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Mycobacterium marinum is an opportunistic pathogen inducing infection in fresh and marine water fish. This pathogen causes necrotizing granuloma like tuberculosis, morbidity and mortality in fish. The cell wall-associated lipid phthiocerol dimycocerosates, phenolic glycolipids and ESAT-6 secretion system 1 (ESX-1) are the conserved virulence determinant of the organism. Human infections with Mycobacterium marinum hypothetically are classified into four clinical categories (type I-type IV) and have been associated with the exposure of damaged skin to polluted water from fish pools or contacting objects contaminated with infected fish. Fish mycobacteriosis is clinically manifested and characterized in man by purple painless nodules, liable to develop into superficial crusting ulceration with scar formation. Early laboratory diagnosis of M. marinum including histopathology, culture and PCR is essential and critical as the clinical response to antibiotics requires months to be attained. The pathogenicity and virulence determinants of M. marinum need to be thoroughly and comprehensively investigated and understood. In spite of accumulating information on this pathogen, the different relevant data should be compared, connected and globally compiled. This article is reviewing the epidemiology, virulence factors, diagnosis and disease management in fish while casting light on the potential associated public health hazards.

Aloe vera is a traditional medicinal plant; however, its use in fish is fairly recent. We evaluated the effects of dietary A. vera on stress, innate immunity, and energy metabolism in pacu inoculated with Aeromonas hydrophila. For 7 days, 192 fish were fed with diets supplemented with 0% (control), 0.5%, 1.0%, and 2.0% of the plant extract and then inoculated with bacteria and sampled 3, 6, and 24 h later. All concentrations of A. vera reduced basal levels of cortisol, and 1.0% reduced cortisol levels more intensely 3 h after inoculation. A. vera increased the basal respiratory activity of leukocytes/RAL (0.5 and 1.0%), increased the serum levels of lysozyme (1.0 and 2.0%) 6 h after inoculation, and increased the activity of the complement system after 3 h. Spleen somatic index/SSI increased with 1.0 and 2.0% A. vera. A. vera also promoted metabolic effects. It increased basal levels of lipids in the liver and muscle, as well as hepatosomatic index (1.0%) and, 3 h after inoculation, prevented the reduction of serum triglyceride (1.0%) and reduced the mesenteric fat (1.0%). Bacterial inoculation increased RAL from 3 to 24 h and lysozyme levels at 24 h, increased serum cholesterol at 24 h, and decreased serum triglyceride from 3 to 24 h, regardless of A. vera. We concluded that A. vera offered for only 7 days had stress-reducing effects, stimulated innate immunity, protected triglyceride levels in blood, lipid depots in the liver and muscle, and directed the energy mobilization to visceral depots.

Global fish production from aquaculture has rapidly grown over the past decades, and grass carp shares the largest portion. However, hemorrhagic disease caused by grass carp reovirus (GCRV) results in tremendous loss of grass carp (Ctenopharyngodon idella) industry. During the past years, development of molecular biology and cellular biology technologies has promoted significant advances in the understanding of the pathogen and the immune system. Immunoprophylaxis based on stimulation of the immune system of fish has also got some achievements. In this review, authors summarize the recent progresses in basic researches on GCRV; viral nucleic acid sensors, high-mobility group box proteins (HMGBs); pattern recognition receptors (PRRs), Toll-like receptors (TLRs) and retinoic acid inducible gene I- (RIG-I-) like receptors (RLRs); antiviral immune responses induced by PRRs-mediated signaling cascades of type I interferon (IFN-I) and IFN-stimulated genes (ISGs) activation. The present review also notices the potential applications of molecule genetic markers. Additionally, authors discuss the current preventive and therapeutic strategies (vaccines, RNAi, and prevention medicine) and highlight the importance of innate immunity in long term control for grass carp hemorrhagic disease.

The mucosal surfaces of animals are habitat for microbes, including viruses. Bacteriophages—viruses that infect bacteria—were shown to be able to bind to mucus. This may result in a symbiotic relationship in which phages find bacterial hosts to infect, protecting the mucus-producing animal from bacterial infections in the process. Here, we studied phage binding on mucus and the effect of mucin on phage-bacterium interactions. The significance of our research is in showing that phage adhesion to mucus results in preventive protection against bacterial infections, which will serve as basis for the development of prophylactic phage therapy approaches. Besides, we also reveal that exposure to mucus upregulates bacterial virulence and that this is exploited by phages for infection, adding one additional layer to the metazoan-bacterium-phage biological interactions and ecology. This phenomenon might be widespread in the biosphere and thus crucial for understanding mucosal diseases, their outcome and treatment. Metazoans were proposed to host bacteriophages on their mucosal surfaces in a symbiotic relationship, where phages provide an external immunity against bacterial infections and the metazoans provide phages a medium for interacting with bacteria. However, scarce empirical evidence and model systems have left the phage-mucus interaction poorly understood. Here, we show that phages bind both to porcine mucus and to rainbow trout ( Oncorhynchus mykiss ) primary mucus, persist up to 7 days in the mucosa, and provide protection against Flavobacterium columnare . Also, exposure to mucus changes the bacterial phenotype by increasing bacterial virulence and susceptibility to phage infections. This trade-off in bacterial virulence reveals ecological benefit of maintaining phages in the metazoan mucosal surfaces. Tests using other phage-bacterium pairs suggest that phage binding to mucus may be widespread in the biosphere, indicating its importance for disease, ecology, and evolution. This phenomenon may have significant potential to be exploited in preventive phage therapy. IMPORTANCE The mucosal surfaces of animals are habitat for microbes, including viruses. Bacteriophages—viruses that infect bacteria—were shown to be able to bind to mucus. This may result in a symbiotic relationship in which phages find bacterial hosts to infect, protecting the mucus-producing animal from bacterial infections in the process. Here, we studied phage binding on mucus and the effect of mucin on phage-bacterium interactions. The significance of our research is in showing that phage adhesion to mucus results in preventive protection against bacterial infections, which will serve as basis for the development of prophylactic phage therapy approaches. Besides, we also reveal that exposure to mucus upregulates bacterial virulence and that this is exploited by phages for infection, adding one additional layer to the metazoan-bacterium-phage biological interactions and ecology. This phenomenon might be widespread in the biosphere and thus crucial for understanding mucosal diseases, their outcome and treatment.

Background As aquaculture continues to expand globally, diseases caused by Vibrio species are becoming increasingly prevalent. Vibriosis encompasses a range of infections, which can lead to symptoms such as skin lesions, hemorrhaging, and high mortality rates in fish and shellfish, especially in high-density farming systems, resulting in significant economic losses. Simultaneously, the extensive use of antibiotics has fostered the emergence of antibiotic-resistant bacteria, exacerbated disease outbreaks, and complicated control measures. Phage therapy, which leverages bacteriophages as natural antibacterial agents, offers a promising eco-friendly alternative to the antibiotics used in aquaculture. This study aimed to evaluate the potential of two vibriophages for phage therapy in aquaculture. Results Two virulent vibriophages, vB_VcaP_R24D and vB_VcaP_R25D, were isolated from aquaculture wastewater from seafood markets using Vibrio campbellii LMG 11216 T as the host strain. The two vibriophages were identified based on their morphology, infection dynamics, host range, genomic features, lytic activity, and environmental stability. Both phages belong to the podovirus morphotype and exhibit a lytic life cycle characterised by a short latent period (< 10 min). Genomic analyses confirmed the absence of lysogenic genes, virulence factors, and antibiotic-resistance genes, thereby ensuring genetic safety. Additionally, both phages demonstrated high stability over a broad range of temperatures (4–45 °C) and pH (3–10). Lytic curve analyses further indicated a robust lytic efficiency during the logarithmic growth phase of the vibriophages. Conclusions These biological and genomic characteristics highlight the potential of vB_VcaP_R24D and vB_VcaP_R25D as effective biocontrol agents for mitigating vibriosis in aquaculture. Although this study demonstrates their narrow host range, the possibility of phage infection in other untested hosts cannot be entirely excluded. Furthermore, the findings offer valuable insights for future research on phage-host interactions and the development of phage cocktails to improve disease management in aquaculture systems.

Edwardsiella piscicida causes significant economic losses to the aquaculture industry worldwide. Phage-based biocontrol methods are experiencing a renaissance because of the spread of drug-resistant genes and bacteria resulting from the heavy use of antibiotics. Here, we showed that the novel Edwardsiella phage EPP-1 could achieve comparable efficacy to florfenicol using a zebrafish model of Edwardsiella piscicida infection and could reduce the content of the floR resistance gene in zebrafish excreta. Specifically, phage EPP-1 inhibited bacterial growth in vitro and significantly improved the zebrafish survival rate in vivo ( P  = 0.0035), achieving an efficacy comparable to that of florfenicol ( P  = 0.2304). Notably, integrating the results of 16S rRNA sequencing, metagenomic sequencing, and qPCR, although the effects of phage EPP-1 converged with those of florfenicol in terms of the community composition and potential function of the zebrafish gut microbiota, it reduced the floR gene content in zebrafish excreta and aquaculture water. Overall, our study highlights the feasibility and safety of phage therapy for edwardsiellosis control, which has profound implications for the development of antibiotic alternatives to address the antibiotic crisis.

Increasing antibiotic resistance poses an urgent global public health threat and a serious concern worldwide. Bacteriophage (phage) therapy has been identified as a promising alternative to antibiotics for treating bacterial diseases in both humans and animals. The excessive use of antibiotics in aquaculture is a major threat to sustainable aquaculture, promoting the spread of antibiotic resistance in the aquaculture environment and the contamination of aquaculture products with antibiotic residues. Consequently, interest in alternative approaches that reduce reliance on antibiotics has grown within the aquaculture sector. As a promising alternative, extensive phage research targeted at aquaculture has demonstrated the protective efficacy of phages against diseases in aquatic animals. Although numerous studies have employed in vitro models, research supported by in vivo experiments remains scarce. Without in vivo evidence, phage therapy cannot fulfill the requirements of aquaculturists. The first part of this review outlines the bacterial diseases severely affecting the health and survival of aquatic animals. The second part provides updates on phage applications for the therapy and prophylaxis of pathogenic bacterial infection in aquatic animals, including administration routes and key accomplishments. Therefore, this review provides insights into effective real-world phage biocontrol strategies that enable sustainable aquaculture.

Antimicrobial resistance (AMR) is a growing threat to human and animal health. However, in aquatic animals—the fastest growing food animal sector globally—AMR trends are seldom documented, particularly in Asia, which contributes two-thirds of global food fish production. Here, we present a systematic review and meta-analysis of 749 point prevalence surveys reporting antibiotic-resistant bacteria from aquatic food animals in Asia, extracted from 343 articles published in 2000–2019. We find concerning levels of resistance to medically important antimicrobials in foodborne pathogens. In aquaculture, the percentage of antimicrobial compounds per survey with resistance exceeding 50% (P50) plateaued at 33% [95% confidence interval (CI) 28 to 37%] between 2000 and 2018. In fisheries, P50 decreased from 52% [95% CI 39 to 65%] to 22% [95% CI 14 to 30%]. We map AMR at 10-kilometer resolution, finding resistance hotspots along Asia’s major river systems and coastal waters of China and India. Regions benefitting most from future surveillance efforts are eastern China and India. Scaling up surveillance to strengthen epidemiological evidence on AMR and inform aquaculture and fisheries interventions is needed to mitigate the impact of AMR globally. Trends in antimicrobial resistance (AMR) in aquatic food animals are seldom documented, particularly in Asia. Here, Schar et al. review 749 point prevalence surveys, describing AMR trends in Asian aquaculture and fisheries over two decades, and identifying resistance hotspots as well as regions that would benefit most from future surveillance efforts.

Mandarin fish (Siniperca chuatsi) is a prominent freshwater species with significant economic value in China, while disease poses a major hindrance to the advancement of mandarin fish aquaculture. To date, the understanding of the prevention and management of bacterial disease in mandarin fish remains incomplete. Therefore, there is a need for more comprehensive insights into the preventive and curative strategies to address these bacterial infections. In this review, we summarize the information pertaining to the predominant bacterial pathogens such as Aeromonas spp., Flavobacterium columnare, Edwardsiella tarda, Streptococcus uberis and Vibrio cholerae in the mandarin fish aquaculture, and point out the current strategies for diagnosis and combating these bacterial pathogens, as well as deliberate on the prospective alternative treatments such as vaccines, herbal remedies, and phage therapy for the prevention and control of these bacterial diseases. Furthermore, we also highlights the importance to implement an integrated bacterial disease management (IBDM) approach for the prevention and control of these pathogenic bacteria in aquaculture.

Several farmed fish species, including carps, tilapia, salmon, and catfish, have experienced significant economic losses in aquaculture due to motile Aeromonas septicemia caused by Aeromonas hydrophila . In the present study, a novel lytic bacteriophage infecting hypervirulent Aeromonas hydrophila (vAh) was isolated and characterized. This is the first report of a phage against vAh. Phage AhFM11 demonstrated lytic activity against both vAh strains and the A. hydrophila reference strain ATCC 35654. The AhFM11 genome was sequenced and assembled, comprising 168,243 bp with an average G + C content of 41.5%. The genome did not harbor any antibiotic resistance genes. Genomic information along with transmission electron microscopy revealed that phage AhFM11 belongs to the Straboviridae family. Therapeutic application of monophage AhFM11 in fish showed 100% survival in injection, 95% in immersion and 93% in oral feeding of phage top-coated feed. Fish and chicken meat spiked with A. hydrophila and phage showed significant reduction of A. hydrophila . These findings support that phage AhFM11 can be used as a biocontrol agent against vAh as an alternative to antibiotics.