Adhesion, invasion, intracellular survival and cytotoxic activity of strains of Aeromonas spp. in HEp-2, Caco-2 and T-84 cell lines

Cytotoxicity and Antimicrobial Resistance of Aeromonas Strains Isolated from Fresh Produce and Irrigation Water

The genus Aeromonas has received constant attention in different areas, from aquaculture and veterinary medicine to food safety, where more and more frequent isolates are occurring with increased resistance to antibiotics. The present paper studied the interaction of Aeromonas strains isolated from fresh produce and water with different eukaryotic cell types with the aim of better understanding the cytotoxic capacity of these strains. To study host-cell pathogen interactions in Aeromonas, we used HT-29, Vero, J774A.1, and primary mouse embryonic fibroblasts. These interactions were analyzed by confocal microscopy to determine the cytotoxicity of the strains. We also used Galleria mellonella larvae to test their pathogenicity in this experimental model. Our results demonstrated that two strains showed high cytotoxicity in epithelial cells, fibroblasts, and macrophages. Furthermore, these strains showed high virulence using the G. mellonella model. All strains used in this paper generally showed low levels of resistance to the different families of the antibiotics being tested. These results indicated that some strains of Aeromonas present in vegetables and water pose a potential health hazard, displaying very high in vitro and in vivo virulence. This pathogenic potential, and some recent concerning findings on antimicrobial resistance in Aeromonas, encourage further efforts in examining the precise significance of Aeromonas strains isolated from foods for human consumption.

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.

Asymmetric profiles of infection and innate immunological responses in human iPS cell-derived small intestinal epithelial-like cell monolayers following infection with mammalian reovirus

The intestinal mucosa plays an important role as an immune barrier due to its continual exposure to invading pathogens, including viruses. It is thus highly important to evaluate virus infection profiles in the intestinal mucosa for prevention of virus infection and development of antivirus medicines; however, only a few enterocyte lines are available as in vitro intestinal models for the evaluation of virus infection. In this study, we evaluated profiles of infection and innate immune responses following infection with a mammalian orthoreovirus (hereafter reovirus), which has often been used as a tractable model for studies of viral pathogenesis, in human iPS cell-derived small intestinal epithelial-like cell (hiPS-SIEC) monolayers and cells of a human colon adenocarcinoma cell line, Caco-2. The levels of reovirus infection were similar between hiPS-SIEC and Caco-2 cell monolayers, which are often used as an intestinal model, after apical and basolateral infection. In hiPS-SIEC monolayers, more efficient replication of the virus genome was observed following basolateral infection than apical infection, while apical infection resulted in higher levels of virus protein expression and progeny virus production than basolateral infection. Reovirus significantly induced innate immune responses, including expression of type I and III interferons (IFNs), in hiPS-SIEC monolayers more efficiently than Caco-2 cells. Higher levels of type I and III interferon (IFN) expression were found in hiPS-SIEC monolayers following apical infection than basolateral infection. These results suggested that hiPS-SIECs are a promising in vitro model for the evaluation of virus infection.

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.

Comparison of type 5d autotransporter phospholipases demonstrates a correlation between high activity and intracellular pathogenic lifestyle

Autotransporters, or type 5 secretion systems, are widespread surface proteins of Gram-negative bacteria often associated with virulence functions. Autotransporters consist of an outer membrane β-barrel domain and an exported passenger. In the poorly studied type 5d subclass, the passenger is a patatin-like lipase. The prototype of this secretion pathway is PlpD of Pseudomonas aeruginosa, an opportunistic human pathogen. The PlpD passenger is a homodimer with phospholipase A1 (PLA1) activity. Based on sequencing data, PlpD-like proteins are present in many bacterial species. We characterized the enzymatic activity, specific lipid binding and oligomeric status of PlpD homologs from Aeromonas hydrophila (a fish pathogen), Burkholderia pseudomallei (a human pathogen) and Ralstonia solanacearum (a plant pathogen) and compared these with PlpD. We demonstrate that recombinant type 5d-secreted patatin domains have lipase activity and form dimers or higher-order oligomers. However, dimerization is not necessary for lipase activity; in fact, by making monomeric variants of PlpD, we show that enzymatic activity slightly increases while protein stability decreases. The lipases from the intracellular pathogens A. hydrophila and B. pseudomallei display PLA2 activity in addition to PLA1 activity. Although the type 5d-secreted lipases from the animal pathogens bound to intracellular lipid targets, phosphatidylserine and phosphatidylinositol phosphates, hydrolysis of these lipids could only be observed for FplA of Fusobacterium nucleatum Yet, we noted a correlation between high lipase activity in type 5d autotransporters and intracellular lifestyle. We hypothesize that type 5d phospholipases are intracellularly active and function in modulation of host cell signaling events.

Interaction of Vibrio to Biotic and Abiotic Surfaces: Relationship between Hydrophobicity, Cell Adherence, Biofilm Production, and Cytotoxic Activity

Vibrio parahaemolyticus and Vibrio alginolyticus are important pathogenic agents for both humans and aquatic animals. Twenty-five bacterial strains were isolated from infected sea bass (Dicentrarchus labrax) on thiosulfate citrate bile salts sucrose (TCBS) agar plates. For the species-specific detection of V. alginolyticus and V. parahaemolyticus, a multiplex PCR assay using two collagenase-targeted primer pairs allows the detection of four strains of V. parahaemolyticus and three strains of V. alginolyticus. The seven identified isolates were partitioned for capsule production, hydrophobicity, adherence, biofilm formation, invasion, and cytotoxicity against Hep-2 cells. Two V. parahaemolyticus (Spa2 and Spa3) and one V. alginolyticus (Va01) were capsule producers developing almost black colonies on CRA, they showed a strong hydrophobicity using bacterial adhesion to hydrocarbons test (BATH), and were able to produce high biofilm. Isolates were able to adhere and invade Hep-2 cells and exhibited dissimilar levels of cytotoxicity in epithelial cells. This study shows the strong relationship between adhesion, biofilm formation, invasion and the cytotoxicity of Vibrio strains. Thus, we found a strong and significant positive correlation between different virulence properties of these isolates. The present study shows that bacterial contact with the cells as well as adhesion and invasion are essential steps to induce cytotoxicity. However, the invasion is seen to be a post adherence event.