Search Results (107)

The incidence of furunculosis in juvenile Atlantic salmon, Salmo salar, has increased in recent years in Chile, with isolates of Aeromonas salmonicida being the primary cause. However, in some cases, molecular diagnostics failed to identify the etiological agent. We previously demonstrated that a proportion of undiagnosed cases was produced by a new A. salmonicida strain. In those cases where the pathogen remained unidentified, we isolated colonies with an A. salmonicida-like appearance. Subsequent phylogenetic analysis presented in this work grouped those A. salmonicida-like isolates within the Aeromonas piscicola clade. Whole genome sequencing confirmed the taxonomic affiliation, giving additional insights into virulence and antibiotic resistance markers. Indeed, one of the strains showed reduced susceptibility to oxytetracycline. Virulence potential was assessed by in vivo testing in S. salar, which resulted in disease with pathognomonic signs of furunculosis. Although the pathogen presents common antigens with A. salmonicida, the current vaccine triggered only a modest IgM response against A. piscicola in the field. Our results support the hypothesis that the increasing incidence of furunculosis in Chile cannot solely be ascribed to the emergence of the new less-virulent A. salmonicida strain, but may partially result from furunculosis-like infections caused by A. piscicola strains which exhibit a comparable virulence level. Full article

Antimicrobial use (AMU) in finfish aquaculture production raises concerns about the link between AMU and the development of antimicrobial resistance (AMR) in bacteria found in aquatic organisms and potential transmission to humans and the environment. The objective of this study was to describe the antimicrobial susceptibilities of a historical collection of bacterial isolates from diagnostic submissions from farmed finfish in British Columbia (BC), Canada. Antimicrobial susceptibility data were obtained from the BC Ministry of Agriculture via submissions to the Animal Health Centre for 2007 to 2018 for florfenicol (FLOR), oxytetracycline (OXY), trimethoprim-sulfadiazine (SXT), and triple-sulfa compound (TRI). There were 1237 unique isolates from all finfish species (68 unique bacterial species), of which 1042 were from Atlantic salmon. For all fish species, the most common bacterial species isolated were Aeromonas salmonicida (n = 174), Aliivibrio wodanis (n = 84), and Yersinia ruckeri (n = 79). Resistance was detected to most antimicrobials tested, but levels were generally low. Resistance to FLOR was only detected in A. salmonicida. Low annual isolate numbers precluded genera-specific annual comparisons for all pathogens. Multi-drug resistance was detected, but at low levels. These results provide an important baseline for antimicrobial susceptibility data from bacterial isolates that may cause disease in finfish aquaculture in BC, Canada that will support future Canadian AMR surveillance in farmed aquaculture. Full article

The development of effective vaccines is a critical step in effective disease management in aquaculture. This study introduces a novel Multiepitope Chimeric Vaccine (MCV) designed to enhance immunity in lumpfish against Vibrio anguillarum, Aeromonas salmonicida, Yersinia ruckeri, Moritella viscosa and Piscirickettsia salmonis. Epitopes from major toxins and virulence factors were selected to construct the MCV in silico. Structural validation showed 96.7% of residues in favored regions, confirming stability. Codon optimization yielded a G+C content of 54.61% and a Codon Adaptation Index (CAI) of 1, indicating strong expression potential in Escherichia coli. Immune simulations predicted robust B- and T-cell responses, suggesting induction of both humoral and cell-mediated immunity. Experimental vaccination of lumpfish (n = 35/group) with E. coli-expressed MCV led to significantly elevated IgM levels at four- and six-weeks post-vaccination (p ≤ 0.05, p ≤ 0.01, respectively). Upon pathogen challenge, vaccinated groups showed delayed mortality against V. anguillarum, A. salmonicida, and P. salmonis, though survival differences were not statistically significant across treatments. These results highlight the immunogenicity potential of the MCV and its capacity to elicit targeted immune responses. However, further optimization is necessary to improve protective efficacy and survival outcomes. This study lays a foundation for the application of multiepitope vaccines in lumpfish aquaculture and supports ongoing efforts toward sustainable disease control strategies. Full article

Aeromonas salmonicida is a major pathogen in aquaculture, and its ability to form biofilms contributes significantly to antibiotic resistance and chronic infections. This study investigated the effects of four antibiotics—ampicillin, amoxicillin, oxytetracycline, and doxycycline—at various concentrations on bacterial growth, biofilm formation, and gene expression related to antibiotic resistance and quorum sensing (QS) in two subspecies: A. salmonicida subsp. masoucida (ASM) and A. salmonicida subsp. salmonicida (ASS). Bacterial isolates from Atlantic salmon were identified using 16S rRNA and vapA gene sequencing. Growth inhibition was more pronounced in ASS than ASM under high antibiotic concentrations. Conversely, sub-inhibitory concentrations (sub-MICs) enhanced biofilm formation in both subspecies, particularly in ASM. PCR results showed that tetA and tetE resistance genes were present only in ASM. qRT-PCR analysis revealed that expression of QS-related genes (ahyI and ahyR) was generally downregulated under tetracycline treatment, while litR expression varied across antibiotic conditions and strains. Some isolates showed increased litR expression alongside elevated biofilm formation, suggesting involvement of additional regulatory mechanisms. These results highlight the potential for sub-MIC antibiotic exposure to promote biofilm development and modulate gene expression, emphasizing the need for careful antibiotic use in aquaculture and providing insight into alternative pathogen control strategies. Full article

Background/Objectives: This study aimed to characterize Vibrio anguillarum strain 23FBVib0271 (VA) isolated from rainbow trout and Aeromonas salmonicida salmonicida strain 17FBASa0016 (ASS) and A. salmonicida masoucida strain 23FBAer0174 (ASM) isolated from Atlantic salmon in the Republic of Korea. Their physiological traits, pathogenicity, and antigenicity were examined, and formalin-inactivated vaccines were developed to evaluate safety and immunogenicity in Atlantic salmon (Salmo salar). Methods: Formalin-inactivated VA, ASS and ASM were administered intraperitoneally, and protective efficacy was determined after six weeks. Serum biochemical parameters (AST, ALT, ALP, glucose) and histopathology were analyzed for safety. ELISA and real-time PCR targeting IL-1β, BCL6, membrane-bound IgM, and secretory IgM were performed to assess immune responses. Results: Vaccination provided relative percent survivals of 100%, 75%, and 95% for VA, ASS and ASM, respectively, without adverse physiological or histological effects. Immunological analyses revealed strong antibody production and upregulation of immune-related genes. Conclusions: Formalin-inactivated vaccines from VA, ASS and ASM are safe and effectively induce protective humoral immunity in Atlantic salmon by promoting antigen-specific antibody responses and immune gene activation. Full article

Aeromonas hydrophila is a typical pathogen that causes fish diseases and can easily infect different fish species. This study investigated the antibacterial activity, physicochemical properties and antibacterial mechanism of the BLIS UI-11 produced by Lactobacillus plantarum HYH-11, isolated from traditional kimchi in Hebei, China. It was found that BLIS UI-11 showed excellent inhibitory effect on the growth of A. hydrophila, and it also had a good antibacterial effect on various pathogens such as Vagococcus fluvialis, Listeria monocytogenes, Aeromonas dhakensis, Aeromonas salmonicida, Salmonella Typhimurium, Escherichia coli and Staphylococcus aureus. By measuring growth kinetics, it was found that the maximum antibacterial activity was reached after 30 h of culture, and both the optical density value at 600 nm (OD₆₀₀₎ and pH basically entered the stable phase after 20 h. Whole-genome analysis and gene cluster prediction identified a RiPP-like biosynthetic gene cluster, which comprises genes encoding precursor peptides, modification enzymes, and transport/immunity components. The molecular weight of the antimicrobial active substance was detected by dialysis and Tricine-SDS-PAGE, and it was shown to be an ultra-small molecular substance (<1 kDa). BLIS UI-11 was sensitive to protease K, but its antibacterial activity remained stable after treatment with acidic environment (pH 3.0–6.0), high-temperature treatment (121 °C for 30 min), and ultraviolet irradiation (4 h). After the sub-live cell assay (PI/SYTO9) and scanning electron microscopy (SEM), BLIS UI-11 inhibited the growth of bacteria by destroying the cell membrane of A. hydrophila to deform, collapse, and form holes that lead to accounting leakage. The hemolysis assay indicated that BLIS UI-11 exhibited incomplete hemolysis, suggesting its safety for application. The results showed that BLIS UI-11 produced by strain HYH-11 has great potential as an antimicrobial agent against A. hydrophila infection. Full article

Low-fishmeal feed is increasingly being adopted across the global aquaculture industry. This study evaluated dietary Clostridium butyricum and alanyl-glutamine (Ala-Gln) supplementation in juvenile triploid rainbow trout (Oncorhynchus mykiss) with a low-fishmeal diet. Four diets were tested: basal diet (SBM, 15% fishmeal and 21.6% soybean meal), SBM + 0.5% C. butyricum (CB), SBM + 1.0% Ala-Gln, and SBM + 0.5% C. butyricum + 1.0% Ala-Gln (CB-AG). Fish were fed in 500 L tanks in recirculating aquaculture systems for 8 weeks (62.52 ± 0.47 g). Each group comprised three tanks, with each tank housing 30 fish. Then 10 fish per tank were challenged with Aeromonas salmonicida. CB-AG showed significantly higher weight gain and specific growth rates than the SBM group (p < 0.05). Mortality was significantly lower in CB-AG and AG than in SBM after A. salmonicida challenge. Histomorphology revealed significant differences (p < 0.05) between CB-AG and SBM in muscularis thickness, villus width, and height. SBM sections showed inflammatory infiltration and border damage were attenuated in supplemented groups. Serum malondialdehyde (MDA) and dioxygenase (DAO) were significantly lower in CB-AG than SBM (p < 0.05), while serum and hepatic lysozyme (LZM) and hepatic superoxide dismutase (SOD) were higher. Digestive enzymes indicated significantly higher trypsin and lipase activities in CB-AG (p < 0.05). CB-AG upregulated intestinal tight junction proteins and PepT1 and downregulated pro-inflammatory mediators. Combined 0.5% C. butyricum and 1.0% Ala-Gln inclusion effectively preserved growth performance, antioxidant capacity, gut microbiome homeostasis, and intestinal health in rainbow trout on low-fishmeal diets. Full article

Furunculosis caused by Aeromonas salmonicida is one of the most common diseases in aquaculture, leading to significant economic losses. This study comprehensively investigated the dynamics of pathophysiological and histopathological disorders in rainbow trout (Oncorhynchus mykiss) infected with the moderately virulent strain A. salmonicida SL0n. Whole-genome analysis showed that strain SL0n belongs to the A. salmonicida species complex, possessing a single circular chromosome. The genome encodes a wide range of virulence factors, including adhesion systems (type IV pili, fimbriae), toxins (aerolysin, hemolysins), and a type II secretion system (T2SS), but notably lacks plasmids and a type III secretion system (T3SS). This genomic profile likely dictates a pathogenic mechanism reliant on secreted exotoxins (via T2SS), explaining the observed systemic cytotoxic damage. In an acute experiment, the 4-day LD₅₀ was determined to be 1.63 × 10⁶ CFU/fish. In a prolonged experiment, fish were injected with a sublethal dose (1.22 × 10⁶ CFU/fish—75% of LD50). The disease progressed through three consecutive stages. The early stage (1–2 DPI) was characterized by maximal bacterial load and activation of nonspecific immunity. The acute stage (4 DPI) manifested as severe septicemia and anemia, associated with systemic organ damage, which correlated with peak AST and ALT enzyme activity. The recovery stage (6 DPI) was marked by partial regression of inflammation, key biochemical and histological parameters indicated persistent liver and kidney dysfunction, signifying an incomplete recovery. These results demonstrate the pathogenesis of acute furunculosis and reveal that the genomic profile of the SL0n strain causes a sequential, systemic infection characterized by severe organ dysfunction. Full article

Using the one-strain-many-compounds (OSMAC) culturing approach, metabolomic studies, and bioassay-guided purification, we have isolated and characterised three new chlorinated natural products, agelolines B-D (1–3), together with two known compounds, ageloline A (4) and gausemycin A (5), which have been identified by high-resolution mass spectrometry and 1D and 2D NMR analyses. The preliminary evaluation of three small-scale extracts (M400, R358 and SGG) against the fish pathogen, Aeromonas salmonicida subsp. achromogenes KELDUR265-87, showed that the R358 extract displayed significant activity. Furthermore, the natural products (1–5) were evaluated against the fish pathogen Aeromonas salmonicida and human pathogens (Stenotrophomonas maltophilia L2125, Staphylococcus aureus ATCC6538P, and S. pneumoniae L44) using a serial dilution assay. Compound 3 displayed activity against Staphylococcus aureus ATCC6538P, S. maltophilia L2125, and S. pneumoniae L44 with MIC values of 6, 32, and 64 µg/mL, respectively. Interestingly, only gausemycin A (5) exhibited considerable inhibition against A. salmonicida with an MIC value of 32 µg/mL, and the activity increased by two-fold when supplemented with 0.45 mM calcium salt, while 2 and 4 showed moderate inhibition against S. maltophilia L2125. The biosynthetic pathways of compounds 1–4 were proposed. This is the first report of specific inhibition of A. salmonicida by 5. Full article

Pseudomonas fragi and Aeromonas salmonicida are major spoilage microorganisms in refrigerated grass carp. This study systematically investigated the physicochemical and metabolomic characteristics of chilled grass carp that were artificially inoculated with P. fragi and A. salmonicida in mono- and co-culture. The results indicated that P. fragi was the dominant bacterium in the co-culture of grass carp. The P. fragi-inoculated group exhibited significantly higher levels of total volatile basic nitrogen and thiobarbituric acid reactive substances (TBARs, byproducts of lipid peroxidation) compared with the A. salmonicida group. Moreover, the TBAR levels were greater in the co-culture than in the A. salmonicida group at the end of storage. A metabolomic analysis revealed that 712, 424, and 465 differential metabolites were identified in grass carp inoculated with A. salmonicida, P. fragi, and their co-culture, respectively. The metabolic pathway enrichment showed that purine metabolism, aminoacyl-tRNA biosynthesis, glycerophospholipid metabolism, and amino acid metabolism were prevalent across all three inoculated groups. A total of 175 amino acids, peptides, and analogues were identified in the A. salmonicida group, indicating that A. salmonicida played a vital role in protein degradation. P. fragi was primarily enriched in linoleic acid metabolism and the biosynthesis of unsaturated fatty acids and fatty acids, demonstrating its advantages in lipid metabolism. Additionally, six potential spoilage biomarkers were identified, including inosine, cytidine, L-aspartic acid, L-tyrosine, Pro-Ile and PS(17:1(9Z)22:0). These results elucidated the complex and competitive interactions between A. salmonicida and P. fragi in the spoilage of grass carp, providing a scientific basis for the quality monitoring of grass carp and targeted preservation strategies. Full article

Strains of Aeromonas salmonicida subsp. salmonicida, a major pathogen of salmonids, typically do not grow at temperatures above 30 °C. The effects of thermal stress on this bacterium have been extensively studied. Recently, we demonstrated that repeated exposure to cyclical thermal stress, reaching up to 37 °C, can induce permanent thermoadaptation in certain strains of this bacterium. Many aspects of this adaptation process remain poorly understood. We generated 88 thermoadapted strains of A. salmonicida subsp. salmonicida capable of sustained growth at 33 °C or higher demonstrating that prolonged heat exposure can shift a substantial proportion of psychrophilic strains toward a more mesophilic-like behavior. Although growth at 35 °C was still weaker than in naturally mesophilic A. salmonicida strains, some thermoadapted strains were able to grow up to 37 °C. North American strains harboring the genomic island AsaGEI1a, a known biomarker, exhibited a significantly reduced capacity for thermoadaptation, suggesting a possible genetic constraint, although genomic analyses indicate that AsaGEI1a itself is not directly responsible for this limitation. Genotyping and phenotypic analyses revealed that thermoadaptation is frequently associated with the loss of Type III secretion system and the A-layer, two key virulence factors. Only 7% of the thermoadapted strains retained both features. Overall, our findings suggest that thermoadaptation may represent a potential mechanism influencing the persistence of some psychrophilic A. salmonicida subsp. salmonicida strains in warming aquatic environments under climate change. Full article

Furunculosis caused by Aeromonas salmonicida poses a significant challenge to the sustainable production of maraena whitefish (Coregonus maraena). This case report outlines a multi-year disease management strategy at a European whitefish facility with two production departments, each specialising in different life-cycle stages. Recurrent outbreaks of A. salmonicida necessitated the development of effective vaccination protocols. Herd-specific immersion vaccines failed to confer protection, while injectable formulations with plant-based adjuvants caused severe adverse reactions and mortality rates exceeding 30%. In contrast, the bivalent vaccine Alpha Ject 3000, containing inactivated A. salmonicida and Vibrio anguillarum with a mineral oil adjuvant, yielded high tolerability and durable protection in over one million whitefish. Post-vaccination mortality remained low (3.3%), aligning with industry benchmarks, and furunculosis-related losses were fully prevented in both departments. Transcriptomic profiling of immune-relevant tissues revealed distinct gene expression signatures depending on vaccine type and time post-vaccination. Both the herd-specific vaccine and Alpha Ject 3000 induced the expression of immunoglobulin and inflammatory markers in the spleen, contrasted by reduced immunoglobulin transcript levels in the gills and head kidney together with the downregulated expression of B-cell markers. These results demonstrate that an optimised injectable vaccination strategy can significantly improve health outcomes and disease resilience in maraena whitefish aquaculture. Full article

Aeromonas salmonicida is an age-old fish pathogen widely distributed in seawater and freshwater environments that causes significant economic losses to the global aquaculture industry. Genetic mutations and the emergence of thermophilic strains are factors in the continuous expansion of A. salmonicida’s host range. Beyond infecting fish, A. salmonicida poses a potential threat to mammalian and human health. This review synthesizes recent global research advances concerning A. salmonicida, encompassing strain characteristics, genomic features, virulence factors, and pathogenic mechanisms, as well as the clinical manifestations in infected fish and mammals, and discusses prevention and treatment methods. Particular emphasis is placed on evaluating the potential prophylactic roles of Chinese herbs and bacteriophages against A. salmonicida infection. Furthermore, the review provides perspectives on future research directions, diagnostics, and disease management, informed by contemporary domestic and international studies on this pathogen. Full article

The skin and its products, such as the mucus, represent an important defense mechanism against infection by pathogens. Various environmental conditions can alter mucus composition and/or cells embedded in this matrix. The analysis of skin mucus is considered a useful method to evaluate the biological response of fish to stimuli. The mucus and cells can be considered suitable non-invasive biomarkers. With this preliminary study, an antibacterial capacity method was applied to cutaneous mucus samples of a European eel population. This standardized method highlighted the ability of the mucus to significantly counteract the proliferation of two bacteria, the opportunistic pathogen Aeromonas hydrophila and the primary pathogen Aeromonas salmonicida. The cytological method using skin scraping has proven to be a useful non-invasive tool, having allowed the highlighting of the two most represented cellular populations of the cutaneous covering, the epidermal cells and the goblet cells, in combination with mucous strands. Cytological findings did not disclose pathologic elements in the mucus. A broader use of these two non-invasive microbiological and cytological methods can provide useful information on fish health, indirectly contributing to the conservation of the species. Full article

Aeromonas salmonicida is a common spoilage bacterium found in refrigerated fish. In this study, a virulent bacteriophage was isolated from wastewater using A. salmonicida AS08 as the host, and it was designated as TSW001. Based on morphological characterization and whole-genome analysis, bacteriophage TSW001 was classified within the genus Tedavirus. Biological characterization revealed that TSW001 maintained a stable titer within a temperature range of 4~60 °C, a pH range of 4~9, and a salinity range of 50~1000 mM. The optimal multiplicity of infection (MOI) for TSW001 was 0.1, with a short latency period of approximately 10 min and a burst size of approximately 68 PFU/cell. When applied during the cold storage of large yellow croaker, the A. salmonicida count in the fish juice decreased by approximately 2.1~2.3 log₁₀ CFU/mL over the first two days, while the count in the fish fillets decreased by approximately 1.1~1.8 log₁₀ CFU/g. Furthermore, TSW001 demonstrated the ability to inhibit the formation of A. salmonicida biofilms. These results suggest that phage TSW001 is a promising biological antimicrobial agent for controlling A. salmonicida during the cold storage of seafood. Full article