Potential involvement of galectin-3 and SNAP23 in Aeromonas hydrophila cytotoxic enterotoxin-induced host cell apoptosis

Exploring Aeromonas dhakensis in Aldabra giant tortoises: a debut report and genetic characterization

Aeromonas dhakensis (A. dhakensis) is becoming an emerging pathogen worldwide, with an increasingly significant role in animals and human health. It is a ubiquitous bacteria found in terrestrial and aquatic milieus. However, there have been few reports of reptile infections. In this study, a bacterial strain isolated from a dead Aldabra giant tortoise was identified as A. dhakensis HN-1 through clinical observation, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS), and gene sequencing analysis. Subsequently, to evaluate its pathogenicity, the detection of virulence genes and mice infection experiments were performed. A. dhakensis HN-1 was found to contain seven virulence genes, including alt, ela, lip, act, aerA, fla, and hlyA. Mice infected with A. dhakensis HN-1 exhibited hemorrhage of varying degrees in multiple organs. The half-maximal lethal dose (LD50) value of A. dhakensis HN-1 for mice was estimated to be 2.05 × 107 colony forming units (CFU)/mL. The antimicrobial susceptibility test revealed that A. dhakensis HN-1 was resistant to amoxicillin, penicillin, ampicillin and erythromycin. This is the first report of A. dhakensis in Aldabra giant tortoises, expanding the currently known host spectrum. Our findings emphasize the need for One Health surveillance and extensive research to reduce the spread of A. dhakensis across the environment, humans, and animals.

Illustration on phenotypic and genotypic characteristics of typical multi-antibiotic resistant bacteria in aquatic environments through complete genomes and comparative genomics

Antibiotic-resistant bacteria, especially multi-antibiotic-resistant bacteria (MARBs), greatly threaten environmental safety and human health. However, studies on the phenotypic resistance and complete genotypic characterization of MARB in aquatic environments are lacking. In this study, a multi-resistant superbug (TR3) was screened by the selective pressure of multi-antibiotics from the activated sludge of the aeration tanks of urban wastewater treatment plants (WWTPs) in 5 different regions of China. Based on the 16 S rDNA sequence alignment it was found that the sequence similarity between strain TR3 and Aeromonas was as high as 99.50%. The genome-wide sequence showed that the base content of the chromosome of strain TR3 is 4,521,851 bp. It contains a plasmid with a length of 9182 bp. All antibiotic resistance genes (ARGs) of strain TR3 are located on the chromosome, which means that it has passage stability. There are multiple types of resistance genes in the genome and plasmid of strain TR3, enduing it with resistance to 5 antibiotics (ciprofloxacin, tetracycline, ampicillin, clarithromycin, and kanamycin), accompanied by the strongest resistance to kanamycin (aminoglycosides) and the worst resistance to clarithromycin (quinolones). From the perspective of gene expression, we show the resistance mechanism of strain TR3 to different types of antibiotics. In addition, the potential pathogenicity of strain TR3 is also discussed. Chlorine and ultraviolet (UV) sterilization on strain TR3 showed that UV is ineffective at low intensity, and it is easy to be revived by light. A low concentration of hypochlorous acid is effective for sterilization, but it can cause the release of DNA, becoming a potential source of ARGs discharged from WWTPs to environmental water bodies.

Sanguinarine Protects Channel Catfish against Aeromonas hydrophila Infection by Inhibiting Aerolysin and Biofilm Formation

Aeromonas hydrophila is a pathogenic bacterium that can cause serious infections both in humans and aquatic animals. Antibiotics are the main approach for fighting against the pathogen. However, the emergence of antibiotic resistance has resulted in treatment failure. Therefore, drugs with novel strategies need to be developed. Quorum sensing has been recognized as a promising method for identifying anti-virulence drugs against bacterial infections. The aim of this study was to identify novel drugs targeting quorum sensing of A. hydrophila as alternatives of antibiotics in aquaculture. Thus, hemolytic activity, biofilm formation, qPCR and experimental therapeutics assays were conducted. The results showed that sanguinarine inhibited the growth of A. hydrophila at concentrations higher than 16 μg/mL, but the production of aerolysin and biofilm formation was significantly inhibited at sub-inhibitory concentrations by disrupting the quorum sensing system. Cell viability results showed that sanguinarine could provide protection for A549 cells from aerolysin-induced cell injury. In addition, the mortality of channel catfish administered with sanguinarine at a dosage of 20 mg/kg decreased to 40%, which showed a significant decrease compared with fish in positive group. Taken together, these findings demonstrated that anti-virulence strategies can be a powerful weapon for fighting against bacterial pathogens and sanguinarine appears to be a promising candidate in the treatment of A. hydrophila infections.

Isolation and characterization of bacteriophages against virulent Aeromonas hydrophila

Background

Aeromonas hydrophila is an important water-borne pathogen that leads to a great economic loss in aquaculture. Along with the abuse of antibiotics, drug-resistant strains rise rapidly. In addition, the biofilms formed by this bacterium limited the antibacterial effect of antibiotics. Bacteriophages have been attracting increasing attention as a potential alternative to antibiotics against bacterial infections.

Results

Five phages against pathogenic A. hydrophila, named N21, W3, G65, Y71 and Y81, were isolated. Morphological analysis by transmission electron microscopy revealed that phages N21, W3 and G65 belong to the family Myoviridae, while Y71 and Y81 belong to the Podoviridae. These phages were found to have broad host spectra, short latent periods and normal burst sizes. They were sensitive to high temperature but had a wide adaptability to the pH. In addition, the phages G65 and Y81 showed considerable bacterial killing effect and potential in preventing formation of A. hydrophila biofilm; and the phages G65, W3 and N21 were able to scavenge mature biofilm effectively. Phage treatments applied to the pathogenic A. hydrophila in mice model resulted in a significantly decreased bacterial loads in tissues.

Conclusions

Five A. hydrophila phages were isolated with broad host ranges, low latent periods, and wide pH and thermal tolerance. And the phages exhibited varying abilities in controlling A. hydrophila infection. This work presents promising data supporting the future use of phage therapy.

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.

Molecular Identification and Virulence Potential of the Genus Aeromonas Isolated from Wild Rainbow Trout (Oncorhynchus mykiss) in Mexico

The members of the Aeromonas genus are important foodborne pathogens, with a worldwide distribution. Wild rainbow trout, from the national protected area Santuario del Agua State Park, Corral de Piedra, were analyzed. Species of Aeromonas were isolated from the trout, and their pathogenic potential was analyzed based on different pathogenicity and virulence factors. The isolates were identified as A. allosaccharophila (n = 15), A. sobria (n = 8), A. veronii (n = 3), A. rivipollensis (n = 2), A. piscicola (n = 2), and A. popoffii (n = 1), by RNA polymerase sigma factor (rpoD) gene sequencing. Sequence similarity with the type strain was 92.2 to 99.6% for A. sobria isolates, 97.8 to 98.0% for A. allosaccharophila isolates, 99.2% for the A. popoffii isolate, 99.2 to 100% for A. piscicola isolates, and 98.2 to 99.2% for A. veronii isolates. Notably, isolates A30T2-gills and A30T2-spleen showed sequence similarity of 98.0% with strain A. media CECT 4232T and 99.0% with strain A. rivipollensis P2G1T. Virulence genes were detected by PCR at the following frequencies: fla and serine protease, 96.77%; aerA, 93.54%; aexT, 87.09%; lipases, 74.19%; ascV and ahyB, 67.74%; exu, 61.29%; act, 41.93%; ascF-G, 38.70%; lafA, 32.26%; alt, 6.46%; aopP, 9.67%; and ast, 3.23%. These results indicate that several Aeromonas species had the potential pathogenicity to infect wild rainbow trout in the waterway created by the Corral de Piedra dam, suggesting they could be an emerging zoonotic pathogen.

Gut Bacteria of Water Monitor Lizard (Varanus salvator) Are a Potential Source of Antibacterial Compound(s)

For the past few decades, there has been limited progress in the development of novel antibacterials. Previously, we postulated that the gut microbiota of animals residing in polluted environments are a forthcoming supply of antibacterials. Among various species, the water monitor lizard is an interesting species that feeds on organic waste and the carcass of wild animals. Gut microbiota of the water monitor lizard were sequestered, identified and cultivated in RPMI-1640 to produce conditioned medium (CM). Next, the antimicrobial properties of CM were evaluated versus a selection of Gram-negative (Escherichia coli K1, Serratia marcescens, Pseudomonas aeruginosa, Salmonella enterica and Klebsiella pneumoniae) and Gram-positive bacteria (Streptococcus pyogenes, methicillin-resistant Staphylococcus aureus, and Bacillus cereus). CM were partially characterized by heat inactivation at 95°C for 10 min and tested against P. aeruginosa and S. pyogenes. CM were also tested against immortalized human keratinocytes (HaCaT) cells lines. The results demonstrated that gut microbiota isolated from water monitor lizard produced molecules with remarkable bactericidal activities. To determine the identity of the active molecules, CM were subjected to Liquid Chromatography-Mass Spectrometry. Several molecules were identified belonging to the classes of flavonoids, terpenoids, alkaloids, polyhydroxy alkaloids, polyacetylenes, bisphenols, amides, oxylipin and pyrazine derivatives with known broad-spectrum antimicrobial, anti-tumour, anti-oxidant, anti-inflammatory, and analgesic attributes. Furthermore, the detailed analysis of these molecules could lead us to develop effective therapeutic antibacterials.

Phagolysosomal activity of macrophages in Nile tilapia (Oreochromis niloticus) infected in vitro by Aeromonas hydrophila: Infection and immunotherapy

The biochemical mechanisms involved in phagocytosis and the intracellular survival of Aeromonas hydrophila (Ah) in host macrophages (MΦs) are complex processes that affect infection success or failure. Thus, in the present study, we described the in vitro infection of Nile tilapia MΦs by a homologous bacterium and tested the effects of anti-A. hydrophila immunoglobulin Y (IgY) on the phagolysosomal activity and intracellular survival of the pathogen. The anti-Ah IgY modulated lysosomal acid phosphatase (LAP) activity as well as the production of reactive oxygen intermediates (ROIs) and nitric oxide (NO), thereby potentiating phagocytosis and the elimination of Ah. Thus, we assume that the specific IgY had a beneficial effect on infection control and postulated the use of the Nile tilapia MΦs as an important in vitro experimental model for the functional and therapeutic study of Ah infection.

Identifying genetic diversity of O antigens in Aeromonas hydrophila for molecular serotype detection

Aeromonas hydrophila is a globally occurring, potentially virulent, gram-negative opportunistic pathogen that is known to cause water and food-borne diseases around the world. In this study, we use whole genome sequencing and in silico analyses to identify 14 putative O antigen gene clusters (OGCs) located downstream of the housekeeping genes acrB and/or oprM. We have also identified 7 novel OGCs by analyzing 15 publicly available genomes of different A. hydrophila strains. From the 14 OGCs identified initially, we have deduced that O antigen processing genes involved in the wzx/wzy pathway and the ABC transporter (wzm/wzt) pathway exhibit high molecular diversity among different A. hydrophila strains. Using these genes, we have developed a multiplexed Luminex-based array system that can identify up to 14 A. hydrophila strains. By combining our other results and including the sequences of processing genes from 13 other OGCs (7 OGCs identified from publicly available genome sequences and 6 OGCs that were previously published), we also have the data to create an array system that can identify 25 different A. hydrophila serotypes. Although clinical detection, epidemiological surveillance, and tracing of pathogenic bacteria are typically done using serotyping methods that rely on identifying bacterial surface O antigens through agglutination reactions with antisera, molecular methods such as the one we have developed may be quicker and more cost effective. Our assay shows high specificity, reproducibility, and sensitivity, being able to classify A. hydrophila strains using just 0.1 ng of genomic DNA. In conclusion, our findings indicate that a molecular serotyping system for A. hydrophila could be developed based on specific genes, providing an important molecular tool for the identification of A. hydrophila serotypes.

Tetrahymena thermophila Predation Enhances Environmental Adaptation of the Carp Pathogenic Strain Aeromonas hydrophila NJ-35

Persistence of Aeromonas hydrophila in aquatic environments is the principle cause of fish hemorrhagic septicemia. Protistan predation has been considered to be a strong driving force for the evolution of bacterial defense strategies. In this study, we investigated the adaptive traits of A. hydrophila NJ-35, a carp pathogenic strain, in response to Tetrahymena thermophila predation. After subculturing with Tetrahymena, over 70% of A. hydrophila colonies were small colony variants (SCVs). The SCVs displayed enhanced biofilm formation, adhesion, fitness, and resistance to bacteriophage infection and oxidative stress as compared to the non-Tetrahymena-exposed strains. In contrast, the SCVs exhibited decreased intracellular bacterial number in RAW264.7 macrophages and were highly attenuated for virulence in zebrafish. Considering the outer membrane proteins (OMPs) are directly involved in bacterial interaction with the external surroundings, we investigated the roles of OMPs in the antipredator fitness behaviors of A. hydrophila. A total of 38 differentially expressed proteins were identified in the SCVs by quantitative proteomics. Among them, three lipoproteins including SurA, Slp, and LpoB, and a serine/threonine protein kinase (Stpk) were evidenced to be associated with environmental adaptation of the SCVs. Also, the three lipoproteins were involved in attenuated virulence of SCVs through the proinflammatory immune response mediated by TLR2. This study provides an important contribution to the understanding of the defensive traits of A. hydrophila against protistan predators.

Catecholamine-Stimulated Growth of Aeromonas hydrophila Requires the TonB2 Energy Transduction System but Is Independent of the Amonabactin Siderophore

The growth-stimulating effects of catecholamine stress hormones have been demonstrated in many pathogens. However, catecholamine-induced growth and its underlying mechanisms remain poorly understood in Aeromonas hydrophila. The present study sought to demonstrate that norepinephrine (NE), epinephrine (Epi), dopamine (Dopa), and L-dopa stimulate the growth of A. hydrophila in iron-restricted media containing serum. NE exhibited the strongest growth stimulation, which could be blocked by adrenergic antagonists. Furthermore, it was demonstrated that NE could sequester iron from transferrin, thereby providing a more accessible iron source for utilization by A. hydrophila. The deletion of the amoA gene associated with amonabactin synthesis revealed that the amonabactin siderophore is not required for NE-stimulated growth. However, the deletion of the TonB2 energy transduction system resulted in the loss of growth promotion by NE, indicating that a specific TonB-dependent outer membrane receptor might be involved in the transport of iron from transferrin. Collectively, our data show that catecholamine sensing promotes the growth of A. hydrophila in a manner that is dependent on the TonB2 energy transduction system.

SNAP23 promotes the malignant process of ovarian cancer

Background

Ovarian cancer (OC) was the primary malignant gynecological cancer and SNARE protein is closely related with tumor progression. Here, we identified SNAP23, a member of SNARE complex, as a potential oncogene in OC.

Methods

We determined the expression of SNAP23 in OC tissues and explored the clinical significance through bioinformatics analysis. The effects of SNAP23 on OC cell proliferation, migration, invasion, cell cycle and apoptosis were then evaluated in vitro.

Results

SNAP23 is hyper-expressed in OC tumor tissues compared to normal tissues, and increased expression of SNAP23 is associated with a poor progression free survival (HR = 1.24, 95% CI = 1.07–1.44, p = 0.0042). SNAP23 knock down increases cell apoptosis and inhibits cell proliferation, migration and invasion of OC cells. GO analysis reveals that most genes correlated highly with SNAP23 were enriched in metabolic process.

Conclusions

Our data suggest that SNAP23 may serve as an oncogene promoting tumorigenicity of OC cells by decreasing apoptotic process.

Prevalence, virulence and antimicrobial resistance patterns of Aeromonas spp. isolated from children with diarrhea

BACKGROUND

Aeromonas spp. cause various intestinal and extraintestinal diseases. These bacteria are usually isolated from fecal samples, especially in children under five years old. The aim of this study was to assess the prevalence of Aeromonas spp. and their antimicrobial resistance profile in children with diarrhea referred to the Children Medical Center in Tehran, between 2013 and 2014.

METHODS

A total number of 391 stool samples were collected from children with ages between 1 day and 14 years old, with diarrhea (acute or chronic), referred to the Children Hospital, Tehran, Iran, between 2013 and 2014. Samples were enriched in alkaline peptone water broth for 24 hours at 37 °C and then cultured. Suspicious colonies were analyzed through biochemical tests. Furthermore, antimicrobial susceptibility tests were carried out for the isolates. Isolates were further studied for act, ast, alt, aerA and hlyA virulence genes using polymerase chain reaction.

RESULTS

In total, 12 isolates (3.1%) were identified as Aeromonas spp.; all were confirmed using the API-20E test. Of these isolates, five A. caviae (42%), four A. veronii (33%) and three A. hydrophila (25%) were identified in cases with gastroenteritis. Second to ampicillin (which was included in the growth medium used), the highest rate of antimicrobial resistance was seen against nalidixic acid and trimethoprim-sulfamethoxazole (5 isolates each, 41.6%) and the lowest rate of antimicrobial resistance was seen against gentamicin, amikacin and cefepime (none of the isolates). Results included 76.4% act, 64.7% ast, 71.5% alt, 83.3% aerA and 11.7% hlyA genes.

CONCLUSION

Aeromonas spp. are important due to their role in diarrhea in children; therefore, isolation and identification of these fecal pathogens should seriously be considered in medical laboratories. Since virulence genes play a significant role in gastroenteritis symptoms caused by these bacteria, Aeromonas species that include virulence genes are potentially suspected to cause severe infections. Moreover, bacterial antimicrobial resistance is increasing, especially against trimethoprim-sulfamethoxazole and nalidixic acid.

Functional genomic characterization of virulence factors from necrotizing fasciitis-causing strains of Aeromonas hydrophila

The genomes of 10 Aeromonas isolates identified and designated Aeromonas hydrophila WI, Riv3, and NF1 to NF4; A. dhakensis SSU; A. jandaei Riv2; and A. caviae NM22 and NM33 were sequenced and annotated. Isolates NF1 to NF4 were from a patient with necrotizing fasciitis (NF). Two environmental isolates (Riv2 and -3) were from the river water from which the NF patient acquired the infection. While isolates NF2 to NF4 were clonal, NF1 was genetically distinct. Outside the conserved core genomes of these 10 isolates, several unique genomic features were identified. The most virulent strains possessed one of the following four virulence factors or a combination of them: cytotoxic enterotoxin, exotoxin A, and type 3 and 6 secretion system effectors AexU and Hcp. In a septicemic-mouse model, SSU, NF1, and Riv2 were the most virulent, while NF2 was moderately virulent. These data correlated with high motility and biofilm formation by the former three isolates. Conversely, in a mouse model of intramuscular infection, NF2 was much more virulent than NF1. Isolates NF2, SSU, and Riv2 disseminated in high numbers from the muscular tissue to the visceral organs of mice, while NF1 reached the liver and spleen in relatively lower numbers on the basis of colony counting and tracking of bioluminescent strains in real time by in vivo imaging. Histopathologically, degeneration of myofibers with significant infiltration of polymorphonuclear cells due to the highly virulent strains was noted. Functional genomic analysis provided data that allowed us to correlate the highly infectious nature of Aeromonas pathotypes belonging to several different species with virulence signatures and their potential ability to cause NF.

Modulation of host immune defenses by Aeromonas and Yersinia species: convergence on toxins secreted by various secretion systems

Like other pathogenic bacteria, Yersinia and Aeromonas species have been continuously co-evolving with their respective hosts. Although the former is a bonafide human pathogen, the latter has gained notararity as an emerging disease-causing agent. In response to immune cell challenges, bacterial pathogens have developed diverse mechanism(s) enabling their survival, and, at times, dominance over various host immune defense systems. The bacterial type three secretion system (T3SS) is evolutionarily derived from flagellar subunits and serves as a vehicle by which microbes can directly inject/translocate anti-host factors/effector proteins into targeted host immune cells. A large number of Gram-negative bacterial pathogens possess a T3SS empowering them to disrupt host cell signaling, actin cytoskeleton re-arrangements, and even to induce host-cell apoptotic and pyroptotic pathways. All pathogenic yersiniae and most Aeromonas species possess a T3SS, but they also possess T2- and T6-secreted toxins/effector proteins. This review will focus on the mechanisms by which the T3SS effectors Yersinia outer membrane protein J (YopJ) and an Aeromonas hydrophila AexU protein, isolated from the diarrheal isolate SSU, mollify host immune system defenses. Additionally, the mechanisms that are associated with host cell apoptosis/pyroptosis by Aeromonas T2SS secreted Act, a cytotoxic enterotoxin, and Hemolysin co-regulated protein (Hcp), an A. hydrophila T6SS effector, will also be discussed.

Evasion of mucosal defenses during Aeromonas hydrophila infection of channel catfish (Ictalurus punctatus) skin

The mucosal surfaces of fish serve as the first line of defense against the myriad of aquatic pathogens present in the aquatic environment. The immune repertoire functioning at these interfaces is still poorly understood. The skin, in particular, must process signals from several fronts, sensing and integrating environmental, nutritional, social, and health cues. Pathogen invasion can disrupt this delicate homeostasis with profound impacts on signaling throughout the organism. Here, we investigated the transcriptional effects of virulent Aeromonas hydrophila infection in channel catfish skin, Ictalurus punctatus. We utilized a new 8 × 60 K Agilent microarray for catfish to examine gene expression profiles at critical early timepoints following challenge--2 h, 8 h, and 12 h. Expression of a total of 2,168 unique genes was significantly perturbed during at least one timepoint. We observed dysregulation of genes involved in antioxidant, cytoskeletal, immune, junctional, and nervous system pathways. In particular, A. hydrophila infection rapidly altered a number of potentially critical lectins, chemokines, interleukins, and other mucosal factors in a manner predicted to enhance its ability to adhere to and invade the catfish host.

The main Aeromonas pathogenic factors

The members of the Aeromonas genus are ubiquitous, water-borne bacteria. They have been isolated from marine waters, rivers, lakes, swamps, sediments, chlorine water, water distribution systems, drinking water and residual waters; different types of food, such as meat, fish, seafood, vegetables, and processed foods. Aeromonas strains are predominantly pathogenic to poikilothermic animals, and the mesophilic strains are emerging as important pathogens in humans, causing a variety of extraintestinal and systemic infections as well as gastrointestinal infections. The most commonly described disease caused by Aeromonas is the gastroenteritis; however, no adequate animal model is available to reproduce this illness caused by Aeromonas. The main pathogenic factors associated with Aeromonas are: surface polysaccharides (capsule, lipopolysaccharide, and glucan), S-layers, iron-binding systems, exotoxins and extracellular enzymes, secretion systems, fimbriae and other nonfilamentous adhesins, motility and flagella.

The two-component QseBC signalling system regulates in vitro and in vivo virulence of Aeromonas hydrophila

We recently demonstrated that the N-acyl-homoserine lactone [autoinducer (AI)-1] and LuxS (AI-2)-based quorum-sensing (QS) systems exerted positive and negative regulation, respectively, on the virulence of a diarrhoeal isolate SSU of Aeromonas hydrophila. However, the role of a newly identified, two-component-based QseBC QS system in the regulation of bacterial virulence in general is not well understood, with only a limited number of studies showing its function in bacterial pathogenesis. In this report, we identified and characterized the QseBC QS system in A. hydrophila SSU and found that, as was the case with enterohaemorrhagic Escherichia coli, the open reading frames for the qseB (the response regulator) and qseC (the sensor histidine kinase) genes overlapped by 4 bp at the ATGA motif. Our data provide evidence that deletion of the qseB gene from A. hydrophila resulted in attenuation of bacterial virulence in a septicaemic mouse model of infection and diminished swimming and swarming motility, and the mutant bacteria formed denser biofilms compared with those from the parental strain of A. hydrophila. The decrease in the virulence of the A. hydrophila ΔqseB mutant correlated with reduced production of protease and the cytotoxic enterotoxin, which has associated haemolytic activity. The swimming and swarming motility, haemolytic activity, protease production and biofilm formation were restored in the qseBC-complemented strain to a level similar to that of the wild-type A. hydrophila SSU. Our study is the first, to our knowledge, to report a functional QseBC QS system in A. hydrophila which may be linked to AI-1 and AI-2 QS systems in modulating bacterial virulence, possibly through the cyclic diguanosine monophosphate.

Immunomodulatory and protective roles of quorum-sensing signaling molecules N-acyl homoserine lactones during infection of mice with Aeromonas hydrophila

Aeromonas hydrophila leads to both intestinal and extraintestinal infections in animals and humans, and the underlying mechanisms leading to mortality are largely unknown. By using a septicemic mouse model of infection, we showed that animals challenged with A. hydrophila die because of kidney and liver damage, hypoglycemia, and thrombocytopenia. Pretreatment of animals with quorum-sensing-associated signaling molecules N-acyl homoserine lactones (AHLs), such as butanoyl and hexanoyl homoserine lactones (C(4)- and C(6)-HSLs), as well as N-3-oxododecanoyl (3-oxo-C(12))-HSL, prevented clinical sequelae, resulting in increased survivability of mice. Since little is known as to how different AHLs modulate the immune response during infection, we treated mice with the above AHLs prior to lethal A. hydrophila infection. When we compared results in such animals to those in controls, the treated animals exhibited a significantly reduced bacterial load in the blood and other mouse organs, as well as various levels of cytokines/chemokines. Importantly, neutrophil numbers were significantly elevated in the blood of C(6)-HSL-treated mice compared to those in animals given phosphate-buffered saline and then infected with the bacteria. These findings coincided with the fact that neutropenic animals were more susceptible to A. hydrophila infection than normal mice. Our data suggested that neutrophils quickly cleared bacteria by either phagocytosis or possibly another mechanism(s) during infection. In a parallel study, we indeed showed that other predominant immune cells inflicted during A. hydrophila infections, such as murine macrophages, when they were pretreated with AHLs, rapidly phagocytosed bacteria, whereas untreated cells phagocytosed fewer bacteria. This study is the first to report that AHL pretreatment modulates the innate immune response in mice and enhances their survivability during A. hydrophila infection.

Yeast proteomics and protein microarrays

Our understanding of biological processes as well as human diseases has improved greatly thanks to studies on model organisms such as yeast. The power of scientific approaches with yeast lies in its relatively simple genome, its facile classical and molecular genetics, as well as the evolutionary conservation of many basic biological mechanisms. However, even in this simple model organism, systems biology studies, especially proteomic studies had been an intimidating task. During the past decade, powerful high-throughput technologies in proteomic research have been developed for yeast including protein microarray technology. The protein microarray technology allows the interrogation of protein–protein, protein–DNA, protein–small molecule interaction networks as well as post-translational modification networks in a large-scale, high-throughput manner. With this technology, many groundbreaking findings have been established in studies with the budding yeast Saccharomyces cerevisiae, most of which could have been unachievable with traditional approaches. Discovery of these networks has profound impact on explicating biological processes with a proteomic point of view, which may lead to a better understanding of normal biological phenomena as well as various human diseases.

Distribution of virulence factors and molecular fingerprinting of Aeromonas species isolates from water and clinical samples: suggestive evidence of water-to-human transmission

A total of 227 isolates of Aeromonas obtained from different geographical locations in the United States and different parts of the world, including 28 reference strains, were analyzed to determine the presence of various virulence factors. These isolates were also fingerprinted using biochemical identification and pulse-field gel electrophoresis (PFGE). Of these 227 isolates, 199 that were collected from water and clinical samples belonged to three major groups or complexes, namely, the A. hydrophila group, the A. caviae-A. media group, and the A. veronii-A. sobria group, based on biochemical profiles, and they had various pulsotypes. When virulence factor activities were examined, Aeromonas isolates obtained from clinical sources had higher cytotoxic activities than isolates obtained from water sources for all three Aeromonas species groups. Likewise, the production of quorum-sensing signaling molecules, such as N-acyl homoserine lactone, was greater in clinical isolates than in isolates from water for the A. caviae-A. media and A. hydrophila groups. Based on colony blot DNA hybridization, the heat-labile cytotonic enterotoxin gene and the DNA adenosine methyltransferase gene were more prevalent in clinical isolates than in water isolates for all three Aeromonas groups. Using colony blot DNA hybridization and PFGE, we obtained three sets of water and clinical isolates that had the same virulence signature and had indistinguishable PFGE patterns. In addition, all of these isolates belonged to the A. caviae-A. media group. The findings of the present study provide the first suggestive evidence of successful colonization and infection by particular strains of certain Aeromonas species after transmission from water to humans.

N-acylhomoserine lactones involved in quorum sensing control the type VI secretion system, biofilm formation, protease production, and in vivo virulence in a clinical isolate of Aeromonas hydrophila

In this study, we delineated the role of N-acylhomoserine lactone(s) (AHLs)-mediated quorum sensing (QS) in the virulence of diarrhoeal isolate SSU of Aeromonas hydrophila by generating a double knockout Delta ahyRI mutant. Protease production was substantially reduced in the Delta ahyRI mutant when compared with that in the wild-type (WT) strain. Importantly, based on Western blot analysis, the Delta ahyRI mutant was unable to secrete type VI secretion system (T6SS)-associated effectors, namely haemolysin coregulated protein and the valine-glycine repeat family of proteins, while significant levels of these effectors were detected in the culture supernatant of the WT A. hydrophila. In contrast, the production and translocation of the type III secretion system (T3SS) effector AexU in human colonic epithelial cells were not affected when the ahyRI genes were deleted. Solid surface-associated biofilm formation was significantly reduced in the Delta ahyRI mutant when compared with that in the WT strain, as determined by a crystal violet staining assay. Scanning electron microscopic observations revealed that the Delta ahyRI mutant was also defective in the formation of structured biofilm, as it was less filamentous and produced a distinct exopolysaccharide on its surface when compared with the structured biofilm produced by the WT strain. These effects of AhyRI could be complemented either by expressing the ahyRI genes in trans or by the exogeneous addition of AHLs to the Delta ahyRI/ahyR(+) complemented strain. In a mouse lethality experiment, 50 % attenuation was observed when we deleted the ahyRI genes from the parental strain of A. hydrophila. Together, our data suggest that AHL-mediated QS modulates the virulence of A. hydrophila SSU by regulating the T6SS, metalloprotease production and biofilm formation.

beta-Glucan administration enhances disease resistance and some innate immune responses in zebrafish (Danio rerio)

The present study was conducted to investigate the effect of beta-glucan (derived from Saccharomyces cerevisiae) on the immune response and its protection against an infection of the bacterial pathogen Aeromonas hydrophila in zebrafish (Danio rerio). Zebrafish received beta-glucan by intraperitoneal injection at three different concentrations (5, 2 and 0.5 mgml(-1)) at 6, 4 and 2 days prior the challenge. On challenge day the control and beta-glucan pretreated zebrafish were intraperitoneally injected with A. hydrophila and mortality was recorded for 4 days. Intraperitoneal injection of 5 mgml(-1) of beta-glucan significantly reduced the mortality. A single injection of 5 mgml(-1) of beta-glucan 6 days before challenge also enhanced significantly the survival against the infection. The treatment with beta-glucan increased the myelomonocytic cell population in the kidney at 6h postchallenge with A. hydrophila. Moreover it enhanced the ability of kidney cells to kill A. hydrophila. beta-glucan did not affect the expression of TNFalpha or IL-1 beta but seemed to modulate IFNgamma and chemokine expression in kidney.

Cold shock exoribonuclease R (VacB) is involved in Aeromonas hydrophila pathogenesis

In this study, we cloned and sequenced a virulence-associated gene (vacB) from a clinical isolate SSU of Aeromonas hydrophila. We identified this gene based on our recently annotated genome sequence of the environmental isolate ATCC 7966(T) of A. hydrophila and the vacB gene of Shigella flexneri. The A. hydrophila VacB protein contained 798 amino acid residues, had a molecular mass of 90.5 kDa, and exhibited an exoribonuclease (RNase R) activity. The RNase R of A. hydrophila was a cold-shock protein and was required for bacterial growth at low temperature. The vacB isogenic mutant, which we developed by homologous recombination using marker exchange mutagenesis, was unable to grow at 4 degrees C. In contrast, the wild-type (WT) A. hydrophila exhibited significant growth at this low temperature. Importantly, the vacB mutant was not defective in growth at 37 degrees C. The vacB mutant also exhibited reduced motility, and these growth and motility phenotype defects were restored after complementation of the vacB mutant. The A. hydrophila RNase R-lacking strain was found to be less virulent in a mouse lethality model (70% survival) when given by the intraperitoneal route at as two 50% lethal doses (LD(50)). On the other hand, the WT and complemented strains of A. hydrophila caused 80 to 90% of the mice to succumb to infection at the same LD(50) dose. Overall, this is the first report demonstrating the role of RNase R in modulating the expression of A. hydrophila virulence.

Identification of a new hemolysin from diarrheal isolate SSU of Aeromonas hydrophila

A clinical strain SSU of Aeromonas hydrophila produces a potent cytotoxic enterotoxin (Act) with cytotoxic, enterotoxic, and hemolytic activities. A new gene, which encoded a hemolysin of 439-amino acid residues with a molecular mass of 49 kDa, was identified. This hemolysin (HlyA) was detected based on the observation that the act gene minus mutant of A. hydrophila SSU still had residual hemolytic activity. The new hemolysin gene (hlyA) was cloned, sequenced, and overexpressed in Escherichia coli. The hlyA gene exhibited 96% identity with its homolog found in a recently annotated genome sequence of an environmental isolate, namely the type strain ATCC 7966 of A. hydrophila subspecies hydrophila. The hlyA gene did not exhibit any homology with other known hemolysins and aerolysin genes detected in Aeromonas isolates. However, this hemolysin exhibited significant homology with hemolysin of Vibrio vulnificus as well as with the cystathionine beta synthase domain protein of Shewanella oneidensis. The HlyA protein was activated only after treatment with trypsin and the resulting hemolytic activity was not neutralizable with antibodies to Act. The presence of the hlyA gene in clinical and water Aeromonas isolates was investigated and DNA fingerprint analysis was performed to demonstrate its possible role in Aeromonas virulence.

Mutations within the catalytic motif of DNA adenine methyltransferase (Dam) of Aeromonas hydrophila cause the virulence of the Dam-overproducing strain to revert to that of the wild-type phenotype

In this study, we demonstrated that the methyltransferase activity associated with Dam was essential for attenuation of Aeromonas hydrophila virulence. We mutated aspartic acid and tyrosine residues to alanine within the conserved DPPY catalytic motif of Dam and transformed the pBAD/damD/A, pBAD/damY/A, and pBAD/damAhSSU (with the native dam gene) recombinant plasmids into the Escherichia coli GM33 (dam-deficient) strain. Genomic DNA (gDNA) isolated from either of the E. coli GM33 strains harboring the pBAD vector with the mutated dam gene was resistant to DpnI digestion and sensitive to DpnII restriction endonuclease cutting. These findings were contrary to those with the gDNA of E. coli GM33 strain containing the pBAD/damAhSSU plasmid, indicating nonmethylation of E. coli gDNA with mutated Dam. Overproduction of mutated Dam in A. hydrophila resulted in bacterial motility, hemolytic and cytotoxic activities associated with the cytotoxic enterotoxin (Act), and protease activity similar to that of the wild-type (WT) bacterium, which harbored the pBAD vector and served as a control strain. On the contrary, overproduction of native Dam resulted in decreased bacterial motility, increased Act-associated biological effects, and increased protease activity. Lactone production, an indicator of quorum sensing, was increased when the native dam gene was overexpressed, with its levels returning to that of the control strain when the dam gene was mutated. These effects of Dam appeared to be mediated through a regulatory glucose-inhibited division A protein. Infection of mice with the mutated Dam-overproducing strains resulted in mortality rates similar to those for the control strain, with 100% of the animals dying within 2 to 3 days with two 50% lethal doses (LD50s) of the WT bacterium. Importantly, immunization of mice with a native-Dam-overproducing strain at the same LD50 did not result in any lethality and provided protection to animals after subsequent challenge with a lethal dose of the control strain.