Aeromonas popoffii sp. nov., a mesophilic bacterium isolated from drinking water production plants and reservoirs

A Novel Aeromonas popoffii Phage AerP_220 Proposed to Be a Member of a New Tolavirus Genus in the Autographiviridae Family

Aeromonas popoffii is one of the environmental Aeromonas species. A number of factors of virulence have been described for this species and it has been reported as a causative agent of urinary tract infection. The first A. popoffii bacteriophage AerP_220 along with its host strain A. popoffii CEMTC 4062 were isolated from river water. The phage has a podovirus morphotype, shows a narrow host range and is lytic against the host strain. The AerP_220 genome comprises 45,207 bp and does not contain genes responsible for antibiotic resistance and toxin production. Fifty-nine co-directional putative ORFs were found in the AerP_220 genome. Thirty-three ORFs encoded proteins with predicted functions; the products of 26 ORFs were hypothetical proteins. AerP_220 genome analysis revealed that this phage can be considered a novel species within the Autographiviridae family. Comparative genomic and proteomic analysis revealed that AerP_220 along with the Aeromonas phage vB_AspA_Tola (OM913599) are members of a new putative Tolavirus genus in the family Autographiviridae. The Gajwadongvirus and proposed Tolavirus genera along with Pantoea phage Nufs112 and phage Reminis could form a new Tolavirinae subfamily within the Autographiviridae family.

Draft Genome Sequence of Aeromonas popoffii ID682, Isolated from a Natural Water Source in Idaho

A draft genome sequence of Aeromonas popoffii ID682, isolated from a natural water source in Idaho, is presented here. A. popoffii is a relatively understudied species within a diverse, expanding freshwater genus of bacteria. Here, we describe only the second genome published for this species to date.

Growth-Stimulatory Effect of Quorum Sensing Signal Molecule N-Acyl-Homoserine Lactone-Producing Multi-Trait Aeromonas spp. on Wheat Genotypes Under Salt Stress

Salinity is one of the major threats to agricultural productivity worldwide. Soil and plant management practices, along with inoculation with plant-beneficial bacteria, play a key role in the plant’s tolerance toward salinity stress. The present study demonstrates the potential of acyl homoserine lactone (AHL)-producing plant growth promoting rhizobacteria (PGPR) strains of Aeromonas sp., namely, SAL-17 (accession no. HG763857) and SAL-21 (accession no. HG763858), for growth promotion of two wheat genotypes inherently different for salt tolerance potential. AHLs are the bacterial signal molecules that regulate the expression of various genes in bacteria and plants. Both Aeromonas spp., along with innate plant-growth-promoting (PGP) and salt tolerance traits, showed AHL production which was identified on tandem mass spectrometry as C6-HSL, 3-OH-C5-HSL, 3-OH-C6-HSL, 3-oxo-C7-HSL C10-HSL, 3-oxo-C10-HSL, 3-OH-C10-HSL, 3-oxo-C12-HSL and C6-HSL, and 3-oxo-C10-HSL. The exogenous application of purified AHLs (mix) significantly improved various root parameters at 200 mM NaCl in both salt-sensitive (SSG) and salt-tolerant (STG) genotypes, where the highest increase (≈80%) was observed where a mixture of both strains of AHLs was used. Confocal microscopic observations and root overlay assay revealed a strong root colonization potential of the two strains under salt stress. The inoculation response of both STG and SSG genotypes was evaluated with two AHL-producing strains (SAL-17 and SAL-21) and compared to non-AHL-producing Aeromonas sp. SAL-12 (accession no. HG763856) in saline (EC = 7.63 ms/cm²) and non-saline soil. The data reveal that plants inoculated with the bacterial consortium (SAL-21 + SAL-17) showed a maximum increase in leaf proline content, nitrate reductase activity, chlorophyll a/b, stomatal conductance, transpiration rate, root length, shoot length, and grain weight over non-inoculated plants grown in saline soil. Both STG and SSG showed relative effectiveness toward inoculation (percent increase for STG: 165–16%; SSG: 283–14%) and showed a positive correlation of grain yield with proline and nitrate reductase activity. Furthermore, principal component analysis (PCA) and categorical PCA analysis clearly showed an inoculation response in both genotypes, revealing the effectiveness of AHL-producing Aeromonas spp. than the non-AHL-producing strain. The present study documents that the consortium of salt-tolerant AHL-producing Aeromonas spp. is equally effective for sustaining the growth of STG as well as SSG wheat genotypes in saline soil, but biosafety should be fully ensured before field release.

An Update on the Genus Aeromonas: Taxonomy, Epidemiology, and Pathogenicity

The genus Aeromonas belongs to the Aeromonadaceae family and comprises a group of Gram-negative bacteria widely distributed in aquatic environments, with some species able to cause disease in humans, fish, and other aquatic animals. However, bacteria of this genus are isolated from many other habitats, environments, and food products. The taxonomy of this genus is complex when phenotypic identification methods are used because such methods might not correctly identify all the species. On the other hand, molecular methods have proven very reliable, such as using the sequences of concatenated housekeeping genes like gyrB and rpoD or comparing the genomes with the type strains using a genomic index, such as the average nucleotide identity (ANI) or in silico DNA–DNA hybridization (isDDH). So far, 36 species have been described in the genus Aeromonas of which at least 19 are considered emerging pathogens to humans, causing a broad spectrum of infections. Having said that, when classifying 1852 strains that have been reported in various recent clinical cases, 95.4% were identified as only four species: Aeromonas caviae (37.26%), Aeromonas dhakensis (23.49%), Aeromonas veronii (21.54%), and Aeromonas hydrophila (13.07%). Since aeromonads were first associated with human disease, gastroenteritis, bacteremia, and wound infections have dominated. The literature shows that the pathogenic potential of Aeromonas is considered multifactorial and the presence of several virulence factors allows these bacteria to adhere, invade, and destroy the host cells, overcoming the immune host response. Based on current information about the ecology, epidemiology, and pathogenicity of the genus Aeromonas, we should assume that the infections these bacteria produce will remain a great health problem in the future. The ubiquitous distribution of these bacteria and the increasing elderly population, to whom these bacteria are an opportunistic pathogen, will facilitate this problem. In addition, using data from outbreak studies, it has been recognized that in cases of diarrhea, the infective dose of Aeromonas is relatively low. These poorly known bacteria should therefore be considered similarly as enteropathogens like Salmonella and Campylobacter.

Phage-Encoded LuxR-Type Receptors Responsive to Host-Produced Bacterial Quorum-Sensing Autoinducers

Bacteria communicate with chemical signal molecules to regulate group behaviors in a process called quorum sensing (QS). In this report, we find that genes encoding receptors for Gram-negative bacterial QS communication molecules are present on genomes of viruses that infect these bacteria. These viruses are called phages. We show that two phage-encoded receptors, like their bacterial counterparts, bind to the communication molecule produced by the host bacterium, suggesting that phages can “listen in” on their bacterial hosts. Interfering with bacterial QS and using phages to kill pathogenic bacteria represent attractive possibilities for development of new antimicrobials to combat pathogens that are resistant to traditional antibiotics. Our findings of interactions between phages and QS bacteria need consideration as new antimicrobial therapies are developed.

Quorum sensing (QS) is a process of cell-to-cell communication that bacteria use to orchestrate collective behaviors. QS relies on the cell-density-dependent production, accumulation, and receptor-mediated detection of extracellular signaling molecules called autoinducers (AIs). Gram-negative bacteria commonly use N-acyl homoserine lactones (AHLs) as their AIs, and they are detected by LuxR-type receptors. Often, LuxR-type receptors are insoluble when not bound to a cognate AI. In this report, we show that LuxR-type receptors are encoded on phage genomes, and in the cases we tested, the phage LuxR-type receptors bind to and are solubilized specifically by the AHL AI produced by the host bacterium. We do not yet know the viral activities that are controlled by these phage QS receptors; however, our observations, coupled with recent reports, suggest that their occurrence is more widespread than previously appreciated. Using receptor-mediated detection of QS AIs could enable phages to garner information concerning the population density status of their bacterial hosts. We speculate that such information can be exploited by phages to optimize the timing of execution of particular steps in viral infection.

The Significance of Mesophilic Aeromonas spp. in Minimally Processed Ready-to-Eat Seafood

Minimally processed and ready-to-eat (RTE) seafood products are gaining popularity because of their availability in retail stores and the consumers' perception of convenience. Products that are subjected to mild processing and products that do not require additional heating prior to consumption are eaten by an increasing proportion of the population, including people that are more susceptible to foodborne disease. Worldwide, seafood is an important source of foodborne outbreaks, but the exact burden is not known. The increased interest in seafood products for raw consumption introduces new food safety issues that must be addressed by all actors in the food chain. Bacteria belonging to genus Aeromonas are ubiquitous in marine environments, and Aeromonas spp. has held the title "emerging foodborne pathogen" for more than a decade. Given its high prevalence in seafood and in vegetables included in many RTE seafood meals, the significance of Aeromonas as a potential foodborne pathogen and a food spoilage organism increases. Some Aeromonas spp. can grow relatively uninhibited in food during refrigeration under a broad range of pH and NaCl concentrations, and in various packaging atmospheres. Strains of several Aeromonas species have shown spoilage potential by the production of spoilage associated metabolites in various seafood products, but the knowledge on spoilage in cold water fish species is scarce. The question about the significance of Aeromonas spp. in RTE seafood products is challenged by the limited knowledge on how to identify the truly virulent strains. The limited information on clinically relevant strains is partly due to few registered outbreaks, and to the disputed role as a true foodborne pathogen. However, it is likely that illness caused by Aeromonas might go on undetected due to unreported cases and a lack of adequate identification schemes. A rather confusing taxonomy and inadequate biochemical tests for species identification has led to a biased focus towards some Aeromonas species. Over the last ten years, several housekeeping genes has replaced the 16S rRNA gene as suitable genetic markers for phylogenetic analysis. The result is a more clear and robust taxonomy and updated knowledge on the currently circulating environmental strains. Nevertheless, more knowledge on which factors that contribute to virulence and how to control the potential pathogenic strains of Aeromonas in perishable RTE seafood products are needed.

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.

Electrochemical Characterization of a Novel Exoelectrogenic Bacterium Strain SCS5, Isolated from a Mediator-Less Microbial Fuel Cell and Phylogenetically Related to Aeromonas jandaei

A facultative anaerobic bacterium, designated as strain SCS5, was isolated from the anodic biofilm of a mediator-less microbial fuel cell using acetate as the electron donor and α-FeOOH as the electron acceptor. The isolate was Gram-negative, motile, and shaped as short rods (0.9-1.3 μm in length and 0.4-0.5 μm in width). A phylogenetic analysis of the 16S rRNA, gyrB, and rpoD genes suggested that strain SCS5 belonged to the Aeromonas genus in the Aeromonadaceae family and exhibited the highest 16S rRNA gene sequence similarity (99.45%) with Aeromonas jandaei ATCC 49568. However, phenotypic, cellular fatty acid profile, and DNA G+C content analyses revealed that there were some distinctions between strain SCS5 and the type strain A. jandaei ATCC 49568. The optimum growth temperature, pH, and NaCl (%) for strain SCS5 were 35°C, 7.0, and 0.5% respectively. The DNA G+C content of strain SCS5 was 59.18%. The isolate SCS5 was capable of reducing insoluble iron oxide (α-FeOOH) and transferring electrons to extracellular material (the carbon electrode). The electrochemical activity of strain SCS5 was corroborated by cyclic voltammetry and a Raman spectroscopic analysis. The cyclic voltammogram of strain SCS5 revealed two pairs of oxidation-reduction peaks under anaerobic and aerobic conditions. In contrast, no redox pair was observed for A. jandaei ATCC 49568. Thus, isolated strain SCS5 is a novel exoelectrogenic bacterium phylogenetically related to A. jandaei, but shows distinct electrochemical activity from its close relative A. jandaei ATCC 49568.

Potential pathogenicity ofAeromonas hydrophilacomplex strains isolated from clinical, food, and environmental sources

Aeromonas are autochthonous inhabitants of aquatic environments, including chlorinated and polluted waters, although they can also be isolated from a wide variety of environmental and clinical sources. They cause infections in vertebrates and invertebrates and are considered to be an emerging pathogen in humans, producing intestinal and extra-intestinal diseases. Most of the clinical isolates correspond to A. hydrophila, A. caviae, and A. veronii bv. Sobria, which are described as the causative agents of wound infections, septicaemia, and meningitis in immunocompromised people, and diarrhoea and dysenteric infections in the elderly and children. The pathogenic factors associated with Aeromonas are multifactorial and involve structural components, siderophores, quorum-sensing mechanisms, secretion systems, extracellular enzymes, and exotoxins. In this study, we analysed a representative number of clinical and environmental strains belonging to the A. hydrophila species complex to evaluate their potential pathogenicity. We thereby detected their enzymatic activities and antibiotic susceptibility pattern and the presence of virulence genes (aer, alt, ast, and ascV). The notably high prevalence of these virulence factors, even in environmental strains, indicated a potential pathogenic capacity. Additionally, we determined the adhesion capacity and cytopathic effects of this group of strains in Caco-2 cells. Most of the strains exhibited adherence and caused complete lysis.

Ocorrência de Aeromonas spp. em alimentos de origem animal e sua importância em saúde pública

Aeromonas spp. são bactérias Gram negativas, opor-tunistas, de natureza ubíqua, isoladas principalmente de amostras de água. Até o presente momento foram reconhecidas 31 espé-cies, sendo as de maior importância médica Aeromonas hydrophila, Aeromonas caviae e Aeromonas veronii. A patogenicidade do gênero é considerada multifatorial, sendo este produtor de diversos tipos de toxinas e com envolvimento de outros fatores capazes de facilitar a penetração e o estabelecimento do agente no hospedeiro, causando doença. O objetivo desta revisão é elucidar o papel dos alimentos de origem animal como fontes de contaminação de bactérias do gênero Aeromonas para o ser humano. Isolamentos de aeromonas de diversos produtos de origem animal têm sido relatados, como carne, leite e seus derivados, além de frutos do mar, e em ambientes de processamento, como abatedouros, frigorífcos e laticínios. Tem-se buscado determinar fontes de contaminação dos alimentos, e a água foi definida como o principal disseminador. Aeromonas já foi defnida como sendo a causadora de diversas enfermidades, desde afecções gastrointestinais até casos de meningite e morte. Considerando os alimentos de origem animal como importantes veículos de transmissão para o ser humano e o reconhecimento da água como fonte de disseminação do agente, torna-se imprescindível o tratamento adequado da água utilizada nos estabelecimentos processadores de alimentos para a segurança alimentar.

Clustering subspecies of Aeromonas salmonicida using IS630 typing

Background

The insertion element IS630 found in Aeromonas salmonicida belongs to the IS630-Tc1-mariner superfamily of transposons. It is present in multiple copies and represents approximately half of the IS present in the genome of A. salmonicida subsp. salmonicida A449.

Results

By using High Copy Number IS630 Restriction Fragment Length Polymorphism (HCN-IS630-RFLP), strains of various subspecies of Aeromonas salmonicida showed conserved or clustering patterns, thus allowing their differentiation from each other. Fingerprints of A. salmonicida subsp. salmonicida showed the highest homogeneity while ‘atypical’ A. salmonicida strains were more heterogeneous. IS630 typing also differentiated A. salmonicida from other Aeromonas species. The copy number of IS630 in Aeromonas salmonicida ranges from 8 to 35 and is much lower in other Aeromonas species.

Conclusions

HCN-IS630-RFLP is a powerful tool for subtyping of A. salmonicida. The high stability of IS630 insertions in A. salmonicida subsp. salmonicida indicates that it might have played a role in pathoadaptation of A. salmonicida which has reached an optimal configuration in the highly virulent and specific fish pathogen A. salmonicida subsp. salmonicida.

The main Aeromonas pathogenic factors

The members of the Aeromonas genus are ubiquitous, water-borne bacteria. They have been isolated from marine waters, rivers, lakes, swamps, sediments, chlorine water, water distribution systems, drinking water and residual waters; different types of food, such as meat, fish, seafood, vegetables, and processed foods. Aeromonas strains are predominantly pathogenic to poikilothermic animals, and the mesophilic strains are emerging as important pathogens in humans, causing a variety of extraintestinal and systemic infections as well as gastrointestinal infections. The most commonly described disease caused by Aeromonas is the gastroenteritis; however, no adequate animal model is available to reproduce this illness caused by Aeromonas. The main pathogenic factors associated with Aeromonas are: surface polysaccharides (capsule, lipopolysaccharide, and glucan), S-layers, iron-binding systems, exotoxins and extracellular enzymes, secretion systems, fimbriae and other nonfilamentous adhesins, motility and flagella.

Aeromonas rivuli sp. nov., isolated from the upstream region of a karst water rivulet

Two freshwater isolates (WB4.1-19T and WB4.4-101), sharing 99.9 % 16S rRNA gene sequence similarity, were highly related to Aeromonas sobria (99.7 % similarity; 6 bp differences). A phylogenetic tree derived from a multi-locus phylogenetic analysis (MLPA) of the concatenated sequences of five housekeeping genes (gyrB, rpoD, recA, dnaJ and gyrA; 3684 bp) revealed that both strains clustered as an independent phylogenetic line next to members of Aeromonas molluscorum and Aeromonas bivalvium. The DNA–DNA reassociation value between the two new isolates was 89.3 %. Strain WB4.1-19T had a DNA–DNA relatedness value of <70 % with the type strains of the other species tested. Phenotypic characterization differentiated the two novel strains from all other type strains of species of the genus Aeromonas. It is concluded that the two new strains represent a novel species of the genus Aeromonas, for which the name Aeromonas rivuli sp. nov. is proposed, with the type strain WB4.1-19T (=CECT 7518T=DSM 22539T=MDC 2511T).

Aeromonas spp. clinical microbiology and disease

Members of the genus Aeromonas inhabit various aquatic environments and are responsible for, and are implicated in, a number of intestinal and extra-intestinal infections in humans as well as other animals. This review focuses on invasive human infection and disease and summarizes available findings regarding the microbiology and detection of Aeromonas spp., with emphasis on successful identification and diagnosis, and the control of disease in the population. Antimicrobial resistance and therapy of Aeromonas spp. is also discussed.

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.

Aeromonas fluvialis sp. nov., isolated from a Spanish river

A Gram-stain-negative, facultatively anaerobic bacterial strain, designated 717(T), was isolated from a water sample collected from the Muga river, Girona, north-east Spain. Preliminary analysis of the 16S rRNA gene sequence showed that this strain belonged to the genus Aeromonas, the nearest species being Aeromonas veronii (99.5 % similarity, with seven different nucleotides). A polyphasic study based on a multilocus phylogenetic analysis of five housekeeping genes (gyrB, rpoD, recA, dnaJ and gyrA; 3684 bp) showed isolate 717(T) to be an independent phylogenetic line, with Aeromonas sobria, Aeromonas veronii and Aeromonas allosaccharophila as the closest neighbour species. DNA-DNA reassociation experiments and phenotypic analysis identified that strain 717(T) represents a novel species, for which the name Aeromonas fluvialis sp. nov. is proposed, with type strain 717(T) (=CECT 7401(T) =LMG 24681(T)).

Classification of brown pigmented aeromonads isolated from river water

Nine Aeromonas strains having a brown exopigment were isolated during the microbiological examination of river water. These brown-pigmented aeromonads were characterized by the phenotyping, fatty-acid methyl-ester analysis and ribotyping. All methods identically confirmed that the group of brown-pigmented aeromonads is quite heterogeneous. Apart from the Aeromonas media taxon, the brown-pigmented aeromonads in river water were represented also by strains of A. allosaccharophila and A. salmonicida subsp. pectinolytica.

Prevalence of bacterial pathogens and their anti-microbial resistance in Tilapia and their pond water in Trinidad

In Trinidad, Tilapia (Oreonchromis spp.) is one of the most important fresh water food fish and the number of farms has been increasing annually. A study was conducted in the local tilapia industry to determine the microbial quality of pond water, prevalence of bacterial pathogens and their anti-microbial resistance using the disk diffusion method. Seventy-five apparently healthy fish and 15 pond water samples from three of the four commercial tilapia fish farms in the country were processed. The 202 bacterial isolates recovered from fish slurry and 88 from water, belonged to 13 and 16 genera respectively. The predominant bacteria from fish slurry were Pseudomonas spp. (60.0%), Aeromonas spp. (44.0%), Plesiomonas (41.3%) and Chromobacterium (36.0%) (P < 0.05; chi(2)) compared with isolates from pond water where Bacillus spp. (80.0%), Staphylococcus spp., Alcaligenes spp. and Aeromonas spp. (60.0%) were most prevalent (P < 0.05; chi(2)). Using eight anti-microbial agents, to test bacteria from five genera (Aeromonas, Chromobacterium, Enterobacter, Plesiomonas and Pseudomonas), 168 (97.1%) of 173 bacterial isolates from fish slurry exhibited resistance to one or more anti-microbial agents compared with 47 (90.4%) of 52 from water (P > 0.05; chi(2)). Resistance was high to ampicillin, 90.2% (158 of 173), erythromycin, 66.5% (115 of 173) and oxytetracycline, 52.6%, (91 of 173) but relatively low to chloramphenicol, 9.8% (17 of 173) and sulphamethoxazole/trimethoprim, 6.4% (11 of 173) (P < 0.05; chi(2)). For pond water isolates, the frequency of resistance across bacterial genera ranged from 75% (nine of 12) for Chromobacter spp. to 100% found amongst Enterobacter spp. (six of six), Plesiomonas spp. (nine of nine) and Pseudomonas spp. (eight of eight) (P < 0.05; chi(2)). Resistance was generally high to ampicillin, 78.8% (41 of 52), erythromycin, 51.9% (27 of 52) and oxytetracycline, 34.5% (18 of 52) but low to sulphamethoxazole/trimethoprim, 7.7% (four of 52) and norfloxacin, 3.8% (two of 52) (P < 0.05; chi(2)). It was concluded that the rather high prevalence of bacterial pathogens in tilapia along with their high prevalence of resistance to anti-microbial agents might pose therapeutic problems as well as health risk to consumers. The microbial presence and their anti-microbial resistance in the tilapia industry are being reported for the first time in the country.

Antimicrobial properties of two purified skin peptides from the mink frog (Rana septentrionalis) against bacteria isolated from the natural habitat

Numerous peptides exhibiting antimicrobial properties have been isolated from the skins of many amphibian species. These peptides offer an innate chemical defense system against various microbial agents that exist in the amphibian's environment. Amphibian skin peptides are typically tested for antimicrobial activity against microbial strains that are pathogenic to humans, but not on potential pathogenic or opportunistic bacteria that exist in the organism's habitat. Two peptides, a brevinin-2-related peptide and temporin-1SPb previously isolated from secretions of the mink frog, Rana septentrionalis, were tested for antimicrobial activity on bacterial isolates endemic to the frog's habitat. Ten isolates were identified, using 16S rRNA gene sequencing techniques, in the genera Pseudomonas, Serratia, Bacillus, Aeromonas, Burkholderia, Microbacterium, and Delftia. Bacterial isolates were tested with peptides at concentrations ranging from 0.8 microM to 1000 microM to determine the minimum inhibitory concentration (MIC) to inhibit growth. Growth of four of the isolates was inhibited by temporin-1SPb at the concentrations used, but all of the isolates were inhibited by the brevinin-2-related within the range of peptide concentrations used. This demonstrates the efficacy of both peptides as a component of the frog's innate chemical defense system.

Use of the novel phylogenetic marker dnaJ and DNA-DNA hybridization to clarify interrelationships within the genus Aeromonas

The interrelationships of 27 Aeromonas strains were investigated using dnaJ sequences and DNA-DNA hybridization. dnaJ sequence similarities showed a stronger relationship with DNA-DNA relatedness values than did 16S rRNA gene sequence similarities. Additionally, dnaJ sequence analysis, with interspecies divergence over 5.2 % in most cases, gave better resolution than 16S rRNA gene sequences for the differentiation of strains at the species level. Relationships among Aeromonas species were therefore elucidated on the basis of dnaJ sequences and DNA-DNA reassociation. Strains of Aeromonas encheleia and Aeromonas sp. HG11 were unquestionably grouped in the same genetic species, since they shared 98.7 % dnaJ sequence similarity and 82-85 % genomic relatedness. The phylogenetically close relationships obtained from dnaJ sequence analysis (1.7-3.3 % genetic distance) were corroborated by high DNA-DNA relatedness (73-97 %) to support the previous suggestion that Aeromonas culicicola and Aeromonas allosaccharophila are later heterotypic synonyms of Aeromonas veronii. Our findings will contribute to the clarification of controversial relationships in the genus Aeromonas and also demonstrate that analysis of dnaJ sequences can be a powerful tool for interspecies study of the genus.

Dominant pathogenic species of mesophilic aeromonads isolated from diseased and healthy fish cultured in Poland

Aeromonas isolates were collected from cultured fish, characterized phenotypically and identified to species using 16S rDNA. The pathogenicity of all isolates was assayed on the basis of haemolytic and proteolytic activity and challenge tests were performed for isolates from healthy fish. A total of 131 Aeromonas isolates were obtained and identified as follows: A. hydrophila (13), A. bestiarum (23), A. salmonicida (motile biogroup) (19), A. caviae (2), A. sobria (18), A. veronii bt. sobria (42), A. jandaei (1), A. encheleia (11) and A. allosaccharophila (2). All isolates of A. hydrophila and A. bestiarum and most isolates of A. salmonicida and A. veronii were classified as pathogenic. Aeromonas hydrophila was isolated only from diseased trout except for one isolate obtained from carp fry. The other potentially pathogenic Aeromonas species were present in diseased as well as healthy fish. The pathogenicity of isolates from healthy fish was correlated with their enzymatic activity and was also tested by challenge experiments. The dominant pathogenic species were A. veronii bt. sobria, A. bestiarum and A. salmonicida in common carp and A. hydrophila in rainbow trout.

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

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

Sampling bias created by ampicillin in isolation media forAeromonas

Members of the bacterial genus Aeromonas are widely isolated from aquatic environments and studied in part for their ability to act as opportunistic pathogens in a variety of animals. All aeromonads, with the exception of Aeromonas trota, are generally thought to be resistant to ampicillin, so the antibiotic is frequently added to isolation medium as a selective agent. In this study, 282 aeromonads from environmental sources were isolated on a medium without ampicillin and their resistance to ampicillin determined. Of the 104 of these isolates that were judged to be independent (nonredundant), 18 (17.3%) were susceptible to ampicillin. A chi-square analysis was performed to determine the impact of ampicillin use on enumerating Aeromonas species from environmental samples. Our results indicate that, when ampicillin is used as a selective agent, a significant portion of the aeromonad population in at least some environ ments can be omitted from isolation.Key words: Aeromonas, ampicillin, selective media.

Aeromonas sharmana sp. nov., isolated from a warm spring

A Gram-negative, facultatively anaerobic bacterial strain designated GPTSA-6(T) was isolated from a water sample collected from a warm spring in Assam, India. Preliminary analysis of the 16S rRNA gene sequence of this isolate revealed its affiliation to the family Aeromonadaceae. Detailed characterization using a polyphasic approach indicated that strain GPTSA-6(T) is most closely related to Aeromonas sobria but differs significantly from existing members of the genus Aeromonas. Analysis of the almost-complete (1430 nt) 16S rRNA gene sequence of this strain revealed that its closest relative (99.23 % similarity) is an uncultured bacterial clone, A-8, isolated from an algal bloom. Of the taxa with validly published names, Aeromonas sobria ATCC 43979(T) showed the highest level of sequence similarity (95.13 %) with respect to strain GPTSA-6(T), followed by Aeromonas molluscorum 848T(T) and Aeromonas popoffii LMG 17541(T) (95.04 % similarity in both cases). On the basis of the phenotypic, chemotaxonomic and phylogenetic data, it can be concluded that strain GPTSA-6(T) represents a novel species of the genus Aeromonas, for which the name Aeromonas sharmana sp. nov. is proposed. The type strain is GPTSA-6(T) (=MTCC 7090(T)=DSM 17445(T)).

Antimicrobial susceptibilities of Aeromonas spp. isolated from environmental sources

Aeromonas spp. are ubiquitous aquatic bacteria that cause serious infections in both poikilothermic and endothermic animals, including humans. Clinical isolates have shown an increasing incidence of antibiotic and antimicrobial drug resistance since the widespread use of antibiotics began. A total of 282 Aeromonas pure cultures were isolated from both urban and rural playa lakes in the vicinity of Lubbock, Texas, and several rivers in West Texas and New Mexico. Of these, at least 104 were subsequently confirmed to be independent isolates. The 104 isolates were identified by Biolog and belonged to 11 different species. The MICs of six metals, one metalloid, five antibiotics, and two antimicrobial drugs were determined. All aeromonads were sensitive to chromate, cobalt, copper, nickel, zinc, cefuroxime, kanamycin, nalidixic acid, ofloxacin, tetracycline, and sulfamethoxazole. Low incidences of trimethoprim resistance, mercury resistance, and arsenite resistance were found. Dual resistances were found in 5 of the 104 Aeromonas isolates. Greater numbers of resistant isolates were obtained from samples taken in March versus July 2002 and from sediment versus water. Plasmids were isolated from selected strains of the arsenite- and mercury-resistant organisms and were transformed into Escherichia coli XL1-Blue MRF'. Acquisition of the resistance phenotypes by the new host showed that these resistance genes were carried on the plasmids. Mercury resistance was found to be encoded on a conjugative plasmid. Despite the low incidence of resistant isolates, the six playa lakes and three rivers that were sampled in this study can be considered a reservoir for antimicrobial resistance genes.

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 molluscorum sp. nov., isolated from bivalve molluscs

Five Aeromonas strains (848T(T), 93M, 431E, 849T and 869N), which were isolated from bivalve molluscs and were recognized previously by numerical taxonomy as members of an unknown Aeromonas taxon, were subjected to a polyphasic taxonomic study. DNA-DNA hybridization experiments showed that DNA of strain 848T(T) was <70 % similar (27-45 %) to that of the type/reference strains of the current Aeromonas hybridization groups (HGs), but 93 % similar to that of strain 93M. The DNA G+C content of the five strains ranged from 59.0 to 59.4 mol%. 16S rRNA gene sequence analysis confirmed that the strains belonged to the genus Aeromonas and showed high similarity to Aeromonas encheleia. Amplified fragment length polymorphism fingerprinting clustered the novel strains in a homogeneous group with low genotypic relatedness to other Aeromonas species. Useful phenotypic features for differentiating the five isolates from other Aeromonas species include their negative reactions in tests for indole production, lysine decarboxylase, gas from glucose and starch hydrolysis. From the results of this study, the name Aeromonas molluscorum sp. nov. is proposed for these strains, with the type strain 848T(T) (=CECT 5864(T)=LMG 22214(T)).

Polymorphism of Aeromonas spp. tRNA intergenic spacers

We investigated the length polymorphism of the intergenic spacers lying between tRNA genes of Aeromonas spp. A total of 69 strains representing all known genomic species of Aeromonas were used in the study. tDNA-PCR patterns were examined by Dice coefficient (S(D)) and unweighted pair group method of clustering (UPGMA). The strains were allocated into 15 groups at a similarity level of 70%. The strains belonging to seven genomic species: A. hydrophila (HG 1), A. caviae (HG 4), A. sobria (HG 7), A. veronii (HG 8/10), A. encheleia (HG 16), A. popoffii (HG 17), and A. culicicola (HG 18) formed distinct clusters. Our study revealed a genetic heterogeneity of the following species: A. bestiarum, A. salmonicida, A. media, A. eucrenophila, A. jandaei, A. schubertii, and A. allosaccharophila.

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

AIMS

To examine whether Aeromonas bacteria isolated from municipally treated water had virulence factor genes.

METHODS AND RESULTS

A polymerase chain reaction-based genetic characterization determined the presence of six virulence factors genes, elastase (ahyB), lipase (pla/lip/lipH3/alp-1) flagella A and B (flaA and flaB), the enterotoxins, act, alt and ast, in these isolates. New primer sets were designed for all the target genes, except for act. The genes were present in 88% (ahyB), 88% (lip), 59% (fla), 43% (alt), 70% (act) and 30% (ast) of the strains, respectively. Of the 205 isolates tested only one isolate had all the virulence genes. There was a variety of combinations of virulence factors within different strains of the same species. However, a dominant strain having the same set of virulence factors, was usually isolated from any given tap in different rounds of sampling from a single tap.

CONCLUSIONS

These results show that Aeromonas bacteria found in drinking water possess a wide variety of virulence-related genes and suggest the importance of examining as many isolates as possible in order to better understand the health risk these bacteria may present.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study presents a rapid method for characterizing the virulence factors of Aeromonas bacteria and suggests that municipally treated drinking water is a source of potentially pathogenic Aeromonas bacteria.

Aeromonas popoffii urinary tract infection

Aeromonas popoffii is a recently described species isolated mainly from freshwater. An isolate of Aeromonas popoffii was found to be responsible for a urinary tract infection in a 13-year-old boy suffering from spina bifida with enterocystoplasty. This is the first reported case of human infection attributed to this species.

Restriction Fragment Length Polymorphism of 16S–23S rDNA Intergenic Spacer of Aeromonas spp

We analyzed restriction fragment length polymorphism (RFLP) of 16S-23S rDNA intergenic spacer region (ISR) of Aeromonas species. A total of 69 isolates belonging to 18 DNA hybridization groups (HG; equivalent of genomic species) were used in this study. ISRs were amplified by PCR and the products were digested with four restriction endonucleases: Hin6I, Csp6I, TaqI, and TasI. The RFLP patterns obtained after digesting by particular enzymes revealed ISR polymorphism of isolates allocated to individual genomic species. The combined Hin6I, Csp6I, TaqI, and TasI restriction profiles were examined by Dice coefficient (SD) and unweighted pair group method of clustering (UPGMA). The isolates were allocated into 15 groups, three strains were unclustered. The strains belonging to the following genomic species: A. hydrophila, A. bestiarum, A. salmonicida, A. caviae, A. media, A. schubertii, A. allosaccharophila, A. popoffii, and A. culicicola formed distinct clusters. Strains belonging to HG 6, HG 7, HG 11, and HG 16 revealed similar combined RFLP patterns and constituted one group. Similarly, the strains of A. jandaei (HG 9) and the type strain of A. trota were allocated into one cluster. Two isolates of HG 14 formed distinct cluster. We noticed a genetic diversity among A. veronii isolates, the strains were clustered in two groups. Our study showed that combined ISR-RFLP analysis may be used for identification of some species of Aeromonas.

Aeromonas simiae sp. nov., isolated from monkey faeces

Two Aeromonas strains, IBS S6874(T) and IBS S6652, were isolated from the faeces of two healthy monkeys (Macaca fascicularis) from Mauritius that were kept in quarantine in the Centre for Primatology, Strasbourg, France. Phylogenetic analysis based on 16S rRNA gene sequences showed that the two isolates formed an unknown genetic lineage within the genus Aeromonas. The two isolates had nearly identical sequences (0.1 % nucleotide substitution) that were related closely to those of recognized Aeromonas species (1.7-3.5 % nucleotide substitution). DNA-DNA hybridization showed that strains IBS S6874(T) and IBS S6652 had high DNA-DNA similarity (89 %) to each other and a low level of DNA-DNA similarity to closely related taxa (18 % relatedness to Aeromonas trota and 16 % relatedness to Aeromonas schubertii). Phenotypically, the two monkey isolates differed from most previously described mesophilic Aeromonas species by their lack of haemolysis on sheep-blood agar and inability to produce indole, gas from glucose or acid from mannitol. They differed from the most closely related species, A. schubertii, by their ability to produce acid from D-cellobiose and D-sucrose and by their pyrazinamidase activity. The name Aeromonas simiae sp. nov. is proposed for these isolates; strain IBS S6874(T) (=CIP 107798(T)=CCUG 47378(T)) is the type strain.

Genetic diversity and population structure of Aeromonas hydrophila, Aer. bestiarum, Aer. salmonicida and Aer. popoffii by multilocus enzyme electrophoresis (MLEE)

Genetic diversity, genetic relationship, identification and population structure of 120 Aeromonas strains (including Aer. hydrophila, Aer. bestiarum, Aer. salmonicida and Aer. popoffii) isolated from various sources were studied by analysis of 15 genetic loci by multilocus enzyme electrophoresis (MLEE). All 15 loci were polymorphic, with an average of 9.4 alleles per locus and a mean genetic diversity (H) of 0.64. Cluster analysis defined at H < or = 0.7 differentiated most of the taxa analysed except the Aer. popoffii and Aer. bestiarum strains, which showed a close genetic relationship. Allelic frequencies of five loci (EST1, HEX, IDH, LDH1 and MDH) identified 94% of the strains. The index of association (IA) for the total sample was 2.38 and IA values calculated for the different populations were always significantly different from zero. These results suggest that the population structure of this Aeromonas sample is strongly clonal, confirm the taxonomic status of the analysed species in population genetics terms, and show the usefulness of MLEE for identifying Aeromonas species.

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

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

Phylogenetic affiliation of Aeromonas culicicola MTCC 3249(T) based on gyrB gene sequence and PCR-amplicon sequence analysis of cytolytic enterotoxin gene

We determined the gyrB gene sequences of all 17 hybridizations groups of Aeromonas. Phylogenetic trees showing the evolutionary relatedness of gyrB and 16S rRNA genes in the type strains of Aeromonas were compared. Using this approach, we determined the phylogenetic position of Aeromonas culicicola MTCC 3249(T), isolated from midgut of Culex quinquefasciatus. In the gyrB based-analysis A. culicicola MTCC 3249(T) grouped with A. veronii whereas, it grouped with A. jandaei in the 16S rRNA based tree. The number of nucleotide differences in 16S rRNA sequences was less than found with the gyrB sequence data. Most of the observed nucleotide differences in the gyrB gene were synonymous. The Cophenetic Correlation Coefficient (CCC) for gyrB sequences was 0.87 indicating this gene to be a better molecular chronometer compared to 16S rRNA for delineation of Aeromonas species. This strain was found to be positive for the cytolytic enterotoxin gene. PCR-Amplicon Sequence Analysis (PCR-ASA) of this gene showed that the isolate is affiliated to type I and is potentially pathogenic. These PCR-ASA results agreed in part with the gyrB sequence results.

The genus Aeromonas: biochemical characteristics, atypical reactions, and phenotypic identification schemes

A total of 193 strains representing 14 different Aeromonas genomospecies were evaluated for 63 phenotypic properties to create useful tables for the reference identification of mesophilic aeromonads. Only 9 of 62 biochemical tests (14%) yielded uniform results, and the fermentation of certain carbohydrates was found to be linked to specific species. A number of unusual or aberrant properties for the genus Aeromonas were also detected in the collection of 428 strains (193 in the phenotypic study, 235 in a retrospective review). These tests included susceptibility to the vibriostatic agent, fermentation of m-inositol and D-xylose, hydrolysis of urea, and the lack of cytochrome oxidase activity. Fermentation of melibiose was linked to raffinose fermentation in all Aeromonas species except A. jandaei. Keys are provided for clinical laboratories choosing to identify aeromonads to species level based upon initial Møeller decarboxylase and dihydrolase reactions. In addition, several new tests were identified that help to separate members of the A. caviae complex (A. caviae, A. media, and A. eucreonophila).

Niche-specific association of Aeromonas Ribotypes from human and environmental origin

A total of 88 Aeromonas isolates from distinct locations and sources (39 from extraintestinal infections, 31 from diarrhoeic, ten from non-diarrhoeic faeces, all human, and eight from fresh water) were subjected to phenospecies identification, serotyping, ribotyping and detection of some virulence markers. The strains belonged to four different phenospecies marked by 19 O serogroups and 38 ribotypes. No strong correlation between these parameters was found, and no group, as defined by the typing methods, could be characterized with a particular set of virulence markers. There was a clear association of ribotypes with the source of the strains. Cluster analysis allowed the identification of a complex of ribotypes belonging to distinct but related sources, including clinical and environmental isolates. These results suggest that ribotyping may be an epidemiological tool suitable for the study of Aeromonas infections.

Distribution of Aeromonas spp. as identified by 16S rDNA restriction fragment length polymorphism analysis in a trout farm

AIMS

This study used restriction fragment length polymorphism (RFLP) with Aeromonas-specific primers to identify species of Aeromonas and to investigate their distribution in a trout farm and stream.

METHODS AND RESULTS

In January, May, August and November 2000, presumptive Aeromonas species were recovered from a farm and a sedimentation pond in a fish farm and stream, and identified by PCR-RFLP analysis with Aeromonas-specific primers. The specificity of Aeromonas-specific primers and the suitability of PCR-RFLP analysis for identifying Aeromonas spp. were confirmed with fatty acid methyl esters (FAMEs) and 16S rDNA sequencing analyses, respectively. Levels of Aeromonas spp. sampled in May and August were higher than in January and November at all sampling sites. Aeromonas salmonicida was the dominant species in January and November, and the proportion of pathogenic species (Aer. hydrophila, Aer. caviae and Aer. veronii) increased in May and August.

CONCLUSIONS

PCR-RFLP analysis with Aeromonas-specific primers is a rapid and reliable method for identifying widely distributed Aeromonas spp. from environmental samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

To minimize human health risk, monitoring the levels and species composition of Aeromonas in fish farm is advisable.

Phenotypic characteristics and pathogenicity of Aeromonas genomospecies isolated from common carp (Cyprinus carpio L.)

AIMS

To evaluate the relationship between the genomospecies, phenotypic profile and pathogenicity for carp of 37 motile Aeromonas strains.

METHODS AND RESULTS

Aeromonas strains were identified to genomospecies level by the 16S rDNA restriction fragment length polymorphism (RFLP) method and characterized phenotypically by the API 20E and API Zym systems and by conventional tube or plate methods. 16S rDNA RFLP analysis showed that the strains belonged to five species, Aeromonas bestiarum (5), Aerom. salmonicida (13), Aerom. veronii (11), Aerom. sobria (6) and Aerom. encheleia (2). Most strains of Aerom. bestiarum (80%) and Aerom. salmonicida (85%) could be separated by growth at 4 and 42 degrees C, autoagglutination after boiling, reaction for lipase (C14) and naphthol-AS-BI-phosphohydrolase. All strains of Aerom. veronii corresponded to Aerom. veronii biotype sobria and could be separated from Aerom. sobria by citrate utilization, growth at 37 and 42 degrees C, amygdalin and cellobiose fermentation. All strains of Aerom. bestiarum and most strains of Aerom. salmonicida (76.9%) and Aerom. veronii (63.6%) were pathogenic for carp.

CONCLUSIONS

The biochemical identification of carp Aeromonas strains is not entirely clear. Some association between Aeromonas species, phenotypic profile and specific disease signs was observed.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results will be useful for ichthyopathology laboratories in the diagnosis of motile aeromonad septicaemia in carp.

Aeromonas hydrophila subsp. ranae subsp. nov., isolated from septicaemic farmed frogs in Thailand

A group of seven sucrose-negative Aeromonas strains (referred to as group Au) isolated from the internal organs of septicaemic farmed frogs (Rana rugulosa) in Thailand was subjected to a polyphasic taxonomic study including fluorescent amplified fragment length polymorphism (FAFLP) and ERIC-PCR fingerprinting, 16S rDNA sequencing, microplate DNA-DNA hybridizations and extensive phenotypic characterization. Comparison of FAFLP and ERIC-PCR fingerprints indicated that the group Au isolates belonged to the species Aeromonas hydrophila DNA hybridization group (HG) 1 in which they represent a genotypic subgroup closely affiliated to A. hydrophila subsp. hydrophila and subsp. dhakensis. One representative of the Au group exhibited > or = 99.0% 16S rDNA sequence similarity with the type strains of the two A. hydrophila subspecies. DNA-DNA hybridization with type and reference strains of all known Aeromonas taxa revealed that the Au group represented a homogeneous taxon that exhibited the highest relatedness with members of the two A. hydrophila subspecies, ranging from 75 to 93%. Phenotypic characterization on the basis of 152 features further revealed that the Au group isolates differed from A. hydrophila subsp. hydrophila or subsp. dhakensis in a total of 13 biochemical properties. Of these, assimilation of L-glycine and isobutyrate as sole carbon source, acid production from salicin and D-sucrose, and aesculin hydrolysis were of diagnostic value. From the results of this study, it can be concluded that the Aeromonas frog isolates of the Au group represent a new subspecies of A. hydrophila, for which the name Aeromonas hydrophila subsp. ranae subsp. nov. is proposed. Its type strain is Au-1D12(T) (=LMG 19707(T) = CCUG 46211(T)).

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

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

Induced colistin resistance as an identifying marker for Aeromonas phenospecies groups

AIMS

To investigate the taxonomic interest of colistin resistance as an identifying marker for Aeromonas phenospecies groups.

METHODS AND RESULTS

Colistin resistance was investigated in 387 Aeromonas isolates identified at species level using a 14-test format protocol with miniaturized tests combined with determination of urocanic acid utilization whenever necessary. Colistin resistance, determined by the disc diffusion method, was unreliable when compared with minimum inhibitory concentration (MIC) determination. In some strains, the MIC values and resistance rates of colistin could be increased after overnight induction with a 50- microg colistin disc in 20 ml of Mueller-Hinton broth (2.5 mg l(-1)). Colistin-induced resistance level was raised to 85.8% in the Aeromonas hydrophila complex, 2.1% in the A. caviae complex and 2.5% in the A. veronii complex except for A. jandaei (100% colistin resistant). This new marker allowed the identification of 96.2 and 93.6% of Aeromonas isolates to phenospecies and species level, respectively.

CONCLUSIONS

Colistin-induced colistin resistance is a new phenotypic marker for Aeromonas isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

With the present protocol, colistin resistance determination may improve the identification of Aeromonas isolates to phenogroup level, when results obtained by conventional biochemical methods are ambiguous.

PCR detection of potentially pathogenic aeromonads in raw and cold-smoked freshwater fish

AIMS

Development of a PCR assay for detection of aeromonads carrying the hlyA and/or aerA genes in fish.

METHODS AND RESULTS

The protocol involves an overnight selective enrichment step in tryptic soy broth yeast extract containing 10 microg ml(-1) of ampicillin followed by extraction of DNA and PCR amplification of two haemolysin genes that contribute to the virulence of Aer. hydrophila. This procedure can detect initial populations of 1-10 cfu g(-1) within 24 h in artificially contaminated samples. In naturally contaminated fish, both genes were detected in 13 out of 14 fresh fish lots (aeromonads levels between < 1 and 5.42 log cfu g(-1)) and in 4 out of 16 lots of vacuum-packed cold-smoked fish (aeromonads levels between < 1 and 3.37 log cfu g(-1)). Before enrichment, dominant species were Aer. hydrophila HG1 (aerA+hlyA+), Aer. bestiarum HG2 (aerA+hlyA+) and Aer. caviae HG4 (aerA-hlyA-). After enrichment, Aer. hydrophila HG1 (aerA+hlyA+) was dominant.

CONCLUSIONS

Fresh fish and even smoked fish carry hlyA+ and/or aerA+ aeromonads that can be detected by PCR within 24 h.

SIGNIFICANCE AND IMPACT OF THE STUDY

The PCR assay described offers considerable potential as a rapid method with specificity, sensitivity and simplicity.

Biochemical identification and numerical taxonomy of Aeromonas spp. isolated from environmental and clinical samples in Spain

AIMS

To study the phenotypic characteristics of Aeromonas spp. from environmental and clinical samples in Spain and to cluster these strains by numerical taxonomy.

METHODS AND RESULTS

A collection of 202 Aeromonas strains isolated from bivalve molluscs, water and clinical samples was tested for 64 phenotypic properties; 91% of these isolates were identified at species level. Aeromonas caviae was predominant in bivalve molluscs and Aerom. bestiarum in freshwater samples. Cluster analyses revealed eight different phena: three containing more than one DNA-DNA hybridization group but including strains that belong to the same phenospecies complex (Aerom. hydrophila, Aerom. sobria and Aerom. caviae), Aerom. encheleia, Aerom. trota and three containing unidentified Aeromonas strains isolated from bivalve molluscs.

CONCLUSIONS

Aeromonas spp. are widely distributed in environmental and clinical sources. A selection of 16 of the phenotypical tests chosen allowed the identification of most isolates (91%), although some strains remain unidentified, mainly isolates from bivalve molluscs, suggesting the presence of new Aeromonas species. Numerical taxonomy was not in total concordance with the identification of the studied strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

Numerical taxonomy of Aeromonas strains isolated from different sources revealed the presence of potentially pathogenic Aeromonas spp., especially in bivalve molluscs, and phena with unidentified strains that suggest new Aeromonas species.

Phenotypic study by numerical taxonomy of strains belonging to the genus Aeromonas

AIMS

This study was undertaken to cluster and identify a large collection of Aeromonas strains.

METHODS AND RESULTS

Numerical taxonomy was used to analyse phenotypic data obtained on 54 new isolates taken from water, fish, snails, sputum and 99 type and reference strains. Each strain was tested for 121 characters but only the data for 71 were analysed using the 'SSM' and 'SJ' coefficients, and the UPGMA clustering algorithm. At SJ values of > or = 81.6% the strains clustered into 22 phenons which were identified as Aer. jandaei, Aer. hydrophila, Aer. encheleia, Aer. veronii biogroup veronii, Aer. trota, Aer. caviae, Aer. eucrenophila, Aer. ichthiosmia, Aer. sobria, Aer. allosaccharophila, Aer. media, Aer. schubertii and Aer. salmonicida. The species Aer. veronii biogroup sobria was represented by several clusters which formed two phenotypic cores, the first related to reference strain CECT 4246 and the second related to CECT 4835. A good correlation was generally observed among this phenotypic clustering and previous genomic and phylogenetic data. In addition, three new phenotypic groups were found, which may represent new Aeromonas species.

CONCLUSIONS

The phenetic approach was found to be a necessary tool to delimitate and identify the Aeromonas species.

SIGNIFICANCE AND IMPACT OF THE STUDY

Valuable traits for identifying Aeromonas as well as the possible existence of new Aeromonas species or biotypes are indicated.

Foodborne pathogenic bacteria in prepackaged fresh retail portions of farmed rainbow trout and salmon stored at 3 degrees C

Twelve lots of fresh unskinned fillets of rainbow trout (Oncorhynchus mykiss) and 10 lots of fresh sliced salmon (Salmo salar) prepacked in trays wrapped with an oxygen-permeable film were obtained immediately after packing from two supermarkets having in-plant facilities for packaging wet fish. During storage at 3 degrees C, Listeria innocua was detected in eight lots of trout fillets after 4 days storage. L. monocytogenes was recovered from a single lot also contaminated with L. innocua. Initial numbers of aeromonads were significantly (p < 0.05) lower in trout fillets (3.35 +/- 0.62 log cfu g(-1)) than in salmon slices (4.20 +/- 0.89 log cfu g(-1)). In both fish products, these bacteria significantly (p < 0.05) increased up until spoilage. Most Aeromonas spp. isolates from trout fillets were assigned to A. veronii biovar sobria HG8 (hybridisation group 8), A. caviae HG4, A. eucrenophila HG6, A. hydrophila HG1 and A. veronii biovar veronii HG10. Strains of HG12 (A. schubertii), HG4 and HG8 formed the majority of aeromonads recovered from salmon slices.

Potential virulence and antimicrobial susceptibility of Aeromonas popoffii recovered from freshwater and seawater

Aeromonas popoffii is the most recent species within the genus Aeromonas described from freshwater. In our study this species was also recovered from this habitat and for the first time from seawater. Most of the virulence factors known in Aeromonas spp. (aerolysin/hemolysin, serine protease, lipases and DNases) were highly prevalent in this species. Third-generation cephalosporins and quinolones were the most active antimicrobial agents against A. popoffii.