Freeze-drying of live attenuated Vibrio anguillarum mutant for vaccine preparation

Bacterial Pathogenesis in Various Fish Diseases: Recent Advances and Specific Challenges in Vaccine Development

Aquaculture is a fast-growing food sector but is plagued by a plethora of bacterial pathogens that infect fish. The rearing of fish at high population densities in aquaculture facilities makes them highly susceptible to disease outbreaks, which can cause significant economic loss. Thus, immunity development in fish through vaccination against various pathogens of economically important aquaculture species has been extensively studied and has been largely accepted as a reliable method for preventing infections. Vaccination studies in aquaculture systems are strategically associated with the economically and environmentally sustainable management of aquaculture production worldwide. Historically, most licensed fish vaccines have been developed as inactivated pathogens combined with adjuvants and provided via immersion or injection. In comparison, live vaccines can simulate a whole pathogenic illness and elicit a strong immune response, making them better suited for oral or immersion-based therapy methods to control diseases. Advanced approaches in vaccine development involve targeting specific pathogenic components, including the use of recombinant genes and proteins. Vaccines produced using these techniques, some of which are currently commercially available, appear to elicit and promote higher levels of immunity than conventional fish vaccines. These technological advancements are promising for developing sustainable production processes for commercially important aquatic species. In this review, we explore the multitude of studies on fish bacterial pathogens undertaken in the last decade as well as the recent advances in vaccine development for aquaculture.

Protective effects of immersion immunization of koi with Escherichia coli DH5α carrying DNA vaccine against koi herpesvirus

This study aims to immunize the koi fingerlings immersion using the formalin-killed and freeze-dried E. coli DH5α carrying plasmid for the KHV DNA vaccine. 200 fish on each tank in a total water volume of 20 L. Each tanks consists of different vaccination group: PBS as control (10 mL; C), empty E. coli DHα (10 mL at 108 CFU mL-1; E), formalinkilled E. coli DHα:ORF81 (10 mL at 108 CFU mL-1; KE), freezedried E.coli DHα:ORF81 without formalin inactivation (10 mL at 108 CFU mL-1; FE), and formalin-killed and then freeze-dried E. coli DHα:ORF81 (10 mL at 108 CFU mL-1; KFE). The bath vaccination was conducted for 1 × 30 min. For the challenged test, fish were immersed with the 100 mL of LD50 dose of KHV (10-2 dilution from the KHV stock) for 30 min. The vaccination using E. coli DH5α:ORF81 could significantly modulate the innate and adaptive immunity of the fish and result in higher fish survival after KHV infection. The vaccination using formalin-killed or formalin-killed and freezedried E. coli DH5α:ORF81 will be further developed as an alternative to the costefficient koi or carp fingerlings vaccination method.

Efficient Citrus (Citrus unshiu) Byproduct Extract-Based Approach for Lactobacillus sakei WiKim31 Shelf-Life Extension

Lactic acid bacteria produce various bioactive compounds widely used in human healthcare. However, studies on cryoprotective agents for the efficient storage of lactic acid bacteria after freeze-drying are still lacking. Here, we report the shelf-life extension effects of a highly efficient and eco-friendly cryoprotective agent and a cold adaptation method on Lactobacillus sakei WiKim31. Cold adaptation of L. sakei WiKim31 increased exopolysaccharide expression in response to abiotic stress. As a possible cryoprotective agent, the citrus byproduct (CP) contains a variety of sugars, amino acids, and cations, exhibiting high antioxidant activity. L. sakei WiKim31 powders formulated with CP or a mixture of soy powder (SP) and CP exhibited high cell viability at 58.3 and 76.3%, respectively, after 56 days of storage. These results indicate that CP can be efficiently used as a novel cryoprotective agent either alone or in combination with SP to improve the storage conditions of L. sakei WiKim31 and preserve it longer.

A new protectant medium preserving bacterial viability after freeze drying

Freeze-drying technology has been widely considered for decades as a suitable technique to preserve microorganisms. However, protective agents must be added prior to freeze drying to improve the survival and storage stability of the bacteria. The objective of our study was to evaluate the effect of a new protectant medium containing sucrose (10 %), trehalose (10 %), skimmed milk (10 %) and antioxidants on the viability of gut bacteria under different storage conditions. Two strains were tested, Escherichia coli and Akkermansia muciniphila, as examples of facultative aerobic and anaerobic bacteria, respectively. We studied the cell viability and bacterial morphology in 5 fecal samples in the presence and absence of this protectant medium using plating technique, flow cytometry and scanning electron microscopy. The results of bacterial viability assessed by plating method showed that the protectant medium yielded higher survival rates for both strains whatever the storage conditions (85-93 %) compared to normal saline solution (0.36-37.50 %). It also showed its effectiveness on fecal samples, where bacterial viability after freeze-drying was 89.47 ± 7.63 % and 84.01 ± 7.44 %, as evidenced by flow cytometry analysis and plating method. However unprotected samples showed the lowest cell viability at 19.01 ± 12.88 % and 13.23 ± 9.56 %, as measured by flow cytometry and plating method. In addition, bacterial size and shape were conserved in the protectant medium. In contrast, storage without protectant medium severely damaged bacterial morphology. In conclusion, our study is the first to use morphological features as well as culture-dependant and culture-independent tests to evaluate the effectiveness of a new protectant medium.

Improved stability of live attenuated vaccine gdhA derivative Pasteurella multocida B:2 by freeze drying method for use as animal vaccine

The efficacy of attenuated strain of gdhA derivative Pasteurella multocida B:2 mutant as a live vaccine to control haemorrhagic septicaemia (HS) disease in cattle and buffaloes has been demonstrated. In order to use P. multocida B:2 mutant as a commercial product, it is essential to optimise its formulation for high viability and stability of the live cells. The effectiveness of freeze-drying process using different protective agent formulations for improving cells viability was explored. Sugar and nitrogen compounds were used as protective agents in freeze-drying and the capability of these compounds in maintaining the viability of mutant P. multocida B:2 during subsequent storage was investigated. A complete loss in viability of freeze-dried mutant P. multocida B:2 was monthly observed until 6-12 months of storage at -30 °C, 4 °C and 27 °C when nitrogen compound or no protective agent was added. Trehalose and sucrose showed significantly high survival rate of 93-95% immediately after freeze-drying and the viability was retained during the subsequent storage at -30 °C and 4 °C. A smooth cell surface without any cell-wall damage was observed for the cells formulated with trehalose under scanning electron micrograph. This study presented a freeze-drying process generating a dried live attenuated vaccine formulation with high stability for commercial applications.

Optimization of a protective medium for freeze-dried Pichia membranifaciens and application of this biocontrol agent on citrus fruit

AIMS

To optimize a protective medium for freeze-dried Pichia membranifaciens and to evaluate biocontrol efficacies of agents against blue and green mould and anthracnose in citrus fruit.

METHODS AND RESULTS

Based on the screening assays of saccharides and antioxidants, response surface methodology was used to optimize sucrose, sodium glutamate and skim milk to improve viability of freeze-dried Pi. membranifaciens. Biocontrol assays were conducted between fresh and freeze-dried Pi. membranifaciens against Penicillium italicum, Penicillium digitatum and Colletotrichum gloeosporioides in citrus fruit. Solving the regression equation indicated that the optimal protective medium was 6·06% (w/v) sucrose combined with 3·40% (w/v) sodium glutamate and 5·43% (w/v) skim milk. Pi. membranifaciens freeze-dried in the optimal protective medium showed 76·80% viability, and retained biocontrol efficacy against Pe. italicum, Pe. digitatum and Co. gloeosporioides in citrus fruit.

CONCLUSIONS

The optimal protective medium showed more effective protective properties than each of the three protectants used alone. The viability of freeze-dried Pi. membranifaciens finally reached 76·80%. Meanwhile, the biocontrol efficacies showed no significant difference between fresh and freeze-dried yeast against Pe. italicum, Pe. digitatum and Co. gloeosporioides in citrus fruit.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results showed the potential value of Pi. membranifaciens CICC 32259 for commercialization.

Th17-like immune response in fish mucosal tissues after administration of live attenuated Vibrio anguillarum via different vaccination routes

This study aimed to investigate the protective mucosal immunity elicited by live attenuated Vibrio anguillarum in fish. Zebrafish were immunized by bath or injection way, and undertook bath challenge at 28 days post vaccination. The results implied that bath vaccination was the better delivery route for inducing the protective immunity against bath challenge in zebrafish. The expressions of genes related to Th1, Th2 and Th17 cells were measured in the mucosal tissues of vaccinated and challenged zebrafish. Gene expression profiles showed that Th17-like responses were induced in mucosal immune system by vaccination via bath and injection routes while Th1 and Th2-like responses were not remarkable. Compared to injection vaccination, bath vaccination elicited the intense Th17-like immune responses in the gut tissue of zebrafish. Additionally, in gills and skin, Th17-like mucosal immunity elicited by injection vaccination occurred later than that by bath vaccination. Our results proved the immunological importance of gut in bath vaccination and the presence of two-compartmental model for immune response in zebrafish. In conclusion, bath vaccination more efficiently elicited protective Th17-like immunity than injection vaccination in mucosal tissues of vaccinated zebrafish. In turbot, effective immune protection against wild-type V. anguillarum was obtained by bath-vaccinated and the Th17-like responses were found in mucosal and systemic tissues.

Development of lyophilization cycle and effect of excipients on the stability of catalase during lyophilization

Introduction:

The purpose of the present study was to screen excipients such as amino acids and non-aqueous solvents for their stabilizing effect on catalase, a model protein, for lyophilization. The present study also includes optimization of lyophilization cycle for catalase formulations, which is essential from the commercial point of view, since lyophilization is an extremely costly process.

Materials and Methods:

Activity of catalase was determined using catalase activity assay. Differential scanning calorimetry was used to determine eutectic melting temperature of the frozen catalase solution, which is essential for the optimization of lyophilization cycle.

Results:

When catalase was lyophilized without excipients, it was found that about 65-78% of the initial activity of catalase was lost during the lyophilization process in a concentration dependent manner. The maximum stability of catalase during lyophilization was observed at pH 7.0. Amino acids like alanine, glycine, lysine, serine and 4-hydroxy proline showed strong stabilizing effect on catalase during lyophilization by protecting catalase activity above 95%, whereas valine and cysteine hydrochloride showed destabilizing effect on catalase. Non-aqueous solvents such as dimethyl formamide, dimethyl sulphoxide, polyethylene glycol (PEG) 200, PEG 400, PEG 600 and ethylene glycol also showed destabilizing effect on catalase during lyophilization.

Conclusions:

In order to prevent loss of catalase activity during lyophilization of catalase, use of amino acids like alanine, glycine, lysine, serine and 4-hydroxy proline in optimum concentration is highly advisable.

Optimization of physicochemical parameters influencing the fabrication of protein-loaded chitosan nanoparticles

Aim: In the development of controlled-release protein therapeutics, the high encapsulation of proteins into biodegradable nanoparticles with uniform size in an anhydrous process along with an excellent redispersion is of practical interest. The objective of this work was to study the physicochemical and in vitro release properties of chitosan nanoparticles with different molecular weights (low, medium and high) using bovine serum albumin (BSA) as a model protein for developing nanoparticle formulations that were stable and reproducible after lyophilization. Materials & methods: The BSA-loaded chitosan nanoparticles were prepared by an ionic gelation method using pentasodium tripolyphosphate as the polyanions. The physicochemical properties and in vitro release kinetics of the nanoparticles were evaluated along with Fourier transform infrared spectroscopy studies. Furthermore, the nanoparticles were freeze-dried for long-term stability in the formulation. To optimize the size of the freeze-dried nanoparticles after redispersion, various types of lyoprotectants (natural and synthetic) were tested in varying concentration in the process of lyophilization. Results: The dynamic light scattering measurements revealed the increase in size of chitosan nanoparticles with the increase in molecular weight of chitosan with no significant change, irrespective of the concentration of BSA entrapped. In addition, the entrapment efficiency of the nanoparticles increased with the increasing molecular weight of chitosan and BSA concentration. By contrast, the redispersity of the freeze-dried samples resulted in further increase of the mean diameter of the nanoparticles. Conclusion: Among the various types of lyoprotectants (natural and synthetic) examined, sucrose proved to be very effective in reducing the size of freeze-dried nanoparticles on redispersion without significant change in surface charge of nanoparticles. Finally, the in vitro release kinetics of BSA from nanoparticles of different molecular weights of chitosan, with and without sucrose, was evaluated and found to depend upon the molecular weight of chitosan.