Multidrug-resistant Aeromonas bacteria prevalence in Nile tilapia broodstock

Advances and Challenges in Aeromonas hydrophila Vaccine Development: Immunological Insights and Future Perspectives

Aeromonas hydrophila presents a significant threat to global aquaculture due to its ability to infect freshwater and marine fish species, leading to substantial economic losses. Effective mitigation methods are essential to address these challenges. Vaccination has emerged as a promising strategy to reduce A. hydrophila infections; however, it faces several obstacles, including variability in immune responses, pathogen diversity, and environmental factors affecting vaccine efficacy. To enhance vaccine performance, researchers focus on adjuvants to boost immune responses and develop multivalent vaccines targeting multiple A. hydrophila strains. Tailoring vaccines to specific environmental conditions and optimizing vaccination schedules can further address the challenges posed by pathogen diversity and variable immune responses. This review provides an in-depth analysis of the immunological hurdles associated with A. hydrophila vaccine development. Current vaccine types-live attenuated, inactivated, subunit, recombinant, and DNA-exhibit diverse mechanisms for stimulating innate and adaptive immunity, with varying levels of success. Key focus areas include the potential of advanced adjuvants and nanoparticle delivery systems to overcome existing barriers. The review also highlights the importance of understanding host-pathogen interactions in guiding the development of more targeted and effective immune responses in fish. Complementary approaches, such as immunostimulants, probiotics, and plant-based extracts, are explored as adjuncts to vaccination in aquaculture health management. Despite notable progress, challenges remain in translating laboratory innovations into scalable, cost-effective solutions for aquaculture. Future directions emphasize the integration of advanced genomic and proteomic tools to identify novel antigen candidates and the need for industry-wide collaborations to standardize vaccine production and delivery. Addressing these challenges can unlock the potential of innovative vaccine technologies to safeguard fish health and promote sustainable aquaculture practices globally.

Anti-inflammatory, immunostimulant and antimicrobial properties of tannic acid in the diet of Oreochromis niloticus infected with Aeromonas hydrophila

The study aimed to assess the impact of dietary supplementation with tannic acid on the growth, health, and survival of Oreochromis niloticus following exposure to Aeromonas hydrophila. A total of 320 fish were divided into 16 tanks and assigned to four treatment groups: feed with 0.2 % tannic acid (TA0.2 %), 0.4 % tannic acid (TA0.4 %), 0.8 % tannic acid (TA0.8 %), or no tannic acid (Control0%), with each treatment replicated four times, over a 50-day period. At the end of the 50-day period, biological samples were collected from the fish, which were then intraperitoneally injected with A. hydrophila. No significant differences in growth performance were detected between treatments. As expected, levels of total leukocytes, lymphocytes, monocytes, hemoglobin, and mean corpuscular hemoglobin concentration (MCHC) were notably higher in the blood of the fish after infection, regardless of the treatment received. During both the pre- and post-infection periods, monocytes were more abundant in the TA0.2 % and TA0.8 % treatments compared to the TA0.4 % treatment. Additionally, there was a significant interaction between the factors affecting thrombocytes, neutrophils, basophils, hemoglobin, and MCHC. Thrombocytosis and neutrophilia were significantly greater in the TA0.8 % treatment pre-infection than in the post-infection and control group. Conversely, a higher number of basophils were observed in the post-infection period in the TA0.8 % treatment group compared to the pre-infection period. Total plasma protein levels decreased significantly in the post-infection period, regardless of tannic acid supplementation levels, while immunoglobulin levels increased after exposure to A. hydrophila. Histological analyses revealed a significant increase in the perimeter and number of intestinal villi in the TA0.4 % treatment group before infection. The number of goblet cells also increased in the control group (0 %), TA0.4 %, and TA0.8 % before infection. In splenic tissue, the TA0.4 % treatment resulted in a reduction in eosinophilic and mononuclear infiltrates, as well as decreased congestion and vacuolation. Hemosiderin levels were lower in the TA0.4 % and TA0.2 % treatment groups. In the liver, lymphocytic infiltrates were reduced in the TA0.2 % and TA0.4 % treatment groups, and portal vein congestion was decreased in the TA0.2 % post-infection and TA0.4 % pre-infection groups. Post-infection survival rates were significantly higher (p < 0.05) in the TA0.4 % treatment group (91 %) compared to the TA0.8 % treatment group (85 %) and the control group (71 %). The results of the present study show that tannic acid has a positive effect on the immune system of Nile tilapia. This is supported by improvements in innate immunity in the blood, as well as the antimicrobial and anti-inflammatory effects seen in histological analyses. Therefore, it is suggested to use a 0.4 % tannic acid dose for dietary supplementation of Nile tilapia, along with further studies on the potential benefits of this food additive for tilapia.

Necrotizing Fasciitis-Induced Septic Shock due to Aeromonas hydrophila: A Case Report

Aeromonas hydrophila (A. hydrophila), a Gram-negative bacterium commonly found in aquatic environments, has the capacity to be transmitted to humans through consumption of contaminated fish, water, or seafood. In this study, we present a case report concerning a 77-year-old female patient who experienced an acute exacerbation of chronic heart failure, subsequently developing severe septic shock due to necrotizing fasciitis caused by A. hydrophila. Infections caused by A. hydrophila are more prevalent during warmer months, particularly in regions characterized by dense aquaculture or the presence of natural water bodies. The excessive use of antibiotics in aquaculture has contributed to the emergence of antibiotic-resistant A. hydrophila strains. The proliferation of multidrug-resistant A. hydrophila presents a significant challenge for clinicians. In the context of atypical bacterial infections, the initial empiric therapy typically involves the use of third-generation cephalosporins in conjunction with quinolone antibiotics. In the present case, the patient's successful recovery was achieved through the administration of a combination of cefoperazone/sulbactam and levofloxacin, as determined by sensitivity testing. This case study underscores the critical importance of considering A. hydrophila infection in patients with septic shock who present with necrotizing fasciitis.

Deciphering spread of quinolone resistance in mariculture ponds: Cross-species and cross-environment transmission of resistome

Mariculture is known to harbor antibiotic resistance genes (ARGs), which can be released into marine ecosystems via oceanic farming ponds, posing a public health concern. In this study, metagenomic sequencing was used to decipher the profiles of quinolone-resistant microbiomes and the mechanisms of quinolone resistance in sediment, seawater, and fish gill samples from five mariculture ponds. Residues of both veterinary-specific (enrofloxacin and sarafloxacin) and prohibited quinolones (ofloxacin, ciprofloxacin, pefloxacin, norfloxacin, and lomefloxacin) were detected. We identified a total of 285 subtypes of ARGs across all samples. Pathogens played a crucial role in the prevalence and distribution of these ARGs. Out of the annotated 629 bacterial species, 42 were identified as pathogenic, predominantly belonging to the Proteobacteria phylum. Notably, the Acinetobacter genus was prevalent in the gills and exhibited correlations with various ARGs. The presence of the plasmid-mediated quinolone resistance (PMQR) genes in various bacterial species and the identification of sulfonamide resistance genes across different samples indicated the potential for cross-species and cross-environment transmission of ARGs. Metagenomic binning revealed that Exiguobacterium harbored five ARGs (vanA, vanB, fexA, msr(G), mefF), while Shewanella carried six ARGs (blaOXA-436, adeF, qacl, ANT (2'')-Ia, dfrA1, rsmA). Mutations in gyrA and parC contributed to quinolone resistance in these multidrug-resistant Exiguobacterium and Shewanella. Our findings suggest a potential for ARG transmission across various bacterial species and environments in mariculture. This study emphasized the risk of resistance spread within the mariculture ecosystem.

Efficacy of Feed-Based Genome-Free Bacterial Vaccine Against Aeromonas hydrophila Infection in Red Tilapia (Oreochromis sp.)

Aeromonas hydrophila causes motile Aeromonas septicemia (MAS), a disease with a high mortality rate in tilapia culture. Feed-based vaccines with the incorporation of inactivated whole-cell bacteria into the feed offer promising tools to control MAS. Currently, the incorporation of genome-free bacteria as bacterial vaccine through the implementation of SimCells® technology into the feed has become a particular interest. Background/Objectives: This study investigates the efficacy of a feed-based vaccine incorporating genome-free A. hydrophila (FBV-GFAH) against MAS infection in red tilapia. Methods: The vaccine was prepared and delivered at 5% fish body weight for three consecutive days in weeks 0 (prime vaccination) and 2 (first booster vaccination), orally. Throughout a five-week experimental period, the immune-related genes (IL-1β, MHC-II, CD4, IgT, and IgM) expression in the hindgut and head kidney of the fish was determined using RT-qPCR assay. Lysozyme (serum) and overall IgM (serum, gut lavage, and skin mucus) productions were also detected. Results: Fish vaccinated with FBV-GFAH showed a significant (p ≤ 0.05) improvement in relative percent survival compared with unvaccinated fish following bacterial challenge. FBV-GFAH induced the expression of immune-related genes in the hindgut and head kidney, especially after booster vaccination. Furthermore, serum lysozyme activity and overall IgM production in serum, skin mucus, and gut lavage were also significantly (p ≤ 0.05) improved in the FBV-GFAH vaccinated fish than the unvaccinated fish. Conclusions: This study showed that FBV-GFAH is a promising feed-based vaccine technology to control MAS in cultured tilapia.

Selenium Nanoparticles Ameliorate Adverse Impacts of Aflatoxin in Nile Tilapia with Special Reference to Streptococcus agalactiae Infection

Aflatoxin B1 (AFB1) is a plant-origin toxin that could induce oxidative stress in fish. The micromineral selenium (Se) possesses well-documented antioxidant properties. To assess the ameliorative effects of SeNPs (1 mg/kg fish feed) on oxidative stress induced by AFB1 (500 μg/kg fish feed), Nile tilapia (32.2±1.7 g body weight) were distributed randomly and even in six groups for 8-week feeding trial. Live enzymes, AST, ALT, and ALP levels were increased in the serum of fish fed AFB1-contaminated diet, and the addition of SeNPs could restore normal values compared to the control. The gene expression of antioxidant enzymes, superoxide dismutase (SOD) enzyme and catalase (CAT) enzyme, and DNA fragmentation were significantly increased in response to aflatoxin exposure, while dietary SeNPs could mitigate the generated oxidative stress. The innate immunity, serum antibacterial activity (SAA), oxidative burst activity (OBA), phagocytic activities (PA and PI), and gene expression of cytokines (interleukin (IL)-1β, heat shock protein70 (Hsp), and tumor necrosis factor (TNF)-α) revealed a status of immunosuppression in Nile tilapia fed on AFB1-contaminated diet. These findings showed that fish became more vulnerable to Streptococcus agalactiae infection with a high mortality rate while dietary SeNPs provided a high relative protection level (RPL). From the obtained findings, SeNPs could mitigate the oxidative stress induced by feeding the AFB1 diet and could boost the immunity of stressed Nile tilapia.

Immune response and bacterial resistance of Oreochromis niloticus against bacterial fish pathogen with saffron diet

Background

The global demand for fish and fish products has increased due to population growth and healthier food choices. However, bacterial infections caused by Aeromonas species pose a challenge. Antibiotics are crucial for disease control, but multidrug resistance is a global concern. Eco-friendly disease management methods, like saffron, have been identified as potential treatments.

Aim

The study investigated the effects of dietary supplementation with Saffron on Nile tilapia's growth performance, immune response, and disease resistance.

Methods

180 fish were acclimatized for 2 weeks and randomly allocated into three groups. The first group served as a control, while the other two groups were fed a basal diet supplemented with Saffron at 1.5 g/kg (T1) and 0.5 g/kg (T2), respectively, for 12 weeks. Biochemical blood parameters. Histopathology and immunohistochemical studies were performed on the gills, liver, and spleen tissues.

Results

Following the feeding trial with Saffron supplement, especially at higher levels enhanced weight gain, Growth performance, plasma total protein, and globulin showed higher levels in fish groups with dietary with Saffron at 1.5 g/kg (T1) and 0.5 g/kg (T2) than in fish fed the control diet Regulate the immune response in lysozyme activity and immunoglobulin M (IgM). Regeneration of gills, liver, and spleen tissues was noticed Furthermore, saffron-treated organs exhibited immunoreactivity to TNF-α was mostly seen in the liver and gills, although it was also somewhat in the kidney and spleen and CD68, the group were challenged with Aeromonas hydrophila, improved its defenses against A. hydrophila, immunity, and disease resistance than the control group.

Conclusion

The results showed that saffron supplementation significantly increased the survival rate of fish challenged with A. hydrophila. It also enhanced the immune response of fish, as evidenced by increased levels of serum immunoglobulins and lysozyme activity. These findings suggest that saffron supplementation could be a promising strategy for the prevention and treatment of bacterial infections in aquaculture.

Use of Matrix-Assisted and Laser Desorption/Ionization Time-of-Flight Technology in the Identification of Aeromonas Strains Isolated from Retail Sushi and Sashimi

The genus Aeromonas includes well-known pathogenic species for fishes and humans that are widely distributed in the aquatic environment and foods. Nowadays, one of the main issues related to wild Aeromonas isolates is their identification at the species level, which is challenging using classical microbiological and biomolecular methods. This study aims to test MALDI-TOF MS technology in the identification of Aeromonas strains isolated from n. 60 retail sushi and sashimi boxes using an implemented version of the SARAMIS software V4.12. A total of 43 certified Aeromonas strains were used to implement the SARAMIS database by importing the spectra obtained from their identification. The original SARAMIS version (V4.12) failed to recognize 62.79% of the certified strains, while the herein-implemented version (V4.12plus) allowed the identification of all the certified strains at least to the genus level with a match of no less than 85%. Regarding the sushi and sashimi samples, Aeromonas spp. was detected in n. 18 (30%) boxes. A total of 127 colonies were identified at the species level, with A. salmonicida detected as the most prevalent species, followed by A. bestiarum and A. caviae. Based on the results of the present study, we could speculate that MALDI-TOF technology could be a useful tool both for the food industry to monitor product contamination and for clinical purposes to make diagnoses effectively and quickly.

Cross-sectional analysis of risk factors associated with Mugil cephalus in retail fish markets concerning methicillin-resistant Staphylococcus aureus and Aeromonas hydrophila

Introduction

Aeromonas hydrophila and methicillin-resistant Staphylococcus aureus (MRSA) are potent bacterial pathogens posing major hazards to human health via consuming fish harboring these pathogens or by cross-contamination beyond the contaminated environment. The aim of this study was to determine risk variables associated with the presence of certain pathogenic bacteria from Mugil cephalus fish in retail markets in Egypt. The virulence genes of A. hydrophila and S. aureus were also studied. Furthermore, the antibiotic sensitivity and multidrug resistance of the microorganisms were evaluated.

Methods

In a cross-sectional investigation, 370 samples were collected from mullet skin and muscle samples, washing water, fish handlers, knives, and chopping boards. Furthermore, fish handlers' public health implications were assessed via their response to a descriptive questionnaire.

Results

S. aureus and Aeromonas species dominated the investigated samples with percentages of 26.76% and 30.81%, respectively. Furthermore, A. hydrophila and MRSA were the predominant recovered bacterial pathogens among washing water and knives (53.85% and 46.66%, respectively). The virulence markers aerA and hlyA were found in 90.7% and 46.5% of A. hydrophila isolates, respectively. Moreover, the virulence genes nuc and mec were prevalent in 80% and 60% of S. aureus isolates, respectively. Antimicrobial susceptibility results revealed that all A. hydrophila isolates were resistant to amoxicillin and all MRSA isolates were resistant to amoxicillin and ampicillin. Remarkably, multiple drug resistance (MDR) patterns were detected in high proportions in A. hydrophila (88.37%) and MRSA (100%) isolates. The prevalence of Aeromonas spp. and S. aureus had a positive significant correlation with the frequency of handwashing and use of sanitizer in cleaning of instruments. MRSA showed the highest significant prevalence rate in the oldest age category.

Conclusion

The pathogenic bacteria recovered in this study were virulent and had a significant correlation with risk factors associated with improper fish handling. Furthermore, a high frequency of MDR was detected in these pathogenic bacteria, posing a significant risk to food safety and public health.

Long-term exposure to lead nitrate and zinc sulfate Nile tilapia impact the Aeromonas hydrophila treatment

BACKGROUND

Pollution with heavy metals (HMs) is time- and concentration-dependent. Lead and zinc pollute the aquatic environment, causing severe health issues in aquatic animals.

MATERIALS AND METHODS

Nile tilapia, the predominant cultured fish in Egypt, were experimentally exposed to 10% of LC50 of lead nitrate (PbNO3) and zinc sulfate (ZnSO4). Samples were collected in three different periods, 4, 6, and 8 weeks, in addition to a trial to treat the experimental fish infected with Aeromonas hydrophila, with an antibiotic (florfenicol).

RESULTS

Liver enzymes were linearly upsurged in a time-dependent manner in response to HMs exposure. ALT was 92.1 IU/l and AST was 82.53 IU/l after eight weeks. In the eighth week of the HMs exposure, in the hepatic tissue, the levels of glutathione peroxidase (GPx), catalase (CAT), and metallothionein (MT) were increased to 117.8 U/mg prot, 72.2 U/mg prot, and 154.5 U/mg prot, respectively. On exposure to HMs, gene expressions of some cytokines were linearly downregulated in a time-dependent manner compared to the control. After four weeks of exposure to the HMs, the oxidative burst activity (OBA) of immune cells was decreased compared to the control 9.33 and 10.3 cells, respectively. Meanwhile, the serum bactericidal activity (SBA) significantly declined to 18.5% compared to the control 32.6% after eight weeks of exposure. Clinical signs of A. hydrophila infection were exaggerated in polluted fish, with a mortality rate (MR) of 100%. The re-isolation rate of A. hydrophila was decreased in fish treated with florfenicol regardless of the pollution impacts after eight weeks of HMs exposure.

CONCLUSION

It could be concluded that the immune suppression and oxidative stress resulting from exposure to HMs are time-dependent. Clinical signs and post-mortem lesions in polluted fish infected with A. hydrophila were prominent. Infected-Nile tilapia had weak responses to florfenicol treatment due to HMs exposure.

In vitro determination of probiotic efficacy of Bacillus subtilis TLDK301120C24 isolated from tilapia against warm water fish pathogens and in vivo validation using gnotobiotic zebrafish model

Eco-friendly alternatives such as probiotics are needed to prevent economically relevant infectious diseases for a successful disease-free harvest in aquaculture. The use of antibiotics has been the favored practice, but its empirical and indiscriminate use has led to antibiotic resistance in the aquatic environment and residues in the food fish. With this rationale, a probiotic was isolated from tilapia, a commercially important cultured fish worldwide. The characteristics of the probiotic were checked against common bacterial pathogens affecting aquaculture. In vitro tests demonstrated the inhibitory effects of the isolated probiotic on the growth of Aeromonas hydrophila, Edwardsiella tarda, Vibrio anguillarum, and V. alginolyticus. The candidate probiotic, referred to as TLDK301120C24, was identified as Bacillus subtilis by a battery of biochemical tests and genotypic confirmation by 16S rDNA sequencing. The in vitro results revealed the ability of the probiotic to withstand the gut conditions that included pH range of 3-9, salt concentration of 0.5-6%, and bile salt concentration of up to 6%. The isolate could hydrolyze starch (12-14 mm clearance zone), protein (20-22 mm clearance zone), and cellulose (22-24 mm clearance zone). Further, the inhibitory ability of the probiotic against aquatic pathogens was determined in vivo using gnotobiotic zebrafish by employing a novel approach that involved tagging the probiotic with a red fluorescent protein and the pathogens with a green fluorescent protein, respectively. The colonizing ability of probiotics and its inhibitory effects against the pathogens were evaluated by fluorescence microscopy, PCR, and estimation of viable counts in LBA + Amp plates. Finally, the competitive inhibition and exclusion of fish pathogens A. hydrophila and E. tarda by B. subtilis was confirmed semi-quantitatively, through challenge experiments. This study shows the potential of B. subtilis as a probiotic and its excellent ability to inhibit major fish pathogens in vivo and in vitro. It also shows promise as a potent substitute for antibiotics.

First Report of Aeromonas veronii as an Emerging Bacterial Pathogen of Farmed Nile Tilapia (Oreochromis niloticus) in Brazil

Brazil is one of the world's leading producers of Nile tilapia, Oreochromis niloticus. However, the industry faces a major challenge in terms of infectious diseases, as at least five new pathogens have been formally described in the last five years. Aeromonas species are Gram-negative anaerobic bacteria that are often described as fish pathogens causing Motile Aeromonas Septicemia (MAS). In late December 2022, an epidemic outbreak was reported in farmed Nile tilapia in the state of São Paulo, Brazil, characterized by clinical signs and gross pathology suggestive of MAS. The objective of this study was to isolate, identify, and characterize in vitro and in vivo the causative agent of this epidemic outbreak. The bacterial isolates were identified as Aeromonas veronii based on the homology of 16S rRNA (99.9%), gyrB (98.9%), and the rpoB gene (99.1%). A. veronii showed susceptibility only to florfenicol, while it was resistant to the other three antimicrobials tested, oxytetracycline, enrofloxacin, and amoxicillin. The lowest florfenicol concentration capable of inhibiting bacterial growth was ≤0.5 µg/mL. The phenotypic resistance of the A. veronii isolate observed for quinolones and tetracycline was genetically confirmed by the presence of the qnrS2 (colE plasmid) and tetA antibiotic-resistant genes, respectively. A. veronii isolate was highly pathogenic in juvenile Nile tilapia tested in vivo, showing a mortality rate ranging from 3 to 100% in the lowest (1.2 × 104) and highest (1.2 × 108) bacterial dose groups, respectively. To our knowledge, this study would constitute the first report of highly pathogenic and multidrug-resistant A. veronii associated with outbreaks and high mortality rates in tilapia farmed in commercial net cages in Brazil.

Impacts of dietary zinc oxide nanoparticles on the growth and immunity of Nile tilapia could be ameliorated using Nigella sativa oil

BACKGROUND

Zinc nanoparticles are documented to be harmful to fish because their accumulation in fish bring about many irreversible changes in their health. Nigella sativa and its oil have been endorsed in aquaculture to improve fish health.

METHODS

Two hundred seventy experimental fish (113 ± 5 g body weight) were divided into 6 groups G1-6; control fish fed a diet without any treatment (G1), 0.3% of NSO (G2), 0.5% of NSO (G3), ZnO NPs (40 mg/kg diet) (G4), 0.3% of NSO and ZnO NPs (40 mg/kg diet) (G5), 0.5% of NSO and ZnO NPs (40 mg/kg diet) (G6), the trial lasted for six weeks.

RESULTS

Growth performance was enhanced in fish received diets containing NSO, final weight (FW), weight gain (WG), daily weight gain (DWG), and relative growth rate (RGR) were significantly increased with lower food conversion ratios (FCR) compared to the control. The hepatic glutathione peroxidase (GPx), catalase (CAT), and metallothionein (MT) were increased in response to ZnO NPs stress and only 0.5% NSO supplementation could ameliorate such increment. The immune-related genes [interleukin1-beta (IL-1β), tumor necrosis factor-beta (TNF-β), transforming growth factor-beta 2 (TGF-β2) and C-type lysozyme] as well as growth-related gene [insulin-like growth factor 1 (IGF1)] in liver showed an upregulation in fish fed with NSO diets. Administration of ZnO NPs lowered the resistance of Oreochromis niloticus against bacterial infection with Aeromonas hydrophila and NSO could enhance the immunity in the highest tested concentration (0.5%) (G₆).

CONCLUSIONS

The obtained results implied that NSO could enhance the oxidative and immune status of O. niloticus which could compensate ZnO NPs stress as well as experimental infection of a virulent strain of A. hydrophila. Our results revealed that NSO might increase fish growth and immunity only at a high dose (0.5%).