Evaluation of two miniaturized systems, MicroScan W/A and BBL Crystal E/NF, for identification of clinical isolates of Aeromonas spp

Technical specifications for a EU-wide baseline survey of antimicrobial resistance in bacteria from aquaculture animals

The European Commission requested scientific and technical assistance in the preparation of a EU-wide baseline survey of antimicrobial resistance (AMR) in bacteria from aquaculture animals. It is recommended that the survey would aim at estimating the occurrence of AMR in Aeromonas spp. isolated from Atlantic Salmon (Salmo salar), European seabass (Dicentrarchus labrax) and trout (Salmo trutta, Salvelinus fontinalis, Oncorhynchus mykiss) intended to consumption, at harvesting (at farm/slaughter), at the EU level and in addition, at estimating the occurrence and diversity of AMR of Escherichia coli, Enterococcus faecium, Enterococcus faecalis, Vibrio parahaemolyticus and Vibrio alginolyticus in blue mussel (Mytilus edulis) and Mediterranean mussel (Mytilus galloprovincialis) from production areas and at dispatch centres at the EU level. These technical specifications define the target populations, the sample size for the survey, sample collection requirements, the analytical methods (for isolation, identification, phenotypic susceptibility testing and further genotypic analysis of some of the bacteria targeted) and the data reporting requirements. The data to be reported by the EU Member States to support this baseline survey are presented in three data models. The results of the survey should be reported using the EFSA reporting system.

Aeromonas species obtained from different farmed aquatic species in India and Taiwan show high phenotypic relatedness despite species diversity

Objectives

Aeromonads cause severe diseases in farmed aquatic organisms. Herein, we examined 28 isolates causing disease in farmed aquatic organisms from India (n = 24) and Taiwan (n = 4) to gain insight of their genotypic and phenotypic properties.

Results

API 20NE biochemical phenotyping showed ≥ 90% similarity classifying all isolates as Aeromonas hydrophila. 16S rRNA genotyping showed ≥ 98% homology among all isolates with A. sobria (NR119044.1ATCC), A. veronii (MK990549.1), A. caviae (NR029252.1) and A. hydrophila (MG984625.1ATCC) and other reference strains. In contrast, gyrB showed a higher intraspecies diversity (≥ 96%) than 16S rRNA delineating the 28 isolates into three groups. Group-I consisted of seven Indian isolates clustered with A. sobria (MK484163.1ATCC), group-II comprised of five Indian and two Taiwanese isolates clustered with A. veronii AF417626.1ATCC while group-III had 11 Indian and three Taiwanese isolates grouped with A. hydrophila (AY987520.1 and DQ519366.1) reference strains. None of our isolates clustered with A. caviae (AJ868400.1ATCC) reference strain. These findings suggest that A. sobria, A. veronii and A. hydrophila could be the etiological agents of diseases observed in farmed fish and soft-shelled turtles (Pelodiscus sinensis) examined in this study. Overall, our findings accentuate the importance of combining phenotyping with genotyping for correct taxonomic classification of Aeromonas spp. in Aquaculture.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05716-3.

Molecular Typing, Antibiogram and PCR-RFLP Based Detection of Aeromonas hydrophila Complex Isolated from Oreochromis niloticus

Motile Aeromonas septicemia is a common bacterial disease that affects Oreochromis niloticus and causes tremendous economic losses globally. In order to investigate the prevalence, molecular typing, antibiogram and the biodiversity of Aeromonas hydrophila complex, a total of 250 tilapia (Oreochromis niloticus) were collected randomly from 10 private tilapia farms (25 fish/farm) at El-Sharkia Governorate, Egypt. The collected fish were subjected to clinical and bacteriological examinations. The majority of infected fish displayed ulcerative necrosis, exophthalmia, and internal signs of hemorrhagic septicemia. The prevalence of A. hydrophia complex was 13.2%, where the liver was the most predominant affected organ (54.1%). Polymerase chain reaction (PCR) was used to verify the identification of A. hydrophila complex using one set of primers targeting gyrB as well as the detection of virulent genes (aerA, alt, and ahp). All isolates were positive for the gyrB-conserved gene and harbored aerA and alt virulence genes. However, none of those isolates were positive for the ahp gene. The antimicrobial sensitivity was carried out, where the recovered strains were completely sensitive to ciprofloxacin and highly resistant to amoxicillin. All retrieved strains showed the same phenotypic characteristics and were identical based on the restriction fragment length polymorphism (RFLP). Experimentally challenged fish presented a high mortality rate (76.67%) and showed typical signs as in naturally infected ones. In conclusion, the synergism of phenotypic and genotypic characterization is a valuable epidemiological tool for the diagnosis of A. hydrophila complex. RFLP is a fundamental tool for monitoring the biodiversity among all retrieved strains of A. hydrophia.

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

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

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

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

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

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

Chlorinated and ultraviolet radiation -treated reclaimed irrigation water is the source of Aeromonas found in vegetables used for human consumption

Wastewater is increasingly being recognized as a key water resource, and reclaimed water (or treated wastewater) is used for irrigating vegetables destined for human consumption. The aim of the present study was to determine the diversity and prevalence of Aeromonas spp. both in reclaimed water used for irrigation and in the three types of vegetables irrigated with that water. Seven of the 11 (63.6%) samples of reclaimed water and all samples of vegetables were positive for the presence of Aeromonas. A total of 216 Aeromonas isolates were genotyped and corresponded to 132 different strains that after identification by sequencing the rpoD gene belonged to 10 different species. The prevalence of the species varied depending on the type of sample. In the secondary treated reclaimed water A. caviae and A. media dominated (91.4%) while A. salmonicida, A. media, A. allosaccharophila and A. popoffii represented 74.0% of the strains in the irrigation water. In vegetables, A. caviae (75.0%) was the most common species, among which a strain isolated from lettuce had the same genotype (ERIC pattern) as a strain recovered from the irrigation water. Furthermore, the same genotype of the species A. sanarellii was recovered from parsley and tomatoes demonstrating that irrigation water was the source of contamination and confirming the risk for public health.

Reassessment of the Enteropathogenicity of Mesophilic Aeromonas Species

Cases of Aeromonas diarrhea have been described all over the world. The genus Aeromonas includes ca. 30 species, of which 10 have been isolated in association with gastroenteritis. The dominating species that account for ca. 96% of the identified strains are Aeromonas caviae, A. veronii, A. dhakensis, and A. hydrophila. However, the role of Aeromonas as a true enteropathogen has been questioned on the basis of the lack of outbreaks, the non-fulfillment of Koch's postulates and the low numbers of acute illnesses in the only existing human challenge study. In the present study we reassess the enteropathogenicity of Aeromonas using dose response models for microbial infection and acute illness. The analysis uses the data from the human challenge study and additional data from selected outbreak investigations where the numbers exposed and the dose were reported, allowing their inclusion as "natural experiments". In the challenge study several cases of asymptomatic shedding were found (26.3%, 15/57), however, only 3.5% (2/57) of those challenged with Aeromonas developed acute enteric symptoms (i.e., diarrhea). The "natural experiments" showed a much higher risk of illness associated with exposure to Aeromonas, even at moderate to low doses. The median dose required for 1% illness risk, was ~1.4 × 104 times higher in the challenge study (1.24 × 104 cfu) compared to natural exposure events (0.9 cfu). The dose response assessment presented in this study shows that the combined challenge and outbreak data are consistent with high infectivity of Aeromonas, and a wide range of susceptibility to acute enteric illness. To illustrate the outcomes, we simulate the risk associated with concentrations of Aeromonas found in different water and food matrices, indicating the disease burden potentially associated with these bacteria. In conclusion this study showed that Aeromonas is highly infectious, and that human susceptibility to illness may be high, similar to undisputed enteropathogens like Campylobacter or Salmonella.

Aeromonas australiensis sp. nov., isolated from irrigation water

A Gram-negative, facultatively anaerobic bacillus, designated strain 266T, was isolated from an irrigation water system in the south-west of Western Australia. Analysis of the 16S rRNA gene sequence confirmed that strain 266T belonged to the genus Aeromonas , with the nearest species being Aeromonas fluvialis (99.6 % similarity to the type strain, with 6 nucleotide differences) followed by Aeromonas veronii and Aeromonas allosaccharophila (both 99.5 %). Analysis of gyrB and rpoD sequences suggested that strain 266T formed a phylogenetic line independent of other species in the genus. This was confirmed using the concatenated sequences of six housekeeping genes (gyrB, rpoD, recA, dnaJ, gyrA and dnaX) that also indicated that A. veronii and A. allosaccharophila were the nearest relatives. DNA–DNA reassociation experiments and phenotypic analysis further supported the conclusion that strain 266T represents a novel species, for which the name Aeromonas australiensis sp. nov. is proposed, with type strain 266T ( = CECT 8023T  = LMG 2670T).

Molecular characterization of clinical isolates of Aeromonas species from Malaysia

Background

Aeromonas species are common inhabitants of aquatic environments giving rise to infections in both fish and humans. Identification of aeromonads to the species level is problematic and complex due to their phenotypic and genotypic heterogeneity.

Methodology/Principal Findings

Aeromonas hydrophila or Aeromonas sp were genetically re-identified using a combination of previously published methods targeting GCAT, 16S rDNA and rpoD genes. Characterization based on the genus specific GCAT-PCR showed that 94 (96%) of the 98 strains belonged to the genus Aeromonas. Considering the patterns obtained for the 94 isolates with the 16S rDNA-RFLP identification method, 3 clusters were recognised, i.e. A. caviae (61%), A. hydrophila (17%) and an unknown group (22%) with atypical RFLP restriction patterns. However, the phylogenetic tree constructed with the obtained rpoD sequences showed that 47 strains (50%) clustered with the sequence of the type strain of A. aquariorum, 18 (19%) with A. caviae, 16 (17%) with A. hydrophila, 12 (13%) with A. veronii and one strain (1%) with the type strain of A. trota. PCR investigation revealed the presence of 10 virulence genes in the 94 isolates as: lip (91%), exu (87%), ela (86%), alt (79%), ser (77%), fla (74%), aer (72%), act (43%), aexT (24%) and ast (23%).

Conclusions/Significance

This study emphasizes the importance of using more than one method for the correct identification of Aeromonas strains. The sequences of the rpoD gene enabled the unambiguous identication of the 94 Aeromonas isolates in accordance with results of other recent studies. Aeromonas aquariorum showed to be the most prevalent species (50%) containing an important subset of virulence genes lip/alt/ser/fla/aer. Different combinations of the virulence genes present in the isolates indicate their probable role in the pathogenesis of Aeromonas infections.

Identification and genomovar assignation of clinical strains of Pseudomonas stutzeri

The identification of Pseudomonas stutzeri clinical isolates through conventional phenotypic methods was compared with identification through partial rpoD gene sequencing. We observed that commercial phenotypic systems easily confuse P. stutzeri with other Pseudomonas species. We also demonstrated that most of the clinical strains of P. stutzeri herein studied (79%) belonged to genomovar 1 of the species. We propose the use of partial rpoD gene sequence analysis as a complementary molecular tool for the precise routine identification and genomovar assignation of P. stutzeri clinical isolates, as well as for typing and epidemiological studies.

Evaluation of VITEK 2, MicroScan, and Phoenix for identification of clinical isolates and reference strains

To compare the identification accuracies of VITEK 2 (bioMérieux), MicroScan (Siemens Healthcare), and Phoenix (Becton Dickinson), microbial identification was performed on 160 clinical isolates and 50 reference strains on each of these 3 systems, using the appropriate identification kit provided by each system. Of the 142 clinical isolates that were identified at the species level, VITEK 2, MicroScan, and Phoenix correctly identified 93.7%, 82.4%, and 93.0%, and incorrectly identified 2.1%, 7.0%, and 0%, respectively. In the reference strain tests, VITEK 2, MicroScan, and Phoenix correctly identified 55.3%, 54.4%, and 78.0% of the reference strains at the species level and incorrectly identified 10.6%, 13.0%, and 6.0% of the reference strains, respectively. In conclusion, the identification rate of VITEK 2, Phoenix, and MicroScan was high or acceptable on clinical isolates. Phoenix showed a significantly higher performance than VITEK 2 or MicroScan in identifying the reference strains.

The genus Aeromonas: taxonomy, pathogenicity, and infection

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

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 genus Aeromonas: taxonomy, pathogenicity, and infection

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

Aeromonas taiwanensis sp. nov. and Aeromonas sanarellii sp. nov., clinical species from Taiwan

Two clinical Aeromonas strains (A2-50(T) and A2-67(T)) recovered from the wounds of two patients in Taiwan could not be assigned to any known species of this genus based on their 16S rRNA gene sequences, which showed similarities of 99.6-99.8 % to those of the type strains of Aeromonas caviae, A. trota and A. aquariorum. The rpoD phylogenetic tree allocated these strains to two novel and independent phylogenetic lines, the neighbouring species being A. caviae, the type strain of which showed 93.2 % similarity (56 bp differences) to strain A2-50(T) and 92.2 % (63 bp differences) to strain A2-67(T). A multilocus phylogenetic analysis of five housekeeping genes (gyrB, rpoD, recA, dnaJ and gyrA; 3684 bp) confirmed that the two strains formed independent phylogenetic lineages within the genus. These data, together with phenotypic characterization and DNA-DNA reassociation results, revealed that these strains represent novel Aeromonas species, for which the names Aeromonas taiwanensis sp. nov. (type strain A2-50(T) =CECT 7403(T) =LMG 24683(T)) and Aeromonas sanarellii sp. nov. (type strain A2-67(T) =CECT 7402(T) =LMG 24682(T)) are proposed.

Clinical relevance of the recently described species Aeromonas aquariorum

Twenty-two human extraintestinal isolates (11 from blood) and three isolates recovered from patients with diarrhea were genetically characterized as Aeromonas aquariorum, a novel species known only from ornamental fish. The isolates proved to bear a considerable number of virulence genes, and all were resistant to amoxicillin (amoxicilline), cephalothin (cefalotin), and cefoxitin. Biochemical differentiation from the most relevant clinical species is provided.

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

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

Surgical site infection due to Aeromonas species: report of nine cases and literature review

Gastrointestinal and wound infections are the most common clinical presentation of Aeromonas. Surgical site infections (SSIs) due to this microorganism are rare. We studied the clinical and microbiological characteristics of 9 cases that appeared at 2 Spanish hospitals and reviewed 15 cases available in the literature. All patients (including our cases) had gastrointestinal or biliary diseases. 21 patients (91.3%) developed SSIs after abdominal or pelvic surgery. The mean duration from surgery to the onset of wound infection was 2.2 d in our 9 patients. The infection was polymicrobial in 17 patients (77.2%) and 19 cases were nosocomial (95%). Clinical outcome of all cases was uniformly good after treatment except for 2 patients. Two patients were cured only with surgical drainage. In conclusion, SSIs due to Aeromonas species have a probable endogenous source after abdominal or pelvic surgery and the onset is rapid in most cases. Clinical outcome is good after antibiotic treatment but surgical drainage without antibiotic therapy can be sufficient to clear the infection in some cases.

[Extraintestinal infection due to Aeromonas spp.: review of 38 cases]

INTRODUCTION

Aeromonas spp. typically cause gastroenteritis, but can occasionally produce extraintestinal infections. The aim of this study was to determine the clinical and microbiological characteristics of extraintestinal infections caused by Aeromonas spp. in our area.

PATIENTS AND METHODS

The clinical histories of patients with extraintestinal infections by Aeromonas spp. diagnosed in Hospital Universitario de Guadalajara (Guadalajara, Spain) from January 1990 to December 2005 were reviewed. Identification and susceptibility testing of the strains were performed by the MicroScan WalkAway-40 automated method (DadeBerhing).

RESULTS

Thirty-eight cases of extraintestinal infections were diagnosed: 18 abdominal infections, 11 skin and soft tissue infections, 3 urinary tract infections, and 3 episodes of bacteremia with no primary focus. The species most frequently found was A. hydrophila (16 cases). Infection occurred most often in patients with underlying diseases (76.3%), including malignancy (34.2%) and diabetes mellitus (21%). Polymicrobial infections were detected in 50% and the etiology was nosocomial in 21%. The mortality rate was 16.2%. Gentamicin, amikacin, cefotaxime and ciprofloxacin had the highest activity against the Aeromonas species isolated.

CONCLUSIONS

Aeromonas spp. as the causative infectious agent should be kept in mind in patients with infections of the biliary system, surgical wounds in the abdomen and posttraumatic cellulitis. Extraintestinal infection is usually polymicrobial, appears most commonly in patients with underlying diseases, and generally has a good prognosis. The most active antibiotics in vitro were gentamicin, amikacin, cefotaxime and ciprofloxacin.

Aeromonas hemolytic uremic syndrome. A case and a review of the literature

Although rarely, hemolytic uremic syndrome can be induced by Aeromonas. We report a case in a 40-year-old Spanish female produced by Aeromonas veronii bv. sobria and review the previous cases described in the literature. This is the 2nd case described in adults.

Comparative typing of Pseudomonas species isolated from the aquatic environment in Greece by SDS-PAGE and RAPD analysis

AIMS

Three broadly used typing methods were employed in order to assess and compare the identification and classification of environmental Pseudomonas strains. The reproducibility, typeability and discriminatory power of the methods were also compared to evaluate their application. Finally, the potential impact on public health of the isolates is to be discussed.

METHODS AND RESULTS

Pseudomonas strains (160) isolated from the aquatic environment in Greece and identified by a rapid identification commercially available system (API20NE), were subjected to whole-cell protein electrophoresis (Sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and Randomly Amplified Polymorphic DNAs (RAPD) using two 10-mer primers. In general, the obtained results were in agreement. Twenty isolates that could not be identified by the API20NE system were classified by the other methods.

CONCLUSIONS

Rapid identification systems may serve only for a first rough identification of environmental Pseudomonads. In order to acquire further information, so that conclusions about their role in the ecosystem and human health could be drawn, other phenotypic or genotypic methods have to be applied.

SIGNIFICANCE AND IMPACT OF STUDY

It is important, from a public health point of view, to monitor the identities of environmental Pseudomonas isolates using specific methods due to their ubiquity, heterogeneity and their pathogenicity, either established or potential.

Lack of agreement between biochemical and genetic identification of Aeromonas spp

Biochemical and genetic identification by RFLP (restriction fragment length polymorphism) of the PCR-amplified 16S r-RNA sequence were compared for a selection of 171 clinical and environmental isolates of Aeromonas spp. The investigation revealed large differences between the two methods. The species phenotypic identification scheme and the genetic technique applied to the environmental strains gave divergent results for 96% of the strains tested. There was 46% discrepancy between the two methods for the clinical isolates. The distribution of species differed between clinical and environmental isolates. A. hydrophila, A. caviae, A. jandaei and A. veronii dominated the clinical material (81% of isolates by RFLP), whilst only 21% of the environmental isolates belonged to those four species. From the environmental group A. salmonicida, A. bestiarum, A. sobria, A. media, and A. encheleia contributed 72% of the strains tested. The poor parity between the biochemical and the genetic identification of the environmental isolates, and to a lesser extent for the clinical isolates, underlines the fact that our current biochemical methods cannot adequately differentiate Aeromonas spp. This work also shows that the biochemical schemes derived from clinical isolates are incomplete for the identification of environmental strains.

Aeromonas hydrophilaclinical and environmental ecotypes as revealed by genetic diversity and virulence genes

Aeromonas hydrophila strains recovered from clinical samples and ambient sources were phenotypically and genetically identified. In addition, the distribution of putative virulence factors was assayed. To determine the genetic diversity of these strains, random amplification of polymorphic DNA (RAPD) and enterobacterial repetitive intergenic consensus (ERIC)-PCR markers were used. The discriminatory ability of the techniques, using Simpson's index, was 0.96 for both methods. The most consistent dendrogram was obtained when RAPD and ERIC data were combined. The genetic diversity revealed a high intra-specific genetic diversity (h=0.364+/-0.024 and I=0.538+/-0.030). The strains showed a tendency to cluster according to their origin of isolation (best-cut test 0.80 and bootstrap values >50%). The present study demonstrates and quantifies the high intra-specific diversity within this species and reveals a clear differentiation of strains according to their ecological origin. The distribution of virulence-related genes confirm that A. hydrophila is a genetically heterogeneous species that harbour ecotypes which have different pathogenic potential to human and other animals.

Manual and automated instrumentation for identification of Enterobacteriaceae and other aerobic gram-negative bacilli

Identification of gram-negative bacilli, both enteric and nonenteric, by conventional methods is not realistic for clinical microbiology laboratories performing routine cultures in today's world. The use of commercial kits, either manual or automated, to identify these organisms is a common practice. The advent of rapid or "spot" testing has eliminated the need for some commonly isolated organisms to be identified with the systems approach. Commercially available systems provide more in-depth identification to the species level as well as detect new and unusual strains. The answers obtained from these systems may not always be correct and must be interpreted with caution. The patient demographics, laboratory workload and work flow, and technologist's skill levels should dictate the system of choice. Cost considerations introduce another variable into the equation affecting choice. Each system has its own strengths and weaknesses, and each laboratory must decide on the level of sophistication that fulfills its particular needs.