteria in the aquaculture environment.

Aeromonas↗
PubMed2005

The development of a matrix-assisted laser desorption/ionization mass spectrometry-based method for the protein fingerprinting and identification of Aeromonas species using whole cells.

This report describes the development of a method to detect the waterborne pathogen Aeromonas using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The genus Aeromonas is one of several medically significant genera that have gained prominence due to their evolving taxonomy and controversial role in human diseases. In this study, MALDI-MS was applied to the characterization of seventeen species of Aeromonas. These seventeen species were represented by thirty-two strains, which included type, reference and clinical isolates. Intact cells from each strain were used to generate a reproducible library of protein mass spectral fingerprints or m/z signatures. Under the test conditions used, peak lists of the mass ions observed in each species revealed that three mass ions were conserved among all the seventeen species tested. These common mass ions having an average m/z of 6301, 12,160 or 12,254, and 13,450, can be potentially used as genus-specific biomarkers to identify Aeromonas in unknown samples. A dendrogram generated using the m/z signatures of all the strains tested indicated that the mass spectral data contained sufficient information to distinguish between genera, species, and strains. There are several advantages of using MALDI-MS based protein mass spectral fingerprinting of whole cells for the identification of microorganisms as well as for their differentiation at the sub-species level: (1) the capability to detect proteins, (2) high throughput, and (3) relatively simple sample preparation techniques. The accuracy and speed with which data can be obtained makes MALDI-MS a powerful tool especially suited for environmental monitoring and detection of biological hazards.

Aeromonas↗
PubMed2002

Isolation and characterization of Aeromonas species from an eutrophic tropical estuary.

Isolation and characterization of Aeromonas species were undertaken in the Ebrié lagoon (Abidjan, Côte d'Ivoire) over a one year period. Overall 63% of 501 water samples were identified as positive for Aeromonas spp. A. sobria, A. hydrophila and A. caviae represent respectively 49.20%, 20.63% and 30.15% of the positive samples. Thirty nine of the positive samples were recovered from surface water samples; while 24 bottom water samples were positive for Aeromonas. Aeromonas species are most frequently (82.53) present in the Ebrié lagoon urban area during the rainy and flood seasons when the salinity is low and below 10 per thousand. A lower isolation frequency is noticed during the dry season when water salinity is over 10 per thousand. Finally, a higher isolation frequency occurred in samples with highest counts of Escherichia coli.

Aeromonas↗
PubMed2000

Prevalence and diversity of Aeromonas and Vibrio spp. in coastal waters of Southern Italy.

A survey was undertaken to examine sea water and sediment for the presence of Vibrio and Aeromonas spp. along approximately 900 km of coast in Southern Italy during early and late summer. A quantitative analysis was also done to evaluate the water fecal contamination at the stations examined. The results indicate that all the investigated areas were submitted to a wide spatial fluctuation of fecal contamination and that Vibrio and Aeromonas spp. were present in both high and low fecal-contaminated stations. Sixty two percent of the investigated samples were positive for Aeromonas spp., while 42% of samples were positive for Vibrio spp. It was interesting to note that 38% of the positive stations for both Aeromonas and Vibrio spp. showed a fecal coliform contamination of water at < 10(2) cells 100 ml(-1). Thus, these findings support the hypothesis that the bacterial indicators (such as fecal coliforms) do not always satisfactorily reflect the hygienic quality of water. The presence of Vibrionaceae on copepods was also investigated. Copepods were sampled at a station located inside the harbour of the city of Naples and were found contaminated by V. cholerae non-O1, V. alginolyticus, V. fluvialis and A. caviae. Furthermore, the antibiotic resistance patterns of isolated bacteria showed the presence of a number of resistant strains among the isolates. In order to discriminate the isolates on the basis of their biochemical profiles and/or antibiotic resistance patterns, cluster analysis was carried out which showed that no unique assay could fully discern these isolates. However, the best discrimination resulted from complete pattern profile based on both biochemical profiles and antibiotic resistance patterns.

Aeromonas↗
PubMed2004

Control of Aeromonas on minimally processed vegetables by decontamination with lactic acid, chlorinated water, or thyme essential oil solution.

Aeromonas is an opportunistic pathogen, which, although in low numbers, may be present on minimally processed vegetables. Although the intrinsic and extrinsic factors of minimally processed prepacked vegetable mixes are not inhibitory to the growth of Aeromonas species, multiplication to high numbers during processing and storage of naturally contaminated grated carrots, mixed lettuce, and chopped bell peppers was not observed. Aeromonas was shown to be resistant towards chlorination of water, but was susceptible to 1% and 2% lactic acid and 0.5% and 1.0% thyme essential oil treatment, although the latter provoked adverse sensory properties when applied for decontamination of chopped bell peppers. Integration of a decontamination step with 2% lactic acid in the processing line of grated carrots was shown to have the potential to control the overall microbial quality of the grated carrots and was particularly effective towards Aeromonas.

Aeromonas↗
PubMed1997

Effects of temperature, medium composition, pH, salt and dissolved oxygen on haemolysin and cytotoxin production by Aeromonas hydrophila isolated from oyster.

The effects of temperature, medium composition, pH, salt content and dissolved oxygen (DO) on the production of haemolysin and cytotoxin by one strain of Aeromonas hydrophila isolated from oyster were investigated. Four media were tested: brain heart infusion broth (BHIB), casamino acid-yeast extract broth (CAYEB), nutrient broth (NB), and trypticase soy broth (TSB). BHIB was the best for toxin production even though the growth rates for Aeromonas hydrophila in all of these media were quite similar. Aeromonas hydrophila could produce haemolysin and cytotoxin at 37, 28 and 5 degrees C; however, the toxins were produced faster and were more stable at 28 degrees C than at 37 degrees C. Although Aeromonas hydrophila itself is tolerant to 5% (w/v) salt in BHIB and a pH range of pH 5.5 to 10.0, the production of haemolysin and cytotoxin was apparently decreased in the presence of 1-5% (w/v) NaCl or when the pH of the medium was greater or less than 7.2. The DO values in the culture medium during the stationary growth phase also seemed to affect toxin production; greater quantities of toxins were produced when the DO values were higher.

Aeromonas hydrophila↗
PubMed2003

[Phenotypes of beta-lactam resistance in the genus Aeromonas].

This work aimed to investigate resistance profiles towards beta-lactam antibiotics in correlation with beta-lactamases production in the genus Aeromonas. In a series of 417 wild-type strains, biochemical identification and testing with 11 beta-lactams by the disk-diffusion method revealed 5 predominant phenotypes: A. hydrophila complex/class B, C and D beta-lactamases; A. caviae complex/class C and D beta-lactamases; A. veronii complex/class B and D beta-lactamases; A. schubertii spp./class D beta-lactamase; A. trota spp./class C beta-lactamase. A subgroup of 64 representative strains was submitted to MIC determination with 8 beta-lactam compounds alone and in combination with 3 beta-lactamase inhibitors (clavulanic acid, tazobactam and BRL 42715). Visualisation of beta-lactamases and pI determination were performed in all these 64 isolates by isoelectric focusing from crude extracts. The different Aeromonas species produced 1 to 3 of the following inducible enzymes: an imipenemase with low expression, which is difficult to detect with routine phenotype studies (class B, pI 8, imipenem MIC > 2 micrograms/ml), a cephalosporinase (class C, pI > 7 +/- 0.5, cephalothin MIC > 256 micrograms/ml), and an oxacillinase widely produced in the genus Aeromonas (class D, pI > 8.5, ticarcillin MIC > 256 micrograms/ml). In Aeromonas spp. resistance profile to beta-lactam antibiotics is correlated with naturally occurring phenotypes of beta-lactamases production. As a conclusion, the characterisation of these different enzymes is of therapeutic and taxonomic interest, in species notoriously difficult to identify.

Aeromonas↗