Aeromonas jandaei (formerly genospecies DNA group 9 A. sobria), a new sucrose-negative species isolated from clinical specimens

Isolation, identification and characterization of Aeromonas jandaei from diseased Chinese soft-shell turtles

Aeromonas jandaei is a gram-negative bacterium commonly found in aquatic environments and can induce illnesses in amphibians, reptiles and aquatic animals. In this study, a strain of bacteria was isolated from the diseased Chinese soft-shell turtle (Pelodiscus sinensis), then named strain JDP-FX. This isolate was identified as A. jandaei after analysis of morphological, physiological and biochemical characteristics, as well as 16S rRNA and gyrB gene sequences. Virulence genetic testing further detected temperature-sensitive protease (eprCAI), type III secretion system (TTSS) (ascv), nuclease (nuc), cytotonic enterotoxin (alt) and serine proteinase (ser) in JDP-FX. Compared with healthy Chinese soft-shell turtle, the serum levels of total protein (TP), albumin (ALB) and globulin (GLB) were significantly decreased in the diseased Chinese soft-shell turtle, while, the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) were significantly increased. Histopathological observations showed that multiple tissues, including intestinal mucosa, liver and kidney, were severely damaged in the diseased Chinese soft-shell turtle. Moreover, the diseased Chinese soft-shell turtle had significant cell degeneration, necrosis, sloughing and interstitial inflammatory cell infiltration. The pathogenicity of JDP-FX was tested via artificial infection. The median lethal dosage (LD50 ) of the strain was 1.05 × 105 colony forming units (CFU/g) per weight of Chinese soft-shell turtle. Drug susceptibility analysis revealed that JDP-FX was susceptible to ceftazidime, minocycline, cefoperazone, ceftriaxone and piperacillin. In addition, JDP-FX was resistant to doxycycline, florfenicol, sulfonamides, gentamicin, ampicillin and neomycin. Therefore, this study may provide guidance for further research into the diagnosis, prevention and treatment of JDP-FX infection.

Highly Colistin-resistant Aeromonas jandaei from a Human Blood Sample

Aeromonas species are Gram-negative rods known to cause infections such as gastroenteritis, bacteremia and wound infections. Colistin is one of few treatments for multidrug-resistant Gram-negative bacteria. However, colistin-resistant bacteria carrying the mobilized colistin resistance (mcr) gene are a threat in healthcare settings worldwide. In recent years, colistin-resistant Aeromonas species have been detected in environmental and clinical samples. We analyzed the genomic characteristics of one highly colistin-resistant A. jandaei isolated from a blood sample in Nepal, which harbored four novel mcr-like genes on its chromosome. Our study strongly suggests that A. jandaei is a reservoir of colistin-resistant genes. Inappropriate use of drugs in medicine and food production should be reduced and continued global surveillance for colistin-resistant bacteria is necessary.

Occurrence of Aeromonas Species in the Cutaneous Mucus of Barbour’s Seahorses (Hippocampus barbouri) as Revealed by High-Throughput Sequencing

Although several studies have described the bacterial community composition associated with marine fish, there is limited information related to seahorses. Moreover, previous studies have demonstrated that the skin microbiota is useful for determining health status and common disorders in the host. This study, therefore, aimed to explore the skin bacterial community composition in Barbour’s seahorse (Hippocampus barbouri) using high-throughput sequencing of 16S ribosomal RNA genes. Water and sediment samples from the surrounding environment were also analyzed for comparative purposes. The results revealed that sequences affiliated with the Shewanellaceae family were dominant in the skin of female Barbour’s seahorses and sediment samples, whereas sequences affiliated with the Bacillaceae family were dominant in the skin of male Barbour’s seahorses. Interestingly, sequences affiliated with the Aeromonas genus were found in the skin of Barbour’s seahorses, whose abundance was slightly similar between the female and male specimens. Further comparative analysis showed that the presence of Aeromonas species in the skin of Barbour’s seahorses was strongly influenced by the surrounding sediment. Given that some Aeromonas species are known to be important pathogens in humans and fish, these results may be used for further research on the dependency of the skin microbial composition on the environment as well as determine whether the presence of Aeromonas and other detected species has implications on seahorse health.

Immune Response of the Monocytic Cell Line THP-1 Against Six Aeromonas spp

Aeromonas are autochthonous bacteria of aquatic environments that are considered to be emerging pathogens to humans, producing diarrhea, bacteremia, and wound infections. Genetic identification shows that 95.4% of the strains associated with clinical cases correspond to the species Aeromonas caviae (37.26%), Aeromonas dhakensis (23.49%), Aeromonas veronii (21.54%), and Aeromonas hydrophila (13.07%). However, few studies have investigated the human immune response against some Aeromonas spp. such as A. hydrophila, Aeromonas salmonicida, and A. veronii. The present study aimed to increase the knowledge about the innate human immune response against six Aeromonas species, using, for the first time, an in vitro infection model with the monocytic human cell line THP-1, and to evaluate the intracellular survival, the cell damage, and the expression of 11 immune-related genes (TLR4, TNF-α, CCL2, CCL20, JUN, RELA, BAX, TP53, CASP3, NLRP3, and IL-1β). Transcriptional analysis showed an upregulated expression of a variety of the monocytic immune-related genes, with a variable response depending upon the Aeromonas species. The species that produced the highest cell damage, independently of the strain origin, coincidentally induced a higher expression of immune-related genes and corresponded to the more prevalent clinical species A. dhakensis, A. veronii, and A. caviae. Additionally, monocytic cells showed an overexpression of the apoptotic and pyroptotic genes involved in cell death after A. dhakensis, A. caviae, and Aeromonas media infection. However, the apoptosis route seemed to be the only way of producing cell damage and death in the case of the species Aeromonas piscicola and Aeromonas jandaei, while A. veronii apparently only used the pyroptosis route.

Isolation and characterization of two virulent Aeromonads associated with haemorrhagic septicaemia and tail-rot disease in farmed climbing perch Anabas testudineus

Diseased Anabas testudineus exhibiting signs of tail-rot and ulcerations on body were collected from a fish farm in Assam, India during the winter season (November 2018 to January 2019). Swabs from the infected body parts were streaked on sterilized nutrient agar. Two dominant bacterial colonies were obtained, which were then isolated and labelled as AM-31 and AM-05. Standard biochemical characterisation and 16S rRNA and rpoB gene sequencing identified AM-31 isolate as Aeromonas hydrophila and AM-05 as Aeromonas jandaei. Symptoms similar to that of natural infection were observed on re-infecting both bacteria to disease-free A. testudineus, which confirmed their virulence. LC50 was determined at 1.3 × 104 (A. hydrophila) and 2.5 × 104 (A. jandaei) CFU per fish in intraperitoneal injection. Further, PCR amplification of specific genes responsible for virulence (aerolysin and enterotoxin) confirmed pathogenicity of both bacteria. Histopathology of kidney and liver in the experimentally-infected fishes revealed haemorrhage, tubular degeneration and vacuolation. Antibiotic profiles were also assessed for both bacteria. To the best of our knowledge, the present work is a first report on the mortality of farmed climbing perch naturally-infected by A. hydrophila as well as A. jandaei, with no records of pathogenicity of the latter in this fish.

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.

Three species of Aeromonas (A. dhakensis, A. hydrophila and A. jandaei) isolated from freshwater crocodiles (Crocodylus siamensis) with pneumonia and septicemia

Hundreds of farmed Siamese crocodiles (Crocodylus siamensis) died during July 2016 at a farm in Wenchang, Hainan, China. In two necropsied crocodiles, we observed symptoms of dermatorrhagia, hepatomegaly and hepatic congestion. Pulmonitis was diagnosed by pulmonary congestion and pulmonary fibrinous exudate. Septicaemia was diagnosed by isolation of three Aeromonas species from blood and visceral tissues; A. dhakensis, A. hydrophila and A. jandaei were identified by biochemical and molecular tests. We used a zebrafish model to determine the half-maximal lethal dose (LD₅₀ ), and A. dhakensis was found to be the most virulent species, with an LD₅₀ of 8·91 × 10⁵ CFU per ml. The results of a drug sensitivity test indicated that these species were sensitive to 11 antibiotics. This is the first report of A. dhakensis, A. hydrophila and A. jandaei being isolated from a mixed infection in Siamese crocodiles. SIGNIFICANCE AND IMPACT OF THE STUDY: In this study, we isolated three species of Aeromonas (A. dhakensis, A. hydrophila and A. jandae) from farmed Siamese crocodiles with fatal fibrinous pneumonia and septicaemia. This is the first description of a mixed infection with three Aeromonas species among captive crocodilians.

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.

Novel Plasmid-Mediated Colistin Resistance Gene mcr-3 in Escherichia coli

The mobile colistin resistance gene mcr-1 has attracted global attention, as it heralds the breach of polymyxins, one of the last-resort antibiotics for the treatment of severe clinical infections caused by multidrug-resistant Gram-negative bacteria. To date, six slightly different variants of mcr-1, and a second mobile colistin resistance gene, mcr-2, have been reported or annotated in the GenBank database. Here, we characterized a third mobile colistin resistance gene, mcr-3. The gene coexisted with 18 additional resistance determinants in the 261-kb IncHI2-type plasmid pWJ1 from porcine Escherichia coli. mcr-3 showed 45.0% and 47.0% nucleotide sequence identity to mcr-1 and mcr-2, respectively, while the deduced amino acid sequence of MCR-3 showed 99.8 to 100% and 75.6 to 94.8% identity to phosphoethanolamine transferases found in other Enterobacteriaceae species and in 10 Aeromonas species, respectively. pWJ1 was mobilized to an E. coli recipient by conjugation and contained a plasmid backbone similar to those of other mcr-1-carrying plasmids, such as pHNSHP45-2 from the original mcr-1-harboring E. coli strain. Moreover, a truncated transposon element, TnAs2, which was characterized only in Aeromonas salmonicida, was located upstream of mcr-3 in pWJ1. This ΔTnAs2-mcr-3 element was also identified in a shotgun genome sequence of a porcine E. coli isolate from Malaysia, a human Klebsiella pneumoniae isolate from Thailand, and a human Salmonella enterica serovar Typhimurium isolate from the United States. These results suggest the likelihood of a wide dissemination of the novel mobile colistin resistance gene mcr-3 among Enterobacteriaceae and aeromonads; the latter may act as a potential reservoir for mcr-3.

The emergence of the plasmid-mediated colistin resistance gene mcr-1 has attracted substantial attention worldwide. Here, we examined a colistin-resistant Escherichia coli isolate that was negative for both mcr-1 and mcr-2 and discovered a novel mobile colistin resistance gene, mcr-3. The amino acid sequence of MCR-3 aligned closely with phosphoethanolamine transferases from Enterobacteriaceae and Aeromonas species originating from both clinical infections and environmental samples collected in 12 countries on four continents. Due to the ubiquitous profile of aeromonads in the environment and the potential transfer of mcr-3 between Enterobacteriaceae and Aeromonas species, the wide spread of mcr-3 may be largely underestimated. As colistin has been and still is widely used in veterinary medicine and used at increasing frequencies in human medicine, the continuous monitoring of mobile colistin resistance determinants in colistin-resistant Gram-negative bacteria is imperative for understanding and tackling the dissemination of mcr genes in both the agricultural and health care sectors.

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.

Fecal Bacterial Composition of the Endangered Yangtze Finless Porpoises Living Under Captive and Semi-natural Conditions

Intestinal microbiota is essential to the health and physiology of host animals. We undertook the first microbiological study of the fecal bacterial composition from critically endangered (CR) Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis; YFPs) living under captive and semi-natural conditions using both high-throughput sequencing method and 16S rRNA gene clone library method. As determined by high-throughput sequencing of V3-V4 regions of the 16S rRNA gene, semi-natural samples harbored 30 and 36 operational taxonomic units (OTUs), which was more than the 22 and 27 OTUs detected from YFPs living in captivity. In captive YFPs Firmicutes was the predominant phylum, whereas this was Proteobacteria for YFPs living in semi-nature conditions. This suggests habitat-specific fecal bacterial composition of YFPs. Plesiomonas spp. and Aeromonas spp., which are potentially pathogenic, were identified in all the feces. Bacterial diversity from one porpoise living in captivity was also determined by constructing a 16S rRNA gene clone library and only 1 phylum was identified. High-throughput sequencing was more effective at determining the bacterial diversity compared to the 16S rRNA gene clone library. This study provides important information for the management and conservation of the CR YFPs.

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.

Identification of Aeromonas species isolated from freshwater fish with the microplate hybridization method

Aeromonas isolates were obtained from the intestinal tracts of six species of cultured freshwater fish and identified on the basis of their genotypic and phenotypic characters. The microplate hybridization method could differentiate type strains of Aeromonas species and related bacteria. DNA-DNA hybridization analysis showed that 65 aeromonad isolates were 72 to 100% related with either Aeromonas caviae, Aeromonas hydrophila, Aeromonas jandaei, Aeromonas sobria, or Aeromonas veronii. As many as 48% of the genotypically identified A. caviae, A. hydrophila, and A. sobria isolates differed from the type strains of corresponding species in one to three phenotypic characters. These results strongly suggest that not all aeromonad isolates from freshwater fish could be identified correctly on the basis of only the phenotypic characters, indicating the usefulness of the microplate hybridization method for the identification of aeromonads.

Accuracy of 6 commercial systems for identifying clinical Aeromonas isolates

We compared the accuracy of 6 commercial systems for Aeromonas identification by testing 87 clinical isolates in routine conditions, using partial rpoB gene sequencing as the reference standard. The systems were API-20E, API-32GN, the ID-GN card with the Vitek2 system (bioMérieux, Marcy l'Etoile, France), the identification portion of the NFC47 panel (MicroScan Walk/Away system; Siemens Healthcare, Sacramento, CA), ID69 (Phoenix system; BD Diagnostic Systems, Sparks, MD), and GN2 microplates (Omnilog system; Biolog, Hayward, CA), for which 67 (77.1%), 80 (91.9%), 72 (82.7%), 70 (80.5%), 64 (73.5%), and 59 (67.8%) isolates, respectively, were correctly identified at the genus and species level. Confusion with Vibrio affected 6.9% and 16.1% of results obtained with NFC47 and API-20E, respectively. Overall, the accuracy of identification for aeromonads was hampered by outdated databases and taxonomy, weak algorithms, and impractical additional tests. Commercial identification systems should be redesigned to make Aeromonas identification algorithms more robust and to cover infrequent clinical species of this genus.

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.

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

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

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.

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)).

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.

Stress related changes of cell surface hydrophilicity in Bacillus subtilis

The changes of cell surface hydrophilicity in Bacillus subtilis were analyzed in response to oxygen-limitation, heat shock, salt stress, pH-shock, phosphate- and carbon-limitation. Although cell surface hydrophilicity varied during growth phases, an increase of surface hydrophilicity was observed under several of these stress conditions. An observed drop in intracellular GTP and/or ATP may be an element of the signal transduction pathway leading to an increase in surface hydrophilicity in response to environmental stresses. Attachment of cells to soil particles under salt stress conditions is strongly influenced by the degS/degU two-component system, which thereby provides a mechanism for the bacteria to escape from the hostile environment.

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.

Computer aided assignment of motile Aeromonas strains to genospecies level by standard biochemical tests

A procedure is given for differentiation of motile Aeromonas spp. Based on nine to 12 biochemical properties it allows an assignment of isolated Aeromonas strains first to phenotypes and, in the second step, to hybridization groups (HGs) 1-13 as well as to the genotypically defined species Aer. allosaccharophila and Aer. encheleia. The computer aided classification is carried out according to the principles of numerical taxonomy. Using this differentiation scheme 23 Aeromonas strains, which were isolated from food, and two reference strains were speciated. A total of 16 strains were assigned to Aer. hydrophila, six strains to Aer. caviae and one strain to Aer. sobria. Of the 16 Aer. hydrophile strains, 11 were attached to HG 1, one to HG 2 and four could not be classified clearly as HG 3 or HG 1. All six Aer. caviae isolated were assigned to HG 5 and the Aer. sobria strain was ranked among HG 8. The reference strains were assigned to the same genotypes by this method than by DNA-DNA hybridization assays.

Expression of the AsbA1, OXA-12, and AsbM1 beta-lactamases in Aeromonas jandaei AER 14 is coordinated by a two-component regulon

Aeromonas jandaei AER 14 (formerly Aeromonas sobria AER 14) expresses three inducible beta-lactamases, AsbA1, OXA-12 (AsbB1), and AsbM1. Mutant strains that constitutively overexpress all three enzyme simultaneously, suggesting that they share a common regulatory pathway, have been isolated. Detectable expression of the cloned genes of AsbA1 and OXA-12 in some Escherichia coli K-12 laboratory strains is achieved only in the presence of a blp mutation. These mutations map to the cre operon at 0 min, which encodes a classical two-component regulatory system of unknown function. Two regulatory elements from A. jandaei which permit high-level constitutive expression of OXA-12 in E. coli were cloned. Both loci encode proteins with characteristics of response regulator proteins of two-component regulatory systems. One of these loci, designated blrA, bestowed constitutive expression of all three beta-lactamases in A. jandaei AER 14 when present on a multicopy plasmid, confirming its role in the regulatory pathway of beta-lactamase production in this organism.

Increasing antibiotic resistance in clinical isolates of Aeromonas strains in Taiwan

A total of 234 clinical isolates of Aeromonas, primarily A. hydrophila, were collected for the present study. Most were isolates from blood. By the agar dilution method, more than 90% of the Aeromonas strains were found to be susceptible to moxalactam, ceftazidime, cefepime, aztreonam, imipenem, amikacin, and fluoroquinolones, but they were more resistant to tetracycline, trimethoprim-sulfamethoxazole, some extended-spectrum cephalosporins, and aminoglycosides than strains from the United States and Australia.

Distribution of Aeromonas species in the intestinal tracts of river fish

Aeromonas isolates were obtained from fish intestines, water, and sediments from an urban river and identified by the DNA-DNA microplate hybridization method. The isolates were Aeromonas veronii (22%), Aeromonas caviae (18%), Aeromonas hydrophila (13%), Aeromonas sobria (8%), Aeromonas jandaei (7%), and other Aeromonas spp. (33%). Aeromonas species occurred at high densities with high incidences, regardless of season. The results strongly suggest that aeromonads are indigenous in fish intestines, water, and sediments of rivers and have the potential to be predominant in aquatic environments.

RAPD analysis of Aeromonas salmonicida and Aeromonas hydrophila

The randomly amplified polymorphic DNA (RAPD) technique was used to analyse the genetic differentiation of 13 strains of Aeromonas salmonicida subsp. salmonicida, and seven strains of Aer. hydrophila. Reproducible profiles of genomic DNA fingerprints were generated by polymerase chain reaction (PCR) using a single randomly designed primer. The RAPD profiles of all the non-motile aeromonads, Aer. salmonicida subsp. salmonicida were identical. However, profiles of the motile aeromonads, Aer. hydrophila differed between isolates. These findings reveal genomic homogeneity in Aer. salmonicida subsp. salmonicida and genetic variety in Aer. hydrophila strains.

Diversity of Aeromonas sp. in Flemish drinking water production plants as determined by gas-liquid chromatographic analysis of cellular fatty acid methyl esters (FAMEs)

Gas-liquid chromatography of cellular fatty acid methyl esters (FAMEs) was used to determine the phenotypic and genotypic diversity among 489 presumptive Aeromonas strains isolated from five Flemish drinking water production plants. FAME profiles were compared with the predetermined library profiles of a representative database, AER48C, which contains the mean FAME data of all 14 currently established hybridization groups (HGs) or genospecies within Aeromonas. Using AER48C, more than 93% (457 strains) of all presumptive aeromonads isolated on ampicillin-dextrin agar were unequivocally identified as belonging to this genus. Moreover, 85.5% and 73.5% of these strains could be assigned to a particular phenospecies or HG, respectively. Raw and treated surface water samples were dominated by members of the Aer. hydrophila complex (38.8%, comprising HGs 1-3), followed by the Aer. caviae complex (22.7%, comprising HGs 4-6) and the Aer. sobria complex (16.7%, comprising HGs 7-9). HGs 3, 5A/B and 8 were the most prominent genospecies in this type of water. On the other hand, it was found that raw and treated phreatic groundwater samples displayed a much more limited species diversity since these were almost entirely dominated (95.8%) by strains belonging to HGs 2 and 3 of the Aer. hydrophila complex. In general, flocculation-decantation and sand filtration were not shown to influence the overall species distribution in any of the plants examined.

Rapid identification of Aeromonas species using 16S rDNA targeted oligonucleotide primers: a molecular approach based on screening of environmental isolates

Published 16S rDNA sequencing data for Aeromonas species were analysed and the validity of signature sequences derived from our investigations of these sequences was examined by sequencing the corresponding 16S rDNA regions of 67 environmental isolates from sewage effluents and receiving waters around Sydney and one clinical isolate, all previously classified as Aeromonas species. Species-specific probes for Aer. hydrophila and Aer. veronii were designed and tested in PCR assays and clearly discriminated these species from the other Aeromonas isolates as identified by 16S rDNA sequences.

O-serogrouping and surface components of Aeromonas hydrophila and Aeromonas jandaei pathogenic for eels

The relationship between virulence, O-serogroup, and some cell-surface features (self-pelleting [SP] and precipitation after boiling [PAB], profile of lipopolysaccharides [LPSs] and outer membrane proteins [OMPs]) was investigated in strains of the pathogenic species Aeromonas hydrophila and A. jandaei isolated from eels. Virulent strains of A. hydrophila reacted mostly with O:19 antiserum, and those of A. jandaei reacted with O:4, O:11, O:15 and O:29 antisera (Guinée and Jansen system). Regarding the PAB and LPS profiles two groups could be distinguished; (i) five PAB+ strains of serotype O:19 that possessed a homogeneous O polysaccharide side chain and (ii) thirteen PAB- strains antigenically diverse that either exhibited a heterogeneous side chain or were side chain deficient. A major 50 kDa protein was only found in the PAB+ strains, whereas major OMPs detected in PAB- strains ranged from 33 to 45 kDa irrespective of the species. Epizootic eel isolates of A. hydrophila belong to serotype O:19 and share cell-surface features with the Aeromonas highly virulent for other hosts. In contrast, epizootic A. jandaei isolates were antigenically diverse. These findings reinforce the importance of an O-serotype as an epidemiological marker in motile Aeromonas strains pathogenic for eels.

Identification of Aeromonas schubertii and Aeromonas jandaei by using a polymerase chain reaction-probe test

Two oligonucleotide primers were used in a polymerase chain reaction-protocol to amplify a region (approx. 850 bp) of the 16S rRNA gene of Aeromonas schubertii and Aeromonas jandaei. Hybridization of the polymerase chain reaction products to specific internal probes provided a highly specific method for the identification of these two species.

Bacterial diarrhoea

Diarrhoeal disease caused by enteric bacterial pathogens has become less prevalent in industrialized countries, but remains an important cause of morbidity and mortality in developing countries. Although better management of acute diarrhoeal episodes has led to more favourable outcomes, persistent diarrhoea remains a problem for which risk factors are being recognized and associated bacterial pathogens identified. Unusual or intractable diarrhoea should alert health workers to the possibility of impaired immune function, which is associated with a range of enteric pathogens and opportunistic infections. Improved microbiological methods have resulted in more frequent detection of pathogens in association with diarrhoea, as well as greater understanding of pathogenesis. Clinical features of diarrhoeal disease and mechanisms involved in pathogenesis are discussed in relation to specific bacterial enteric pathogens.

Bacterioplankton community structure and dynamics after large-scale release of nonindigenous bacteria as revealed by low-molecular-weight-RNA analysis

A set of freshwater mesocosms (1.7 m3 each) was inoculated with large amounts of Escherichia coli, Pseudomonas putida, and their culture medium to substantially disturb the natural microbial community. To monitor microbial community dynamics, low-molecular-weight RNA (5S rRNA and tRNA) obtained directly from bacterioplankton was analyzed by using high-resolution electrophoresis. The introduced bacteria showed no significant effect on the community structure of the natural bacterial assemblage and its dynamics for 16 days. In contrast, the addition of culture medium resulted within 2 days in a reduction of community diversity due to dominance of a single 5S rRNA band from an indigenous bacterium. Partial sequencing of several 5S rRNAs demonstrated the molecular homogeneity of most of the abundant bands and enabled the identification of corresponding bacterial isolates and/or species. The dominating bacterium (around 54% of the total 5S rRNA) in the nutrient-amended mesocosms could be identified by partial sequencing as a member of the Aeromonas hydrophila complex. Another bloom of heterotrophic bacteria belonging to the Cytophaga johnsonae complex was detected in the nutrient-amended mesocosms after 13 days. The dominance of this C. johnsonae-like bacterium could even be seen in the environmental tRNAs of the bacterioplankton, where its specific tRNAs prevailed from day 13 onward. This event was also independent of the introduced nonindigenous bacteria because it occurred at the same time in all nutrient-amended mesocosms. By contrast, in the unamended experiments, a different small 5S rRNA could by observed from day 10 onward with less pronounced dominance.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid identification of motile Aeromonas

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

Structural and pathogenic properties of Aeromonas schubertii

We investigated the phenotypic, structural, and pathogenic properties of 11 Aeromonas schubertii strains recovered from extraintestinal sites. Most A. schubertii strains were autoagglutination positive, possessed a high surface charge but low hydrophobicity, and fell into one or two biogroups on the basis of carbon substrate utilization patterns. Fatty acid methyl ester analysis of A. schubertii revealed this species to contain a relatively high percentage of branched fatty acids (i-13:0, i-15:0, i-17:1, i-17:0) compared with A. hydrophila. Immunologic and biochemical analysis of the lipopolysaccharides of A. schubertii strains allowed for two groups to be distinguished, namely, (i) a collection of six strains belonging to serogroup O:11 that possessed a characteristic homogeneous O polysaccharide side chain profile by silver staining and immunoblotting techniques and (ii) a second antigenically diverse group (five strains) that either exhibited a heterogeneous side chain profile or were side chain deficient. A, schubertii O:11 strains were all found to contain a 55-kDa major protein associated with the outer membrane fraction which was glycine-hydrochloride extractable; non-O:11 strains did not harbor a similar protein molecule. Screening of A. schubertii strains for reputed virulence factors indicated (i) that slightly more than half of the isolates produce an apparent contact-dependent hemolysin that is not cell associated or released extracellularly, (ii) a potent cytotoxin active against HEp-2 cells that is devoid of hemolytic activity, and (iii) lack of enterotoxigeniclike activity as determined by suckling mouse assays. All A. schubertii strains were pathogenic for mice as determined by 50% lethal dose assays, although no single factor correlated with mouse pathogenicity.

Identification of Aeromonas strains to the genospecies level in the clinical laboratory

One hundred thirty-three strains of Aeromonas (human, n = 102; animal, n = 16; environmental, n = 15) previously identified to the DNA group level by molecular methods were biochemically analyzed for 58 properties. On the basis of the use of between 9 and 16 selected tests, 132 of the 133 strains (99%) could be assigned to their correct hybridization group using this biochemical scheme. The results suggest a feasible approach for identifying aeromonads to genospecies level under appropriate conditions.

Numerical classification and identification of Aeromonas genospecies

A total of 176 Aeromonas strains representing all currently characterized genospecies were tested for 329 biochemical characters. Overall similarities of all strains were determined by numerical taxonomic techniques, the UPGMA algorithm and the SSM and the SJ coefficients as measures of similarity. Sixteen clusters (two or more strains) and seven unclustered strains were recovered at the 93.5% similarity level (SSM). Genospecies 1, 4, 5, 6, 7, 9, 12 and 13 were largely represented by single phena, whereas strains of genospecies 2 and 3 were found in closely-related phena. Strains belonging to genospecies 8 formed two distinct biotypes. Strains belonging to genospecies 11 formed a subcluster within a cluster representing different genospecies. In general, similar groupings were obtained with the Jaccard coefficient at a similarity level of 80.0% (SJ) with minor changes in the definition of clusters. The phenetic data showed good correlation with the taxa defined by DNA/DNA hybridization and those obtained by multilocus enzyme analysis. For all genospecies (independent from cluster assignment) 30 diagnostic characters were selected to construct a matrix for probabilistic identification. The correct identification rate of the matrix was 71.51% taking a Willcox probability greater than 0.99, and 83.7% taking a Willcox probability greater than 0.9 as identification threshold levels.