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.

Arcobacter lacus sp. nov. and Arcobacter caeni sp. nov., two novel species isolated from reclaimed water.

Two strains (RW43-9T and RW17-10T) recovered from secondary treated wastewater from the Wastewater Treatment Plant (WWTP) in Reus (Spain) were characterized by a polyphasic taxonomic study, showing evidence that they represented two novel Arcobacter species. Based on the 16S rRNA gene for strain RW43-9T, the closest relative was Arcobacter butzleri LMG 10828T (99.9 % similarity), while for strain RW17-10T it was Arcobacter venerupis CECT 7836T (99.4 %). Additionally, multilocus phylogenetic analysis of five concatenated housekeeping genes (atpA, gyrA, gyrB, hsp60 and rpoB) showed that the two strains formed separate branches that are different from known Arcobacter species. Whole genome sequences of the two strains (RW43-9T and RW17-10T) were obtained and they were compared with those of the type strains of their nearest species. Using average nucleotide identity and in silico DNA-DNA hybridization gave values that were below 96 and 70 %, respectively. These results clearly confirm that they represent novel species. Additionally, the phenotypic characterization of the strains allowed their differentiation from other species. Therefore, the strains are proposed as representing two novel species with the names Arcobacter lacus sp. nov. (type strain RW43-9T=CECT 8994T=LMG 29062T) and Arcobacter caeni sp. nov. (type strain RW17-10T=CECT 9140T=LMG 29151T).

Arcobacter canalis sp. nov., isolated from a water canal contaminated with urban sewage.

Four bacterial strains recovered from shellfish (n=3) and from the water (n=1) of a canal contaminated with urban sewage were recognized as belonging to a novel species of the genus Arcobacter (represented by strain F138-33T) by using a polyphasic characterization. All the new isolates required 2 % NaCl to grow. Phylogenetic analyses based on 16S rRNA gene sequences indicated that all strains clustered together, with the most closely related species being Arcobacter marinus and Arcobactermolluscorum. However, phylogenetic analyses using the concatenated sequences of housekeeping genes (atpA, gyrB, hsp60, gyrA and rpoB) showed that all the novel strains formed a distinct lineage within the genus Arcobacter. Results of in silico DNA-DNA hybridization and the average nucleotide identity between the genome of strain F138-33T and those of the closely related species A. marinus and other relatively closely related species such as A. molluscorum and Arcobacterhalophilus were all below 70 and 96 %, respectively. All the above results, together with the 15 physiological and biochemical tests that could distinguish the newly isolated strains from the closely related species, confirmed that these strains represent a novel species for which the name Arcobacter canalis sp. nov. is proposed, with the type strain F138-33T (=CECT 8984T=LMG 29148T).

Arcobacter haliotis Tanaka et al. 2017 is a later heterotypic synonym of Arcobacter lekithochrous Diéguez et al. 2017.

The draft whole-genome sequence of Arcobacter haliotis strain LMG 28652T was obtained and compared against the type strain of Arcobacter lekithochrous LFT 1.7T. High similarity was found between the two strains, showing average nucleotide identity and in silico DNA-DNA hybridization values of 98.40 and 86.10 %, respectively. These values indicated that both genomes belonged to the same species, confirming the evidences derived from the phylogenetic analysis performed with the 16S rRNA gene and the concatenated sequences of five housekeeping genes. In addition, the metabolic, physiological and chemotaxonomic features of A. haliotis LMG 28652T were shown to be congruent with those of A. lekithochrous. We conclude that Arcobacter haliotis Tanaka et al. 2017 is a later heterotypic synonym of Arcobacter lekithochrousDiéguez et al. 2017.

First record of the rare species Aeromonas schubertii from mussels: phenotypic and genetic reevaluation of the species and a review of the literature.

In a study where the prevalence of Aeromonas in shellfish was analysed, three isolates of Aeromonas schubertii were identified, representing this the first report of this species from mussels. This species was originally described in 1988 from strains isolated from extra-intestinal human infections and since then has been cited in only 18 occasions. For many years, A. schubertii was the only mannitol-negative species of the genus. However, three additional mannitol-negative species (Aeromonas simiae, Aeromonas diversa and Aeromonas australiensis) have been described. This, together with the fact that A. schubertii is a rare human pathogenic species, motivated the present study to characterize its biochemical behaviour and differentiation from the other mannitol-negative species. The molecular similarity (16S rRNA, rpoD and gyrB genes) of the strains, presence of virulence genes and antimicrobial resistance were determined. All A. schubertii strains showed the same phenotypic behaviour, i.e. they use citrate, are positive for lysine decarboxylase and DL-lactate, but negative for production of mannitol, indole and acid from sucrose and could be easily differentiated from other mannitol-negative species. All strains carried the aerA and lafA virulence genes and showed susceptibility to all antibiotics tested. Seafood could be a transmission route of this bacterium to humans.

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.

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.

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.

Higher water temperature and incubation under aerobic and microaerobic conditions increase the recovery and diversity of Arcobacter spp. from shellfish.

Some Arcobacter species are considered emerging food-borne and waterborne pathogens, and shellfish have been suggested as one of their reservoirs. However, only a few studies have investigated the presence of Arcobacter in this kind of food. This study assesses the prevalence and diversity of Arcobacter spp. in shellfish by multiplex PCR (m-PCR) and culturing methods (under different atmospheric conditions) and evaluates the possible influence of environmental parameters (temperature, salinity, and harvesting bay). Arcobacter was detected by m-PCR and/or culturing in 61 (29.9%) of 204 shellfish samples. Of the positive samples by culturing, 41.1% were obtained under only aerobic incubation conditions, while 23.2% were obtained under only microaerobic conditions. Of 476 investigated isolates, 118 belonged to different enterobacterial repetitive intergenic consensus (ERIC)-PCR genotypes (strains) and to 11 different species. This study shows the highest diversity of Arcobacter species ever observed in samples from any origin. The most prevalent species was Arcobacter butzleri (60.2%), followed by Arcobacter molluscorum (21.2%). The prevalence of Arcobacter was significantly higher during the summer than in other seasons, being associated with an increase in water temperature. Results confirm that shellfish are a reservoir for a remarkable diversity of Arcobacter spp.

Interactions between Aeromonas caviae and Yersinia enterocolitica isolated from a case of diarrhea: evaluation of antimicrobial susceptibility and immune response of infected macrophages.

Aeromonas species cause a wide spectrum of human diseases, primarily gastroenteritis, septicemia, and wound infections. Several studies have shown that about 40% of these cases involve mixed or polymicrobial infections between Aeromonas spp. and bacteria from other genera. However, the immune response of macrophages in front of the bacteria present in the mixed infections, as well as their impact on antimicrobial therapy, have not been investigated. This study evaluated the cell damage and immune response of the mouse macrophage BALB/c cell line (J774A.1) after performing a single and a mixed infection with a strain of Aeromonas caviae and Yersinia enterocolitica, both recovered from the same fecal sample from a patient with diarrhea. Macrophage cell damage was measured by the release of lactate dehydrogenase (LDH) while the immune response was evaluated studying the expression by RT-qPCR of six relevant immune-related genes. Additionally, the antimicrobial susceptibility pattern of the single and mixed strains in front of seventeen antibiotics was evaluated to determine the potential impact on the infection treatment. Macrophages infected with the mixture of the two strains showed a higher cell damage in comparison with the single infections and the immune-related genes, i.e., cytokines and chemokines genes (TNF-α, CCL20), and apoptotic and pyroptotic genes (TP53 and IL-1ß) were overexpressed. After infection with the mixed cultures, an increase in the antimicrobial resistance was observed for ciprofloxacin, trimethoprim, chloramphenicol, gentamicin and ertapenem. This study increased the knowledge about the synergetic effect of the bacteria involved in mixed infection and on their potential impact on the treatment and evolution of the infection.

Repositioning of the Antihyperlipidemic Drug Fenofibrate for the Management of Aeromonas Infections.

Fenofibrate is a fibric acid derivative used as an antihyperlipidemic drug in humans. Its active metabolite, fenofibric acid, acts as an agonist to the peroxisome proliferator-activated receptor alpha (PPAR-α), a transcription factor involved in different metabolic pathways. Some studies have reported the potential protective role of this drug in cell lines and in vivo models against bacterial and viral infections. The aim of this study was to assess the in vitro effect of fenofibrate in the macrophage cell line J744A.1 against infections produced by Aeromonas, a pathogen for humans whose resistance to antibiotics has increased in recent decades. Macrophages were infected at MOI 10 with four strains of Aeromonas caviae and Aeromonas hydrophila isolated from human clinical samples and subsequently treated with fenofibrate. It was observed that fenofibrate-treated macrophages showed lower levels of cytotoxicity and intracellular bacteria compared to non-treated macrophages. In addition, the viability of treated macrophages was dependent on the dose of fenofibrate used. Furthermore, transcriptional analysis by RT-qPCR revealed significant differences in the expression of the PPAR-α gene and immune-related genes TNF-α, CCL3, and BAX in fenofibrate-treated macrophages compared to the macrophages without treatment. This study provides evidence that fenofibrate offered some protection in vitro in macrophages against Aeromonas infection. However, further studies are needed with other bacteria to determine its potential antibacterial effect and the route by which this protection is achieved.

Adherence to and invasion of human intestinal cells by Arcobacter species and their virulence genotypes.

The genus Arcobacter is composed of 17 species which have been isolated from various sources. Of particular interest are A. butzleri, A. cryaerophilus, and A. skirrowii, as these have been associated with human cases of diarrhea, the probable transmission routes being through the ingestion of contaminated drinking water and food. To date, only limited studies of virulence traits in this genus have been undertaken. The present study used 60 Arcobacter strains isolated from different sources, representing 16 of the 17 species of the genus, to investigate their ability to adhere to and invade the human intestinal cell line Caco-2. In addition, the presence of five putative virulence genes (ciaB, cadF, cj1349, hecA, and irgA) was screened for in these strains by PCR. All Arcobacter species except A. bivalviorum and Arcobacter sp. strain W63 adhered to Caco-2 cells, and most species (10/16) were invasive. The most invasive species were A. skirrowii, A. cryaerophilus, A. butzleri, and A. defluvii. All invasive strains were positive for ciaB (encoding a putative invasion protein). Other putative virulence genes were present in other species, i.e., A. butzleri (cadF, cj1349, irgA, and hecA), A. trophiarum (cj1349), A. ellisii (cj1349), and A. defluvii (irgA). No virulence genes were detected in strains which showed little or no invasion of Caco-2 cells. These results indicate that many Arcobacter species are potential pathogens of humans and animals.

Performance of five molecular methods for monitoring Arcobacter spp.

BACKGROUND: Bacteria belonging to the Arcobacter genus are emerging enteropathogens and potential zoonotic agents. Their taxonomy has evolved very rapidly, and there are presently 18 recorded species. The prevalence of species belonging to Arcobacter is underestimated because of the limitations of currently available methods for species identification.The aim of this study was to compare the performance of five PCR based methods that target regions of 16S rRNA, 23S rRNA or gyrA genes to identify Arcobacter species, and to review previous results reported in the literature using these methods. RESULTS: The five tested methods were found not to be reliable. They misidentified between 16.8% and 67.4% of the studied strains; this was dependent upon the target regions of the tested genes. The worst results obtained were for the identification of Arcobacter cryaerophilus and Arcobacter butzleri when the 23S rRNA gene was used as the target. These species were confused with many non-targeted species. CONCLUSION: Our results suggest that the known diversity of Arcobacter spp. in different environments could be expanded if reliable identification methods are applied in future studies.

Aeromonas australiensis sp. nov., isolated from irrigation water.

A Gram-negative, facultatively anaerobic bacillus, designated strain 266(T), was isolated from an irrigation water system in the south-west of Western Australia. Analysis of the 16S rRNA gene sequence confirmed that strain 266(T) 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 266(T) 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 266(T) represents a novel species, for which the name Aeromonas australiensis sp. nov. is proposed, with type strain 266(T) (=CECT 8023(T) =LMG 26707(T)). [corrected].

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.

Heterotrophic Plate Count Can Predict the Presence of Legionella spp. in Cooling Towers.

Legionella pneumophila (Lp) colonizes aquatic environments and is a potential pathogen to humans, causing outbreaks of Legionnaire's disease. It is mainly associated with contaminated cooling towers (CTs). Several regulations, including Spanish legislation (Sl), have introduced the analysis of heterotrophic plate count (HPC) bacteria and Legionella spp. (Lsp) in management plans to prevent and control Legionella outbreaks from CTs. The 2003 Sl for CTs (RD 865/2003) considered that concentrations of HPC bacteria ≤10,000 cfu/mL and of Lsp ≤100 cfu/L are safe; therefore, no action is required, whereas management actions should be implemented above these standards. We have investigated to what extent the proposed standard for HPC bacteria is useful to predict the presence of Lsp in cooling waters. For this, we analyzed Lsp and HPC concentrations, water temperature, and the levels of chlorine in 1376 water samples from 17 CTs. The results showed that in the 1138 water samples negative for Legionella spp. (LN), the HPC geometric mean was significantly lower (83 cfu/mL, p < 0.05) than in the positive Lsp. samples (135 cfu/mL). Of the 238 (17.3%) LP samples, 88.4% (210/238) were associated with values of HPC ≤10,000 cfu/mL and most of them showed HPC concentrations ≤100 (53.7%). In addition, a relatively low percentage of LP (28/238, 11.6%) samples were associated with HPC bacteria concentrations >10,000 cfu/mL, indicating that this standard does not predict the colonization risk for Legionella in the CTs studied. The present study has demonstrated that a threshold concentration ≤100 cfu/mL of HPC bacteria could better predict the higher concentration of Legionella in CTs, which will aid in preventing possible outbreaks.

Drosophila melanogaster Systemic Infection Model to Study Altered Virulence during Polymicrobial Infection by Aeromonas.

BACKGROUND: Polymicrobial infections are complex infections associated with worse outcomes compared to monomicrobial infections. We need simple, fast, and cost-effective animal models to assess their still poorly known pathogenesis. METHODS: We developed a Drosophila melanogaster polymicrobial infection model for opportunistic pathogens and assessed its capacity to discriminate the effects of bacterial mixtures taken from cases of human polymicrobial infections by Aeromonas strains. A systemic infection was obtained by needle pricking the dorsal thorax of the flies, and the fly survival was monitored over time. Different lineages of the flies were infected by a single strain or paired strains (strain ratio 1:1). RESULTS: Individual strains killed more than 80% of the flies in 20 h. The course of infection could be altered with a microbial mix. The model could distinguish between the diverse effects (synergistic, antagonistic, and no difference) that resulted in a milder, more severe, or similar infection, depending on the paired strain considered. We then investigated the determinants of the effects. The effects were maintained in deficient fly lineages for the main signaling pathways (Toll deficient and IMD deficient), which suggests an active microbe/microbe/host interaction. CONCLUSION: These results indicate that the D. melanogaster systemic infection model is consistent with the study of polymicrobial infection.

Updated 16S rRNA-RFLP method for the identification of all currently characterised Arcobacter spp.

BACKGROUND: Arcobacter spp. (family Campylobacteraceae) are ubiquitous zoonotic bacteria that are being increasingly recognised as a threat to human health. A previously published 16S rRNA-RFLP Arcobacter spp. identification method produced specific RFLP patterns for the six species described at that time, using a single endonuclease (MseI). The number of characterised Arcobacter species has since risen to 17. The aim of the present study was to update the 16S rRNA-RFLP identification method to include all currently characterised species of Arcobacter. RESULTS: Digestion of the 16S rRNA gene with the endonuclease MseI produced clear, distinctive patterns for 10 of the 17 species, while the remaining species shared a common or very similar RFLP pattern. Subsequent digestion of the 16S rRNA gene from these species with the endonucleases MnlI and/or BfaI generated species-specific RFLP patterns. CONCLUSIONS: 16S rRNA-RFLP analysis identified 17 Arcobacter spp. using either polyacrylamide or agarose gel electrophoresis. Microheterogeneities within the 16S rRNA gene, which interfered with the RFLP identification, were also documented for the first time in this genus, particularly in strains of Arcobacter cryaerophilus isolated from animal faeces and aborted foetuses.

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-1ß). 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.

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.