Protection against Vibrio alginolyticus in crimson snapper Lutjanus erythropterus immunized with a DNA vaccine containing the ompW gene

Holistic analysis of lysine acetylation in aquaculture pathogenic bacteria Vibrio alginolyticus under bile salt stress

Lysine acetylation modification is a dynamic and reversible post-translational modification, which plays an important role in the metabolism and pathogenicity of pathogenic bacteria. Vibrio alginolyticus is a common pathogenic bacterium in aquaculture, and bile salt can trigger the expression of bacterial virulence. However, little is known about the function of lysine acetylation in V. alginolyticus under bile salt stress. In this study, 1,315 acetylated peptides on 689 proteins were identified in V. alginolyticus under bile salt stress by acetyl-lysine antibody enrichment and high-resolution mass spectrometry. Bioinformatics analysis found that the peptides motif ^****A^*Kac^**** and ^*******Kac^****A^* were highly conserved, and protein lysine acetylation was involved in regulating various cellular biological processes and maintaining the normal life activities of bacteria, such as ribosome, aminoacyl-tRNA biosynthesis, fatty acid metabolism, two-component system, and bacterial secretion system. Further, 22 acetylated proteins were also found to be related to the virulence of V. alginolyticus under bile salt stress through secretion system, chemotaxis and motility, and adherence. Finally, comparing un-treated and treated with bile salt stress lysine acetylated proteins, it was found that there were 240 overlapping proteins, and found amino sugar and nucleotide sugar metabolism, beta-Lactam resistance, fatty acid degradation, carbon metabolism, and microbial metabolism in diverse environments pathways were significantly enriched in bile salt stress alone. In conclusion, this study is a holistic analysis of lysine acetylation in V. alginolyticus under bile salt stress, especially many virulence factors have also acetylated.

Strategies for Prevention and Control of Vibriosis in Asian Fish Culture

It is estimated that vibriosis account for about half of the economic losses in Asian fish culture. Consequently, the prevention and control of vibriosis is one of the priority research topics in the field of Asian fish culture disease. Relevant measures have been proposed to control some Vibrios that pose a threat to Asian fish culture, but there are currently only a few effective vaccines available to combat these Vibrios. The purpose of our review is to sum up the main prevention methods and the latest control strategies of seven Vibrio species that cause great harm to Asian aquaculture, including Vibrio harveyi, Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio mimicus, Vibrio anguillarum, Vibrio alginolyticus and Vibrio cholerae. Strategies such as antibiotics, probiotics, bacteriophages, antimicrobials from plants and other natural sources, as well as vaccines, are compared and discussed here. We expect this review will provide some new views and recommendations for the future better prevention and control of vibriosis in Asian fish culture.

Transcriptome profiles of genes related to growth and virulence potential in Vibrio alginolyticus treated with modified clay

Vibrio alginolyticus is a globally distributed opportunistic pathogen that causes different degrees of disease in various marine organisms, such as fish, shrimp and shellfish. At present, vibriosis caused by V. alginolyticus has a wide epidemic range and causes frequent outbreaks, resulting in substantial losses in aquaculture. According to previous studies, modified clay (MC) could effectively flocculate and reduce the density of Vibrio in water, but it is still unknown whether MC inhibits growth and how it affects virulence in bottom flocs. Here, we studied the response mechanism of V. alginolyticus in flocs treated with MC at the transcriptome level and verified the transcriptomic data combined with relevant physiological experiments and reverse transcription quantitative real-time PCR (RT-qPCR) for the first time. It was found that the morphology of Vibrio in the MC flocs changed, the membrane function was damaged, the antioxidant system was activated, and the material and energy metabolism also changed. In addition, MC could inhibit the expression of virulence factors of V. alginolyticus; for example, flagella, pilus, siderophores, quorum sensing, and other related genes were significantly downregulated. In general, MC effectively inhibited the growth of Vibrio and reduced its virulence potential in flocs, which could provide theoretical support for a new model of healthy aquaculture.

Thermostable Vaccines in Veterinary Medicine: State of the Art and Opportunities to Be Seized

The COVID-19 pandemic has highlighted the weakness of the vaccine supply chain, and the lack of thermostable formulations is one of its major limitations. This study presents evidence from peer-reviewed literature on the development of thermostable vaccines for veterinary use. A systematic review and meta-analysis were performed to evaluate the immunogenicity and/or the efficacy/effectiveness of thermostable vaccines against infectious diseases. The selected studies (n = 78) assessed the vaccine’s heat stability under different temperature conditions and over different periods. Only one study assessed the exposure of the vaccine to freezing temperatures. Two field studies provided robust evidence on the immunogenicity of commercial vaccines stored at temperatures far in excess of the manufacturer’s recommended cold-chain conditions. The drying process was the most-used method to improve the vaccine’s thermostability, along with the use of different stabilizers. The pooled vaccine efficacy was estimated to be high (VE = 69%), highlighting the importance of vaccination in reducing the economic losses due to the disease impact. These findings provide evidence on the needs and benefits of developing a portfolio of heat- and freeze-stable veterinary vaccines to unleash the true potential of immunization as an essential component of improved animal health and welfare, reduce the burden of certain zoonotic events and thus contribute to economic resilience worldwide.

Antibacterial activity in secondary metabolite extracts of heterotrophic bacteria against Vibrio alginolyticus, Aeromonas hydrophila, and Pseudomonas aeruginosa

Background: Disease causing bacteria such as Vibrio alginolyticus, Aeromonas hydrophila, and Pseudomonas aeruginosa present a problem for fish farming. Treatment to remove them are generally carried out using antibiotics which have side effects on fish, the environment and humans. However, the use of antibacterial compounds derived from heterotrophic bacteria serve as a good alternative for antibiotics. Therefore, this study aimed to explore antibacterial activity in the secondary metabolite extracts of heterotrophic bacteria against Vibrio alginolyticus, Aeromonas hydrophila, and Pseudomonas aeruginosa. Methods: Heterotrophic bacteria namely Bacillus sp. JS04 MT102913.1, Bacillus toyonensis JS08 MT102920.1, Bacillus cereus JS10 MT102922.1, Bacillus sp. JS11 MT102923.1, Pseudoalteromonas sp. JS19 MT102924.1, Bacillus cereus JS22 MT102926.1, and Bacillus sp. strain JS25 MT102927.1 were used in this study. The sequences of these bacteria have been deposited and are available from NCBI GenBank. Each heterotrophic bacterium was cultured on 6L nutrient broth for 8 days, and extracts produced using ethyl acetate to obtain their secondary metabolites. These extracts were tested for their phytochemical contents using FT-IR and also tested for their inhibitory property in pathogenic bacteria by agar diffusion method. Results: Phytochemical test results showed that the seven heterotrophic bacterial isolates produced terpenoid compounds. Based on the inhibitory test, the secondary metabolite extracts from Bacillus sp strain JS04 had the highest inhibitory effect on the growth of pathogenic bacteria namely, V. alginolyticus (17.5 mm), A. hydrophila (16.8 mm), and P. aeruginosa (17.3 mm). Conclusion: It was concluded that the secondary metabolite extracts of heterotrophic bacteria inhibit the growth of V. alginolyticus, A. hydrophila, and P. aeruginosa.

Identification of common antigens of three pathogenic Nocardia species and development of DNA vaccine against fish nocardiosis

Fish nocardiosis is a chronic granulomatous bacterial disease and three pathogens have been reported so far, including Nocardia asteroids, N. seriolae and N. salmonicida. However, the absence of antigen markers is a bottleneck for developing effective vaccines against fish nocardiosis. In this study, the antigenicity of whole-cell protein of these three pathogenic Nocardia species were profiled by immunoproteomic analysis and 7 common immunogenic proteins were identified as follows: molecular chaperone DnaK (DnaK), molecular chaperone GroEL (GroEL), 30 S ribosomal protein S1 (RpsA), TerD family protein (TerD), FHA domain-containing protein (FHA), 50 S ribosomal protein L7/L12 (RplL) and PspA/IM30 family protein (PspA). Furthermore, the DNA vaccine encoding FHA gene against fish nocardiosis was developed and its efficacy was investigated in hybrid snakehead. The results suggested that it needed at least 7 d to transport pcDNA-FHA DNA vaccine from injected muscle to head kidney, spleen and liver and stimulate host's immune system for later protection. In addition, non-specific immunity paraments (serum lysozyme (LYZ), peroxidase (POD), acid phosphatase (ACP), alkaline phosphatase (AKP) and superoxide dismutase (SOD) activities), specific antibody (IgM) titers production and immune-related genes (MHCIα, MHCIIα, CD4, CD8α, IL-1β and TNFα) were used to evaluate the immune response induced in pcDNA-FHA vaccinated hybrid snakehead, it proved that all these mentioned immune activities were significantly enhanced after immunization. The results also showed hybrid snakehead vaccinated with pcDNA-FHA had higher survival rate (79.33%) compared with the controls after challenge with N. seriolae, indicating that the pcDNA-FHA DNA vaccine can supply immune protection against N. seriolae infection. Taken together, this study may warrant further development of these common immunogenic proteins as the antigens for vaccine or diagnosis and facilitate the prevention and treatment of fish nocardiosis.

An IL-6 gene in humphead snapper (Lutjanus sanguineus): Identification, expression analysis and its adjuvant effects on Vibrio harveyi OmpW DNA vaccine

Interleukin 6 (IL-6) is a pleiotropic cytokine that plays important role in mediating the innate and adaptive immune responses against pathogen infection. In this study, an IL-6 homolog (Ls-IL6) was identified and characterized from humphead snapper, Lutjanus sanguineus. The full-length cDNA of Ls-IL6 was 1066 bp, containing an open reading frame (ORF) of 639 bp encoding 212 amino acids, 5' untranslated region(UTR) of 63 bp and 3' UTR of 605 bp. The predicted Ls-IL6 protein had typical motif of IL-6 family and shared high identities to teleost IL-6s. Ls-IL6 extensively expressed in various tissues, and the highest expression of Ls-IL6 was detected in head kidney, spleen and thymus. In vivo, the transcript levels of Ls-IL6 were significantly up-regulated in response to Vibrio harveyi infection. Moreover, the DNA plasmid containing the OmpW of V. harveyi together with the gene encoding Ls-IL6 were successfully constructed and administered to fish, the protective efficacy of Ls-IL6 was investigated. Compared with the pcDNA-OmpW group, the level of specific antibodies against V. harveyi increased in pcDNA-IL6-OmpW injected group. After V. harveyi infection, the pcDNA-IL6-OmpW vaccinated fish showed higher relative percent survival (76%) than the relative survival of fish immunized with pcDNA-OmpW (60%). These results indicated that Ls-IL6 was involved in immune response against V. harveyi infection and could be applied as a promising adjuvant for DNA vaccines against V. harveyi.

Integrative mRNA-miRNA interaction analysis associated with the immune response of Epinephelus coioddes to Vibrio alginolyticus infection

MicroRNAs (miRNAs) are a kind of small non-coding RNAs that have been reported to play a vital role in mediating host-pathogen interactions. High-throughput sequencing technology was applied to identify and illuminate mRNAs and miRNAs from grouper infected with Vibrio alginolyticus. The KEGG pathway enrichment analysis showed that the most significate DEGs are associated with Toll-like receptor signaling pathway and NOD-like receptor signaling pathway. We obtained 374 known miRNAs and 116 novel miRNAs. During them, there are 31 up-regulated miRNAs and 93 down-regulated miRNAs. miRNA-mRNA GO and KEGG analysis show that there are 90 miRNAs associated with the immune system. The target genes of immune-related miRNAs (miR-142, miR-146, miR-150, miR-155, miR-203, miR-205, miR-24, miR-31) and genes (CD80, IL-2, AMPK, PI3K) in Epinephelus coioddes were predicted and validated. This study provides an opportunity to further understanding the molecular mechanisms especially the immune system of miRNA regulation in Epinephelus coioddes host-pathogen interactions.

Protection against Vibrio alginolyticus in pearl gentian grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatu) immunized with an acfA-deletion live attenuated vaccine

Vibrio alginolyticus is well-known as an opportunistic Gram-negative pathogen, which endangers the development of global aquaculture as well as human health. In this study, a ΔacfA mutant strain and complementation of the ΔacfA mutant (C-acfA) were constructed. The ΔacfA mutant was tested in pearl gentian grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatu) to observe the changes in virulence and evaluate its potential as an attenuated live vaccine. The results showed that the ΔacfA mutant caused a high antibody titer and a significant reduction in the ability to colonize the intestine of pearl gentian grouper. Grouper vaccinated with ΔacfA mutant were more tolerant of the infection by virulent V. alginolyticus HY9901 without inducing clinical symptoms and obvious pathological changes. The relative percent survival value of pearl gentian grouper vaccinated with ΔacfA mutant intraperitoneal injection reached 81.1% after challenging with V. alginolyticus HY9901. The specific antibody titers immunized with ΔacfA was significantly higher than that in the PBS group. The antibody titer of ΔacfA group displayed the tendency of rising up from the first to fourth week and declining from fifth to eighth week and reached the peak at the fourth week. In the meanwhile, the expression level of genes associated with immunity, including IL-1β, TNF-α, IL-16, IgM, CD8α and MHC-Iα, was up-regulated after vaccination, indicating that the ΔacfA can induce effective and durable immune response in pearl gentian grouper and it may be an effective attenuated live vaccine candidate for the prevention of infections by V. alginolyticus.

Identification of fish source Vibrio alginolyticus and evaluation of its bacterial ghosts vaccine immune effects

Vibrio alginolyticus (V. alginolyticus) is a common pathogen for humans and marine aquatic animals. Vibriosis of marine aquatic animals, caused by V. alginolyticus, has become more prevalent globally in recent years. Hence, a safe and effective vaccine is urgently needed for the control of this disease. Here, the strain 16‐3 isolated from the large yellow croaker (Larimichthys crocea) suffered from canker was identified as V. alginolyticus based on morphological, biochemical, and 16S rDNA sequencing analysis. Then, recombinant temperature‐controlled lysis plasmid pBV220‐lysisE was electroporated into the strain 16‐3 to generate V. alginolyticus bacterial ghosts (VaBGs) by inducing lysis gene E expression, and the safety and immune effects of VaBGs were further investigated in mice and large yellow croaker. The results showed that VaBGs were as safe as formalin‐killed V. alginolyticus cells (FKC) to mice and fish. Compared with FKC and PBS groups, significant elevations of the serum agglutinating antibody titer, serum bactericidal activity, lymphocyte proliferative responses, and levels of four different cytokines (Th1 type: IL‐2, TNF‐α; Th2 type: IL‐4 and IL‐6) in serum were detected in the VaBGs group, indicating that a Th1/Th2‐mediated mixed immune response was elicited by the VaBGs. More importantly, after challenged with the parent strain 16‐3, VaBGs‐vaccinated mice and fish showed higher protection than FKC‐vaccinated mice, the relative percent of survival (RPS) being 60%, 66.7% and 40%, respectively. Taken together, this is the first demonstration that the newly constructed V. alginolyticus ghosts may be developed as a safe and effective vaccine against V. alginolyticus infection in aquaculture.

AcfA is an essential regulator for pathogenesis of fish pathogen Vibrio alginolyticus

V. alginolyticus is an important opportunistic pathogen which causes vibriosis in aquatic animals. AcfA, as an accessory colonization factor, is hypothesized to be involved in the pathogenesis of infection. In this study, a mutant strain with an in-frame deletion removed nucleotides 86 to 561 of the acfA gene was constructed to reveal the role of AcfA in the physiology and virulence from V. alginolyticus. An acfA mutant showed a similar growth level, an obvious decrease in swarming motility and the activity of ECPase, a higher LD₅₀ value by intraperitoneal injection of grouper fish compared to that of the wild-type. Furthermore, the deletion of acfA could enhance the level of biofilm formation and suppress the polar flagellum forming. The comparative proteomic analysis demonstrated the deletion mutation of acfA could up-regulate the expression of 4 proteins of p4alcd, deoD, phb and DctP, and down-regulate the expression of 8 proteins of Clp, hpV36980, ABCtp, pepD, arA, aggp, fla and ompA compared to that of the wild-type. The analysis of RT-qPCR showed the mRNA levels of DctP and deoD were significantly induced, and the mRNA levels of pepD, arA, fla and ompA were significantly reduced in acfA mutant compared with the wild-type. The results suggest that acfA may contribute to the overall success in the pathogenesis of V. alginolyticus by regulating the expression of some relevant genes.

Role of the toxR Gene from Fish Pathogen Vibiro alginolyticus in the Physiology and Virulence

A mutant strain of Vibiro alginolyticus with an in-frame deletion of the toxR gene was constructed to reveal the role of ToxR in the physiology and virulence of V. alginolyticus. The statistical analysis showed no significant difference in the growth ability, swarming motility, activity of extracellular protease and the virulence by injection (the value of LD₅₀) between the wild-type and the toxR mutant. However, the deletion of toxR could decrease the level of biofilm formation. The comparative proteomic analysis demonstrated the deletion mutation of toxR could up-regulate the expression of glutamine synthetase and levansucrase, and down-regulate the expression of 10 proteins such as OmpU, DnaK, etc. These results suggest that ToxR may be involved in the early stages of infection by influencing colonization of the bacteria on the surface of the intestine through enhancing the biofilm information of V. alginolyticus via modulating the expression of glutamine synthetize, levansucrase and OmpU.

Immunogenicity and efficacy of DNA vaccine encoding antigenic AcfA via addition of the molecular adjuvant Myd88 against Vibrio alginolyticus in Epinephelus coioides

DNA vaccines had been widely used against microbial infection in animals. The use of molecular adjuvants to improve the immunogenicity of DNA vaccines has been increasingly studied in recent years. MyD88 is one of the adapter molecules to activate the signaling cascades and produces inflammatory mediators, and its immunological role and adjuvant potential which had been proved in mammals were rarely reported in fish species. In this study, plasmid pcMyD88 was constructed and the capacity of MyD88 as molecular adjuvant was explored by co-injecting with a DNA vaccine encoding AcfA against Vibrio alginolyticus infection in orange spotted grouper. The results suggested that it needed at least 7 days to transported DNA vaccine pcacfA or molecular adjuvant pcMyD88 from the injected muscle to kidney and spleens and stimulate host's immune system for later protection. The co-injection of pcMyD88 with DNA vaccine pcacfA could increase significantly specific antibody levels and the expression levels of the immune-related genes including MHCIα, MHCIIα, CD4, CD8α, IL-1β and TNFα. Furthermore, pcMyD88 enhanced the immunoprotection of pcacfA against V. alginolyticus infection, with the significantly higher RPS of 83.3% in pcMyD88 + pcacfA group compared with that of pcacfA alone (73.3%) at challenging test of 10 weeks post vaccination. Together, these results clearly demonstrate that MyD88 is an effective adjuvant for the DNA vaccine pcacfA in orange spotted grouper.

Aeromonas hydrophila OmpW PLGA Nanoparticle Oral Vaccine Shows a Dose-Dependent Protective Immunity in Rohu (Labeo rohita)

Aeromonas hydrophila is a Gram-negative bacterium that causes high mortality in different fish species and at different growth stages. Although vaccination has significantly contributed to the decline of disease outbreaks in aquaculture, the use of oral vaccines has lagged behind the injectable vaccines due to lack of proven efficacy, that being from primary immunization or by use of boost protocols. In this study, the outer membrane protein W (OmpW) of A. hydrophila was cloned, purified, and encapsulated in poly d,l-lactide-co-glycolic acid (PLGA) nanoparticles (NPs) for oral vaccination of rohu (Labeo rohita Hamilton). The physical properties of PLGA NPs encapsulating the recombinant OmpW (rOmpW) was characterized as having a diameter of 370–375 nm, encapsulation efficiency of 53% and −19.3 mV zeta potential. In vitro release of rOmpW was estimated at 34% within 48 h of incubation in phosphate-buffered saline. To evaluate the efficacy of the NP-rOmpW oral vaccine, two antigen doses were orally administered in rohu with a high antigen (HiAg) dose that had twice the amount of antigens compared to the low antigen (LoAg) dose. Antibody levels obtained after vaccination showed an antigen dose dependency in which fish from the HiAg group had higher antibody levels than those from the LoAg group. The antibody levels corresponded with post challenge survival proportions (PCSPs) and relative percent survival (RPS) in which the HiAg group had a higher PCSP and RPS than the LoAg group. Likewise, the ability to inhibit A. hydrophila growth on trypticase soy agar (TSA) by sera obtained from the HiAg group was higher than that from the LoAg group. Overall, data presented here shows that OmpW orally administered using PLGA NPs is protective against A. hydrophila infection with the level of protective immunity induced by oral vaccination being antigen dose-dependent. Future studies should seek to optimize the antigen dose and duration of oral immunization in rohu in order to induce the highest protection in vaccinated fish.