Potential Pathogenicity of Aeromonas spp. Recovered in River Water, Soil, and Vegetation from a Natural Recreational Area

The genus Aeromonas is widely distributed in aquatic environments and is recognized as a potential human pathogen. Some Aeromonas species are able to cause a wide spectrum of diseases, mainly gastroenteritis, skin and soft-tissue infections, bacteremia, and sepsis. Currently, untreated river water is used for irrigation and recreational purposes. In this study, the Aeromonas spp. present in a river recreational environment was investigated by quantifying its presence in water, soil, and vegetation using three techniques: qPCR, plate counting in selective ADA medium, and Most Probable Number, in parallel. The presence of clones in the three types of samples was elucidated through genotyping with the ERIC-PCR technique, whereas the identification of the isolated Aeromonas was carried out by sequencing the rpoD gene. Finally, the pathogenic potential of some of the strains was explored by studying the presence and expression of virulence genes characteristic of the genus, their antimicrobial susceptibility profile, as well as the quantification of their cell damage and intracellular survival in an in vitro macrophages infection model. The results showed the presence of Aeromonas in all samples with the three quantification methods, with Aeromonas popoffii being the most prevalent species. The presence of strains with the same genotype (ERIC-PCR) was also confirmed in different samples. Some of the strains showed a high level of cell damage and intracellular bacterial survival, as well as the presence of various virulence factors. Furthermore, these strains showed resistance to some of the antibiotics tested and used therapeutically in both humans and animals. These results indicate that the presence of Aeromonas in this environment may represent a biosanitary risk that could be a public health problem.

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.

Microbiological contamination of conventional and reclaimed irrigation water: Evaluation and management measures

The wide diversity of irrigation water sources (i.e., drinking water, groundwater, reservoir water, river water) includes reclaimed water as a requested measure for increasing water availability, but it is also a challenge as pathogen exposure may increase. This study evaluates the level of microbial contamination in different irrigation waters to improve the knowledge and analyses management measures for safety irrigation. Over a one-year period, the occurrence of a set of viruses, bacteria and protozoa, was quantified and the performance of a wetland system, producing reclaimed water intended for irrigation, was characterized. Human fecal pollution (HAdV) was found in most of the irrigation water types analysed. Hepatitis E virus (HEV), an emerging zoonotic pathogen, was present in groundwater where porcine contamination was identified (PAdV). The skin-carcinoma associated Merkel cell polyomavirus (MCPyV), was found occasionally in river water. Noroviruses were detected, as expected, in winter, in river water and reclaimed water. Groundwater, river water and reservoir water also harboured potential bacterial pathogens, like Helicobacter pylori, Legionella spp. and Aeromonas spp. that could be internalized and viable inside amoebas like Acanthamoeba castellanii, which was also detected. Neither Giardia cysts, nor any Cryptosporidium oocysts were detected. The wetland system removed 3 Log₁₀ of viruses and 5 Log₁₀ of bacteria, which resembled the river water quality. Irrigation waters were prone to variable contamination levels and according to the European guidance documents, the E. coli (EC) levels were not always acceptable. Sporadic detection of viral pathogens as NoV GII and HAdV was identified in water samples presenting lower EC than the established limit (100MNP/100 mL). When dealing with reclaimed water as a source of irrigation the analysis of some viral parameters, like HAdV during the peak irrigation period (summer and spring) or NoV during the coldest months, could complement existing water management tools based on bacterial indicators.

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.

T6SS and ExoA of flesh-eating Aeromonas hydrophila in peritonitis and necrotizing fasciitis during mono- and polymicrobial infections

An earlier report described a human case of necrotizing fasciitis (NF) caused by mixed infection with 4 Aeromonas hydrophila strains (NF1-NF4). While the NF2, NF3, and NF4 strains were clonal and possessed exotoxin A (ExoA), the NF1 strain was determined to be phylogenetically distinct, harboring a unique type 6 secretion system (T6SS) effector (TseC). During NF1 and NF2 mixed infection, only NF1 disseminated, while NF2 was rapidly killed by a contact-dependent mechanism and macrophage phagocytosis, as was demonstrated by using in vitro models. To confirm these findings, we developed 2 NF1 mutants (NF1ΔtseC and NF1ΔvasK); vasK encodes an essential T6SS structural component. NF1 VasK and TseC were proven to be involved in contact-dependent killing of NF2 in vitro, as well as in its elimination at the intramuscular injection site in vivo during mixed infection, with overall reduced mouse mortality. ExoA was shown to have an important role in NF by both NF1-exoA (with cis exoA) and NF2 during monomicrobial infection. However, the contribution of ExoA was more important for NF2 than NF1 in the murine peritonitis model. The NF2∆exoA mutant did not significantly alter animal mortality or NF1 dissemination during mixed infection in the NF model, suggesting that the ExoA activity was significant at the injection site. Immunization of mice to ExoA protected animals from NF2 monomicrobial challenge, but not from polymicrobial infection because of NF2 clearance. This study clarified the roles of T6SS and ExoA in pathogenesis caused by A. hydrophila NF strains in both mouse peritonitis and NF models in monomicrobial and polymicrobial infections.

The Metallochaperone Encoding Gene hypA Is Widely Distributed among Pathogenic Aeromonas spp. and Its Expression Is Increased under Acidic pH and within Macrophages

Metallochaperones are essential proteins that insert metal ions or metal cofactors into specific enzymes, that after maturation will become metalloenzymes. One of the most studied metallochaperones is the nickel-binding protein HypA, involved in the maturation of nickel-dependent hydrogenases and ureases. HypA was previously described in the human pathogens Escherichia coli and Helicobacter pylori and was considered a key virulence factor in the latter. However, nothing is known about this metallochaperone in the species of the emerging pathogen genus Aeromonas. These bacteria are native inhabitants of aquatic environments, often associated with cases of diarrhea and wound infections. In this study, we performed an in silico study of the hypA gene on 36 Aeromonas species genomes, which showed the presence of the gene in 69.4% (25/36) of the Aeromonas genomes. The similarity of Aeromonas HypA proteins with the H. pylori orthologous protein ranged from 21−23%, while with that of E. coli it was 41−45%. However, despite this low percentage, Aeromonas HypA displays the conserved characteristic metal-binding domains found in the other pathogens. The transcriptional analysis enabled the determination of hypA expression levels under acidic and alkaline conditions and after macrophage phagocytosis. The transcriptional regulation of hypA was found to be pH-dependent, showing upregulation at acidic pH. A higher upregulation occurred after macrophage infection. This is the first study that provided evidence that the HypA metallochaperone in Aeromonas might play a role in acid tolerance and in the defense against macrophages.

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.

Delineation of Taxonomic Species within Complex of Species: Aeromonas media and Related Species as a Test Case

Aeromonas media is an opportunistic pathogen for human and animals mainly found in aquatic habitats and which has been noted for significant genomic and phenotypic heterogeneities. We aimed to better understand the population structure and diversity of strains currently affiliated to A. media and the related species A. rivipollensis. Forty-one strains were included in a population study integrating, multilocus genetics, phylogenetics, comparative genomics, as well as phenotypics, lifestyle, and evolutionary features. Sixteen gene-based multilocus phylogeny delineated three clades. Clades corresponded to different genomic groups or genomospecies defined by phylogenomic metrics ANI (average nucleotide identity) and isDDH (in silico DNA-DNA hybridization) on 14 whole genome sequences. DL-lactate utilization, cefoxitin susceptibility, nucleotide signatures, ribosomal multi-operon diversity, and differences in relative effect of recombination and mutation (i.e., in evolution mode) distinguished the two species Aeromonas media and Aeromonas rivipollensis. The description of these two species was emended accordingly. The genome metrics and comparative genomics suggested that a third clade is a distinct genomospecies. Beside the species delineation, genetic and genomic data analysis provided a more comprehensive knowledge of the cladogenesis determinants at the root and inside A. media species complex among aeromonads. Particular lifestyles and phenotypes as well as major differences in evolution modes may represent putative factors associated with lineage emergence and speciation within the A. media complex. Finally, the integrative and populational approach presented in this study is considered broadly in order to conciliate the delineation of taxonomic species and the population structure in bacterial genera organized in species complexes.

'Aeromonas intestinalis' and 'Aeromonas enterica' isolated from human faeces, 'Aeromonas crassostreae' from oyster and 'Aeromonas aquatilis' isolated from lake water represent novel species

Four Aeromonas strains from clinical and environmental samples differed from known species on the basis of rpoD gene sequence. Multilocus phylogenetic analysis and in silico DNA-DNA hybridization confirmed them as four new species even though their 16S rRNA gene sequence similarity with their closest relatives was >98.7%, as occurred for other Aeromonas spp.

'Arcobacter porcinus' sp. nov., a novel Arcobacter species uncovered by Arcobacter thereius

Arcobacter thereius is a species associated with human disease. A group of A. thereius pork strains (represented by strain LMG 24487) clustered separately from the type strain (LMG 24486^T) in the 16S rRNA and multilocus phylogenetic trees. In silico DNA-DNA hybridization and average nucleotide identity results between their genomes (93.3 and 51.1%) confirmed ‘Arcobacter porcinus’ (LMG 24487^T) as a new species.

Evaluation of the microbiological quality of reclaimed water produced from a lagooning system

The use of lagooning as a complementary natural method of treating secondary effluents of wastewater treatment plants has been employed as an affordable and easy means of producing reclaimed water. However, using reclaimed water for some purposes, for example, for food irrigation, presents some risks if the effluents contain microbial pathogens. Classical bacterial indicators that are used to assess faecal contamination in water do not always properly indicate the presence of bacterial or viral pathogens. In the current study, the presence of faecal indicator bacteria (FIB), heterotrophic bacterial counts (HBC), pathogens and opportunistic pathogens, such as Legionella spp., Aeromonas spp., Arcobacter spp., free-living amoeba (FLA), several viral indicators (human adenovirus and polyomavirus JC) and viral pathogens (noroviruses and hepatitis E virus) were analysed for 1 year in inlet and outlet water to assess the removal efficiency of a lagooning system. We observed 2.58 (1.17-4.59) and 1.65 (0.15-3.14) log reductions in Escherichia coli (EC) and intestinal enterococci (IE), respectively, between the inlet and outlet samples. Genomic copies of the viruses were log reduced by 1.18 (0.24-2.93), 0.64 (0.12-1.97), 0.45 (0.04-2.54) and 0.72 (0.22-2.50) for human adenovirus (HAdV), JC polyomavirus (JCPyV) and human noroviruses (NoV GI and GII), respectively. No regrowth of opportunistic pathogens was observed within the system. FLA, detected in all samples, did not show a clear trend. The reduction of faecal pathogens was irregular with 6 out of 12 samples and 4 out of 12 samples exceeding the EC and IE values, specified in the Spanish legislation for reclaimed water (RD 1620/2007). This data evidences that there is a need for more studies to evaluate the removal mechanisms of lagooning systems in order to optimize pathogen reduction. Moreover, surveillance of water used to irrigate raw edible vegetables should be conducted to ensure the fulfilment of the microbial requirements for the production of safe reclaimed water.

Occurrence of emerging food-borne pathogenic Arcobacter spp. isolated from pre-cut (ready-to-eat) vegetables

Given that changes in consumer food behaviours have led to an increase in the demand for pre-cut ready-to-eat (RTE) vegetables, and that few data are currently available on the occurrence of Arcobacter spp. in such foods, the aim of the present study was to assess the occurrence of Arcobacter spp. that carry virulence-associated genes on pre-cut RTE vegetables, using cultural and molecular methods. Arcobacter was detected using biomolecular identification methods in 44/160 (27.5%) of the samples, of which 40/44 (90.9%) isolates corresponded to A. butzleri and 4/44 (9.1%) to A. cryaerophilus. Studying the incidence of 9 virulence-associated genes revealed the widespread distribution of these genes among the Arcobacter isolates tested. The results obtained in our research provided plenty of information on the health risks associated with the direct consumption of raw vegetables, and highlight the need to implement further studies at each level of the production chain, in order to obtain further information to help protect human health.

Occurrence of potentially pathogenic arcobacters in shellfish

Considering that several recent cases of human gastroenteritis have been associated with species from the Arcobacter genus, and that few data are currently available about the occurrence of this genus in Italian shellfish, the aim of the present study was to evaluate the occurrence of Arcobacter spp. and the presence of virulence-associated genes. The approach consisted of cultural and biomolecular (multiplex-PCR and 16S-RFLP) methods identifying isolates, followed by PCR assays aimed at the cadF, ciaB, cjl349, irgA, hecA putative virulence genes. Arcobacter spp. was detected in 16/70 (22.8%) shellfish samples. Specifically, Arcobacter spp. was highlighted in 10/42 (23.8%) mussel and in 6/28 (21.4%) clam samples. Subsequently, biomolecular assays revealed Arcobacter butzleri in 12/16 (75%) and Arcobacter cryaerophilus 1B in 4/16 (25%) isolates. PCRs aimed at the five putative virulence genes demonstrated widespread distribution of these genes among Arcobacter isolates and some differences from the results published by other authors. Our research provides more information regarding the health risks associated with the consumption of raw bivalve molluscs and underlines the need to implement an adequate control plan by performing intensive and continuous monitoring in order to guarantee human health.

Evidence of viral dissemination and seasonality in a Mediterranean river catchment: Implications for water pollution management

Conventional wastewater treatment does not completely remove and/or inactive viruses; consequently, viruses excreted by the population can be detected in the environment. This study was undertaken to investigate the distribution and seasonality of human viruses and faecal indicator bacteria (FIB) in a river catchment located in a typical Mediterranean climate region and to discuss future trends in relation to climate change. Sample matrices included river water, untreated and treated wastewater from a wastewater treatment plant within the catchment area, and seawater from potentially impacted bathing water. Five viruses were analysed in the study. Human adenovirus (HAdV) and JC polyomavirus (JCPyV) were analysed as indicators of human faecal contamination of human pathogens; both were reported in urban wastewater (mean values of 10(6) and 10(5) GC/L, respectively), river water (10(3) and 10(2) GC/L) and seawater (10(2) and 10(1) GC/L). Human Merkel Cell polyomavirus (MCPyV), which is associated with Merkel Cell carcinoma, was detected in 75% of the raw wastewater samples (31/37) and quantified by a newly developed quantitative polymerase chain reaction (qPCR) assay with mean concentrations of 10(4) GC/L. This virus is related to skin cancer in susceptible individuals and was found in 29% and 18% of river water and seawater samples, respectively. Seasonality was only observed for norovirus genogroup II (NoV GGII), which was more abundant in cold months with levels up to 10(4) GC/L in river water. Human hepatitis E virus (HEV) was detected in 13.5% of the wastewater samples when analysed by nested PCR (nPCR). Secondary biological treatment (i.e., activated sludge) and tertiary sewage disinfection including chlorination, flocculation and UV radiation removed between 2.22 and 4.52 log10 of the viral concentrations. Climate projections for the Mediterranean climate areas and the selected river catchment estimate general warming and changes in precipitation distribution. Persistent decreases in precipitation during summer can lead to a higher presence of human viruses because river and sea water present the highest viral concentrations during warmer months. In a global context, wastewater management will be the key to preventing environmental dispersion of human faecal pathogens in future climate change scenarios.

Characterization of Arcobacter suis isolated from water buffalo (Bubalus bubalis) milk

During a survey in a dairy plant in Italy, the second strain (strain FG 206) of Arcobacter suis described in the literature was isolated from raw water buffalo milk. The objective of this study was to confirm the species identification, better define the species by comparing its characteristics with those of the reference strain (F41(T) = CECT 7833(T) = LMG 26152(T)) and to investigate its potential clinical relevance by detecting the virulence gene pattern of the new strain. Phenotypical characterization and 16S rRNA-RFLP gave a complete overlap of results for the two strains. As expected, an RFLP pattern common to A. suis and Arcobacter defluvii was obtained by MseI endonuclease digestion, and a pattern specific for A. suis was obtained by BfaI endonuclease digestion. 16S rRNA sequencing and multilocus phylogenetic analysis (MLPA) showed a robust relatedness of strain FG 206 to the A. suis type strain F41(T). The recovery of strain FG 206 from a dairy plant shows that this species of Arcobacter is present in the food chain. Like the type strain recovered from pig meat, the species A. suis may not be confined to a single type of food.

A severe case of persistent diarrhoea associated with Arcobacter cryaerophilus but attributed to Campylobacter sp. and a review of the clinical incidence of Arcobacter spp

Although rarely, Arcobacter spp. have been associated with diarrhoea and bacteraemia. We report a persistent case in a healthy 26-year-old Spanish male of bloody diarrhoea, which was attributed to Campylobacter but in fact was caused by Arcobacter cryaerophilus, as determined by sequencing of the rpoB gene. The isolate was re-identified by matrix-assisted laser desorption ionization time of flight (MALDI-TOF) and genotyped for five putative virulence genes and for seven genes included in the Arcobacter multilocus sequence typing database. The low score obtained by MALDI-TOF indicates the need to complement the database with more isolates. Only the ciaB gene, which encodes for an invasin, was detected. Despite the isolate belonging to a new sequence type, three of the alleles (glnA, pgm and tkt) had been found previously in isolates from faeces of patients with diarrhoea. This study, together with the reviewed literature, indicates that Arcobacter can produce bacteraemia and that the isolation from patients with diarrhoea range from 0.11% to 1.25%. This study also demonstrates that Arcobacter species are confused with Campylobacter spp., as previously suggested. This is one of the factors that leads to underestimation of their incidence together with the use of inappropriate detection and identification methods.

Aeromonas spp. whole genomes and virulence factors implicated in fish disease

It is widely recognized that Aeromonas infections produce septicaemia, and ulcerative and haemorrhagic diseases in fish, causing significant mortality in both wild and farmed freshwater and marine fish species that damage the economics of the aquaculture sector. The descriptions of the complete genomes of Aeromonas species have allowed the identification of an important number of virulence genes that affect the pathogenic potential of these bacteria. This review will focus on the most relevant information derived from the available Aeromonas genomes in relation to virulence and on the diverse virulence factors that actively participate in host adherence, colonization and infection, including structural components, extracellular factors, secretion systems, iron acquisition and quorum sensing mechanisms.

Arcobacter bivalviorum sp. nov. and Arcobacter venerupis sp. nov., new species isolated from shellfish

A group of ten Arcobacter isolates (Gram negative, slightly curved motile rods, oxidase positive) was recovered from mussels (nine) and from clams (one). These isolates could not be assigned to any known species using the molecular identification methods specific for this genus (16S rDNA-RFLP and m-PCR). The aim of this study is to establish the taxonomic position of these isolates. The 16S rRNA gene sequence similarity of mussel strain F4(T) to the type strains of all other Arcobacter species ranged from 91.1% to 94.8%. The species most similar to the clams' strain F67-11(T) were Arcobacter defluvii (CECT 7697(T), 97.1%) and Arcobacter ellisii (CECT 7837(T), 97.0%). On the basis of phylogenetic analyses with 16S rRNA, rpoB, gyrB and hsp60 genes, the mussel and clam strains formed two different, new lineages within the genus Arcobacter. These data, together with their different phenotypic characteristics and MALDI-TOF mass spectra, revealed that these strains represent two new species, for which the names Arcobacter bivalviorum (type strain F4(T)=CECT 7835(T)=LMG 26154(T)) and Arcobacter venerupis (type strain F67-11(T)=CECT 7836(T)=LMG 26156(T)) are proposed.

Human isolates of Aeromonas possess Shiga toxin genes (stx1 and stx2) highly similar to the most virulent gene variants of Escherichia coli

Strains producing Shiga toxins, encoded by stx1 and stx2 genes, can cause diarrhoea, haemorrhagic colitis and haemolytic uremic syndrome. PCR screening of 80 clinical Aeromonas strains showed that 19 were stx1-positive and only one was positive for both stx1 and stx2. PCR bands were very faint for some strains and negative results were obtained after subculturing. The obtained sequences of Aeromonas stx1 and stx2 genes were highly similar to those of the most virulent stx gene variants of Shiga toxin-producing Escherichia coli. These results may lead to a better understanding of the potential pathogenicity and virulence mechanisms of Aeromonas.

Re-identification of Aeromonas isolates from chironomid egg masses as the potential pathogenic bacteria Aeromonas aquariorum

Egg masses of the non-biting midge Chironomous sp. have recently been found to serve as a reservoir for Vibrio cholerae and Aeromonas species. These insects are widely distributed in freshwater and evidence suggests that they may disseminate pathogenic bacteria species into drinking water systems. In the current study the taxonomy of 26 Aeromonas isolates, previously recovered from chironomid egg masses, was re-evaluated. It was found that 23 isolates, which had previously been identified as Aeromonas caviae, could belong to the recently described species Aeromonas aquariorum by their biochemical traits. To date, A. aquariorum has been found in ornamental fish and also in human extra-intestinal infections. ERIC-PCR genotyping differentiated 11 strains within the 23 A. aquariorum isolates, whose identity was confirmed by their rpoD gene sequences. Strains were found to possess the following virulence-associated genes: alt (90.9%), ahpB (81.8%), pla/lip/lipH3/apl-1/lip (54.5%), fla (27.3%), act/hylA/aerA (27.3%), ascF-ascG (81.8%) and aexT (9%) encoding for the cytotonic heat-labile enterotoxin, elastase, lipase, flagella, cytotoxic enterotoxins, the Type III Secretion System and the AexT toxin delivered by this system respectively. These findings indicate that chironomid egg masses harbour strains of A. aquariorum, which bear an important number of virulence genes, and that this species was misidentified originally as A. caviae.

Taxonomy, epidemiology, and clinical relevance of the genus Arcobacter

The genus Arcobacter, defined almost 20 years ago from members of the genus Campylobacter, has become increasingly important because its members are being considered emergent enteropathogens and/or potential zoonotic agents. Over recent years information that is relevant for microbiologists, especially those working in the medical and veterinary fields and in the food safety sector, has accumulated. Recently, the genus has been enlarged with several new species. The complete genomes of Arcobacter butzleri and Arcobacter nitrofigilis are available, with the former revealing diverse pathways characteristic of free-living microbes and virulence genes homologous to those of Campylobacter. The first multilocus sequence typing analysis showed a great diversity of sequence types, with no association with specific hosts or geographical regions. Advances in detection and identification techniques, mostly based on molecular methods, have been made. These microbes have been associated with water outbreaks and with indicators of fecal pollution, with food products and water as the suspected routes of transmission. This review updates this knowledge and provides the most recent data on the taxonomy, species diversity, methods of detection, and identification of these microbes as well as on their virulence potential and implication in human and animal diseases.

Arcobacter defluvii sp. nov., isolated from sewage samples

A study employing a polyphasic taxonomic approach was undertaken to clarify the position of 12 isolates recovered from sewage samples. These isolates were recognized as a potential novel species because a new and specific pattern was produced with the 16S rRNA-RFLP Arcobacter identification method. The sequences of the 16S rRNA gene not only supported the classification of these novel strains as members of the genus Arcobacter, but also showed that they formed a separate phylogenetic line. Strain SW28-11(T), chosen as the representative of these strains, showed 16S rRNA gene sequence similarity of 95.6 % with the closest related species Arcobacter nitrofigilis. The phylogenetic position of the novel strains was further confirmed by analysis of the housekeeping genes hsp60, rpoB and, for the first time, gyrB. The latter proved to be an excellent additional gene for establishing the phylogeny of this genus. These data, together with phenotypic characterization, revealed that this group of isolates represent a novel species of the genus Arcobacter. The name Arcobacter defluvii sp. nov., is proposed, with the type strain SW28-11(T) ( = CECT 7697(T) = LMG 25694(T)).

Diversity and pathogenecity of Vibrio species in cultured bivalve molluscs

Shellfish production is seriously affected by bacterial pathogens that cause high losses in hatcheries and in the aquaculture sector. A number of Vibrio species are considered important pathogens and have provoked severe mortality outbreaks. The pathologies caused by vibrios in bivalves have been described since the 1960s; however, over recent years, successive episodes of high mortality have been recorded due to these microorganisms. The present work provides an updated overview of the different studies performed in relation with the diversity of Vibrio spp. associated to bivalves. Special attention is given to the main Vibrio diseases and implicated species affecting the different life stages of cultured bivalves.

Aeromonas piscicola sp. nov., isolated from diseased fish

Four Aeromonas strains (S1.2(T), EO-0505, TC1 and TI 1.1) isolated from moribund fish in Spain showed a restriction fragment length polymorphism (RFLP) pattern related to strains of Aeromonas salmonicida and Aeromonas bestiarum but their specific taxonomic position was unclear. Multilocus sequence analysis (MLSA) of housekeeping genes rpoD, gyrB, recA and dnaJ confirmed the allocation of these isolates to an unknown genetic lineage within the genus Aeromonas with A. salmonicida, A. bestiarum and Aeromonas popoffii as the phylogenetically nearest neighbours. Furthermore, a strain biochemically labelled as Aeromonas hydrophila (AH-3), showing a pattern of A. bestiarum based on 16S rDNA-RFLP, also clustered with the unknown genetic lineage. The genes rpoD and gyrB proved to be the best phylogenetic markers for differentiating these isolates from their neighbouring species. Useful phenotypic features for differentiating the novel species from other known Aeromonas species included their ability to hydrolyze elastin, produce acid from l-arabinose and salicin, and their inability to produce acid from lactose and use l-lactate as a sole carbon source. A polyphasic approach using phenotypic characterization, phylogenetic analysis of the 16S rRNA gene and of four housekeeping genes, as well as DNA-DNA hybridization studies and an analysis of the protein profiles by MALDI-TOF-MS, showed that these strains represented a novel species for which the name Aeromonas piscicola sp. nov. is proposed with isolate S1.2(T) (=CECT 7443(T), =LMG 24783(T)) as the type strain.

Development of imipenem resistance in an Aeromonas veronii biovar sobria clinical isolate recovered from a patient with cholangitis

Several imipenem-susceptible and -resistant Aeromonas veronii biovar sobria isolates with different morphologies and antimicrobial susceptibilities recovered from bile samples of a patient with cholangitis were analysed. These isolates belonged to the same clone and the imipenem-resistant strains showed overexpression of the imiS gene, encoding a chromosomal carbapenemase. These results should make clinicians aware of the possible emergence of multidrug-resistant A. veronii biovar sobria, perhaps as a consequence of previous treatment of a urinary tract infection with amoxicillin plus clavulanic acid.

Prevalence of Arcobacter in meat and shellfish

Arcobacter is considered an emergent foodborne and waterborne enteropathogen. However, its prevalence in foods of animal origin is only partially known, because most studies have been concentrated on poultry, pork, and beef, and methods applied do not allow identification of all currently accepted Arcobacter species. We investigated the prevalence of Arcobacter in 203 food samples, 119 samples of seven different types of meats and 84 samples of four types of shellfish. Isolates were identified in parallel by using a published multiplex PCR method and a recently described 16S rDNA restriction fragment length polymorphism method that allows all currently accepted Arcobacter species to be characterized. The global prevalence of Arcobacter was 32%; it was highest in clams (5 of 5 samples, 100%) and chicken (9 of 14 samples, 64.3%) followed by pork (9 of 17 samples, 53.0%), mussels (23 of 56 samples, 41.1%), and duck meat (2 of 5 samples, 40.0%). Turkey meat and beef had a similar recovery rate (10 of 30 samples, 33.3%; 5 of 16 samples, 31.3%; respectively), and rabbit meat had the lowest rate (1 of 10 samples, 10.0%). No arcobacters were found in oysters, frozen shrimps, or sausages. This food survey is the first in which five of the seven accepted Arcobacter species have been isolated. Arcobacter butzleri was the most prevalent species (63.0% of isolates) followed by Arcobacter cryaerophilus (26.6%), Arcobacter mytili (4.7%), Arcobacter skirrowii (3.1%), and Arcobacter nitrofigilis (3.1%). Three (4.7%) of the isolates were classified as belonging to three potentially new phylogenetic lines. Our results indicated that Arcobacter species are widely distributed in the food products studied.

Updated phylogeny of the genus Aeromonas

Recent phylogenetic studies of the genus Aeromonas based on gyrB and rpoD gene sequences have improved the phylogeny based on 16S rRNA gene sequences first published in 1992, particularly in the ability to split closely related species. These studies did not include the recently described species Aeromonas simiae and Aeromonas molluscorum and only a single strain of Aeromonas culicicola was available for analysis at that time. In the present work, these Aeromonas species and newly isolated strains of A. culicicola were examined. Sequence analysis indicates that A. simiae and A. molluscorum belong to non-described phylogenetic lines of descent within this genus, which supports the original description of both species. The most closely related species are Aeromonas schubertii and Aeromonas encheleia, respectively, which is consistent with 16S rRNA gene sequencing results. However, while the five strains of A. molluscorum showed nucleotide differences in their gyrB and rpoD gene sequences, the only two known A. simiae strains exhibited identical gene sequences, suggesting that they are isolates of the same strain. On the basis of the rpoD gene sequence phylogeny, A. culicicola strains from the original description and new isolates from drinking water and ornamental fish clustered within the species Aeromonas veronii, suggesting inconsistencies with previous results. Other strains with previously controversial taxonomy and new isolates from other studies were included in this study in order to clarify their phylogenetic affiliation at the species level.

A preliminary study of the occurrence of actidione-resistant fungi in sediments of Catalonian river mouths (Spain). I. Keratinolytic fungi and related Onygenales

Sediments from eight river mouths along the Catalonian coast (Spain) were surveyed for keratinolytic fungi and related Onygenales. The actidione plating technique was employed. Of 532 actidione-treated sediment samples, 268 (50.3%) were positive for the fungi. Altogether, 384 fungal strains from 35 species were isolated from the samples. Narasimhella marginospora, Aphanoascus fulvescens, Neoarachnotheca keratinophila with its anamorph Myriodontium keratinophilum, Narasimhella hyalinospora, Beauveria alba, Sporothrix schenckii, Chrysosporium lobatum and Gymnoascus littoralis were the predominant species in sediments. Abundance of N. marginospora was clearly correlated with the degree of water pollution with sewage.

First record of the rare species Aeromonas culicicola from a drinking water supply

We describe the recovery of the rare species Aeromonas culicicola, so far known only in mosquitoes in India, from a drinking water supply in Spain. Typing, using enterobacterial repetitive intergenic consensus-PCR, revealed that the 27 new isolates belonged to 3 very closely related strains. These strains were genetically identified by 16S rRNA gene sequencing. Spanish strains differed from the mosquito strains in three nucleotide positions. The AHCYTOEN gene was present in these water strains, which may have a public health significance.

Phylogenetic analysis of the genus Aeromonas based on two housekeeping genes

The phylogenetic relationships of all known species of the genus Aeromonas, and especially Aeromonas bestiarum and Aeromonas salmonicida, were investigated on 70 strains using the rpoD sequence, which encodes the sigma70 factor. This analysis was complemented with the sequence of gyrB, which has already proven useful for determining the phylogenetic relationships in the genus. Nucleotide sequences of rpoD and gyrB showed that both genes had similar substitution rates (< 2 %) and a similar number of variable positions (34 % for rpoD versus 32 % for gyrB). Strain groupings by analysis of rpoD, gyrB and a combination of both genes were consistent with the taxonomic organization of all Aeromonas species described to date. However, the simultaneous analysis of both clocks improved the reliability and the power to differentiate, in particular, closely related taxa. At the inter-species level, gyrB showed a better resolution for differentiating Aeromonas sp. HG11/Aeromonas encheleia and Aeromonas veronii/Aeromonas culicicola/Aeromonas allosaccharophila, while rpoD more clearly differentiated A. salmonicida from A. bestiarum. The analysis of rpoD provided initial evidence for clear phylogenetic divergence between the latter two species.

Pathogenic Aeromonas hydrophila serogroup O:14 and O:81 strains with an S layer

Five autoagglutinating Aeromonas hydrophila isolates recovered from eels and humans were assigned to serogroups O:14 and O:81 of the Sakazaki and Shimada (National Institutes of Health) scheme. They had the following properties in common: positive precipitation after boiling, moderate surface hydrophobicity (salt-aggregation-test value around 1.2), pathogenicity for fish and mice (50% lethal dose, 10(4.61) to 10(7.11)), lipopolysaccharides that contained O-polysaccharide chains of homogeneous chain length, and an external S layer peripheral to the cell wall observed by electron microscopy. A strong cross-reactivity was detected by immunoblotting between the homogeneous O-polysaccharide fraction of O:14 and O:81 strains but not between them and the lipopolysaccharide of A. hydrophila TF7 (O:11 reference strain). Outer membrane fractions of these strains contained a predominant 53- to 54-kDa protein which was glycine extractable under low-pH (pH 2.8) conditions and was identified as the surface array protein. The S-layer proteins of the O:14 and O:81 A. hydrophila strains seemed to be primarily different from those previously purified from strains A. hydrophila TF7 and Aeromonas salmonicida A450 on the basis of colony hybridizations with both the structural genes vapA and ahsA. This is the first report of the presence of an S layer in mesophilic Aeromonas strains not belonging to serogroup O:11.

Type III secretion system genes in clinical Aeromonas isolates

We have identified the genes ascF and ascG, which encode components of a putative type III secretion system (TTSS) in AEROMONAS: We investigated the distribution of these and other TTSS genes in 84 clinical isolates and found hybridizing sequences in 50% of the strains, with a higher prevalence in Aeromonas hydrophila and Aeromonas veronii than in Aeromonas caviae.

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

Fifty-two clinical strains and 22 type and reference Aeromonas strains, previously genetically characterized by 16S rRNA gene restriction fragment length polymorphism, were identified in parallel with the MicroScan Walk/Away and BBL Crystal Enteric/Nonfermenter systems. The former identified only 14.8% of the isolates correctly, and the latter identified only 20.3% correctly, which indicates that neither of these systems is useful for this purpose.

Distribution of virulence genes in clinical and environmental isolates of Aeromonas spp

The distribution and phenotypic activity of the genes encoding for serine protease, glycerophospholipid-cholesterol acyltransferase, lipases, aerolysin/hemolysin and DNases were investigated in 234 isolates identified by 16S rDNA-RFLP representing all the species of Aeromonas. The former three genes were found to be highly conserved among the genus. Aerolysin/hemolysin and DNase genes and beta-hemolytic activity were significantly more frequent in clinical than in environmental isolates. Aerolysin/hemolysin and serine protease genes were present in all beta-hemolytic strains supporting serine protease as possibly important for the activation of the former gene. The high prevalence of virulence factors in clinical isolates indicates that they may play a role in the mechanisms of pathogenesis of these microorganisms.

Misidentification of Aeromonas veronii biovar sobria as Vibrio alginolyticus by the Vitek system

AIMS

To find the cause of misidentification of aeromonads when using the Vitek system.

METHODS AND RESULTS

Two Aeromonas veronii biovar sobria isolates were misidentified as Vibrio alginolyticus by the Vitek system. Both strains' identification was confirmed by biochemical testing, API 20E/20NE kits and/or 16S RFLP analysis. Thirty-one known Aeromonas species were tested by the Vitek system using 0.45 and 0.85% saline in the suspension medium. It was not clear whether low salinity causes misidentification of Aeromonas species more frequently.

CONCLUSIONS

The specified reaction time may be inappropriately short for some critical biochemical tests of some strains. An ingenious reading strategy regarding incubation time is necessary to improve identification of Aeromonas species by the Vitek system.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, this is the first report of misidentification of A. veronii biovar sobria as V. alginolyticus in the Vitek system.

Characterisation of Aeromonas spp. isolated from frozen fish intended for human consumption in Mexico

A total of 82 strains of presumptive Aeromonas spp. were identified biochemically and genetically (16S rDNA-RFLP). The strains were isolated from 250 samples of frozen fish (Tilapia, Oreochromis niloticus niloticus) purchased in local markets in Mexico City. In the present study, we detected the presence of several genes encoding for putative virulence factors and phenotypic activities that may play an important role in bacterial infection. In addition, we studied the antimicrobial patterns of those strains. Molecular identification demonstrated that the prevalent species in frozen fish were Aeromonas salmonicida (67.5%) and Aeromonas bestiarum (20.9%), accounting for 88.3% of the isolates, while the other strains belonged to the species Aeromonas veronii (5.2%), Aeromonas encheleia (3.9%) and Aeromonas hydrophila (2.6%). Detection by polymerase chain reaction (PCR) of genes encoding putative virulence factors common in Aeromonas, such as aerolysin/hemolysin, lipases including the glycerophospholipid-cholesterol acyltransferase (GCAT), serine protease and DNases, revealed that they were all common in these strains. Our results showed that first generation quinolones and second and third generation cephalosporins were the drugs with the best antimicrobial effect against Aeromonas spp. In Mexico, there have been few studies on Aeromonas and its putative virulence factors. The present work therefore highlights an important incidence of Aeromonas spp., with virulence potential and antimicrobial resistance, isolated from frozen fish intended for human consumption in Mexico City.

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

AIMS

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

METHODS AND RESULTS

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

CONCLUSIONS

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

SIGNIFICANCE AND IMPACT OF THE STUDY

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

Aeromonas spp. and traveler's diarrhea: clinical features and antimicrobial resistance

Traveler's diarrhea is the most common health problem of international travelers. We determined the prevalence of Aeromonas spp. associated with traveler's diarrhea and analyzed the geographic distribution, clinical features, and antimicrobial susceptibility. Aeromonas spp. were isolated as a cause of traveler's diarrhea in 18 (2%) of 863 patients. A. veronii biotype sobria was isolated in nine patients, A. caviae in seven patients, and A. jandaei and A. hydrophila in one patient each. Aeromonas spp. were isolated with a similar prevalence in Africa, Latin America, and Asia. Watery and persistent diarrhea, fever, and abdominal cramps were common complaints. All strains were resistant to ampicillin; showed variable resistance to chloramphenicol, tetracycline, and cotrimoxazole; and were susceptible to cefotaxime, ciprofloxacin, and nalidixic acid. The persistence of symptoms made antimicrobial treatment necessary.

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

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

A DNA probe specific for Aeromonas colonies

Members of the genus Aeromonas are important enteropathogens. Commercial identification systems are often unable to correctly identify Aeromonas strains and misidentification as Vibrio spp. is common. A digoxigenin-DNA probe based on a 237 bp of the glycerophospholipid-cholesterol acyltransferase gene has been tested in a colony hybridization assay. The probe hybridized with all Aeromonas species tested (n = 16) but not with strains of other enteropathogenic bacteria (n = 20). The probe allowed the unequivocal identification of Aeromonas in primary isolation media within 36 h.

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

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

[Synovial sarcoma of the tongue. Case report and review of the literature]

Primary synovial sarcoma of the head and neck is a rare entity, nevertheless the literature count on 80 published cases, among them 7 linguals. We contribute with another case: a synovial sarcoma of the tongue, in a 26-year-old man; having a biphasic tumor pattern, with two malignant constituents, epithelial and sarcomatous, similar to other of the same location. Laboratory tests: histochemical, immunohistochemical and electron microscopic were done in order to state the tumor's histogenesis. Our results suggest a pluripotential mesenchymal origin instead of a synovial origin, because the epithelial character of one of the tumor constituents was obviously epithelial.