Phenotypic and genotypic analysis of antimicrobial resistance and population structure of gastroenteritis-related Aeromonas isolates

BACKGROUND

The population structure and the correlation between antimicrobial resistance (AMR) phenotypes and genotypes in Aeromonas species isolated from patients with gastroenteritis are not well understood. The aims of the study were to: (1) investigate the antimicrobial susceptibility profiles of Aeromonas species isolated from patients with gastroenteritis; (2) explore the relationship between AMR genes and resistance phenotypes; and (3) describe the population structure of these isolates and provide evidence of transmission events among them.

METHODS

This microbiological survey was performed at the Microbiology Laboratory of the Emek Medical Center in Afula, Israel. Cultivation of Aeromonas was attempted from stool samples that tested positive by PCR. Antimicrobial susceptibility testing (AST) was performed using the Sensititre GN3F microdilution panel. Whole genome sequencing (WGS) was done using the Illumina NextSeq500/550 system. Phylogenetic studies involved multi-locus sequence typing (MLST) and core genome (cg) MLST. Resistance mechanisms were identified using the Comprehensive Antibiotic Resistance Database and compared with the AST results.

RESULTS

The study included 67 patient-unique isolates. The species that were identified included A. caviae (n = 58), A. dhakensis (n = 3), A. media (n = 2), A. veronii (n = 2) and A. hydrophila (n = 2). Isolates were almost uniformly susceptible to amikacin, gentamicin, aztreonam, cefepime, ceftazidime, ciprofloxacin and meropenem. All isolates with the exception of 1-2 isolates were resistant to ampicillin, cefazolin and ampicillin-sulbactam which was compatible with the presence of the blaOXA genes. Variable resistance rates were observed to cefuroxime, cefoxitin, ceftriaxone, piperacillin-tazobactam that were not correlated with the presence of other β-lactamase genes. Resistance to tetracycline and trimethoprim-sulfamethoxazole correlated with the presence of tetA and sul1, respectively. The population structure of A. caviae was highly diverse with the minority of the isolates (16/57) clustering into six defined sequence types. A cgMLST-based distance of four genes was found in one pair of isolates, suggesting common source transmission.

CONCLUSIONS

A. caviae is the dominant species related to gastroenteritis and is characterized by a diverse population structure, with almost no evidence for common-source transmission. Resistance rates to most antimicrobial agents were low and partially matched with the presence of resistance genes.

Genomic characterization of Aeromonas spp. isolates from striped catfish with motile Aeromonas septicemia and human bloodstream infections in Vietnam

Aeromonas spp. are commonly found in the aquatic environment and have been responsible for motile Aeromonas septicemia (MAS) in striped catfish, resulting in significant economic loss. These organisms also cause a range of opportunistic infections in humans with compromised immune systems. Here, we conducted a genomic investigation of 87 Aeromonas isolates derived from diseased catfish, healthy catfish and environmental water in catfish farms affected by MAS outbreaks in eight provinces in Mekong Delta (years: 2012-2022), together with 25 isolates from humans with bloodstream infections (years: 2010-2020). Genomics-based typing method precisely delineated Aeromonas species while traditional methods such as aerA PCR and MALDI-TOF were unable identify A. dhakensis. A. dhakensis was found to be more prevalent than A. hydrophila in both diseased catfish and human infections. A. dhakensis sequence type (ST) 656 followed by A. hydrophila ST251 were the predominant virulent species-lineages in diseased catfish (43.7 and 20.7 %, respectively), while diverse STs were found in humans with bloodstream infections. There was evidence of widespread transmission of ST656 and ST251 on striped catfish in the Mekong Delta region. ST656 and ST251 isolates carried a significantly higher number of acquired antimicrobial resistance (AMR) genes and virulence factors in comparison to other STs. They, however, exhibited several distinctions in key virulence factors (i.e. lack of type IV pili and enterotoxin ast in A. dhakensis), AMR genes (i.e. presence of imiH carbapenemase in A. dhakensis), and accessory gene content. To uncover potential conserved proteins of Aeromonas spp. for vaccine development, pangenome analysis has unveiled 2202 core genes between ST656 and ST251, of which 78 proteins were in either outer membrane or extracellular proteins. Our study represents one of the first genomic investigations of the species distribution, genetic landscape, and epidemiology of Aeromonas in diseased catfish and human infections in Vietnam. The emergence of antimicrobial resistant and virulent A. dhakensis strains underscores the needs of enhanced genomic surveillance and strengthening vaccine research and development in preventing Aeromonas diseases in catfish and humans, and the search for potential vaccine candidates could focus on Aeromonas core genes encoded for membrane and secreted proteins.

Aeromonas spp. isolated from ready-to-eat seafood on the Norwegian market: prevalence, putative virulence factors and antimicrobial resistance

AIMS

We aim to investigate the prevalence, putative virulence factors and antimicrobial resistance of mesophilic Aeromonas isolated from ready-to-eat (RTE) seafood available on the Norwegian market, and to assess the potential risks by consuming RTE seafood to consumers.

METHODS AND RESULTS

The prevalence of mesophilic Aeromonas in 148 RTE seafood was investigated and the highest prevalence was found in retail sushi (17%), followed by oysters (10%), fresh salmon loins (10%) and scallops (4%). Among 43 Aeromonas isolates, 75% of them were identified as A. media, 23% as A. salmonicida and 2% as A. bestiarum based on partial gryB gene sequencing. Aeromonas isolates were potentially pathogenic due to the presence of four virulence genes: alt (73%), hylA (22%), aerA (17%) and act (6%). In addition, all isolates were resistant to ampicillin and erythromycin. Most of the isolates (98%) were multidrug resistant.

CONCLUSIONS

The occurrence of potentially pathogenic and multidrug-resistant Aeromonas strains in RTE seafood implies a potential risk to consumers. Our finding suggests that RTE seafood could be a potential vehicle for the transfer of virulent and multidrug-resistant Aeromonas.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, this is the first study to report multiple antibiotic resistance in Aeromonas associated with RTE seafood in Norway.

Occurrence, diversity and temperature-dependent growth kinetics of Aeromonas spp. in lettuce

Bagged, pre-cut and prewashed lettuce products are marketed as ready to eat. This concept poses a food safety concern, due to lack of efficient hurdles to eliminate possible microbial contaminants from the fresh produce and/or the processing itself. Aeromonas spp. are potential foodborne pathogens that are frequently isolated from lettuce. High counts of, e.g., A. hydrophila have been found in retail ready-to-eat (RTE) vegetable salads. The aim of this study was to assess the general microbiological quality, the occurrence and diversity of potential human pathogenic mesophilic Aeromonas spp. of retail RTE lettuce products. Additionally, temperature-dependent growth kinetic parameters of Aerobic Plate Counts (APC) and Aeromonas spp. in one selected RTE lettuce product, rocket lettuce, were quantified by performing storage experiments at 4 °C, 8 °C and 12 °C. The Aeromonas isolates were further characterized regarding pathogenic traits and phylogenetic relationship. The overall hygienic quality of the lettuce products was unsatisfactory, as 60% of the products had an APC level higher than 7.0 log CFU/g. Presumptive Aeromonas spp. were detected in 52% of the samples, levels ranging from approximately 2.0-6.0 log CFU/g. Significantly lower counts of APC and Aeromonas spp. were found in uncut and unwashed products. Presumptive Aeromonas spp. were able to proliferate in rocket lettuce stored at 4 °C (μmax = 0.39 ± 0.06/d and μmax = 0.43 ± 0.05/d for lettuce from producers A and B, respectively), and μmax was approximately 2× higher at 8 °C and 3× higher at 12 °C. Eighty-four percent of the collected isolates were identified as A. media, based on partial gyrB sequencing. Additionally A. salmonicida and A. bestiarum were detected. The pathogenic potential in this material was high, most of the isolates harbored at least one of the toxin genes, act, ast, alt.

Distribution and Potential Effects of 17β-Estradiol (E2) on <i>Aeromonas </i>Diversity in Wastewater and Fish Samples

BACKGROUND AND OBJECTIVE

Recently, there has been evidence for the accumulation of steroid hormones in the water environment with negative consequences on fish and humans. However, there is paucity of information on how the steroid hormones influence the microbial community in environmental waters. The objective of this study was to determine the occurrence of 17β-estradiol (E2) and its potential influence on the diversity of Aeromonas spp.

MATERIALS AND METHODS

Wastewater samples were obtained from sewage treatment plants in northern South Africa and fish samples were collected from the Nandoni dam. Aeromonas spp. were isolated using microbiological methods and PCR protocols were used for their identification. A commercial Elisa kit was used for measuring the concentration of 17β-estradiol (E2) from the wastewater samples as well as the fish samples.

RESULTS

17β-estradiol (E2) was found in high concentration in sewage samples varying from 0.32-348.6 pg mL-1 while in fish samples, it ranged from 1.1-73.6 pg mL-1. There was a tendency of samples with high E2 concentrations to have higher diversity of Aeromonas spp., implying that steroid hormones may serve as nutrient for Aeromonas spp. Aeromonas hydrophila was the most prevalent species (71%), followed by A. sobria with (68%).

CONCLUSION

The presence of Aeromonas spp. in environmental waters and fish that is consumed by the local community poses a serious health concern. The high content of E2 in treated wastewater is of serious concern as well. For the first time, the present study showed a positive impact of E2 on Aeromonas growth.

Pathogenic characterization of Aeromonas salmonicida subsp. masoucida turbot isolate from China

Aeromonas salmonicida is a gram-negative bacterium that is the causative agent of furunculosis. An A. salmonicida strain was isolated from diseased turbot (Scophthalmus maximus) with the sign of furunculosis from North China. Based on vapA gene, the strain was further classified as A. salmonicida subsp. masoucida RZ6S-1. Culturing RZ6S-1 strain at high temperature (28°C) obtained the virulence attenuated strain RZ6S. Genome sequence comparison between the two strains revealed the loss of the type IV secretion system (T4SS) and type III secretion system (T3SS) from the native plasmid pAsmB-1 and pAsmC-1 of wild-type strain RZ6S-1, respectively. Further study demonstrated that the wild-type strain RZ6S-1, but not its derivative mutant RZ6S, can stimulate apoptosis. Elevated protein level of cleaved caspase-3 was detected from epithelioma papulosum cyprinid (EPC) cells infected with wild-type strain RZ6S-1 as compared with that infected with RZ6S strain. Meanwhile, the invasion of the mutant strain RZ6S was about 17-fold higher than the wild-type strain RZ6S-1, suggesting that some protein(s) from A. salmonicida subsp. masoucida RZ6S-1 suppress its invasion. The RZ6S mutant strain was attenuated, since its LD₅₀ is over 10,000 times higher compared to the wild-type strain as revealed in the turbot infection model.

Aeromonas spp. Isolated from Pacific Abalone (Haliotis discus hannai) Marketed in Korea: Antimicrobial and Heavy-Metal Resistance Properties

Antimicrobial and heavy-metal resistance of 29 Aeromonas spp. (Aeromonas hydrophila n = 9, Aeromonas enteropelogenes n = 14, Aeromonas veronii n = 3, Aeromonas salmonicida n = 2, and Aeromonas sobria n = 1) isolated from Pacific abalone marketed in Korea were analyzed. All isolates were found to be resistant against ampicillin. High level of resistant to cephalothin (86%), rifampicin (73%), imipenem (42%), and oxytetracycline (35%) were also detected. Thirteen (45%) of the isolates showed multiple antimicrobial resistance (MAR) index ≥ 0.2. The PCR assays implied the presence of qnrS, qnrB, qnrA, tetB, tetA, aac (3')- IIa, aac(6')-Ib, aphAI-IAB, bla_CTX, bla_TEM, and intI1 genes among 76%, 28%, 14%, 17%, 3%, 3%, 41%, 10%, 41%, 28%, and 66% of the isolates, respectively. Class 1 integron gene cassette profiles aadA1(3%) and aadA2 (3%) were also identified. Lead (Pb) resistance was the highest (69%) among 5 heavy metals tested, whereas 38%, 27%, and 20% of the isolates were resistant to Cadmium (Cd), Chromium (Cr), and Copper (Cu), respectively. Heavy-metal resistance genes, CopA, CzcA, and merA were positive in 83%, 75%, and 41% of the isolates, respectively. In conclusion, observed genotypic and phenotypic resistance profiles of Aeromonas spp. against antimicrobials and heavy metals reveal the ability of serving as a source of antimicrobials and heavy-metal-resistant traits.

Characterization of tetracycline effects on microbial community, antibiotic resistance genes and antibiotic resistance of Aeromonas spp. in gut of goldfish Carassius auratus Linnaeus

The gut of aquatic animals was a significant niche for dissemination of antibiotic resistance genes (ARGs) and direct response of living conditions. In this study, the gut microbiota of goldfish Carassius auratus Linnaeus was sampled at 7 days and 21 days after treatment with tetracycline at 0.285 and 2.85 μg L^-1 to investigate the influences on the microbial structure and antibiotic resistance. The proportion of tetracycline resistance bacteria was 1.02% in the control group, while increased to 23.00%, 38.43%, 62.05% in groups of high concentration for 7 days (H7), low concentration for 21 days (L21) and high concentration for 21 days (H21), respectively. Compared to the control group, the diversity of isolated Aeromonas spp. was decreased in the treatment groups and the minimal inhibitory concentration (MIC) of resistant isolates was enhanced from 32 to 256 μg mL^-1 with the treatment of tetracycline in time- and dose-dependent manners. Furthermore, the abundance of most genes was increased in treatment groups and efflux genes mainly responded to the stress of tetracycline with an average level of 1.0 × 10^-2. After treatment with tetracycline, the predominant species were changed both at phylum and genus levels. The present study explored the impact of tetracycline on gut microbiota of goldfish at environmentally realistic concentrations for the first time and our findings will provide a reference for characterizing the microbiome of fish in the natural environment.

Nutritional status regulates algicidal activity of Aeromonas sp. L23 against cyanobacteria and green algae

Algicidal bacteria have received broad acceptance as an ecofriendly tool for controlling harmful algal blooms. However, their practical application is still limited to the lab-scale tests due to the complex alga–bacterium interactions in different nutrient statuses. In this study, the Aeromonas sp. L23 that exhibit relatively wide-spectrum in algicidal activity was isolated from a eutrophic agricultural lake. The physiological response of cyanobacteria and green to the algicidal activity under varied nutritional status were studied in an alga-bacterial co-culture. The algicidal activities of L23 against Microcystis aeruginosa UTEX LB 2385, Microcystis aeruginosa NHSB, Anabaena variabilis AG10064, Scenedesmus quadricauda AG10003, and Chlorella vulgaris AG10034 were 88 ± 1.2%, 94 ± 2.6%, 93 ± 0.5%, 82 ± 1.1%, and 47 ± 0.9%, respectively. The L23 cells had low algicidal activity in cell pellet (3%–9%) compared with the cell-free supernatant (78%–93%), indicating that the activity is induced by extracellular substances. Adding glucose, NaNO₃, NH₄Cl, and KH₂PO₄ to the co-culture raised the algicidal activity of the L23 against green algae by 5%–50%. Conversely, a 10%–20% decrease in activity occurred against the target cyanobacteria except M. aeruginosa UTEX LB 2385. These results indicated that the interspecific algicidal activity changes according to the nutritional status, which means that the alga-bacterium interaction will be more complex in the field where the nutritional status changes from time to time.

Diagnostic methods for identifying different Aeromonas species and examining their pathogenicity factors, their correlation to cytotoxicity and adherence to fish mucus

Aeromonas spp. are ubiquitous in the aquatic environment, acting as facultative or obligate pathogens for fish. Identifying Aeromonas spp. is important for pathogenesis and prognosis in diagnostic cases but can be difficult because of their close relationship. Forty-four already characterized isolates of Aeromonas spp. were analysed by 16S rRNA gene sequencing, by gyrase B sequencing, by analysing their fatty acid profiles, by biochemical reactions and by MALDI-TOF MS. To determine their pathogenicity, cytotoxicity, adhesion to mucus and the expression of 12 virulence factors were tested. The susceptibility of the isolates towards 13 different antibiotics was determined. MALDI-TOF MS was found to be an acceptable identification method for Aeromonas spp. Although the method does not detect all species correctly, it is time-effective and entails relatively low costs and no other methods achieved better results. A high prevalence of virulence-related gene fragments was detected in almost all examined Aeromonas spp., especially in A. hydrophila and A. salmonicida, and most isolates exhibited a cytotoxic effect. Single isolates of A. hydrophila and A. salmonicida showed multiple resistance to antibiotics. These results might indicate the potentially pathogenic capacity of Aeromonas spp., suggesting a risk for aquatic animals and even humans, given their ubiquitous nature.

The determination of the infectious status and prevalence of motile Aeromonas species isolated from disease cases in rainbow trout (Oncorhynchus mykiss) and aquarium fish

The aims of this study were to determine the prevalence and phylogenetic relationship of motile Aeromonas spp. that might be pathogenic species for rainbow trout in infected/mix infection cases (based upon different outbreaks on fish farms). A total of 99 motile Aeromonas isolates (and three reference strains) were analysed that were isolated from four different fish species in different sizes of fish (0.1-3,000 g), different months and water temperatures (6.1-21.2°C). The biochemical characteristics of the isolates were determined using conventional tests and a rapid test kit. Additionally, molecular identification was performed using the gyrB housekeeping gene region and with glycerophospholipid-cholesterol acyltransferase polymerase chain reaction (GCAT-PCR). The sequencing results obtained from the gyrB gene region were deposited in the GenBank database, and phylogenetic relationships were determined with the BioNumerics 7.6 database. Nearly half of the Aeromonas isolates that were isolated from rainbow trout showing signs of disease were determined to be possible infectious agents. Aeromonas species exhibit biochemical variability for many characters, so some Aeromonas species tested negative for GCAT-PCR despite that this test was created especially for Aeromonas identification. The phylogenetic tree based upon gyrB contained 10 different phylogroups that were based on 96% cut-off value in gyrB gene region.

Limited performance of MALDI-TOF for identification of fish Aeromonas isolates at species level

The aim of this study was to evaluate the usefulness of the MALDI-TOF MS to identify 151 isolates of Aeromonas obtained mostly from diseased fish. MALDI-TOF MS correctly identified all isolates to the genus level but important differences in the percentage of isolates correctly identified depending on the species were observed. Considering exclusively the first identification option, Aeromonas bestiarum, Aeromonas hydrophila, Aeromonas salmonicida, Aeromonas veronii and Aeromonas sobria were the best identified with results >95%. However, considering the first and second identification options, the only species that showed values >90% was A. hydrophila. Overall, when the database was supplemented with 14 new spectra, the number of accurate identifications increased (41% vs. 55%) and the number of inconclusive identifications decreased (45% vs. 29%), but great differences in the success of species-level identifications were found. Species-distinctive mass peaks were identified only for A. hydrophila and A. bestiarum (5003 and 7360 m/z in 95.5% and 94.1% of their isolates, respectively). This work demonstrates the utility of MALDI-TOF MS for Aeromonas identification to the genus level, but there is no consistency for the accurate identification of some of the most prevalent species implicated in fish disease.

Impact of stress on Aeromonas diversity in tambaqui (Colossoma macropomum) and lectin level change towards a bacterial challenge

Tambaqui (Colossoma macropomum) is among the most cultivated fish species in tropical countries. Stress is the main cause of disease in fish farms. The genus Aeromonas is a common causative agent of fish diseases. This work reports the identification of Aeromonas species colonizing gills of C. macropomum submitted or not to a confinement stress. We also evaluated changes in serum levels of lectins (carbohydrate-binding proteins that are components of fish immune system) in tambaqui submitted to a challenge using two isolated Aeromonas strains. Gill tissues from stressed and unstressed fishes were used to isolate Aeromonas. Then 72 Aeromonas strains were isolated, 97% being from stressed fishes. Among these, 63 were identified at species level and 6 were classified as atypical Aeromonas strains. The most prevalent species were Aeromonas bestiarum and Aeromonas caviae and their strains were used in bacterial challenges. The lectin serum levels significantly increased after 24 h of infection with A. bestiarum; however, no significant increase was found for infection with A. caviae. In conclusion, C. macropomum gills are susceptible to colonization by different Aeromonas species, mainly at confinement stressful conditions, and serum lectins may have a role in the acute immunological response towards infection by A. bestiarum.

Production of Non-Ribosomal Peptide Synthetase (NRPS)-Dependent Siderophore by Aeromonas Isolates

BACKGROUND

Aeromonas species are Gram-negative ubiquitous bacteria, facultative anaerobic rods that infect both invertebrates and vertebrates. Various fish species develop hemorrhagic disease and furunculosis due to Aeromonas spp. Aeromonas strains generate certain active compounds such as siderophores, which are the final products of non-ribosomal peptide synthetase (NRPS) activity. The present study attempted to investigate the prevalence of Aeromonas isolates in marketed fish sources. We also examined the siderophore production ability of these isolates.

METHODS

Among the molecular tools, 16S rRNA analysis was used to identify Aeromonas species and their epidemiological distributions. The hemolytic activity of the strains and biochemical assays were used to confirm the identity of the isolates. We also determined the chemical nature of siderophores in these strains.

RESULTS

A total of seven Aeromonas isolates obtained from fish were included to determine the siderophore production. Of 7 isolates, 4 produced siderophore, and their chemical nature was also determined. The siderophore produced by Aeromonas was invariably found to be of hydroxamate. Four Aeromonas isolates were selected for PCR identification of NRPS-encoding gene. The conserved sequence was present in all four selected isolates. Furthermore, siderophores were qualitatively tested for their antibacterial activity against pathogenic bacteria and a significant level of inhibitory activity was observed in siderophores from the four isolates.

CONCLUSION

Our results showed the ability of the isolated strains in production of siderophores with a high level of activity against Salmonella paratyphi. These siderophores could find applications in biomedical industries.

Improvement of methyl orange dye biotreatment by a novel isolated strain, Aeromonas veronii GRI, by SPB1 biosurfactant addition

Aeromonas veronii GRI (KF964486), isolated from acclimated textile effluent after selective enrichment on azo dye, was assessed for methyl orange biodegradation potency. Results suggested the potential of this bacterium for use in effective treatment of azo-dye-contaminated wastewaters under static conditions at neutral and alkaline pH value, characteristic of typical textile effluents. The strain could tolerate higher doses of dyes as it was able to decolorize up to 1000 mg/l. When used as microbial surfactant to enhance methyl orange biodecolorization, Bacillus subtilis SPB1-derived lipopeptide accelerated the decolorization rate and maximized slightly the decolorization efficiency at an optimal concentration of about 0.025%. In order to enhance the process efficiency, a Taguchi design was conducted. Phytotoxicity bioassay using sesame and radish seeds were carried out to assess the biotreatment effectiveness. The bacterium was able to effectively decolorize the azo dye when inoculated with an initial optical density of about 0.5 with 0.25% sucrose, 0.125% yeast extract, 0.01% SPB1 biosurfactant, and when conducting an agitation phase of about 24 h after static incubation. Germination potency showed an increase toward the nonoptimized conditions indicating an improvement of the biotreatment. When comparing with synthetic surfactants, a drastic decrease and an inhibition of orange methyl decolorization were observed in the presence of CTAB and SDS. The nonionic surfactant Tween 80 had a positive effect on methyl orange biodecolorization. Also, studies ensured that methyl orange removal by this strain could be due to endocellular enzymatic activities. To conclude, the addition of SPB1 bioemulsifier reduced energy costs by reducing effective decolorization period, biosurfactant stimulated bacterial decolorization method may provide highly efficient, inexpensive, and time-saving procedure in treatment of textile effluents.

Characterization of ceftriaxone-resistant Aeromonas spp. isolates from stool samples of both children and adults in Southern India

BACKGROUND

Aeromonas species can cause a wide spectrum of illnesses varying from intestinal to extra intestinal and vary in their susceptibility to different antibiotics. The current study was undertaken to characterize the third generation cephalosporin-resistant strains of Aeromonas spp. which were isolated from stool specimens.

METHODS

Out of a total of 2780 stool samples, 29 Aeromonas spp. were identified, out of which, 9 were resistant to ceftriaxone by the Kirby-Bauer antibiotic testing method. These strains were subjected to minimum inhibitory concentration (MIC) determination by agar dilution for ceftriaxone. Phenotypic and genotypic testing of AmpC beta-lactamase and extended spectrum beta-lactamase (ESBL) were performed. Gene transfer was carried out to demonstrate transmissibility of these genetic elements by conjugation experiments.

RESULTS

Out of the 29 strains, 9 showed MIC of ≥4 μg/ml. Seven out of 9 showed presence of blaCTX-M, while 2 more strains showed the presence of inducible AmpC beta-lactamase and presence of MOX gene. Gene transfer experiments showed that these elements were transmissible to recipient (Escherichia coli J53 strain) in the presence of ceftriaxone.

CONCLUSIONS

Dissemination of these resistance determinants like plasmids is pivotal in the spread of these resistance genes into the aquatic environment into organisms like Aeromonas. This may further limit the future use of antibiotics for the treatment of diarrhoeal diseases. Hence, detection and antibiotic susceptibility testing of Aeromonas spp. should be performed when isolated from stool samples.

Detection and diversity of aeromonads from treated wastewater and fish inhabiting effluent and downstream waters

A two-season investigation of the wastewater treatment plant (WWTP) effluent, of related waters, sludge and fish across a wide area and 11 stations, with emphasis on Aeromonas spp. was conducted. Aeromonas veronii was the prevailing aeromonad isolated by MALDI TOF MS in the summer period. A rise of Aeromonas hydrophila was observed in summer in raw sewage, treated wastewater and effluent-carrying canal. The ratio of aeromonad species retrieved from fish tissues did not correspond with the water and sludge findings, as in spring in the effluent-carrying canal fish carried Aeromonas salmonicida ssp. salmonicida and Aeromonas bestiarum, while in summer mainly A. veronii and Acinetobacter johnsonii were isolated from fish tissues in the same location. No correlation was established between fecal coliforms/enterococci and aeromonad occurrence. All retrieved Aeromonas species demonstrated a distinct spectral pattern, with peaks showing unique mass distribution ranging from 4000 to 10,000Da. Hierarchical clustering separated aeromonads of all isolated species and clustered closely related strains together. Resistance was determined towards amoxicillin, and frequently towards sulfamethoxazole and erythromycin. In summer, a high proportion of water and sludge Aeromonas species demonstrated multiple resistance patterns towards five or more antimicrobials. The quinolone resistance of water aeromonads was mostly related to A. veronii. There are potential health concerns regarding aeromonad exposure amongst recreational fishermen who come into contact with fish inhabiting waters downstream from the WWTP, and WWTP workers who are occupationally exposed to wastewaters and their aerosols.

Aeromonas dhakensis pneumonia and sepsis in a neonate Risso's dolphin Grampus griseus from the Mediterranean Sea

A neonate Risso's dolphin Grampus griseus was found stranded alive on a beach in Catalonia, Spain. Rehabilitation attempts were unsuccessful and it died 2 d later, showing pneumonia and sepsis. A pure bacterial culture was obtained from all tissues and blood and identified as Aeromonas hydrophila using the API 20NE. However, sequencing the rpoD gene showed that the strain in fact belongs to A. dhakensis, making this the first report of fatal haemorrhagic-necrotizing pneumonia and sepsis due to this species in a marine mammal. The A. dhakensis strain GMV-704 produced β-haemolysis, possessed several virulence genes and showed sensitivity to several antimicrobials. This study provides a new potential host for A. dhakensis, and its potential virulence in dolphins and its presence in the marine environment may warrant considering this species a potential threat to marine mammals.

Histopathological findings in farmed rainbow trout (Oncorhynchus mykiss) naturally infected with 3 different Aeromonas species

This study describes the macroscopic and microscopic lesions in farmed rainbow trout (Oncorhynchus mykiss) naturally infected with genetically identified Aeromonas salmonicida, A. hydrophila, and A. veronii species. The genus Aeromonas includes bacteria that naturally inhabit both waterways and organisms. At least 27 Aeromonas species have been identified to date, some of which can cause significant economic losses in aquaculture. As up to 68.8% of Aeromonas isolates may be misidentified in routine biochemical and phenotypic tests, however, reported cases of Aeromonas infection in fish may be wrongly identified. Our findings confirmed that the 3 Aeromonas species studied are associated with septicemia and dermal lesions in rainbow trout.

[AEROMONAS BACTERIA ISOLATED FROM BITHYNIIDAE MOLLUSKS AND THEIR HABITATS: SPECIES COMPOSITION AND BIOLOGICAL PROPERTIES. COMMUNICATION 1]

The purpose of this investigation was to study the species composition and biological properties of Aeromonas bacteria isolated from Bithyniidae mollusks and their habitat (a water reservoir). The Bithyniidae mollusks and water from their habitat were the material to be studied. A total of 176 Aeromonas strains were isolated from the mollusks and water. A. veronii, A. hydrophila, and A. ichthiosmia were most common in the mollusks and A. veronii and A. ichthiosmia were in the water. All the strains isolated had hemolytic activity and no lysozyme or plasma coagulase activity. The magnitude of lecithinase and antilysozymic activities and biofilm formation of the Aeromonas bacteria varied with the isolation source of their strains.

Comparison of extracellular DNase- and protease-producing spoilage bacteria isolated from Delaware pond-sourced and retail channel catfish (Ictalurus punctatus)

BACKGROUND

Spoilage of fishery products begins immediately following filleting due to microbial growth that degrades fish tissue quality prior to consumption. Extensive research has been conducted to identify such bacterial populations. A better understanding of the mechanisms involved in fish spoilage is necessary as a novel remedy for microbial spoilage inhibition has yet to be established for fish tissue. The present study identified, for the first time, bacterial populations that produce extracellular DNase and protease from Delaware and local retail distributed channel catfish (Ictalurus punctatus) fillets.

RESULTS

A clear trend was identified between bacteria derived from catfish filleted under aseptic conditions where Pseudomonas was the dominant genus. Bacteria isolated from retail catfish contained high quantities of DNase-producing isolates, in contrast to aseptic-filleted catfish tissue which had none. Both types of catfish sample maintained high populations of protease-producing bacterial colonies throughout the duration of the study. Most bacteria isolated from catfish intestines exhibited DNase production with no protease production.

CONCLUSION

Specific spoilage organism populations were significantly higher on retail-derived catfish in comparison to lab-filleted Delaware cultured catfish tissue. It is suggested that DNase production and protease production contribute to the spoilage of fish tissue as a result of mishandling and septic filleting being the major cause of rapid catfish tissue spoilage.

Comparison of MALDI-TOF MS, housekeeping gene sequencing, and 16S rRNA gene sequencing for identification of Aeromonas clinical isolates

PURPOSE

The genus Aeromonas is a pathogen that is well known to cause severe clinical illnesses, ranging from gastroenteritis to sepsis. Accurate identification of A. hydrophila, A. caviae, and A. veronii is important for the care of patients. However, species identification remains difficult using conventional methods. The aim of this study was to compare the accuracy of different methods of identifying Aeromonas at the species level: a biochemical method, matrix-assisted laser desorption ionization mass spectrometry-time of flight (MALDI-TOF MS), 16S rRNA sequencing, and housekeeping gene sequencing (gyrB, rpoB).

MATERIALS AND METHODS

We analyzed 65 Aeromonas isolates recovered from patients at a university hospital in Korea between 1996 and 2012. The isolates were recovered from frozen states and tested using the following four methods: a conventional biochemical method, 16S rRNA sequencing, housekeeping gene sequencing with phylogenetic analysis, and MALDI-TOF MS.

RESULTS

The conventional biochemical method and 16S rRNA sequencing identified Aeromonas at the genus level very accurately, although species level identification was unsatisfactory. MALDI-TOF MS system correctly identified 60 (92.3%) isolates at the species level and an additional four (6.2%) at the genus level. Overall, housekeeping gene sequencing with phylogenetic analysis was found to be the most accurate in identifying Aeromonas at the species level.

CONCLUSION

The most accurate method of identification of Aeromonas to species level is by housekeeping gene sequencing, although high cost and technical difficulty hinder its usage in clinical settings. An easy-to-use identification method is needed for clinical laboratories, for which MALDI-TOF MS could be a strong candidate.

Clinical implications of species identification in monomicrobial Aeromonas bacteremia

BACKGROUND

Advances in Aeromonas taxonomy have led to the reclassification of aeromonads. Hereon, we aimed to re-evaluate the characteristics of Aeromonas bacteremia, including those of a novel species, Aeromonas dhakensis.

METHODOLOGY/PRINCIPAL FINDINGS

A retrospective study of monomicrobial Aeromonas bacteremia at a medical center in southern Taiwan from 2004-2011 was conducted. Species identification was based on rpoB sequencing. Of bacteremia of 153 eligible patients, A. veronii (50 isolates, 32.7%), A. dhakensis (48, 31.4%), A. caviae (43, 28.1%), and A. hydrophila (10, 6.5%) were the principal causative species. A. dhakensis and A. veronii bacteremia were mainly community-acquired and presented as primary bacteremia, spontaneous bacterial peritonitis, or skin and soft-tissue infection, whereas A. caviae was associated with hospital-onset bacteremia. The distribution of the AmpC β-lactamase and metallo-β-lactamase genes was species-specific: bla(AQU-1), bla(MOX), or bla(CepH) was present in A. dhakensis, A. caviae, or A. hydrophila, respectively, and bla(CphA) was present in A. veronii, A. dhakensis, and A. hydrophila. The cefotaxime resistance rates of the A. caviae, A. dhakensis, and A. hydrophila isolates were higher than that of A. veronii (39.5%%, 25.0%, and 30% vs. 2%, respectively). A. dhakensis bacteremia was linked to the highest 14-day sepsis-related mortality rate, followed by A. hydrophila, A. veronii, and A. caviae bacteremia (25.5%, 22.2%, 14.0%, and 4.7%, respectively; P = 0.048). Multivariate analysis revealed that A. dhakensis bacteremia, active malignancies, and a Pitt bacteremia score ≥ 4 was an independent mortality risk factor.

CONCLUSIONS/SIGNIFICANCE

Characteristics of Aeromonas bacteremia vary between species. A. dhakensis prevalence and its associated poor outcomes suggest it an important human pathogen.

Strategies to avoid wrongly labelled genomes using as example the detected wrong taxonomic affiliation for aeromonas genomes in the GenBank database

Around 27,000 prokaryote genomes are presently deposited in the Genome database of GenBank at the National Center for Biotechnology Information (NCBI) and this number is exponentially growing. However, it is not known how many of these genomes correspond correctly to their designated taxon. The taxonomic affiliation of 44 Aeromonas genomes (only five of these are type strains) deposited at the NCBI was determined by a multilocus phylogenetic analysis (MLPA) and by pairwise average nucleotide identity (ANI). Discordant results in relation to taxa assignation were found for 14 (35.9%) of the 39 non-type strain genomes on the basis of both the MLPA and ANI results. Data presented in this study also demonstrated that if the genome of the type strain is not available, a genome of the same species correctly identified can be used as a reference for ANI calculations. Of the three ANI calculating tools compared (ANI calculator, EzGenome and JSpecies), EzGenome and JSpecies provided very similar results. However, the ANI calculator provided higher intra- and inter-species values than the other two tools (differences within the ranges 0.06–0.82% and 0.92–3.38%, respectively). Nevertheless each of these tools produced the same species classification for the studied Aeromonas genomes. To avoid possible misinterpretations with the ANI calculator, particularly when values are at the borderline of the 95% cutoff, one of the other calculation tools (EzGenome or JSpecies) should be used in combination. It is recommended that once a genome sequence is obtained the correct taxonomic affiliation is verified using ANI or a MLPA before it is submitted to the NCBI and that researchers should amend the existing taxonomic errors present in databases.

Population dynamics and antimicrobial susceptibility of Aeromonas spp. along a salinity gradient in an urban estuary in Northeastern Brazil

The main objective of this study was to quantify population and identify culturable species of Aeromonas in sediment and surface water collected along a salinity gradient in an urban estuary in Northeastern Brazil. Thirty sediment samples and 30 water samples were collected from 3 sampling locations (A, B and C) between October 2007 and April 2008. The Aeromonas count was 10-7050CFU/mL (A), 25-38,500CFU/mL (B) and<10CFU/mL (C) for water samples, and ∼100-37,500CFU/g (A), 1200-43,500CFU/g (B) and<10CFU/g (C) for sediment samples. Five species (Aeromonas caviae, A. sobria, A. trota, A. salmonicida and A. allosaccharophila) were identified among 41 isolates. All strains were sensitive to chloramphenicol and ceftriaxone, whereas 33 (80, 4%) strains were resistant to at least 2 of the 9 antibiotics tested. Resistance to erythromycin was mostly plasmidial. In conclusion, due to pollution, the Cocó River is contaminated by pathogenic strains of Aeromonas spp. with a high incidence of antibacterial resistance, posing a serious risk to human health.

Use of cellulolytic marine bacteria for enzymatic pretreatment in microalgal biogas production

In this study, we designed and evaluated a microalgal pretreatment method using cellulolytic bacteria that naturally degrades microalgae in their native habitat. Bacterial strains were isolated from each of two mollusk species in a medium containing 1% carboxymethyl cellulose agar. We selected nine bacterial strains that had endoglucanase activity: five strains from Mytilus chilensis, a Chilean mussel, and four strains from Mesodesma donacium, a clam found in the Southern Pacific. These strains were identified phylogenetically as belonging to the genera Aeromonas, Pseudomonas, Chryseobacterium, and Raoultella. The cellulase-producing capacities of these strains were characterized, and the degradation of cell walls in Botryococcus braunii and Nannochloropsis gaditana was tested with "whole-cell" cellulolytic experiments. Aeromonas bivalvium MA2, Raoultella ornithinolytica MA5, and Aeromonas salmonicida MC25 degraded B. braunii, and R. ornithinolytica MC3 and MA5 degraded N. gaditana. In addition, N. gaditana was pretreated with R. ornithinolytica strains MC3 and MA5 and was then subjected to an anaerobic digestion process, which increased the yield of methane by 140.32% and 158.68%, respectively, over that from nonpretreated microalgae. Therefore, a "whole-cell" cellulolytic pretreatment can increase the performance and efficiency of biogas production.

Characterization and antimicrobial susceptibility of motile aeromonads isolated from freshwater ornamental fish showing signs of septicaemia

A total of 74 phenotypically identified presumptive motile Aeromonas isolates recovered from septicaemic freshwater ornamental fish in Sri Lanka were genetically characterized by sequencing of rpoD and gyrB genes. rpoD/gyrB phylogeny confirmed only 53 isolates as Aeromonas, among which A. veronii was the predominant species (79.2%), followed by A. hydrophila (7.5%), A. caviae (5.7%), A. jandaei (1.9%), A. dhakensis (3.8%) and A. entero pelogenes (1.9%). The aeromonads confirmed by sequencing were further subjected to 16S rDNA PCR-RFLP which substantiated sequencing results for 83% of isolates. Fingerprinting of A. enteropelogenes (n = 42) using ERIC-PCR revealed no dominant clones, and the majority were genetically distinct. All isolates were screened by PCR for 7 virulence determinant genes (aer, act, ast, alt, fla, ser, exu) and 2 integrase encoding genes (intI1, intI2). Each isolate contained ≥3 of the virulence genes tested for, with a heterogeneous distribution. Of the isolates, 77% harboured the intI1 gene, while none had intI2. In vitro antimicrobial susceptibility testing showed highest resistances towards tetracycline (58.5%) and erythromycin (54.7%). Our results indicate the diverse range of aeromonads that could potentially be associated with motile aeromonad septicaemia in ornamental fish. This is the first isolation of A. dhakensis from a septicaemic ornamental fish since its original description from the same host.

Biodegradation of Methyl Orange by alginate-immobilized Aeromonas sp. in a packed bed reactor: external mass transfer modeling

Azo dyes are recalcitrant and xenobiotic nature makes these compounds a challenging task for continuous biodegradation up to satisfactorily levels in large-scale. In the present report, the biodegradation efficiency of alginate immobilized indigenous Aeromonas sp. MNK1 on Methyl Orange (MO) in a packed bed reactor was explored. The experimental results were used to determine the external mass transfer model. Complete MO degradation and COD removal were observed at 0.20 cm bead size and 120 ml/h flow rate at 300 mg/l of initial dye concentration. The degradation of MO decreased with increasing bead sizes and flow rates, which may be attributed to the decrease in surface of the beads and higher flux of MO, respectively. The experimental rate constants (k ps) for various beads sizes and flow rates were calculated and compared with theoretically obtained rate constants using external film diffusion models. From the experimental data, the external mass transfer effect was correlated with a model J D = K Re (-(1 - n)). The model was tested with K value (5.7) and the Colburn factor correlation model for 0.20, 0.40 and 0.60 bead sizes were J D = 5.7 Re (-0.15), J D = 5.7 Re (-0.36) and J D = 5.7 Re (-0.48), respectively. Based on the results, the Colburn factor correlation models were found to predict the experimental data accurately. The proposed model was constructive to design and direct industrial applications in packed bed reactors within acceptable limits.

Bacterial study of fin rot in brown trout by API20E

In order to study caudal fin rot with emphasis on Aeromonas sp. and Pseudomonas sp. in Salmo trutta caspius from the salmonids propagation and breeding center of Shahid Bahonar of kelardasht region, One hundred and eighty brood stocks having fin damage symptoms were chosen. Two bacterial samples from each fish were cultured on Aeromonas and Pseudomonas specific media. To identify isolated bacterial colonies by API20E diagnostic system, samples obtained from bacterial cultures 18 to 24 h were prepared and were inoculated into the cupules of test strips. At the end of incubation, after addition of reagents if they are necessary, the results recorded on the results sheets and were analyzed by Apiwe software. The results of API20E diagnostic systems showed that Aeromonas genus bacteria including Aeromonas hydrophila with 100% frequency while the bacterial genus of Pseudomonas including Pseudomonas fluorescens, Pseudomonas aeruginosa and Pseudomonas putida with 36. 84, 31.57 and 21.05% frequency, respectively. Also 10.25% of Pseudomonas samples were unidentified.

Distribution and virulence gene comparison of Aeromonas strains isolated from diseased fish and water environment

A total of 71 Aeromonas strains were isolated in the south of Jiangsu Province China in order to analyze the difference ofAeromonas spp. distribution between diseased fish and water environment. The sequence of 16S rDNA and gyrB demonstrated that the 71 Aeromonas isolates could be divided into 4 species, including A. veronii (55), A. hydrophila (11), A. salmonicida (3) and A. media (2). A. veronii was the most common species isolated from fish and water environment. All Aeromonas isolates were screened for three putative virulence genes, aer, hly and alt. hly was the most common gene among three virulence genes.

Molecular characterization of fluoroquinolone-resistant Aeromonas spp. isolated from imported shrimp

Sixty-three nalidixic acid-resistant Aeromonas sp. isolates were obtained from imported shrimp. Phylogenetic analysis of gyrB sequences indicated that 18 were A. enteropelogenes, 26 were A. caviae, and 19 were A. sobria. Double missense mutations in the quinolone resistance-determining region (QRDR) of gyrA at codon 83 (Ser→Val/Ile) and codon 92 (Leu→Met) coupled with a point mutation of parC at codon 80 (Ser→Ile/Phe) conferred high levels of quinolone resistance in the isolates. A majority of A. enteropelogenes and A. caviae strains harbored toxin genes, whereas only a few A. sobria strains harbored these genes. The fluoroquinolone-resistant Aeromonas spp. exhibited higher cytotoxicity than fluoroquinolone-sensitive, virulent Aeromonas spp. to rat epithelial cells.

A rapid MALDI-TOF MS identification database at genospecies level for clinical and environmental Aeromonas strains

The genus Aeromonas has undergone a number of taxonomic and nomenclature revisions over the past 20 years, and new (sub)species and biogroups are continuously described. Standard identification methods such as biochemical characterization have deficiencies and do not allow clarification of the taxonomic position. This report describes the development of a matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF MS) identification database for a rapid identification of clinical and environmental Aeromonas isolates.

Aeromonas detection and characterization using genus-specific PCR and single-strand conformation polymorphism (SSCP)

Based on sequence alignment, oligonucleotide primers targeting the Aeromonas extracellular lipase gene were developed for PCR detection of member of the genus. A pair of primers designed for conserved regions of the gene amplified a 276 bp sequence in all Aeromonas species and tested strains, but did not have a positive result with other Gram-positive and Gram-negative bacteria, showing high specificity and sensitivity. Selective enrichment in alkaline peptone water, followed by centrifugation, and direct usage of cells suspension as template, detected initial populations of 10 c.f.u. ml⁻¹. Single-strand conformation polymorphism analysis of the PCR products allowed the characterization of Aeromonas strains with a high discriminatory power (Simpson's index = 0.988). The method presented here provides a useful tool for the rapid detection of Aeromonas and the characterization of Aeromonas isolates.

First case of Aeromonas schubertii infection in the freshwater cultured snakehead fish, Ophiocephalus argus (Cantor), in China

An epizootic in snakehead fish, Ophiocephalus argus, in earthen ponds in Xianning, Hubei Province, central China, from June to August 2009 was found to be caused by Aeromonas schubertii. The cumulative mortality within 40 days was 45%, and the diseased fish were 18 months old and 35-45 cm in length. Multiple, ivory-white, firm nodules, 0.5-1 mm in diameter, were scattered throughout the kidney. Blood clots, 3-5 mm in diameter, were found in the liver. This is a disease frequently found in cultured snakehead throughout China. Isolated bacteria were Gram negative, facultatively anaerobic, motile, short rod-shaped, with a length of 0.3-1.0 μm. Morphological and biochemical tests, as well as phylogenetic analysis derived from 16S rRNA, gyrB, rpoD and dnaJ gene sequencing all strongly indicated that these snakehead isolates are identical to A. schubertii. In addition, the isolates possessed two plasmids: 5.0 kb and 10.0 kb. Antibiotic sensitivity testing of the isolates was carried out by the standard Kirby-Bauer disc diffusion method. Experimental infection assays were conducted, and pathogenicity (by intraperitoneal injection) was demonstrated in snakehead fingerlings and zebrafish, Brachydanio rerio (Hamilton).

Isolation and partial characterization of a virulent bacteriophage IHQ1 specific for Aeromonas punctata from stream water

Aeromonas punctata is the causative agent of septicemia, diarrhea, wound infections, meningitis, peritonitis, and infections of the joints, bones and eyes. Bacteriophages are often considered alternative agents for controlling bacterial infection and contamination. In this study, we described the isolation and preliminary characterization of bacteriophage IHQ1 (family Myoviridae) active against the Gram-negative bacterial strain A. punctata. This virulent bacteriophage was isolated from stream water sample. Genome analysis indicated that phage IHQ1 was a double-stranded DNA virus with an approximate genome size of 25-28 kb. The initial characterization of this newly isolated phage showed that it has a narrow host range and infects only A. punctata as it failed to infect seven other clinically isolated pathogenic strains, i.e., methicillin-resistant Staphylococcus aureus 6403, MRSA 17644, Acinetobacter 33408, Acinetobacter 1172, Pseudomonas aeruginosa 22250, P. aeruginosa 11219, and Escherichia coli. Proteomic pattern of phage IHQ1, generated by SDS-PAGE using purified phage particles, showed three major and three minor protein bands with molecular weights ranging from 25 to 70 kDa. The adsorption rate of phage IHQ1 to the host bacterium was also determined, which was significantly enhanced by the addition of 10 mM CaCl(2). From the single-step growth experiment, it was inferred that the latent time period of phage IHQ1 was 24 min and a burst size of 626 phages per cell. Moreover, the pH and thermal stability of phage IHQ1 were also investigated. The maximum stability of the phage was observed at optimal pH 7.0, and it was totally unstable at extreme acidic pH 3; however, it was comparatively stable at alkaline pH 11.0. At 37°C the phage showed maximum number of plaques, and the viability was almost 100%. The existence of Aeromonas bacteriophage is very promising for the eradication of this opportunistic pathogen and also for future applications such as the design of new detection and phage typing (diagnosis) methods. The specificity of the bacteriophage for A. punctata makes it an attractive candidate for phage therapy of A. punctata infections.

A molecular study on the prevalence and virulence potential of Aeromonas spp. recovered from patients suffering from diarrhea in Israel

Background

Species of the genus Aeromonas are native inhabitants of aquatic environments and have recently been considered emerging human pathogens. Although the gastrointestinal tract is by far the most common anatomic site from which aeromonads are recovered, their role as etiologic agents of bacterial diarrhea is still disputed. Aeromonas-associated diarrhea is a phenomenon occurring worldwide; however, the exact prevalence of Aeromonas infections on a global scale is unknown.

Methodology/Principal Findings

The prevalence and virulence potential of Aeromonas in patients suffering from diarrhea in Israel was studied using molecular methods. 1,033 diarrheal stools were sampled between April and September 2010 and Aeromonas species were identified in 17 (∼2%) patients by sequencing the rpoD gene. Aeromonas species identity and abundance was: A. caviae (65%), A. veronii (29%) and Aeromonas taiwanensis (6%). This is the first clinical record of A. taiwanensis as a diarrheal causative since its recent discovery from a wound infection in a patient in Taiwan. Most of the patients (77%) from which Aeromonas species were isolated were negative for any other pathogens. The patients ranged from 1 to 92 years in age. Aeromonas isolates were found to possess different virulence-associated genes: ahpB (88%), pla/lip/lipH3/apl-1 (71%), act/hlyA/aerA (35%), alt (18%), ast (6%), fla (65%), lafA (41%), TTSS ascV (12%), TTSS ascF-ascG (12%), TTSS-dependent ADP-ribosylating toxins aexU (41%) and aexT (6%) in various combinations. Most of the identified strains were resistant to beta-lactam antibiotics but susceptible to third-generation cephalosporin antibiotics.

Conclusions

Aeromonas may be a causative agent of diarrhea in patients in Israel and therefore should be included in routine bacteriological screenings.

Antimicrobial susceptibilities of Aeromonas strains isolated from clinical and environmental sources to 26 antimicrobial agents

We determined the susceptibilities of 144 clinical and 49 environmental Aeromonas strains representing 10 different species to 26 antimicrobial agents by the agar dilution method. No single species had a predominantly nonsusceptible phenotype. A multidrug nonsusceptible pattern was observed in three (2.1%) clinical strains and two (4.0%) strains recovered from diseased fish. Common clinical strains were more resistant than the corresponding environmental isolates, suggesting that resistance mechanisms may be acquired by environmental strains from clinical strains.

Clinical observations of black disease in fairy shrimps, Streptocephalus sirindhornae and Branchinella thailandensis, from Thailand and pathogen verification

In this study, black disease infecting fairy shrimps, Streptocephalus sirindhornae Sanoamuang, Murugan, Weekers & Dumont, and Branchinella thailandensis Sanoamuang, Saengphan & Murugan, in Thailand, was investigated. The typical signs of the disease are the appearance of black spots on the cuticle, located mainly on the dorsal side and thoracopods. A number of rod-shaped bacteria aggregated in the black spots and were visualized by scanning electron microscopy. The histopathological results showed that a haemocytic response to the infection resulted in a dense melanized core of bacteria. In addition, generalized septicaemia by rod-shaped bacteria was also observed in the infected tissue. Of the 31 isolates, Aeromonas spp. were predominantly isolated and six strains were selected for the experimental infections. The most pathogenic strain was identified molecularly as A. hydrophila. When fairy shrimp were infected at bacterial concentrations of 10(4) and 10(6) cfu mL(-1) , the overall infection levels were 73.33 ± 6.67% and 93.33 ± 6.67%, respectively. The experimentally infected fairy shrimp showed abnormal swimming and died within 24-48 h after the appearance of the dark pigment.

Incidence of class 1 integron and other antibiotic resistance determinants in Aeromonas spp. from rainbow trout farms in Australia

There is limited information on antibiotic resistance determinants present in bacteria of aquaculture origin in Australia. The presence of integron and other resistance determinants was investigated in 90 Aeromonas isolates derived from nine freshwater trout farms in Victoria (Australia). Polymerase chain reaction was carried out for the detection of integrase genes Int1, Int2 and Int3, gene cassette array, integron-associated aadA, sul1 and qac1 genes, streptomycin resistance genes strA-strB, β-lactamase resistance genes bla(TEM) and bla(SHV) , and tetracycline resistance genes tetA-E and tetM. Clonal analysis was performed by pulsed-field gel electrophoresis (PFGE). Class 1 integrons were detected in 28/90 (31%) and class 2 and class 3 in none of the strains, aadA gene in 19/27 (70%) streptomycin-resistant strains, sul1 in 13/15 (86.7%) sulphonamide-resistant strains and qac1 gene in 8/28 (28.6%) integron-bearing strains. Five strains from two different farms carried gene cassettes of 1000 bp each containing the aadA2 gene and PFGE analysis revealed genetic relatedness. tetC was detected in all and tetA in 9/18 (50%) tetracycline-resistant strains. The strA-strB, bla(TEM) or bla(SHV) genes were not detected in any of the strains. Aeromonas spp. carrying integrons and other resistance genes are present in farm-raised fish and sediments even though no antibiotics were licensed for use in Australian aquaculture at the time of the study.

[Phenotypic characteristics and virulence factors in Aeromonas strains isolated from patients with diarrheic disease in Cuba]

Fifty four strains of Aeromonas spp were isolated from patients with acute diarrheic episodes by using Aerokey II and Aeroesquema methods. In vitro antimicrobial susceptibility and virulence factors were analyzed. The most frequently isolated specie was Aeromonas caviae. Over 75% of strains exhibited resistance to penicillins and ce-phalosporins; for the other antibiotic groups resistance was under 20%. Twenty six strains (48.1 %) were multiresist-ant. At least one virulence factor among those evaluated in the study was present in 53 (98.1%) of the 54 strains.

Common key acidogen populations in anaerobic reactors treating different wastewaters: molecular identification and quantitative monitoring

Bacterial population dynamics during the start-up of three lab-scale anaerobic reactors treating different wastewaters, i.e., synthetic glucose wastewater, whey permeate, and liquefied sewage sludge, were assessed using a combination of denaturing gradient gel electrophoresis (DGGE) and real-time PCR techniques. The DGGE results showed that bacterial populations related to Aeromonas spp. and Clostridium sticklandii emerged as common and prominent acidogens in all reactors. Two real-time PCR primer/probe sets targeting Aeromonas or C. sticklandii were developed, and successfully applied to quantitatively investigate their dynamics in relation to changes in reactor performance. Quantitative analysis demonstrated that both Aeromonas- and C. sticklandii-related populations were highly abundant for acidogenic period in all reactors. Aeromonas populations accounted for up to 86.6-95.3% of total bacterial 16S rRNA genes during start-up, suggesting that, given its capability of utilizing carbohydrate, Aeromonas is likely the major acidogen group responsible for the rapid initial fermentation of carbohydrate. C. sticklandii, able to utilize specific amino acids only, occupied up to 8.5-55.2% of total bacterial 16S rRNA genes in the reactors tested. Growth of this population is inferred to be supported, at least in part, by non-substrate amino acid sources like cell debris or extracellular excretions, particularly in the reactor fed on synthetic glucose wastewater with no amino acid source. The quantitative dynamics of the two acidogen groups of interest, together with their putative functions, suggest that Aeromonas and C. sticklandii populations were numerically as well as functionally important in all reactors tested, regardless of the differences in substrate composition. Particularly, the members of Aeromonas supposedly play vital roles in anaerobic digesters treating various substrates under acidogenic, fermentative start-up conditions.

[Phenotypic characterization of Aeromonas isolated from patients with acute diarrheal diseases]

INTRODUCTION

The acute diarrheal diseases are one of the main causes of morbidity and mortality in children aged under 5 years and in the general population; this demands a great deal of care in the healthcare services. The situation worsens due to the overuse of antimicrobials and the development of bacterial resistance, being the latter an emerging health problem in different areas of the world. Among the causative microorganisms of acute diarrheal diseases are those of Aeromonas genus, recognized as second risk emerging pathogens.

OBJECTIVES

To determine the most frequently isolated Aeromonas species in fecal samples from acute diarrheal patients and their antimicrobial susceptibility.

METHODS

The Bauer-Kirby's method allowed identifying the susceptibility to several antimicrobials of 100 isolated samples coming from the provincial hygiene and epidemiology centers during 2007 and 2008.

RESULTS

Identification of the species was accomplished in 67% of isolates, being A. caviae (33%) y A. hydrophila (29%) the predominant species. It was demonstrated that 100% of isolates got resistant to at least one of the studied antimicrobials. Drug resistance to cefalotine, sulfonamides and nalidixic acid showed the highest percentages.

CONCLUSIONS

Tetracycline and chloramphenicol are recommended as the drugs of choice for treating intestinal infections caused by these microorganisms in Cuba.

The genus Aeromonas: taxonomy, pathogenicity, and infection

Over the past decade, the genus Aeromonas has undergone a number of significant changes of practical importance to clinical microbiologists and scientists alike. In parallel with the molecular revolution in microbiology, several new species have been identified on a phylogenetic basis, and the genome of the type species, A. hydrophila ATCC 7966, has been sequenced. In addition to established disease associations, Aeromonas has been shown to be a significant cause of infections associated with natural disasters (hurricanes, tsunamis, and earthquakes) and has been linked to emerging or new illnesses, including near-drowning events, prostatitis, and hemolytic-uremic syndrome. Despite these achievements, issues still remain regarding the role that Aeromonas plays in bacterial gastroenteritis, the extent to which species identification should be attempted in the clinical laboratory, and laboratory reporting of test results from contaminated body sites containing aeromonads. This article provides an extensive review of these topics, in addition to others, such as taxonomic issues, microbial pathogenicity, and antimicrobial resistance markers.

[Isolation and identification of pathogenic Aeromonas veronii isolated from infected Siberian sturgeon (Acipenser baerii)]

OBJECTIVE

Our study aimed at searching for the pathogenic factor causing Siberian sturgeon (Acipenser baerii) disease.

METHODS

A pathogenetic bacterial strain X-1-06909 was isolated from naturally infected Siberian sturgeon in Beijing. The strain was identified according to its physiological and biochemical properties, and the sequence analysis of 16S rRNA gene. The drugs sensitivity was detected with Kirby-Bauer's agar diffusion method.

RESULTS

Based on the result of 16S rRNA sequence analysis, the strain X-1-06909 shares 99.6% sequence identity with the type strain ATTCC35624(T) of Aeromonas veronii. The morphological characteristics of the strain were gram-negative, polar single-flagella. The results of physiological and biochemical tests were that the strain could ferment glucose and produce gas, methyl red (M-R) and Voges-Proskauer (V-P) tests were positive, arginine dihydrolase test was negative, it grew on 3% sodium chloride culture medium, the tests for hydrolysis of gelatin and hydrolysis of esculin were negative. The result for drug sensitive tests showed that among 21 antibiotics, cefadroxil, neomycin etc. had better inhibitive effect on the strain.

CONCLUSION

The isolated strain X-1-06909 was identified as A. veronii. The results will provide evidences for further caring the diseases of sturgeons.

Water quality and ecological status of the Alcantara River estuary (Italy)

The Alcantara River estuary was studied to obtain the first data on both water quality and ecological status of the only River Park in Sicily (Italy). Water samples were seasonally collected from three selected stations in the estuarine area and from one station at the mouth of the estuary in the marine coastal zone. Picoplankton and picophytoplankton counts were among the highest observed in estuarine environments and in other coastal waters of the Mediterranean Sea. The contribution of picophytoplankton to total picoplankton showed greater variations in freshwater (from 0.53% to 8.6%) than in coastal waters (from 1.8% to 4.3%). Picophytoplankton abundance increased in Alcantara waters in winter. Vibrio and Aeromonas spp. abundances ranged from x10(2) to x10(3) CFU 100 ml(-1) and from x10(3) to x10(5) CFU 100 ml(-1) respectively. Vibrio and Aeromonas spp. counts were independent from the fecal contamination level. Bacterial identification of the isolates revealed the presence of pathogenic and potentially pathogenic Vibrio and Aeromonas spp. for humans and animals.

Antibiotic susceptibility profile of Aeromonas spp. isolates from food in Abu Dhabi, United Arab Emirates

A total of 57 Aeromonas isolates from food samples such as fresh and frozen chicken, game birds, pasteurized milk, baby food, bakery products, fruit and vegetables, fish, and water from Abu Dahbi, UAE were investigated for antibiotic susceptibility profile. Most strains were resistant to penicillins (ticarcillin, mezlocillin, oxacillin, piperacillin), sulfamethoxazole, trimethoprim and macrolides (erythromycin, vancomycin, clindamycin) but sensitive to tetracycline, chloramphenicol, nitrofurantoin, aminoglycosides (amikacin, gentamicin, tobramycin), cephalosporins (cefuroxime, ceftrioxone, cefazolin, cephalexin, cephalothin, cefoxitin, cefotaxime), quinolone (ciprofloxacin), colistin sulphate and SXT (trimethoprim-sulfamethoxazole). On the other hand, many antibiotics showed excellent inhibitory activity (>75% strains were sensitive to them) against all the strains tested. These include cefuroxime, ceftrioxone, ciprofloxacin, colistin, amikacin, gentamicin, tetracycline, chloramphenicol, nitrofurantoin, cefotaxime and tobramycin. In conclusion, the results show a detailed pattern of sensitivity of the various Aeromonas spp. isolates to a variety of antibiotics and provide useful information in the context of selective isolation and phenotypic identification of the aeromonads from food.

Issues for Microbial Regulation:Aeromonasas a Model

The decision by public health agencies to regulate specific microorganisms that may be found in drinking water can only be made if specific criteria find that a microorganism poses a health risk. These criteria should include: (1) there is a clinical history of an organism causing disease from the ingestion of drinking water; (2) there is epidemiological evidence that drinking water rather than food or other vectors is a major source of disease; (3) there is sufficient evidence that the target organism, if found in water, possesses virulence factors capable of causing disease in humans; (4) there is sufficient evidence that the target organism is not readily removed or inactivated by multi-barrier conventional water treatment process (e.g., coagulation-filtration-disinfection); (5) there is sufficient evidence that the target organism, if surviving conventional treatment, will be viable, virulent, and present in sufficient numbers to cause disease; (6) there are robust analytical methods for the target organism which have acceptable sensitivity, specificity, and reproducibility to measure accurately the presence of the target organism in treated water; and (7) the performance criteria of analytical method(s) for the target organism have been certified by the appropriate public health agency, and there is intra-laboratory field-test performance data to base this certification.

Analysis of 16S rRNA gene mutations in a subset of Aeromonas strains and their impact in species delineation

Characterization of 999 Aeromonas strains using a published 16S rDNA RFLP identification method showed that 8.1% of the strains produced unexpected (hereafter called "atypical") restriction patterns, making their identification uncertain. Atypical patterns were due to the presence of nucleotide polymorphisms among the rrn operons of the 16S rRNA gene (so-called microheterogeneities). Double sequencing signals at certain positions revealed the nucleotide composition was responsible for the microheterogeneities. Although the number of microheterogeneities was relatively low (0.06-0.66%), trees inferred from the 16S rRNA gene led either to a misidentification or to an inconclusive result for the majority of these strains. Strains with atypical patterns were, however, correctly identified using the rpoD gene sequences, as belonging to Aeromonas caviae, A. veronii, and A. media. All of them, but particularly the two former species, are associated with human disease. Microheterogeneities in 16S rRNA gene sequence were significantly (P 0.01) more prevalent in clinical than in environmental strains. This work also analyzed the effects of these microheterogeneities on the taxonomic position of the investigated strains. The results suggest the need for recording microheterogeneities in the 16S rRNA gene.