Search Results (50)

This study developed a dual-antibody sandwich ELISA detection method for Photobacterium damselae, an important pathogen in aquaculture, based on two outer membrane proteins of outer membrane protein C (OmpC) and β-barrel assembly machinery A (BamA) from the strain of P. damselae XP11. By optimizing the reaction concentrations of the capture antibody of rabbit anti-OmpC or anti-BamA and the HRP-labeled detection antibody of rabbit anti-BamA, it was found that using 1.0 μg/mL of rabbit anti-OmpC or 0.9 μg/mL of rabbit anti-BamA as capture antibodies, and 0.90 μg/mL of HRP-labeled rabbit anti-BamA as the detection antibody, could specifically detect different isolates of P. damselae. The detection limit of this method for the supernatant protein of P. damselae disrupted by ultrasound was 0.2 μg/mL. Repeatability tests showed that the coefficient of variation for detecting 25 strains of bacteria was below 9.1%. Compared with the OmpC-BamA sandwich ELISA detection method, the BamA–BamA combination exhibited better specificity. The results of this study provide an important reference for the rapid detection of P. damselae and other bacterial pathogens in aquaculture. Full article

As aquaculture expands globally, understanding immune responses in non-traditional farmed species like Octopus vulgaris under varying environmental conditions is increasingly important. This study investigated lysozyme activity, a key innate immune marker, in cell-free hemolymph of O. vulgaris following experimental challenge with four Gram-negative fish pathogens (Photobacterium damselae subsp. piscicida, P. damselae subsp. damselae, Vibrio alginolyticus, and V. anguillarum O1) at two temperatures (21 ± 0.5 °C and 24 ± 0.5 °C). These pathogens were selected because octopus farming frequently occurs near fish aquaculture facilities, raising the potential for pathogen crossover. A total of 216 wild octopuses were injected intramuscularly or intravenously and sampled on days 0, 3, and 7 post-challenge. Lysozyme activity varied by pathogen, injection route, sampling time, and temperature. A significant time- and temperature-dependent increase was observed, especially in IM-challenged groups exposed to Photobacterium species. Elevated temperatures supported a more prolonged immune response. These results highlight lysozyme as a responsive biomarker of innate immunity in O. vulgaris and emphasize the role of environmental factors in immune modulation. This work provides a foundation for disease monitoring and health management in cephalopod aquaculture. Future research should examine long-term lysozyme dynamics, broader pathogen exposure, molecular mechanisms, and additional environmental stressors such as salinity and pollution. Full article

This study evaluated the therapeutic potential of 70% ethanol extracts from six medicinal plants (Chenopodium album, Cassia tora, Cudrania tricuspidata, Dioscorea polystachya, Lonicera japonica, Solidago virgaurea subsp. gigantea) through their antibacterial, antioxidant, cytotoxic, and immunomodulatory activities, targeting applications in aquaculture. All extracts exhibited potent antibacterial activity (MIC ≤ 10 μg/mL) against Aeromonas spp. and Photobacterium damselae subsp. damselae, but limited efficacy against Streptococcus parauberis. C. tricuspidata (CTR) and C. tora (CTO) demonstrated superior antioxidant activity (IC₅₀ = 1292 μg/mL and IC₅₀ = 227 μg/mL, respectively), correlating with high polyphenol content (1498 and 1409 mg GAE/g). CTR displayed significant concentration-dependent cytotoxicity (IC₅₀ = 904.2 μg/mL), while C. album (CA) promoted cell proliferation (132.3% viability). In LPS-stimulated CHSE-214 cells, D. polystachya (DP) induced the highest IL-8 expression (207-fold), followed by Chenopodium album (CA) (194-fold IL-8, 49-fold TNF-α) and CTR (245-fold RIPK2), activating NF-κB, MAPK, and NOD-like receptor pathways critical for teleost immunity. Lonicera japonica (LJ) suppressed TNF-α (0.4-fold) and IRF1 (0.3-fold), indicating anti-inflammatory potential, while S. virgaurea subsp. gigantea (SV) showed biphasic TNF-α modulation (79-fold at 10 μg/mL, 5-fold at 100 μg/mL). These diverse bioactivities, particularly the robust immunomodulatory effects, highlight the promise of these extracts as natural therapeutic agents for fish health management in aquaculture. Full article

The presence of cetaceans along the Campania coast has always been documented. Between 2016 and 2022, out of 65 cetaceans stranded along the Campania coast, 46 were studied for bacteriological, virological, parasitological, and histopathological investigations. The results highlighted that for 59% (n = 27) of the specimens, the cause of death was of natural origin, while for only 2% (n = 1) of animals, the origin of death was ascribed to anthropic causes. Unfortunately, for 39% (n = 18) of the cetaceans, it was impossible to determine the cause of death. All the cetaceans that died of natural causes showed viral, bacterial, and parasitic infections. The primary pathogens detected were Cetacean Morbillivirus (CeMV, 65.2%, n = 30/46), Toxoplasma gondii (10.9%, n = 5/46), and Brucella ceti (8.7%, n = 4/46). The animals showed typical lesions of the isolated pathogens, such as systemic infection, meningoencephalitis, and pneumonia. Moreover, even with a lower frequency, other relevant pathogens like Photobacterium damselae, Salmonella enteritidis, Erysipelothrix rhusiopathiae, and Chlamydia abortus were isolated. These data were useful to understand the spread and circulation of these pathogens, some zoonotic, in the coastal marine waters of the Campania region. Full article

Photobacterium damselae subsp. damselae is a well-recognized marine animal pathogen. Herein, 70 P. damselae subsp. damselae isolates were investigated for quinolone susceptibility and prevalence of the genes including quinolone resistance-determining regions (QRDRs) and plasmid-mediated quinolone resistance (PMQR) genes. A total of 18/70 isolates exhibited high-level resistance, and 23/70 isolates exhibited moderate resistance according to the MIC values. QRDR analysis showed that double mutants in both GyrA (Ser⁸³Ile) and ParC (6/17 Ser⁸⁰Phe or 11/17 Ser⁸⁰Tyr) were detected in 94.4% (17/18) high-level quinolone resistance P. damselae subsp. damselae strains. PMQR detection showed that 60.0% (42/70) carried at least one PMQR (1/42 qnrB coexistence with aac(6′)-Ib-cr, 1/42 qnrS coexistence with aac(6′)-Ib-cr, 44/46 qnrS). QnrA, QnrC, qnrD and qepA were not detected in all strains. Among the 42 PMQR-positive strains, 24 showed fluoroquinolones MICs ≤ 0.5 mg/L and 13 MICs ≥ 2 mg/L, all carrying QRDR mutations. For the twenty-eight non-PMQR strains, twenty-three showed fluoroquinolone MICs ≤ 0.5 mg/L without QRDR mutations, and five MICs ≥ 2 mg/L carrying QRDR mutations. In conclusion, qnrS (qnrS2 allele) is the major PMQR widespread in P. damselae subsp. damselae isolated from eastern China; however, QRDR mutation plays a marked role in mediating fluoroquinolone resistance. Full article

Guanidine disinfectants are cationic polymers recognized for their effective sterilization properties and their ability to prevent bacterial resistance. As a result, they are widely utilized in medical, healthcare, household, and animal husbandry settings. However, the bactericidal effects and mechanisms of guanidine in marine aquaculture systems remain unclear due to the polymeric nature of guanidine ions and the complexity of marine environments. The inhibitory effects and bactericidal mechanisms of polyhexamethylene biguanide (PHMB) on key pathogens and probiotics are examined in this study. It was shown that PHMB had inhibitory effects on Vibrio parahaemolyticus (VP), Photobacterium damselae subsp. damselae (PDD), Bacillus subtilis (BS), Escherichia coli (EPEC), and Staphylococcus aureus (SAU), with minimum inhibitory concentrations (MICs) ranging from 3.91 to 125.0 µg/mL, and minimum bactericidal concentrations (MBCs) from 15.63 to 250.0 µg/mL. A stronger bactericidal effect of PHMB on marine bacteria compared to EPEC and SAU was exhibited. It was shown in ion interference experiments that the addition of calcium ions reduced the bactericidal effectiveness of PHMB against VP and PDD by 87.73% and 53.35%, respectively. At a PHMB concentration of 62.50 µg/mL, minor changes in cell surface potential energy (CSPE) were exhibited by Gram-positive bacteria (SAU and BS), while more significant alterations were shown by Gram-negative pathogens. It was revealed by propidium iodide staining and scanning electron microscopy (SEM) analysis that the bacterial cell membrane was directly disrupted by PHMB. DNA and RNA release analysis further revealed that following PHMB treatment, changes in membrane permeability were exhibited by Gram-negative pathogens, with a significant increase in extracellular DNA content as PHMB concentration increased. No such effect was observed in Gram-positive bacteria. Additional evidence was provided by the findings that PHMB effectively inhibits bacterial pathogens in mariculture systems, with a significantly stronger inhibitory effect on Gram-negative pathogens than on Gram-positive bacteria. These results indicated that PHMB could serve as a new antimicrobial agent in mariculture. Full article

The Gram-negative marine bacterium Photobacterium damselae subsp. piscicida (Pdp) is a pathogen responsible for pseudotuberculosis in various fish species, posing significant threats to aquaculture. Pdp employs strong virulence mechanisms, one of which is the production of the piscibactin siderophore, which plays a key role in iron acquisition from the host. In this study, we evaluated the ferrophilic properties of the Pdp strain EKL1 in relation to growth and biofilm production. In vitro iron limitation significantly suppressed biofilm formation and planktonic growth in EKL1. We then investigated the anti-biofilm activity of deferoxamine (DFO), an iron chelator used to treat transfusion-induced iron overload in thalassemia patients, against EKL1. DFO strongly inhibited EKL1 biofilm production (by 82.1%), suggesting that iron chelation therapy could be an effective strategy to prevent Pdp-induced photobacteriosis outbreaks. Finally, we characterized the iron-bound form of piscibactin through extensive spectroscopic analyses of the siderophore produced by EKL1. Our findings contribute to the development of novel piscibactin-targeted inhibitors, advancing siderophore-based anti-virulence strategies against Pdp. Full article

Photobacterium damselae subsp. Piscicida (PDP), a marine bacterium, has been reported to infect a variety of economically important marine species worldwide. Understanding the occurrence and pathogenicity of PDP is crucial for effective disease control and ensuring the success of aquaculture operations. In late August 2023, an epidemic outbreak of P. damselae subsp. piscicida DQ-SS1, accompanied by significant mortality, was recorded in cage-cultured black rockfish (Sebastes schlegelii) located on Daqin Island for the first time. Genomic analysis revealed that DQ-SS1 possesses 2 chromosomes, with a total size of 4,510,445 bp and 3923 predicted CDSs. Pathogenic genes analysis identified 573 and 314 genes related to pathogen–host interactions and virulence, respectively. Additionally, DQ-SS1 displayed susceptibility to 15 antimicrobials, was resistant to 11 antimicrobials, and was intermediately sensitive to four antibiotics. Meanwhile, the in vitro assay revealed that the extracellular products (ECP) of DQ-SS1 were lethal to macrophages and exhibited hemolysin, lipase, and amylase activities. Moreover, DQ-SS1 also demonstrated the ability to survive in fish serum and resist complement-mediated killing. The in vivo assay showed that the infected fish exhibited severe histopathological alterations, such as the infiltration of inflammatory cells, cellular degeneration and necrosis, and loose cell aggregation. Lastly, the in vivo infection assays revealed the LD₅₀ of DQ-SS1 was 1.7 × 10³ CFU/g. This is the first study to elucidate the pathogenicity and genomic characteristics of multidrug-resistant PDP in cage-cultured S. schlegelii, which contributes to the advancement of diagnostic and preventative strategies for this disease in marine-cultured fishes and provides information for an in-depth study of the pathogenic mechanism of PDP. Full article

A chemical investigation of the soft coral Lobophytum sp. and the sponge Xestospongia sp. from the South China Sea led to the isolation of five steroids, including two new compounds (1 and 4) and one known natural product (3). Compounds 1–3 were derived from the soft coral Lobophytum sp., while 4 and 5 were obtained from the sponge Xestospongia sp. The structures of these compounds were determined by extensive spectroscopic analysis, the time-dependent density functional theory–electronic circular dichroism (TDDFT-ECD) calculation method, and comparison with the spectral data previously reported in the literature. The antibacterial and anti-inflammatory activities of isolated compounds were evaluated in vitro. Compounds 1–3, 4, and 5 exhibited weak antibacterial activity against vancomycin-resistant Enterococcus faecium G1, Streptococcus parauberis KSP28, Photobacterium damselae FP2244, Lactococcus garvieae FP5245, and Pseudomonas aeruginosa ZJ028. Moreover, compound 3 showed significant anti-inflammatory activity by inhibiting lipopolysaccharide (LPS)-induced NO production in RAW 264.7 cells, with an IC₅₀ value of 13.48 μM. Full article

Two new cembrane-derived tricyclic diterpenes belonging to the sarcophytin family, namely 4a-hydroxy-chatancin (1) and sarcotoroid (2), together with two known related ones (3 and 4), were isolated from the soft coral Sarcophyton tortuosum collected off Ximao Island in the South China Sea. The structures of the new compounds were elucidated by extensive spectroscopic analysis, a quantum mechanical nuclear magnetic resonance (QM-NMR) method, a time-dependent density functional theory electronic circular dichroism (TDDFT-ECD) calculation, X-ray diffraction analysis, and comparison with the reported data in the literature. A plausible biosynthetic pathway of compounds 1–4 was proposed, involving undergoing a transannular Diels–Alder cycloaddition. In the bioassay, the new compound 1 displayed significant inhibitory activities against the fish pathogens Streptococcus parauberis KSP28, oxytetracycline-resistant Streptococcus parauberis SPOF3K, and Photobacterium damselae FP2244, with MIC values of 9.1, 9.1, and 18.2 μg/mL, respectively. Furthermore, by conducting a luciferase reporter assay on rat liver Ac2F cells, compounds 1, 3, and 4 were evaluated for peroxisome proliferator-activated receptor (PPAR) transcriptional activity, and compound 3 showed selective PPAR-β agonist activity at a concentration of 10 μΜ. Full article

Essential oils (EOs), regarded as secondary metabolites from plants, possess effective antibacterial properties. This study investigates the antibacterial efficacy of seven citrus EOs against six spoilage bacteria: Vibrio parahaemolyticus, V. harveyi, Photobacterium damselae, Shewanella putrefaciens, Carnobacterium divergens, and Lactobacillus pentosus. The antibacterial activity of these EOs was evaluated using solid- and vapor-phase applications. All tested EOs demonstrated effective antibacterial activity at a concentration of 294 μL/L against Gram-negative bacteria. Notably, lemon and orange EOs exhibited dose-dependent inhibition in both solid- and vapor-phase applications, with minimum effective concentrations ranging from 29.4 to 58.8 μL/L. Following treatment with lemon and orange EOs for 6 h at 1/4 minimum inhibitory concentration, leakage of intracellular DNA and proteins was observed, indicating damage to the cell membrane/wall. Proteomic analysis revealed distinct mechanisms: lemon EO impaired bacterial antioxidant defenses, while orange EO disrupted cell division, leading to reduced bacterial viability. These findings provide valuable insights into the potential of different EO application forms in controlling spoilage bacteria. Full article

Photobacterium damselae subsp. damselae (Pdd) is an increasingly common bacterium in post-mortem diagnostics of beached marine mammals, but little is known about its precise etiological responsibility. To estimate the prevalence of Pdd in stranded cetaceans from 2017 to 2022 on the Ligurian coast (Pelagos Sanctuary), we tested tissues from 53 stranded individuals belonging to four cetacean species. DNA extracts from cetacean tissue were screened using a polymerase chain reaction (PCR) assay targeting the Pdd ureC gene. Positive samples were screened by PCR for dly, hlyA_pl and hlyA_ch hemolysin genes, which were confirmed by sequencing. Twenty-two out of 53 (41.5%) cetaceans analyzed by PCR were confirmed for Pdd DNA in at least one tissue among those analyzed. Five of these cetaceans were positive for at least one of the hemolysin genes tested. In all Pdd-positive cetaceans, other pathogens that were considered responsible for the causa mortis of the animals were also found. The results provide new information on the spread of Pdd in cetaceans and support the thesis that Pdd might be an opportunistic agent that could contribute to worsening health conditions in subjects already compromised by other pathogens. However, further studies are needed to investigate and deepen this hypothesis. Full article

In mariculture facilities, bacterial infections pose significant production challenges, with potentially catastrophic impacts on fish species. Bacterial co-infections are a widespread phenomenon in the natural marine environment, although their impact on aquatic organisms remains poorly investigated. This study aimed to detail the pathological findings associated with a natural bacterial co-infection caused by three different pathogens, namely Photobacterium damselae subsp. piscicida, Tenacibaculum maritimum and Vibrio sp., as the cause of mass mortality in European sea bass. The fish had been reared in open-net cages in Sicily and later transferred for experimental research purposes to a user establishment after immunization with an inactivated vaccine. Macroscopic, cytological and histopathological examinations were performed on 109 animals, and bacterial species were identified by the 16S rRNA gene. Overall, ulcerative skin lesions, necrotizing myositis and tail rot with occasional tail loss were associated with tenacibaculosis and vibriosis, while P. damselae subsp. piscicida mainly caused granulomatous inflammation in the spleen and head kidney. Finally, an injection site reaction due to the oil-adjuvanted vaccine administered intraperitoneally was observed in the abdominal fat. Understanding the impact of bacterial pathogens is essential to manage the health and welfare of farmed fish, and the importance of a good health monitoring program cannot be overstated to avoid outbreaks and the possible emergence of new pathogens due to the intensification of the production systems, antibiotic resistance and climate changes. The study would also highlight the importance of the quarantine period when animals supplied for research come from aquaculture farms and how the main goal in the near future should be to better define the procedures to provide completely pathogen-free animals. Full article

To explore the molecular mechanisms of the Litopenaeus vannamei response to infection by Photobacterium damselae, reveal its immune response and energetic metabolic effect, and provide a valuable genetic data source for the scientific prevention and control of Vibrio infection, transcriptomic analysis, RT-qPCR, and physiological and biochemical tests were conducted. The results showed that the expression of key genes involved in lipid and carbohydrate transport, such as apolipoprotein and TPS, was upregulated after pathogenic infection, which brought the accumulation of triacylglycerol and trehalose into the hemolymph. Additionally, the pathogenic infection selectively triggered an immune response in infected L. vannamei, activating certain immune pathways, such as the serpins and MAPK pathways. The pathogenic infection suppressed the activity of phenoloxidase (PO), and the prophenoloxidase (PPO) cascade responses were suppressed by the invasive bacteria. This paper will help us understand the energetic metabolism, immune response, and activation of the immune recognition response after pathogenic infection by P. damselae, and it lays a theoretical foundation for the biological prevention and control of P. damselae infection. Full article

Spotted sea bass (Lateolabrax maculatus) is a high-economic-value aquacultural fish widely distributed in the coastal and estuarine areas of East Asia. In August 2020, a sudden outbreak of disease accompanied by significant mortality was documented in L. maculatus reared in marine cage cultures located in Nanhuang island, Yantai, China. Two coinfected bacterial strains, namely, NH-LM1 and NH-LM2, were isolated from the diseased L. maculatus for the first time. Through phylogenetic tree analysis, biochemical characterization, and genomic investigation, the isolated bacterial strains were identified as Vibrio harveyi and Photobacterium damselae subsp. piscicida, respectively. The genomic analysis revealed that V. harveyi possesses two circular chromosomes and six plasmids, while P. damselae subsp. piscicida possesses two circular chromosomes and two plasmids. Furthermore, pathogenic genes analysis identified 587 and 484 genes in V. harveyi and P. damselae subsp. piscicida, respectively. Additionally, drug-sensitivity testing demonstrated both V. harveyi and P. damselae subsp. piscicida exhibited sensitivity to chloramphenicol, ciprofloxacin, ofloxacin, orfloxacin, minocycline, doxycycline, tetracycline, and ceftriaxone. Moreover, antibiotic resistance genes were detected in the plasmids of both strains. Extracellular product (ECP) analysis demonstrated that both V. harveyi and P. damselae subsp. piscicida can produce hemolysin and amylase, while V. harveyi additionally can produce caseinase and esterase. Furthermore, infected fish displayed severe histopathological alterations, including infiltration of lymphocytes, cellular degeneration and necrosis, and loose aggregation of cells. Artificial infection assays determined that the LD₅₀ of P. damselae subsp. piscicida was 3 × 10⁵ CFU/g, while the LD₅₀ of V. harveyi was too low to be accurately evaluated. Furthermore, the dual infection of V. harveyi and P. damselae subsp. piscicida elicits a more rapid and pronounced mortality rate compared to single challenge, thereby potentially exacerbating the severity of the disease through synergistic effects. Ultimately, our findings offer compelling evidence for the occurrence of coinfections involving V. harveyi and P. damselae subsp. piscicida in L. maculatus, thereby contributing to the advancement of diagnostic and preventative measures for the associated disease. Full article