Hydrophila Strains Research Articles

Osmotic stress response of the coral and oyster pathogen Vibrio coralliilyticus: acquisition of catabolism gene clusters for the compatible solute and signaling molecule myo-inositol.

Marine bacteria experience fluctuations in osmolarity that they must adapt to, and most bacteria respond to high osmolarity by accumulating compatible solutes also known as osmolytes. The osmotic stress response and compatible solutes used by the coral and oyster pathogen Vibrio coralliilyticus were unknown. In this study, we showed that to alleviate osmotic stress V. coralliilyticus biosynthesized glycine betaine (GB) and transported into the cell choline, GB, ectoine, dimethylglycine, and dimethylsulfoniopropionate, but not myo-inositol. Myo-inositol is a stress protectant and a signaling molecule that is biosynthesized and used by algae. Bioinformatics identified myo-inositol (iol) catabolism clusters in V. coralliilyticus and other Vibrio, Photobacterium, Grimontia, and Enterovibrio species. Growth pattern analysis demonstrated that V. coralliilyticus utilized myo-inositol as a sole carbon source, with a short lag time of 3 h. An iolG deletion mutant, which encodes an inositol dehydrogenase, was unable to grow on myo-inositol. Within the iol clusters were an MFS-type (iolT1) and an ABC-type (iolXYZ) transporter and analyses showed that both transported myo-inositol. IolG and IolA phylogeny among Vibrionaceae species showed different evolutionary histories indicating multiple acquisition events. Outside of Vibrionaceae, IolG was most closely related to IolG from a small group of Aeromonas fish and human pathogens and Providencia species. However, IolG from hypervirulent A. hydrophila strains clustered with IolG from Enterobacter, and divergently from Pectobacterium, Brenneria, and Dickeya plant pathogens. The iol cluster was also present within Aliiroseovarius, Burkholderia, Endozoicomonas, Halomonas, Labrenzia, Marinomonas, Marinobacterium, Cobetia, Pantoea, and Pseudomonas, of which many species were associated with marine flora and fauna.IMPORTANCEHost associated bacteria such as Vibrio coralliilyticus encounter competition for nutrients and have evolved metabolic strategies to better compete for food. Emerging studies show that myo-inositol is exchanged in the coral-algae symbiosis, is likely involved in signaling, but is also an osmolyte in algae. The bacterial consumption of myo-inositol could contribute to a breakdown of the coral-algae symbiosis during thermal stress or disrupt the coral microbiome. Phylogenetic analyses showed that the evolutionary history of myo-inositol metabolism is complex, acquired multiple times in Vibrio, but acquired once in many bacterial plant pathogens. Further analysis also showed that a conserved iol cluster is prevalent among many marine species (commensals, mutualists, and pathogens) associated with marine flora and fauna, algae, sponges, corals, molluscs, crustaceans, and fish.

Isolation, Identification, and Characterisation of a Novel ST2378 Aeromonas hydrophila Strain from Naturally Diseased Frogs, Rana dybowskii.

In 2023, Rana dybowskii exhibiting characteristic skin ulcers were found on a farm in northeastern China. Subsequently, two dominant bacteria, Aeromonas hydrophila Rd001 and Acinetobacter johnsonii Rd002, were isolated from naturally infected R. dybowskii. Experimental infection confirmed that Rd001 was the primary pathogen responsible for the disease in R. dybowskii, with a mean lethal dose (LD50) of 6.25 × 102 CFU/g. The virulence genotype of Rd001 was identified as ser+/aha+/lip+/nuc+/hlyA+/aer+/alt+/ast+/act+. Antimicrobial susceptibility testing indicated that Rd001 was sensitive to enrofloxacin, flumequine, and neomycin. MLST analysis showed that Rd001 belonged to a new sequence type of A. hydrophila, named ST2378. This study offered the first comprehensive investigation into the pathogenicity, virulence genotypes, antimicrobial resistance, and genetic traits of A. hydrophila isolated from R. dybowskii, providing a theoretical foundation for preventing and controlling A. hydrophila infections.

Co-infection of Lactococcus garvieae and Aeromonas hydrophila in cultured Nile Tilapia in Kerala, India.

Co-infection of Lactococcus garvieae and Aeromonas hydrophila, has been confirmed from diseased Nile Tilapia (Oreochromis niloticus), Chithralada strain cultured in a freshwater rearing pond of Alappuzha district of Kerala, India. The aetiological agents behind the disease outbreak were bacteriologically proven and confirmed by 16SrRNA sequencing and phylogenetic analysis. PCR detection of the virulent genes, showed existence of adhesin and hemolysin in L. garvieae and aerolysin in A. hydrophila strain obtained. To fulfil Koch's postulates, challenge experiments were conducted and median lethal dose (LD50) of L. garvieae and A. hydrophila was calculated as 1 × 105.91 CFU per mL and 1 × 105.2 CFU per mL respectively. Histopathologically, eyes, spleen, and kidney were the predominantly infected organs by L. garvieae and A. hydrophila. Out of the 13 antibiotics tested to check antibiotic susceptibility, L. garvieae showed resistance to almost 7 antibiotics tested, with a resistance to Ciprofloxacin while A. hydrophila was found resistant to Streptomycin and Erythromycin. Understanding the complex interaction between Gram-positive and Gram-negative bacteria in the disease process and pathogenesis in fish host will contribute to efficient treatment strategies. As a preliminary investigation into this complex interaction, the present study is aimed at phenotypic and genotypic characterization, pathogenicity evaluation, and antibiotic susceptibility of the co-infecting pathogens in a diseased sample of freshwater-farmed Nile tilapia.

Utilizing outer membrane proteins (OMPs) as a vaccine to manage motile Aeromonas septicemia (MAS) in Nile tilapia (Oreochromis niloticus) with evaluating the vaccine immunoprotective effectiveness

Motile aeromonads are an opportunistic and heterogenic bacteria that cause motile Aeromonas septicemia (MAS) which is accompanied with variety of clinical signs and lesions in fish. It has been found that their outer membrane proteins (OMPs) are highly immunogenic and may be used as a vaccine candidate. The present study was undertaken to evaluate OMP protection against Aeromonas hydrophila (A. hydrophila) strain ATCC 7966 (A5 and A8) and A. hydrophila strain DSM 30,187 (A6). Pathogenicity tests revealed that out of 12 isolated strains, seven were highly pathogenic, three were moderate, and two were avirulent. SDS-PAGE analysis of OMPs showed several protein bands (7–22) of different molecular weights ranging from 14 to 346 kDa. The common protein band was 39 kDa. It seems that pathogenicity and the number of protein bands are related in the highly pathogenic strains. Challenged A. hydrophila for Nile tilapia (O. niloticus) previously actively immunized with OMPs (A4, A5, A6, A8, and A11) showed a significant increase in relative percent survival (RPS) ranging from 50 to 100%. Immunological parameters such as immunoglobulin M (IgM), antioxidants (SOD, GSH, and CAT), and nitric oxide (NO) and expression of pro-inflammatory cytokines, interleukin 1β (IL-1β), and tumor necrosis factor-α (TNFα) showed a significant increase in OMP-immunized fish. Challenged A. hydrophila for O. niloticus previously passively immunized with OMPs (A4, A5, A6, A8, and A11) in fish-raised sera showed a significant increase in RPS (20 to 100%) in the vaccinated groups. It is concluded that OMPs from Aeromonas spp. have been identified as suitable target for protection development, especially in the case of heterogenic bacteria.

Molecular characterization and bivalent vaccine development of Aeromonas hydrophila and Aeromonas veronii in Nile tilapia (Oreochromis niloticus)

In the present study, nine strains of Aeromonas spp. were isolated from diseased Nile tilapia in Thailand and identified based on 16S rRNA and gyrB gene sequences and multilocus sequence typing (MLST) analysis. Phenotypic characterization was performed for all the isolates. For the antimicrobial susceptibility test, all isolates were resistant to amoxicillin, whereas most of the isolates were susceptible to enrofloxacin. Pathogenicity analysis revealed that most A. hydrophila strains were highly virulent to fish, corresponding with the hemolytic activity test demonstrating that clear hemolysis occurred on sheep blood agar. To develop a vaccine for fish against A. veronii and A. hydrophila infection, a bivalent vaccine based on the formalin-killed cells (FKC) of A. veronii A5 and A. hydrophila A9, which showed higher virulence to fish, was prepared. This FKC vaccine was administered to Nile tilapia by intraperitoneal injection. The booster vaccination was conducted at 4 weeks after the first vaccination. The specific antibody titer was evaluated during rearing since the first vaccination, and then at 8 weeks after the first vaccination, the fish were challenged with A. veronii A5 and A. hydrophila A9 via intraperitoneal injection. There is not significance different in relative percentage survival of the vaccinated fish against A. veronii (63.49 ± 19.51%) and A. hydrophila (93.33 ± 6.67%). These results suggest that this candidate bivalent vaccine is effective against both A. veronii and A. hydrophila infection in Nile tilapia and could be an “motile Aeromonas septicemia (MAS)” control measure. However, to obtain the promising vaccine efficacy, the optimization of vaccine formulation might be achieved and be validated vaccine efficacy in field trial.

Beneficial effects of the butanoic acid derivative tributyrin on the growth, immunity and intestinal health of large mouth bass (Micropterus salmoides)

Tributyrin (TB) is a novel butanoic acid derivative with potent bioactive functions. In this study, an eight-week feeding trial aimed to investigate the effects of dietary TB on the growth, immunity and intestinal health of large mouth bass (Micropterus salmoides). Five experimental diets containing 0, 0.5, 1.0, 1.5 or 2.0 g/kg tributyrin were formulated and were regarded as TB0 (control), TB0.5, TB1.0, TB1.5 and TB2.0, respectively. Quadruplicate groups (four tanks per group, 30 fish per tank) of juvenile M. salmoides (initial weight: 20.00 ± 1.00 g) were fed to apparent satiation two times daily. After the feeding trial,Aeromonas hydrophila challenge tests were conducted and the A. hydrophila strains were subsequently sampled. As a result, the weight gain rate (WGR) was increased in the TB supplementation groups, and the TB1.5 group obtained the highest value. Furthermore, TB administration improved immune function. The content of serum complement 4 in the TB1.5 group was significantly higher than that in the control group. Increase of lysozyme activity and immunoglobulin M were significant in TB1.0 group than the control group. After A. hydrophila injection, TB1.0, TB1.5 and TB2.0 groups presented markedly higher survival rates than did the control group. Additionally, TB markedly enhanced the activities of amylase and lipase in the gut. Moreover, 16S rRNA sequencing revealed that TB could affect the intestinal microflora composition. Compared to those in the control group, the abundance of Fusobacteria were lower in the TB1.0 and TB1.5 groups. In conclusion, this study demonstrated that TB can improve the growth, immunity and intestinal health of M. salmoides, and the optimal dietary level of TB is determined to be 0.15%.

Coexistence of a novel chromosomal integrative and mobilizable element Tn7548 with two blaKPC-2-carrying plasmids in a multidrug-resistant Aeromonas hydrophila strain K522 from China

Herein, we detected one multidrug-resistant Aeromonas hydrophila strain K522 co-carrying two blaKPC-2 genes together with a novel chromosomal integrative and mobilizable element (IME) Tn7548 from China. To reveal the genetic characteristics of the novel reservoir of blaKPC-2 and IME in Aeromonas, a detailed genomic characterization of K522 was performed, and a phylogenetic analysis of Tn7412-related IMEs was carried out. Carbapenemases were detected by using the immunocolloidal gold technique and antimicrobial susceptibility was tested by using VITEK 2. The whole-genome sequences of K522 were analysed using phylogenetics, detailed dissection, and comparison. Strain K522 carried a Tn7412-related chromosomal IME Tn7548 and three resistance plasmids pK522-A-KPC, pK522-B-KPC, and pK522-MOX. A phylogenetic tree of 82 Tn7412-related IMEs was constructed, and five families of IMEs were divided. These IMEs shared four key backbone genes: int, repC, and hipAB, and carried various profiles of antimicrobial resistance genes (ARGs). pK522-A-KPC and pK522-B-KPC carried blaKPC-2 and belonged to IncG and unclassified type plasmid, respectively. The blaKPC-2 regions of these two plasmids were the truncated version derived from Tn6296, resulting in the carbapenem resistance of K522. We first reported A. hydrophila harbouring a novel Tn7412-related IME Tn7548 together with two blaKPC-2 carrying plasmids and a MDR plasmid. Three of these four mobile genetic elements (MGEs) discovered in A. hydrophila K522 were novel. The emergence of novel MGEs carrying ARGs indicated the rapid evolution of the resistance gene vectors in A. hydrophila under selection pressure and would contribute to the further dissemination of various ARGs in Aeromonas.

Lonicera japonica protects Pelodiscus sinensis by inhibiting the biofilm formation of Aeromonas hydrophila.

Aquaculture has suffered significant financial losses as a result of the infection of zoonotic Aeromonas hydrophila, which has a high level of resistance to classic antibiotics. In this study, we isolated an A. hydrophila strain B3 from diseased soft-shelled turtle (Pelodiscus sinensis), which is one of the most commercially significant freshwater farmed reptiles in East Asia, and found that A. hydrophila was its dominant pathogen. To better understand the inhibition effect and action mechanism of Chinese herbs on A. hydrophila, we conducted Chinese herbs screening and found that Lonicera japonica had a significant antibacterial effect on A. hydrophila B3. Experimental therapeutics of L. japonica on soft-shelled turtle showed that the supplement of 1% L. japonica to diet could significantly upregulate the immunity-related gene expression of soft-shelled turtle and protect soft-shelled turtle against A. hydrophila infection. Histopathological section results validated the protective effect of L. japonica. As the major effective component of L. japonica, chlorogenic acid demonstrated significant inhibitory effect on the growth of A. hydrophila with MIC at 6.4 mg/mL. The in vitro assay suggested that chlorogenic acid could inhibit the hemolysin/protease production and biofilm formation of A. hydrophila and significantly decrease the expression of quorum sensing, biofilm formation, and hemolysin-related genes in A. hydrophila. Our results showed that the Chinese herb L. japonica would be a promising candidate for the treatment of A. hydrophila infections in aquaculture, and it not only improves the immune response of aquatic animals but also inhibits the virulence factor (such as biofilm formation) expression of A. hydrophila. KEY POINTS: • A. hydrophila was the dominant pathogen of the diseased soft-shelled turtle. • L. japonica can protect soft-shelled turtle against A. hydrophila infection. • Chlorogenic acid inhibits the growth and biofilm formation of A. hydrophila.

Effect Of Glutamine on Growth Performance, Biochemical Parameters and Diseases Resistance in Cultured Nile Tilapia Fish

The current investigation was done to examine the impact of some amino acids as glutamine with different concentrations on growth performance, biochemical parameters and resistance to bacterial infection as Aeromonas hydrophila in Nile tilapia. Total number used in our study were two-hundred and eighty O.niloticus fish (100 diseased fish for Aeromonas hydrophila isolation and 180 apparently healthy fish for experimental design). 180 fish were divided into four groups, 45 fish / group. The control group was feeding a baseline diet without additives and the treated groups were feeding a diet containing glutamine of 1, 1.5, or 2% for groups 2, 3 and 4 respectively. Fish from the treated and control groups received intraperitoneal (IP) injections of 0.2 ml suspension of A. hydrophila after the feeding trial has concluded. Results of our investigation showed a total of 14 A. hydrophila strains were recovered from 100 samples of diseased fish with a percentage of 14%. Through the use of, cultural, morphological, biochemical characteristics and PCR technique, the isolates were identified. According to the results of the PCR examination all 7 examined isolates were positive for the Aeromonas hydrophila specific gene (16S rRNA) and act gene and 5 isolates were positive for aerolysin gene but the 7 examined strains were negative for ast gene. Also our study showed a significant differences with control and higher growth performance for groups fed on diet containing glutamine 1.5% and 2% concentrations and also showed that diet containing 2% Glutamine augmented Hb%, RBCs, and MCV% and increased serum SOD, CAT, GPx, and bactericidal activities in addition to elevation in the levels of total protein than the other Glutamine inclusion levels (1% or 1.5%). Also the mortality rate and re-isolation rate decreased in groups fed on diet containing glutamine 1.5% and 2% concentrations than the other groups. In conclusion, dietary supplementation with glutamine at a concentration of 2% enhanced the growth performance, improve biochemical parameters and the resistance to Aeromonas hydrophila infection.

Fountain Water as a Source of Opportunistic Escherichia coli and Aeromonas hydrophila Strains in Atmospheric Air

Fountain Water as a Source of Opportunistic Escherichia coli and Aeromonas hydrophila Strains in Atmospheric Air

Dual resistance to heavy metals and antibiotics of Aeromonas hydrophila isolated from Carassius carassius (Linnaeus, 1758) in Lake Tonga, Algeria

Aeromonas hydrophila, a bacterium with significant virulence potential, is the predominant pathogenic bacteria naturally infecting fish. This study aims to identify the antibiogram and heavy metal resistance pattern of Aeromonas hydrophila obtained from both Carassius carassius fish and their surrounding water environment in Lake Tonga, Algeria. A total of 59 strains of Aeromonas hydrophila were isolated from 168 Carassius carassius samples and 144 waters samples of Lake Tonga. All the strains were tested for resistance to 13 antibiotics and three types of heavy metals (Cobalt, copper and cadmium) using disk diffusion and two-fold agar dilution method, respectively. Clinical macroscopic examination of the fish was also carried out. More than 14% of the examined fishes showed the characteristic clinical signs. Drug screening showed high levels of resistance to β-lactam antibiotics, 100% of the strains were resistant to ampicillin followed by cefalotin (91.53%) and ticarcillin (88.14%). More than 40% of the strains exhibited resistance against gentamicin, amikacin and chloramphenicol. The multiple antibiotic resistance (MAR) indexing of A. hydrophila strains showed that all of them originated from high-risk sources. Among tested heavy metals, bacterial isolates exhibited resistant pattern of Co>Cu >Cd. A positive correlation was observed between antimicrobial resistance and metal tolerance (Odds Ratio>0.1). These resistant profiles could be useful information to avoid unnecessary use of chemical and antimicrobial products in the aquatic environment and to provide a novel approach to manage bacterial infection in fish.

Isolation and characterization of a novel temperate bacteriophage infecting Aeromonas hydrophila isolated from a Macrobrachium rosenbergii larvae pond

Aeromonas hydrophila is an opportunistic pathogen that frequently leads to significant mortality in various commercially cultured aquatic species. Bacteriophages offer an alternative strategy for pathogens elimination. In this study, we isolated, identified, and characterized a novel temperate A. hydrophila phage, designated as P05B. The bacteriophage P05B is a myovirus based on its morphological features, and possesses the capability to lyse A. hydrophila strains isolated from shrimp. The optimal multiplicity of infection (MOI), adsorption rate, latent period, and burst size for phage P05B were determined to be 0.001, 91.7 %, 20 min, and 483 PFU/cell, respectively. Phage P05B displayed stability across a range of temperatures (28–50 °C) and pH values (4.0–10.0). Sequence analysis unveiled that the genome of phage P05B comprises 32,302 base pairs with an average G + C content of 59.4 %. A total of 40 open reading frames (ORF) were encoded within the phage P05B genome. The comparative genomic analyses clearly implied that P05B might represent a novel species of the genus Bielevirus under Peduoviridae family. A phylogenetic tree was reconstructed, demonstrating that P05B shares a close evolutionary relationship with other Aeromonas and Aeromonas phages. In conclusion, this study increased our knowledge about a new temperate phage of A. hydrophila with strong lytic ability.

Phenotypic, molecular detection and antibiogram analysis of Aeromonas Hydrophila from Oreochromis Niloticus (Nile Tilapia) and Ready-To- eat fish products in selected Rift Valley lakes of Ethiopia

BackgroundAeromonas hydrophila is a zoonotic bacterial pathogen that frequently causes disease and mass mortalities among cultured and feral fishes worldwide. In Ethiopia, A. hydrophila outbreak was reported in Sebeta fish ponds and in Lake Tana fishery. However, there is no to little information on the molecular, and phenotypical characteristics of A. hydrophila in Ethiopian fisheries. Therefore, a cross-sectional study was conducted from November 2020 to May 2021 in selected Ethiopian Rift valley lakes.ResultsA total of 140 samples were collected aseptically from fish (Muscle, Gill, Intestine, Spleen and Kidney) from fish landing sites, market and restaurants with purposive sampling methods. Aeromonas selective media (AMB), morphological and biochemical tests were used to isolate and identify A. hydrophila. Accordingly, the pathogen was isolated from 81 (60.45%) of samples. Among the isolates 92.59% expressed virulence trait through β hemolysis on blood agar media with 5% sheep blood. Moreover, 54 strains (66.67%) were further confirmed with Real-Time PCR (qPCR) using ahaI gene specific primers and optimized protocol. The highest (68.51%) were detected from live fish, (24.07%) were from market fish and the lowest (7.4%%) were from ready-to-eat products. Antibiogram analysis was conducted on ten representative isolates. Accordingly, A. hydrophila isolates were susceptible to ciprofloxacin (100%), chloramphenicol (100%) and ceftriaxone (100%). However, all ten isolates were resistant to Amoxicillin and Penicillin.ConclusionsThe study indicates A. hydrophila strains carrying virulence ahaI gene that were ß-hemolytic and resistant to antibiotics commonly used in human and veterinary medicine are circulating in the fishery. The detection of the pathogen in 140 of the sampled fish population is alarming for potential outbreaks and zoonosis. Therefore, further molecular epidemiology of the disease should be studied to establish potential inter host transmission and antibiotic resistance traits. Therefore, raising the public awareness on risk associated with consuming undercooked or raw fish meat is pertinent.

The Screening of the Protective Antigens of Aeromonas hydrophila Using the Reverse Vaccinology Approach: Potential Candidates for Subunit Vaccine Development.

The threat of bacterial septicemia caused by Aeromonas hydrophila infection to aquaculture growth can be prevented through vaccination, but differences among A. hydrophila strains may affect the effectiveness of non-conserved subunit vaccines or non-inactivated A. hydrophila vaccines, making the identification and development of conserved antigens crucial. In this study, a bioinformatics analysis of 4268 protein sequences encoded by the A. hydrophila J-1 strain whole genome was performed based on reverse vaccinology. The specific analysis included signal peptide prediction, transmembrane helical structure prediction, subcellular localization prediction, and antigenicity and adhesion evaluation, as well as interspecific and intraspecific homology comparison, thereby screening the 39 conserved proteins as candidate antigens for A. hydrophila vaccine. The 9 isolated A. hydrophila strains from diseased fish were categorized into 6 different molecular subtypes via enterobacterial repetitive intergenic consensus (ERIC)-PCR technology, and the coding regions of 39 identified candidate proteins were amplified via PCR and sequenced to verify their conservation in different subtypes of A. hydrophila and other Aeromonas species. In this way, conserved proteins were screened out according to the comparison results. Briefly, 16 proteins were highly conserved in different A. hydrophila subtypes, of which 2 proteins were highly conserved in Aeromonas species, which could be selected as candidate antigens for vaccines development, including type IV pilus secretin PilQ (AJE35401.1) and TolC family outer membrane protein (AJE35877.1). The present study screened the conserved antigens of A. hydrophila by using reverse vaccinology, which provided basic foundations for developing broad-spectrum protective vaccines of A. hydrophila.

Characterization and application of a lytic jumbo phage ZPAH34 against multidrug-resistant Aeromonas hydrophila.

Aeromonas hydrophila is an emerging foodborne pathogen causing human gastroenteritis. Aeromonas species isolated from food such as seafood presented multidrug-resistance (MDR), raising serious concerns regarding food safety and public health. The use of phages to infect bacteria is a defense against drug-resistant pathogens. In this study, phage ZPAH34 isolated from the lake sample exerted lytic activity against MDR A. hydrophila strain ZYAH75 and inhibited the biofilm on different food-contacting surfaces. ZPAH34 has a large dsDNA genome of 234 kb which belongs to a novel jumbo phage. However, its particle size is the smallest of known jumbo phages so far. Based on phylogenetic analysis, ZPAH34 was used to establish a new genus Chaoshanvirus. Biological characterization revealed that ZPAH34 exhibited wide environmental tolerance, and a high rapid adsorb and reproductive capacity. Food biocontrol experiments demonstrated that ZPAH34 reduces the viable count of A. hydrophila on fish fillets (2.31 log) and lettuce (3.28 log) with potential bactericidal effects. This study isolated and characterized jumbo phage ZPAH34 not only enriched the understanding of phage biological entity diversity and evolution because of its minimal virion size with large genome but also was the first usage of jumbo phage in food safety to eliminate A. hydrophila.

Mechanisms of low susceptibility to the disinfectant benzalkonium chloride in a multidrug-resistant environmental isolate of Aeromonas hydrophila.

Excessive discharge of quaternary ammonium disinfectants such as benzalkonium chloride (BAC) into aquatic systems can trigger several physiological responses in environmental microorganisms. In this study, we isolated a less-susceptible strain of Aeromonas hydrophila to BAC, designated as INISA09, from a wastewater treatment plant in Costa Rica. We characterized its phenotypic response upon exposure to three different concentrations of BAC and characterized mechanisms related to its resistance using genomic and proteomic approaches. The genome of the strain, mapped against 52 different sequenced A. hydrophila strains, consists of approximately 4.6 Mb with 4,273 genes. We found a massive genome rearrangement and thousands of missense mutations compared to the reference strain A. hydrophila ATCC 7966. We identified 15,762 missense mutations mainly associated with transport, antimicrobial resistance, and outer membrane proteins. In addition, a quantitative proteomic analysis revealed a significant upregulation of several efflux pumps and the downregulation of porins when the strain was exposed to three BAC concentrations. Other genes related to membrane fatty acid metabolism and redox metabolic reactions also showed an altered expression. Our findings indicate that the response of A. hydrophila INISA09 to BAC primarily occurs at the envelop level, which is the primary target of BAC. Our study elucidates the mechanisms of antimicrobial susceptibility in aquatic environments against a widely used disinfectant and will help better understand how bacteria can adapt to biocide pollution. To our knowledge, this is the first study addressing the resistance to BAC in an environmental A. hydrophila isolate. We propose that this bacterial species could also serve as a new model to study antimicrobial pollution in aquatic environments.

Development of Bioluminescent Virulent Aeromonas hydrophila for Understanding Pathogenicity.

Virulent Aeromonas hydrophila (vAh) strains that cause motile Aeromonas septicemia (MAS) in farmed channel catfish (Ictalurus punctatus) have been an important problem for more than a decade. However, the routes of infection of vAh in catfish are not well understood. Therefore, it is critical to study the pathogenicity of vAh in catfish. To this goal, a new bioluminescence expression plasmid (pAKgfplux3) with the chloramphenicol acetyltransferase (cat) gene was constructed and mobilized into vAh strain ML09-119, yielding bioluminescent vAh (BvAh). After determining optimal chloramphenicol concentration, plasmid stability, bacteria number-bioluminescence relationship, and growth kinetics, the catfish were challenged with BvAh, and bioluminescent imaging (BLI) was conducted. Results showed that 5 to 10 µg/mL chloramphenicol was suitable for stable bioluminescence expression in vAh, with some growth reduction. In the absence of chloramphenicol, vAh could not maintain pAKgfplux3 stably, with the half-life being 16 h. Intraperitoneal injection, immersion, and modified immersion (adipose fin clipping) challenges of catfish with BvAh and BLI showed that MAS progressed faster in the injection group, followed by the modified immersion and immersion groups. BvAh was detected around the anterior mouth, barbels, fin bases, fin epithelia, injured skin areas, and gills after experimental challenges. BLI revealed that skin breaks and gills are potential attachment and entry portals for vAh. Once vAh breaches the skin or epithelial surfaces, it can cause a systemic infection rapidly, spreading to all internal organs. To our best knowledge, this is the first study that reports the development of a bioluminescent vAh and provides visual evidence for catfish-vAh interactions. Findings are expected to provide a better understanding of vAh pathogenicity in catfish.

Complete Genome Sequence of Aeromonas hydrophila Strain Y-S01, Isolated from Diseased Dark Sleeper (Odontobutis potamophila) in China

Aeromonas hydrophila is one of the most important pathogenic bacteria for aquaculture animals, such as fish and crustaceans. In this study, we isolated a pathogenic bacterial strain, named Y-SC01, from dark sleeper (Odontobutis potamophila) with rotten gills; the strain was identified as A. hydrophila by physiological and biochemical tests. Furthermore, we sequenced its genome and assembled a chromosome of 4.72 Mb with a GC content of 58.55%, and we report major findings based on the genomic analysis.

Multidrug-resistant Aeromonas bacteria prevalence in Nile tilapia broodstock

BackgroundAeromonas hydrophila is an opportunistic pathogen. Thus, it has received significant attention mainly in the fish sectors with high production scales. Nile tilapia broodstock confined in the environment of fish hatcheries can be stressed. Hence, they are vulnerable to A. hydrophila.ResultsSequencing of the gyr B gene revealed the presence of 18 different A. hydrophila strains (kdy 10,620–10,637), which were deposited in the NCBI under accession numbers ON745861–ON745878. The median lethal doses of the isolates ranged from 2.62 × 104 to 3.02 × 106 CFU/mL. Antibiotic resistant genes, sulfonamide (sul1) and tetracycline (tetA) were found in the eighteen isolates. Approximately 83.3% of A. hydrophila strains were sensitive to ciprofloxacin and florfenicol. Further, eight A. hydrophila strains had high MDR indices at 0.27–0.45. All isolates presented with hemolysin activity. However, only 72.22% of them had proteolytic activity, and only 61.11% could form biofilms. Bacterial isolates harbored different pattern virulence genes, the heat-stable cytotonic enterotoxin (ast), cytotoxic enterotoxin (act), and hemolysin (hly) genes were the most prevalent. Also, a trial to inhibit bacterial growth was conducted using titanium dioxide nanoparticles (TiO2 NPs) with three sizes (13, 32, and 123 nm). If A. hydrophila strains with a high MDR index were tested against TiO2 NPs (20 µg/mL) for 1, 12, and 24 h, those with a small size had a greater bactericidal action than large ones. Bacterial strains were inhibited at different percentages in response to TiO2 NP treatment.ConclusionsNile tilapia broodstock, mortality is associated with different A. hydrophila strains, which harbored virulent and MDR genes. Furthermore, TiO2 NPs had bactericidal activity, thereby resulting in a considerable reduction in bacterial load.

Aeromonas hydrophila ST251 and Aeromonas dhakensis are major emerging pathogens of striped catfish in Vietnam.

Aeromonads are ubiquitous in aquatic environments and several species are opportunistic pathogens of fish. Disease losses caused by motile Aeromonas species, particularly Aeromonas hydrophila, can be challenging in intensive aquaculture, such as at striped catfish (Pangasianodon hypophthalmus) farms in Vietnam. Outbreaks require antibiotic treatments, but their application is undesirable due to risks posed by resistance. Vaccines are an attractive prophylactic and they must protect against the prevalent strains responsible for ongoing outbreaks. This present study aimed to characterize A. hydrophila strains associated with mortalities in striped catfish culture in the Mekong Delta by a polyphasic genotyping approach, with a view to developing more effective vaccines. During 2013-2019, 345 presumptive Aeromonas spp. isolates were collected at farms in eight provinces. Repetitive element sequence-based PCR, multi-locus sequence typing and whole-genome sequencing revealed most of the suspected 202 A. hydrophila isolates to belong to ST656 (n = 151), which corresponds to the closely-related species Aeromonas dhakensis, with a lesser proportion belonging to ST251 (n = 51), a hypervirulent lineage (vAh) of A. hydrophila already causing concern in global aquaculture. The A. dhakensis ST656 and vAh ST251 isolates from outbreaks possessed unique gene sets compared to published A. dhakensis and vAh ST251 genomes, including antibiotic-resistance genes. The sharing of resistance determinants to sulphonamides (sul1) and trimethoprim (dfrA1) suggests similar selection pressures acting on A. dhakensis ST656 and vAh ST251 lineages. The earliest isolate (a vAh ST251 from 2013) lacked most resistance genes, suggesting relatively recent acquisition and selection, and this underscores the need to reduce antibiotics use where possible to prolong their effectiveness. A novel PCR assay was designed and validated to distinguish A. dhakensis and vAh ST251 strains. This present study highlights for the first time A. dhakensis, a zoonotic species that can cause fatal human infection, to be an emerging pathogen in aquaculture in Vietnam, with widespread distribution in recent outbreaks of motile Aeromonas septicaemia in striped catfish. It also confirms vAh ST251 to have been present in the Mekong Delta since at least 2013. Appropriate isolates of A. dhakensis and vAh should be included in vaccines to prevent outbreaks and reduce the threat posed by antibiotic resistance.