Bacteria in fish feed deliver DNA vaccine
Aquaculture is the fastest growing food-producing sector worldwide, increasing at an average annual rate of 6.3 %. However, despite this growth, outbreaks of viral diseases continue to be a significant limiting factor. It is vital to control these viruses if the development of the aquaculture sector is to be sustained. One solution is to individually vaccinate farmed fish through an injection, but this approach is both time consuming and labour intensive. The Horizon 2020 LABVaccFish project generated a novel vaccine vehicle/type that in the future can be administered orally or by immersion – by adding the vaccine to the feed or water. This approach will allow many individuals to be vaccinated at once, while limiting handling and its associated stress. New vaccine vehicle/type Lactic acid bacteria (LAB) are beneficial microbes that are considered safe for humans, animals and the environment, and are generally present in the gut microbiota, or are added as additives to probiotic drinks. “Researchers evaluated the potential of engineered LAB to deliver nucleic acids vaccines to fish cells, providing a proof of principle that food grade lactic acid bacteria (LAB) can be used as a vehicle for the oral vaccination of fish,” says project coordinator Dr Maria Forlenza. DNA vaccines have been shown to be extremely effective in protecting fish against various viral diseases. “We engineered the bacterium Lactococcus lactis, which is used extensively in the production of buttermilk and cheese, to deliver a DNA-based prototype vaccine against spring viraemia of carp virus (SVCV),” explains Dr Forlenza. The choice of virus and antigen is based on work showing that injection vaccination with DNA plasmids encoding the G protein of SVCV is highly successful. Plasmids are small, circular, double-stranded DNA molecules, which are distinct from a cell's chromosomal DNA. However, this vaccination route is less suitable for mass delivery. According to Dr Forlenza: “The use of food-grade lactic acid bacteria as a vaccine vehicle is an attractive strategy for delivering vaccines to the surface of mucosal membranes, which has never been investigated in fish.” A safe way to deliver DNA LABVaccFish showed that LAB can deliver DNA plasmids to fish cells. “The breakthrough is in the modification of the bacteria in a way that allows them to enter fish cells and transfer a DNA plasmid to the cell itself not only in a petri dish, but also in living zebrafish larvae, leading to the expression of the vaccine antigen,” Dr Forlenza points out. The project will benefit the fish vaccine and feed industry, following research to determine whether such bacteria can deliver DNA vaccines to the cells of a range of commercially important fish species. Scientists will also determine the optimal administrative dose and determine the efficacy of the vaccine when delivered orally. “The next step is to validate such a system in an aquaculture species after mixing LAB with the feed,” concludes Dr Forlenza.
Keywords
LABVaccFish, vaccine, DNA, lactic acid bacteria (LAB), aquaculture, spring viraemia of carp virus (SVCV)
