| 1. |
Miñana-Galbis D,
Farfán M,
Fusté MC,
Lorén JG,
( 2004 ) Aeromonas molluscorum sp. nov., isolated from bivalve molluscs. PMID : 15545437 : DOI : 10.1099/ijs.0.63202-0 Abstract >>
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)).
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2. |
Figueira V,
Vaz-Moreira I,
Silva M,
Manaia CM,
( 2011 ) Diversity and antibiotic resistance of Aeromonas spp. in drinking and waste water treatment plants. PMID : 21907383 : DOI : 10.1016/j.watres.2011.08.021 Abstract >>
The taxonomic diversity and antibiotic resistance phenotypes of aeromonads were examined in samples from drinking and waste water treatment plants (surface, ground and disinfected water in a drinking water treatment plant, and raw and treated waste water) and tap water. Bacteria identification and intra-species variation were determined based on the analysis of the 16S rRNA, gyrB and cpn60 gene sequences. Resistance phenotypes were determined using the disc diffusion method. Aeromonas veronii prevailed in raw surface water, Aeromonas hydrophyla in ozonated water, and Aeromonas media and Aeromonas puntacta in waste water. No aeromonads were detected in ground water, after the chlorination tank or in tap water. Resistance to ceftazidime or meropenem was detected in isolates from the drinking water treatment plant and waste water isolates were intrinsically resistant to nalidixic acid. Most of the times, quinolone resistance was associated with the gyrA mutation in serine 83. The gene qnrS, but not the genes qnrA, B, C, D or qepA, was detected in both surface and waste water isolates. The gene aac(6')-ib-cr was detected in different waste water strains isolated in the presence of ciprofloxacin. Both quinolone resistance genes were detected only in the species A. media. This is the first study tracking antimicrobial resistance in aeromonads in drinking, tap and waste water and the importance of these bacteria as vectors of resistance in aquatic environments is discussed.
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3. |
Fontes MC,
Saavedra MJ,
Martins C,
Martínez-Murcia AJ,
( 2011 ) Phylogenetic identification of Aeromonas from pigs slaughtered for consumption in slaughterhouses at the North of Portugal. PMID : 21402427 : DOI : 10.1016/j.ijfoodmicro.2011.02.010 Abstract >>
In the present study, 710 isolates of Aeromonas spp. have been collected from pig carcasses, diaphragm muscle, faeces, dehairing equipment and water in slaughterhouses at the North of Portugal. The isolates were obtained from a total of 154 samples. All presumptive Aeromonas isolates were subjected to ERIC-PCR analysis and those which presented a different pattern were taken and the species classified by gyrB gene sequencing. We have found the species A. hydrophila, A. salmonicida, A. bestiarum, A. caviae, A. media, A. veronii, A. allosaccharophila, A. simiae and A. aquariorum. To our knowledge, this extent of Aeromonas species diversity has not been previously described from meat or from the slaughter environment, perhaps due to the unreliability of available identification methods. A noticeable level of isolate redundancy (strains with identical gyrB sequence) from different samples collected in different dates was also obtained, indicating that only a few predominant strains of these species persist at the slaughter system. It is also important to emphasise the presence of Aeromonas species previously associated with illness in man.
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4. |
Martinez-Murcia AJ,
Monera A,
Saavedra MJ,
Oncina R,
Lopez-Alvarez M,
Lara E,
Figueras MJ,
( 2011 ) Multilocus phylogenetic analysis of the genus Aeromonas. PMID : 21353754 : DOI : 10.1016/j.syapm.2010.11.014 Abstract >>
A broad multilocus phylogenetic analysis (MLPA) of the representative diversity of a genus offers the opportunity to incorporate concatenated inter-species phylogenies into bacterial systematics. Recent analyses based on single housekeeping genes have provided coherent phylogenies of Aeromonas. However, to date, a multi-gene phylogenetic analysis has never been tackled. In the present study, the intra- and inter-species phylogenetic relationships of 115 strains representing all Aeromonas species described to date were investigated by MLPA. The study included the independent analysis of seven single gene fragments (gyrB, rpoD, recA, dnaJ, gyrA, dnaX, and atpD), and the tree resulting from the concatenated 4705 bp sequence. The phylogenies obtained were consistent with each other, and clustering agreed with the Aeromonas taxonomy recognized to date. The highest clustering robustness was found for the concatenated tree (i.e. all Aeromonas species split into 100% bootstrap clusters). Both possible chronometric distortions and poor resolution encountered when using single-gene analysis were buffered in the concatenated MLPA tree. However, reliable phylogenetic species delineation required an MLPA including several "bona fide" strains representing all described species.
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5. |
Farfán M,
Miñana-Galbis D,
Garreta A,
Lorén JG,
Fusté MC,
( 2010 ) Malate dehydrogenase: a useful phylogenetic marker for the genus Aeromonas. PMID : 21095084 : DOI : 10.1016/j.syapm.2010.09.005 Abstract >>
The reconstruction of correct genealogies among biological entities, the estimation of the divergence time between organisms or the study of the different events that occur along evolutionary lineages are not always based on suitable genes. For reliable results, it is necessary to look at full-length sequences of genes under stabilizing selection (neutral or purifying) and behaving as good molecular clocks. In bacteria it has been proved that the malate dehydrogenase gene (mdh) can be used to determine the inter- and intraspecies divergence, and hence this gene constitutes a potential marker for phylogeny and bacterial population genetics. We have sequenced the full-length mdh gene in 36 type and reference strains of Aeromonas. The species grouping obtained in the phylogenetic tree derived from mdh sequences was in agreement with that currently accepted for the genus Aeromonas. The maximum likelihood models applied to our sequences indicated that the mdh gene is highly conserved among the Aeromonas species and the main evolutionary force acting on it is purifying selection. Only two sites under potential diversifying selection were identified (T 108 and S 193). In order to determine if these two residues could have an influence on the MDH structure, we mapped them in a three-dimensional model constructed from the sequence of A. hydrophila using the human mitochondrial MDH as a template. The presence of purifying selection together with the linear relationship between substitutions and gene divergence makes the mdh an excellent candidate gene for a phylogeny of Aeromonas and probably for other bacterial groups.
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6. |
Lorén JG,
Farfán M,
Miñana-Galbis D,
Fusté MC,
( 2010 ) Prediction of whole-genome DNA G+C content within the genus Aeromonas based on housekeeping gene sequences. PMID : 20466501 : DOI : 10.1016/j.syapm.2010.03.007 Abstract >>
Different methods are available to determine the G+C content (e.g. thermal denaturation temperature or high performance liquid chromatography, HPLC), but obtained values may differ significantly between strains, as well as between laboratories. Recently, several authors have demonstrated that the genomic DNA G+C content of prokaryotes can be reliably estimated from one or several protein coding gene nucleotide sequences. Few G+C content values have been published for the Aeromonas species described and the data, when available, are often incomplete or provide only a range of values. Our aim in this current work was twofold. First, the genomic G+C content of the type or reference strains of all species and subspecies of the genus Aeromonas was determined with a traditional experimental method in the same laboratory. Second, we wanted to see if the sequence-based method to estimate the G+C content described by Fournier et al. [7] could be applied to determine the G+C content of the different species of Aeromonas from the sequences of the genes used in taxonomy or phylogeny for this genus.
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7. |
Lamy B,
Laurent F,
Kodjo A,
( 2010 ) Validation of a partial rpoB gene sequence as a tool for phylogenetic identification of aeromonads isolated from environmental sources. PMID : 20453908 : DOI : 10.1139/w10-006 Abstract >>
A collection of 50 aeromonads isolated from environmental sources were studied, together with all known Aeromonas nomenspecies, by phenotypic, amplified 16S rDNA restriction analysis (16S rDNA RFLP) and by partial sequence alignment of both 16S rDNA and rpoB genes. Although most of the type strain showed a unique phenotypic pattern, a database constructed on type strain phenotype allowed the identification of only 24% of the isolates. Analysis of 16S rDNA RFLP and the rpoB sequence were almost concordant in identifying environmental isolates at the species level, except for strains belonging to Aeromonas caviae spp., which were not differentiated from Aeromonas aquariorum, nor Aeromonas hydrophila susbsp. dhakensis by 16S rDNA RFLP. In addition, rpoB gene analysis clustered separately a group of isolates found in snails within the A. hydrophila species. In contrast to 16S rDNA RFLP and rpoB, the partial 16S rDNA sequence analysis was weak in resolving species identity. Part of these results, phenotypic and phylogenetic data, showed that Aeromonas molluscorum and Aeromonas sharmana are distant from all other Aeromonas species and that the type species of A. hydrophila subsp. anaerogenes is similar to A. caviae and should be considered synonymous.
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8. |
Farfán M,
Miñana-Galbis D,
Fusté MC,
Lorén JG,
( 2009 ) Divergent evolution and purifying selection of the flaA gene sequences in Aeromonas. PMID : 19622168 : DOI : 10.1186/1745-6150-4-23 PMC : PMC2724415 Abstract >>
The bacterial flagellum is the most important organelle of motility in bacteria and plays a key role in many bacterial lifestyles, including virulence. The flagellum also provides a paradigm of how hierarchical gene regulation, intricate protein-protein interactions and controlled protein secretion can result in the assembly of a complex multi-protein structure tightly orchestrated in time and space. As if to stress its importance, plants and animals produce receptors specifically dedicated to the recognition of flagella. Aside from motility, the flagellum also moonlights as an adhesion and has been adapted by humans as a tool for peptide display. Flagellar sequence variation constitutes a marker with widespread potential uses for studies of population genetics and phylogeny of bacterial species. We sequenced the complete flagellin gene (flaA) in 18 different species and subspecies of Aeromonas. Sequences ranged in size from 870 (A. allosaccharophila) to 921 nucleotides (A. popoffii). The multiple alignment displayed 924 sites, 66 of which presented alignment gaps. The phylogenetic tree revealed the existence of two groups of species exhibiting different FlaA flagellins (FlaA1 and FlaA2). Maximum likelihood models of codon substitution were used to analyze flaA sequences. Likelihood ratio tests suggested a low variation in selective pressure among lineages, with an omega ratio of less than 1 indicating the presence of purifying selection in almost all cases. Only one site under potential diversifying selection was identified (isoleucine in position 179). However, 17 amino acid positions were inferred as sites that are likely to be under positive selection using the branch-site model. Ancestral reconstruction revealed that these 17 amino acids were among the amino acid changes detected in the ancestral sequence. The models applied to our set of sequences allowed us to determine the possible evolutionary pathway followed by the flaA gene in Aeromonas, suggesting that this gene have probably been evolving independently in the two groups of Aeromonas species since the divergence of a distant common ancestor after one or several episodes of positive selection. This article was reviewed by Alexey Kondrashov, John Logsdon and Olivier Tenaillon (nominated by Laurence D Hurst).
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9. |
Miñana-Galbis D,
Urbizu-Serrano A,
Farfán M,
Fusté MC,
Lorén JG,
( 2009 ) Phylogenetic analysis and identification of Aeromonas species based on sequencing of the cpn60 universal target. PMID : 19567585 : DOI : 10.1099/ijs.0.005413-0 Abstract >>
An analysis of the universal target (UT) sequence from the cpn60 gene was performed in order to evaluate its usefulness in phylogenetic and taxonomic studies and as an identification marker for the genus Aeromonas. Sequences of 555 bp, corresponding to the UT region, were obtained from a collection of 35 strains representing all of the species and subspecies of Aeromonas. From the analysis of these sequences, a range of divergence of 0-23.3% was obtained, with a mean of 11.2+/-0.9%. Comparative analyses between cpn60 and gyrB, rpoD and 16S rRNA gene sequences were carried out from the same Aeromonas strain collection. Sequences of the cpn60 UT region showed similar discriminatory power to gyrB and rpoD sequences. The phylogenetic relationships inferred from cpn60 sequence distances indicated an excellent correlation with the present affiliation of Aeromonas species with the exception of Aeromonas hydrophila subsp. dhakensis, which appeared in a separate phylogenetic line, and Aeromonas sharmana, which exhibited a very loose phylogenetic relationship to the genus Aeromonas. Sequencing of cpn60 from 33 additional Aeromonas strains also allowed us to establish intra- and interspecific threshold values. Intraspecific divergence rates were
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10. |
Akinbowale OL,
Peng H,
Barton MD,
( 2007 ) Diversity of tetracycline resistance genes in bacteria from aquaculture sources in Australia. PMID : 17953612 : DOI : 10.1111/j.1365-2672.2007.03445.x Abstract >>
To determine the genetic determinants responsible for tetracycline resistance in oxytetracycline resistant bacteria from aquaculture sources in Australia. Twenty of 104 (19%) isolates tested were resistant to oxytetracycline (MIC > or = 16 microg ml(-1)). Using polymerase chain reaction (PCR) amplification, one or more tet genes were detected in 15/20 (75%) isolates tested, but none were found in 5/20 (25%). tetM (50%) was the most common determinant, followed by tetE (45%), tetA (35%) and tetD (15%). Five of 12 oxytetracycline resistant isolates studied were able to transfer their R-plasmid to Escherichia coli recipients of chicken, pig and human origin. tetA, tetD and tetM were found to be transferred while tetE was not transferred. Southern hybridization and PCR were used to confirm transfer of determinants. Bacterial isolates from aquaculture sources in Australia harbour a variety of tetracycline resistance genes, which can be transferred to other bacteria of different origin. Bacteria from aquaculture sources in Australia contribute to the resistance gene pool reservoir. The in vitro transfer of tetracycline R-plasmid from aquatic bacteria to E. coli isolates from various sources is an indication of the potential public health risk associated with these resistance determinants.
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11. |
Khor WC,
Puah SM,
Tan JA,
Puthucheary SD,
Chua KH,
( 2015 ) Phenotypic and Genetic Diversity of Aeromonas Species Isolated from Fresh Water Lakes in Malaysia. PMID : 26710336 : DOI : 10.1371/journal.pone.0145933 PMC : PMC4692508 Abstract >>
Gram-negative bacilli of the genus Aeromonas are primarily inhabitants of the aquatic environment. Humans acquire this organism from a wide range of food and water sources as well as during aquatic recreational activities. In the present study, the diversity and distribution of Aeromonas species from freshwater lakes in Malaysia was investigated using glycerophospholipid-cholesterol acyltransferase (GCAT) and RNA polymerase sigma-factor (rpoD) genes for speciation. A total of 122 possible Aeromonas strains were isolated and confirmed to genus level using the API20E system. The clonality of the isolates was investigated using ERIC-PCR and 20 duplicate isolates were excluded from the study. The specific GCAT-PCR identified all isolates as belonging to the genus Aeromonas, in agreement with the biochemical identification. A phylogenetic tree was constructed using the rpoD gene sequence and all 102 isolates were identified as: A. veronii 43%, A. jandaei 37%, A. hydrophila 6%, A. caviae 4%, A. salmonicida 2%, A. media 2%, A. allosaccharophila 1%, A. dhakensis 1% and Aeromonas spp. 4%. Twelve virulence genes were present in the following proportions--exu 96%, ser 93%, aer 87%, fla 83%, enolase 70%, ela 62%, act 54%, aexT 33%, lip 16%, dam 16%, alt 8% and ast 4%, and at least 2 of these genes were present in all 102 strains. The ascV, aexU and hlyA genes were not detected among the isolates. A. hydrophila was the main species containing virulence genes alt and ast either present alone or in combination. It is possible that different mechanisms may be used by each genospecies to demonstrate virulence. In summary, with the use of GCAT and rpoD genes, unambiguous identification of Aeromonas species is possible and provides valuable data on the phylogenetic diversity of the organism.
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12. |
Carriero MM,
Mendes Maia AA,
Moro Sousa RL,
Henrique-Silva F,
( 2016 ) Characterization of a new strain of Aeromonas dhakensis isolated from diseased pacu fish (Piaractus mesopotamicus) in Brazil. PMID : 26850370 : DOI : 10.1111/jfd.12457 Abstract >>
This study provides a detailed description and characterization of a strain of Aeromonas dhakensis isolated from a diseased juvenile Piaractus mesopotamicus obtained from the fish farm of the National Center for Continental Fish Research and Conservation (CEPTA/ICMBio), in the state of S?o Paul, Brazil. Biochemical tests using the VITEK 2 automated bacterial identification system identified the isolate to genus level; however, further molecular analysis of the 16S rRNA, gyrB and rpoD genes showed that the strain belonged to the species A. dhakensis. As expected, the isolated A. dhakensis strain was resistant to ampicillin and ampicillin/sulbactam, as resistance to ampicillin is a typical characteristic of the genus Aeromonas. Resistance to cefoxitin and meropenem was also observed, but the strain was susceptible to most of the tested antibiotics. The isolated strain of A. dhakensis caused acute haemorrhagic septicaemia in experimentally infected P. mesopotamicus, with a fifty per cent lethal dose of 1.14 �� 105 CFU/fish. This is the first report of the occurrence of an A. dhakensis strain causing an infection in a fish species of South America, providing important epidemiologic data relating to this important pathogenic species.
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13. |
Lorén JG,
Farfán M,
Fusté MC,
( 2014 ) Molecular phylogenetics and temporal diversification in the genus Aeromonas based on the sequences of five housekeeping genes. PMID : 24586399 : DOI : 10.1371/journal.pone.0088805 PMC : PMC3930666 Abstract >>
Several approaches have been developed to estimate both the relative and absolute rates of speciation and extinction within clades based on molecular phylogenetic reconstructions of evolutionary relationships, according to an underlying model of diversification. However, the macroevolutionary models established for eukaryotes have scarcely been used with prokaryotes. We have investigated the rate and pattern of cladogenesis in the genus Aeromonas (�^-Proteobacteria, Proteobacteria, Bacteria) using the sequences of five housekeeping genes and an uncorrelated relaxed-clock approach. To our knowledge, until now this analysis has never been applied to all the species described in a bacterial genus and thus opens up the possibility of establishing models of speciation from sequence data commonly used in phylogenetic studies of prokaryotes. Our results suggest that the genus Aeromonas began to diverge between 248 and 266 million years ago, exhibiting a constant divergence rate through the Phanerozoic, which could be described as a pure birth process.
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14. |
Wu CJ,
Wang HC,
Chen PL,
Chang MC,
Sunny Sun H,
Chou PH,
Ko WC,
( 2013 ) AQU-1, a chromosomal class C �]-lactamase, among clinical Aeromonas dhakensis isolates: distribution and clinical significance. PMID : 24055254 : DOI : 10.1016/j.ijantimicag.2013.08.002 Abstract >>
Aeromonas dhakensis, a recently described Aeromonas sp. formerly called Aeromonas aquariorum, is associated with human infections. In this study, a chromosomal gene, blaAQU-1, was identified in A. dhakensis AAK1 that constitutes a 1143-bp open reading frame and is 87% identical to the gene encoding CepH in Aeromonas hydrophila. An Escherichia coli TOP10 cell transformant harbouring blaAQU-1 was resistant to cefotaxime but not to cefepime. mRNA expression of blaAQU-1 in the cefotaxime-resistant mutant strain AAK1m was 70-fold higher than in the wild strain AAK1. In all 16 A. dhakensis isolates (the major species of 51 consecutive Aeromonas blood isolates collected from June 1999 to June 2001) as well as in A. aquariorum MDC47(T) and A. hydrophila subsp. dhakensis LMG 19562(T), but not in the reference strains or clinical isolates of other A. hydrophila subspecies, Aeromonas caviae, Aeromonas veronii or Aeromonas enteropelogenes, blaAQU-1-related genes were detected by PCR. Overall, 13 (81%) of the 16 A. dhakensis blood isolates exhibited either cefotaxime resistance or the in vitro emergence of derepressed cefotaxime-resistant mutants. In vivo selection of an A. dhakensis resistant mutant was noted in a burn patient undergoing cefotaxime monotherapy. These observations suggest that AQU-1 is a chromosomal cephalosporinase in A. dhakensis. Cefotaxime monotherapy for severe A. dhakensis infections should be used cautiously.
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15. |
Chen PL,
Wu CJ,
Chen CS,
Tsai PJ,
Tang HJ,
Ko WC,
( 2014 ) A comparative study of clinical Aeromonas dhakensis and Aeromonas hydrophila isolates in southern Taiwan: A. dhakensis is more predominant and virulent. PMID : 24237662 : DOI : 10.1111/1469-0691.12456 Abstract >>
Aeromonas dhakensis, often phenotypically identified as Aeromonas hydrophila, is an important human pathogen. The present study aimed to compare the clinical and biological features of A. dhakensis and A. hydrophila isolates from human wounds. A total of 80 Aeromonas wound isolates collected between January 2004 and April 2011 were analysed. The species was identified by the DNA sequence matching of rpoD and gyrB (or rpoB if necessary). Most of the Aeromonas isolates were identified as A. dhakensis (37, 46.3%), and 13 (16.3%) as A. hydrophila. Both species alone can cause severe skin and soft-tissue infections. More A. dhakensis isolates were found in wounds exposed to environmental water (32.4% vs 0%, p 0.042). More biofilm formation was noted among A. dhakensis isolates (mean optical density at 570 nm, 1.23 �� 0.09 vs 0.78 �� 0.21, p 0.03). The MICs of ceftriaxone, imipenem and gentamicin for A. dhakensis isolates were higher (p <0.0001, <0.04, and <0.01, respectively). The survival rates of Caenorhabditis elegans co-incubated with A. dhakensis from day 1 to day 3 were lower than those of worms infected with A. hydrophila in liquid toxicity assays (all p values <0.01). Isolates of A. dhakensis exhibited more cytotoxicity, as measured by the released leucocyte lactate dehydrogenase levels in human normal skin fibroblast cell lines (29.6 �� 1.2% vs 20.6 �� 0.6%, p <0.0001). The cytotoxin gene ast was primarily present in A. hydrophila isolates (100% vs 2.7%, p <0.0001). In summary, A. dhakensis is the predominant species among Aeromonas wound isolates, and more virulent than A. hydrophila.
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16. |
Martino ME,
Fasolato L,
Montemurro F,
Novelli E,
Cardazzo B,
( 2014 ) Aeromonas spp.: ubiquitous or specialized bugs? PMID : 23919504 : DOI : 10.1111/1462-2920.12215 Abstract >>
The genus Aeromonas comprises ubiquitous bacteria that are known to play several roles in the environment. These bacteria were first described as fish pathogens, but their presence was documented in other reservoirs, such as animals and humans. Today, these bacteria are described as emerging pathogens, but their effective role in human pathogenicity is still controversial. In addition, their taxonomy is heavily debated, as species distinction is often difficult to achieve. To study the interspecies relationships and to investigate their connection with the environment, a multilocus sequence typing scheme previously developed for Aeromonas spp. was applied to 258 strains, and the genetic data were analysed by population software. Sampling was a fundamental step, including several of the main sources of Aeromonas: fish, food products and human cases of disease. The objective was to characterize the isolates and to find potential associations among them according to the following: species, sharing of virulence factors, source and adaptation to a specific habitat. The strains were characterized and demonstrated exceptionally high nucleotide variability in the Aeromonas genus. Among the sampled sources, different species distributions were found, highlighting the occurrence of adaptation processes towards specific habitats.
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17. |
Wu CJ,
Chen PL,
Wu JJ,
Yan JJ,
Lee CC,
Lee HC,
Lee NY,
Chang CM,
Lin YT,
Chiu YC,
Ko WC,
( 2012 ) Distribution and phenotypic and genotypic detection of a metallo-�]-lactamase, CphA, among bacteraemic Aeromonas isolates. PMID : 22322339 : DOI : 10.1099/jmm.0.038323-0 Abstract >>
The objectives of the study were to investigate the distribution of cphA-related genes (cphA) encoding a CphA metallo-�]-lactamase (MBL) among 51 consecutive Aeromonas blood isolates and to compare different phenotypic methods for detecting CphA. The presence of cphA was detected by PCR. Four phenotypic methods, the imipenem-EDTA combined disc test, imipenem-EDTA MBL Etest, agar dilution test and modified Hodge test (MHT), were used to detect imipenem susceptibility and MBL production. The results showed that 35 (69%) blood isolates had cphA. All (100%) of 16 Aeromonas aquariorum isolates and 12 Aeromonas veronii isolates, and 4 (80%) of 5 Aeromonas hydrophila isolates, carried cphA, but none of 15 Aeromonas caviae isolates did. With the standard inocula, irrespective of the presence or absence of cphA, all but one (50, 98%) isolates were susceptible to imipenem tested by disc diffusion, Etest and agar dilution (10(4) c.f.u. spot inocula), and did not exhibit MBL production by the imipenem-EDTA combined disc test and MBL Etest. By the agar dilution test using large inocula (10(7) c.f.u.), 34 (97%) of 35 cphA(+) isolates had imipenem MICs of ?16 ?g ml(-1), higher than the susceptible breakpoint (4 ?g ml(-1)), and demonstrated positive results for the MHT, while one cphA(+) and all 17 cphA(-) isolates had imipenem MICs of ?4 ?g ml(-1). In conclusion, the distribution of cphA among aeromonads is species-specific, found in A. aquariorum, A. veronii and A. hydrophila, and the MHT may be a phenotypic screening test for CphA production.
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18. |
Roger F,
Marchandin H,
Jumas-Bilak E,
Kodjo A,
N/A N/A,
Lamy B,
( 2012 ) Multilocus genetics to reconstruct aeromonad evolution. PMID : 22545815 : DOI : 10.1186/1471-2180-12-62 PMC : PMC3487998 Abstract >>
Aeromonas spp. are versatile bacteria that exhibit a wide variety of lifestyles. In an attempt to improve the understanding of human aeromonosis, we investigated whether clinical isolates displayed specific characteristics in terms of genetic diversity, population structure and mode of evolution among Aeromonas spp. A collection of 195 Aeromonas isolates from human, animal and environmental sources was therefore genotyped using multilocus sequence analysis (MLSA) based on the dnaK, gltA, gyrB, radA, rpoB, tsf and zipA genes. The MLSA showed a high level of genetic diversity among the population, and multilocus-based phylogenetic analysis (MLPA) revealed 3 major clades: the A. veronii, A. hydrophila and A. caviae clades, among the eleven clades detected. Lower genetic diversity was observed within the A. caviae clade as well as among clinical isolates compared to environmental isolates. Clonal complexes, each of which included a limited number of strains, mainly corresponded to host-associated subsclusters of strains, i.e., a fish-associated subset within A. salmonicida and 11 human-associated subsets, 9 of which included only disease-associated strains. The population structure was shown to be clonal, with modes of evolution that involved mutations in general and recombination events locally. Recombination was detected in 5 genes in the MLSA scheme and concerned approximately 50% of the STs. Therefore, these recombination events could explain the observed phylogenetic incongruities and low robustness. However, the MLPA globally confirmed the current systematics of the genus Aeromonas. Evolution in the genus Aeromonas has resulted in exceptionally high genetic diversity. Emerging from this diversity, subsets of strains appeared to be host adapted and/or disease specialized" while the A. caviae clade displayed an atypical tempo of evolution among aeromonads. Considering that A. salmonicida has been described as a genetically uniform pathogen that has adapted to fish through evolution from a variable ancestral population, we hypothesize that the population structure of aeromonads described herein suggested an ongoing process of adaptation to specialized niches associated with different degrees of advancement according to clades and clusters."
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19. |
Hossain S,
Dahanayake PS,
De Silva BCJ,
Wickramanayake MVKS,
Wimalasena SHMP,
Heo GJ,
( 2019 ) Multidrug resistant Aeromonas spp. isolated from zebrafish (Danio rerio): antibiogram, antimicrobial resistance genes and class 1 integron gene cassettes. PMID : 30790321 : DOI : 10.1111/lam.13138 Abstract >>
Aeromonas spp. are Gram-negative opportunistic bacteria which have been commonly associated with fish diseases. In this study, antibiogram, antimicrobial resistance genes and integrons of 43 zebrafish-borne Aeromonas spp. were studied. The isolates were identified as six Aeromonas species (A. veronii biovar veronii (n = 26), A. veronii biovar sobria (n = 3), A. hydrophila (n = 8), A. caviae (n = 3), A. enteropelogenes (n = 2) and A. dhakensis (n = 1)). Antibiogram of the isolates indicated that most of them were resistant to amoxicillin (100�P00%), nalidixic acid (100�P00%), oxytetracycline (100�P00%), ampicillin (93�P02%), tetracycline (74�P42%), rifampicin (67�P44%) and imipenem (65�P15%). Multiple antimicrobial resistance (MAR) index values ranged from 0�P19-0�P44 to 90�P70% isolates showed multidrug resistance. PCR of antimicrobial resistance genes revealed that the tetracycline resistance gene (tetA) was the most predominant (67�P44%) among the isolates. The qnrS (53�P49%), tetB (30�P23%), tetE (30�P23%), qnrB (23�P26%) and aac(6')-Ib-cr (4�P65%) genes were also detected. Class 1 integrase (IntI1) gene was found in 46�P51% of the isolates. Two types of class 1 integron gene cassette profiles (qacG-aadA6-qacG and drfA1) were identified. The results showed that zebrafish-borne aeromonads can harbour different types of antimicrobial resistance genes and class 1 integrons. SIGNIFICANCE AND IMPACT OF THE STUDY: Aeromonas spp. are important pathogens found in diverse environments. Antimicrobial resistance genes and integrons of ornamental fish-borne Aeromonas spp. are not well studied. The antibiogram, antimicrobial resistance genes and class 1 integrons of Aeromonas spp. isolated from zebrafish were characterized for the first time in Korea. The prevalence of tetracycline resistance genes, plasmid-mediated quinolone resistance genes and class 1 integron gene cassettes were observed among the isolates. The qacG-aadA6-qacG gene cassette was identified for the first time in Aeromonas spp. The results suggest that the wise use of antimicrobials is necessary for the better management of the ornamental fish.
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20. |
Soto-Rodriguez SA,
Lozano-Olvera R,
Garcia-Gasca MT,
Abad-Rosales SM,
Gomez-Gil B,
Ayala-Arellano J,
( 2018 ) Virulence of the fish pathogen Aeromonas dhakensis: genes involved, characterization and histopathology of experimentally infected hybrid tilapia. PMID : 29972371 : DOI : 10.3354/dao03247 Abstract >>
Aeromonas dhakensis (Ad) CAIM 1873 growth was evaluated at different conditions and antibiotic susceptibility. Mortality and histopathological damages in hybrid tilapia Oreochromis niloticus �� O. mossambicus, and virulence factors caused by Ad bacterial cells and extracellular products (ECPs) were evaluated, and the whole genome was obtained. Ad grew between 0.0 and 5.5% NaCl at a pH of between 4 and 10 and from 4 to 37�XC. The lowest minimum inhibitory concentration was found for enrofloxacin (<5 ?g ml-1), and bacteria were resistant to erythromycin, amoxicillin and ampicillin. Ad bacterial cells (1.86 �� 105 cells g-1) and ECPs (0.462 ?g protein fish-1) were highly virulent to challenged hybrid tilapia and caused over 80% mortality at 24 h. The primary clinical sign caused was haemorrhage, and damage was most marked in the spleen, liver, kidney and brain of fish challenged with bacterial cells. To our knowledge, this is the first report that Ad causes pyknotic and karyorrhectic nuclei of erythrocytes in the internal organs of hybrid tilapia, which was the most striking histopathological observation. The virulence of Ad to hybrid tilapia may be primarily related to the activity of haemolysins (hlyA genes) and cytotoxins (aerolysin aerA), along with the production of siderophores and proteases. We also found �]-lactamase, tetracycline and multiple antibiotic resistance genes, as well as adherence, iron acquisition, toxins (aerolysin family, haemolysins) and diverse protease genes.
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Hoel S,
Vadstein O,
Jakobsen AN,
( 2017 ) Species Distribution and Prevalence of Putative Virulence Factors in Mesophilic Aeromonas spp. Isolated from Fresh Retail Sushi. PMID : 28596762 : DOI : 10.3389/fmicb.2017.00931 PMC : PMC5442234 Abstract >>
Aeromonas spp. are ubiquitous bacteria that have received increasing attention as human pathogens because of their widespread occurrence in food, especially seafood and vegetables. The aim of this work was to assess the species identity and phylogenetic relationship of 118 Aeromonas strains isolated from fresh retail sushi from three producers, and to characterize the isolates with respect to genetic and phenotypic virulence factors. We also evaluate the potential hazard associated with their presence in ready-to-eat seafood not subjected to heat treatment. Mesophilic Aeromonas salmonicida was most prevalent (74%), followed by A. bestiarum (9%), A. dhakensis (5%), A. caviae (5%), A. media (4%), A. hydrophila (2%), and A. piscicola (1%). All isolates were considered potentially pathogenic due to the high prevalence of genes encoding hemolysin (hlyA) (99%), aerolysin (aerA) (98%), cytotoxic enterotoxin (act) (86%), heat-labile cytotonic enterotoxin (alt) (99%), and heat-stable cytotonic enterotoxin (ast) (31%). The shiga-like toxins 1 and 2 (stx-1 and stx-2) were not detected. Moreover, there was heterogeneity in toxin gene distribution among the isolates, and the combination of act/alt/hlyA/aerA was most commonly detected (63%). �]-hemolysis was species-dependent and observed in 91% of the isolates. All A. media and A. caviae strains were non-hemolytic. For isolates belonging to this group, lack of hemolysis was possibly related to the absence of the act gene. Swimming motility, linked to adhesion and host invasion, occurred in 65% of the isolates. Partial sequencing of the gyrB gene demonstrated its suitability as a genetic marker for Aeromonas species identification and for assessment of the phylogenetic relationship between the isolates. The gyrB sequence divergence within a given species ranged from 1.3 to 2.9%. A. bestiarum, A. salmonicida, and A. piscicola were the most closely related species; their sequences differed by 2.7-3.4%. The average gyrB sequence similarity between all species was 93%, demonstrating its acceptable taxonomic resolution. The presence of multiple species of potential pathogenic Aeromonas in fresh retail sushi raises new food safety issues related to the increased consumption of ready-to-eat food composed of raw ingredients.
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( 2012 ) Aeromonas hydrophila subsp. dhakensis--a causative agent of gastroenteritis imported into the Czech Republic. PMID : 23020031 : Abstract >>
Out of the twenty-one A. hydrophila complex isolates obtained during a routine examination of human diarrhoeal faeces, two A. hydrophila subsp. dhakensis isolates (P1097 = CCM 7329 and P1165) were successfully identified by ribotyping. The correct taxonomic position of the A. hydrophila subsp. dhakensis CCM 7329 was verified by cpn60 sequencing (GeneBank accession number HM536193). The remaining A. hydrophila complex isolates were identified as A. hydrophila subsp. hydrophila. The ability of biochemical tests and fatty acid methyl ester analysis to reliably discern both A. hydrophila subsp. dhakensis and A. hydrophila subsp. hydrophila was limited. In contrast to the A. hydrophila subsp. hydrophila, the faecal isolates of A. hydrophila subsp. dhakensis did not produce acid from arbutin. When compared in a two-dimensional plot, the A. hydrophila subsp. dhakensis faecal isolates contained higher amounts of the two minor fatty acids C(13:0) and C(17:1) �s8c than the A. hydrophila subsp. hydrophila reference strain. This is the first detected occurrence of the less frequent A. hydrophila subsp. dhakensis in our region and ribotyping was proved as a suitable method for the identification of A. hydrophila subsp. dhakensis.
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( 2012 ) Aeromonas aquariorum septicemia and enterocolitis in a cirrhotic patient. PMID : 22995364 : DOI : 10.1016/j.diagmicrobio.2012.08.005 Abstract >>
Aeromonas aquariorum is a recently described Aeromonas species. We present a cirrhotic patient with septicemia and bloody diarrhea in whom A. aquariorum was isolated from the blood and stool. The species identification was based on sequence analysis of the partial rpoB and rpoD genes. The A. aquariorum isolates carried genes encoding hemolysin, aerolysin, and the cytotonic enterotoxin Alt. Significant A. aquariorum-induced cytotoxicity in intestinal epithelial cells was also demonstrated.
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